hsc_MaintainBalance (2)

Gill Sans BoldBiology HSC Course Stage 6 Maintaining a balance I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 BIOHSC43204 P0025937 Number: 43204 Title: Maintaining a balance This publication is copyright New South Wales Department of Education and Training (DET), however it may contain material from other sources which is not owned by DET. We would like to acknowledge the following people and organisations whose material has been used: Photograph of lizard, courtesy of Jane West Drawing of a platypus from Grant, T and Fanning D (1995) The platypus: a unique mammal, NSW University Press Photograph of human blood under microscope, courtesy of Jane West Photograph of red and white blood cells taken with an electron microscope from Porter, K R and Fonte, G (1996) Biological science, University of Colorado Photographs of arteries, veins and capillaries, courtesy of Jane West Photographs of bull ants, prickly pear and salt crystals on mangrove leaf, courtesy of Jane West Diagram of cross section through rolled leaf of porcupine grass from Web of life (3rd ed, 1981) Australian Academy of Science Part 1 p 18 Part 2 p 29 Part 3 p 12 Part 3 p 12 Part 3 p 38 Part 6 pp 11, 14, 16 Part 6 p 26 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you on behalf of the New South Wales Department of Education and Training (Centre for Learning Innovation) pursuant to Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith. Published by Centre for Learning Innovation (CLI) 51 Wentworth Rd Strathfield NSW 2135 _______________________________________________________________________________________________ _ Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the written authority of the Centre for Learning Innovation (CLI). © State of New South Wales, Department of Education and Training 2008. Contents Module overview ........................................................................iii Objectives ............................................................................................ iii Indicative time...................................................................................... iii Resources............................................................................................ iii Icons .....................................................................................................v Glossary............................................................................................... vi Part 1: Enzymes..................................................................1–27 Part 2: Homeostasis and temperature regulation ................1–33 Part 3: Mammalian blood ....................................................1–39 Part 4: Transport in plants...................................................1–24 Part 5: Excretion..................................................................1–24 Part 6: Maintaining water balance .......................................1–33 Module evaluation ................................................................... 35 Introduction i ii Maintaining a balance There is some information provided with the module and there is more at the end of each part in the Additional resources section. research and developments in biology. Objectives This module increases students’ understanding of the applications and uses of biology. Resources During this module there are some activities that require you to gather and process information. there are Internet sites Introduction iii . biological processes are balanced by a range of internal coordination mechanisms. However.Module overview From the molecular and organelle levels in cells. including humans and native Australian species. is considered in this module. through the specialised organ systems of multicellular species to whole ecosystems. The nature of control mechanisms in plant and animal species. implications for society and the environment and current issues. There are six parts to the module and each part should take approximately five hours. Some organisms maintain a constant internal environment while others tolerate a much greater variation in internal conditions. As well as this information. Indicative time This module should take 30 hours to complete. all species have a range of external conditions under which they can survive and reproduce. A visit to your local library should turn up some useful books too. Part 1 • • • • • • • • • test tube-sized containers of the same size made of glass or heat-resistant plastic glass or heat-resistant plastic containers into which two of the test tube-sized containers will fit 1 junket tablet (You will need to buy a packet.edu.supplied by the LMP Science Online website(www.lmpc.) 1 small container of full cream milk 1 tray of ice blocks 1 eye dropper or pipette 1 medicine measure 1–3 thermometers (0–100°C range) powdered milk Part 4 • • • • fresh stick of celery single sided razor blade glass or container with water food dye Part 5 • • • • • sheep’s kidney cutting board scalpel or knife knitting needle rubber gloves iv Maintaining a balance . You will need the following equipment.au/science). There are also practical activities to complete within this unit. There is an exercise at the end of the part for you to complete. There are suggested answers for the following questions at the end of the part. Discuss ideas with someone else. Introduction v . You could speak with family or friends or anyone else who is available. The meaning of each icon is written beside it. Perhaps you could telephone someone? There is a safety issue that you need to consider. The hand icon means there is an activity for you to do. It may be an experiment or you may make something.Icons The following icons are used within this module. You need to use a computer for this activity. listed here with their meanings. 25 grams of salt per litre of water. excreted diluted in large amounts of water flowering plants blood vessel which carries blood away from the heart the capsule at the end of the vertebrate kidney which contains the glomerulus a solution of two or more chemicals which prevent marked changes in hydrogen ion concentration (pH) when either an acid or base (alkali) is added to the system group of cells which divide to form new xylem and phloem cells microscopic blood vessel with walls one cell thick. across which materials are exchanged between blood and tissues smallest unit of life capable of reproducing itself structure made up of genetic material (DNA) and protein found mainly in the nucleus attraction between molecules of water the amount of a substance in a specific amount of a mixture or solution. ambient temperature) main nitrogenous waste product of bony fish.Glossary The following words. Normally expressed as weight per unit volume (eg. liquids or solutions from where they are more concentrated to where they are less concentrated cambium capillary cell chromosome cohesion concentration denatured diffusion vi Maintaining a balance . They appear bolded the first time they occur in the learning material. are found in the learning material in this module. 25 g/L) or as molarity structural change in proteins movement of particles in gases. activation energy active transport ambient ammonia angiosperms artery Bowman’s capsule buffer the energy necessary to start a chemical reaction movement of substances across a membrane by a process requiring expenditure of energy environmental or surrounding (eg. mainly birds and mammals are endothermic a highly specialised cellular protein that reduces the amount of energy required to initiate a chemical reaction. cellulase enzyme digests cellulose cells which have their genetic material (chromosomes) inside a nucleus bounded by a membrane and which have other membranebound organelles. panting) the elimination of harmful and unwanted products of metabolism organs involved in the removal of wastes (eg. usually part of a specific DNA molecule (chromosome) a bunch of capillaries found in the vertebrate kidney effector ectotherm enantiostasis endocrine system endotherm enzyme Eucaryotic (eukaryotic) endocrine system evaporative cooling excretion excretory organs gene glomerulus Introduction vii .distal tubule DNA part of the nephron where water is extracted abbreviation for deoxyribonucleic acid. thereby increasing the speed of reaction. skin) a unit of inheritance. kidneys. sweating) or from respiratory surfaces (eg. includes cells of protists. heart. fungi. lungs. plants and most animals except for mammals and birds are ectothermic the maintenance of metabolic and physiological functions in response to variations in the environment hormonal system that produces internal secretions which act upon organs animal that regulates its body temperature using heat generated by its metabolism. the molecule which makes up the genetic material of the chromosomes part of an organism which produces a response (eg. the names of enzymes often end in -ase eg. animals and plants the system of glands that secretes hormones removing heat from the body by changing liquid water to water vapour using heat from the skin surface (eg. diaphragm) organism that changes its body temperature by using heat from the environment. gymnosperms haemoglobin herbaceous homeostasis homeothermy cone-bearing plants a complex protein molecule found in red blood cells which transports oxygen Characteristic of a soft plant. heat is produced as a by-product of metabolism microscopic tubules which make up the functional units of the mammalian kidney the system of nerves and nerve centres in an animal Malphigian tubules metabolic pathway metabolism nephron nervous system viii Maintaining a balance . the system is also involved in the immune response and with transport of the breakdown products of fat digestion excretory organ found in insects a series of step-wise chemical reactions. each of which is governed by an enzyme. Cellular respiration and photosynthesis are metabolic pathways all of the biochemical reactions occurring in the cells of the body. the major component of wood system of thin-walled vessels and groups of tissue (lymph nodes) which drain the fluids from around cells back to the bloodstream (as a fluid called lymph). temperature regulation) Having equal osmotic pressures hypothalamus isotonic kidney lignin lymphatic system an organ involved in excretion and osmoregulation a material which strengthens and keeps xylem vessels open. having no woody tissue the tendency in an organism towards maintenance of physiological stability maintenance of a stable body temperature independent of changes in environmental temperature area in the brain which acts to integrate the endocrine and nervous systems in homeostatic control of many body functions (eg. consisting of at least two types of tissues eg. thyroid gland) liquid part of the blood. amino acids) and formed blood elements are carried (red cells. making up around 55% in humans. kidney. sugars. in animals – heart. stems. liver any part of a cell which has a specific functional role. gymnosperms and angiosperms small structure in the brain which secretes hormones. in eucaryotic cells. includes temperature and pH functional and structural unit of most multicellular organisms. It is normally measured as the amount of substrate(s) optimum organ organelle osmosis osmoregulation phloem pituitary plasma platelets procaryotic (prokaryotic) proximal tubule pulse rate rate of reaction Introduction ix .nitrogenous wastes waste products from metabolic activities involving nitrogen-containing compounds (eg. carbon dioxide. leaves. including ones which control the functions of other endocrine glands (eg. proteins. in which materials are dissolved (eg. amino acids) conditions at which enzymes work best. includes Archaebacteria and Eubacteria convoluted tubule between the loop of Henle and Bowman’s capsule measure of heart rate (beats per minute) taken by palpating a position where an artery crosses a bone the speed at which a reaction proceeds. white cells and platelets) fragments of cells found in the blood which are involved in the clotting process cells which do not have their genetic material (chromosomes) bound by a membrane and do not have other membrane-bound organelles in their cells. organelles are normally bound by a membrane the movement of water from where it is in high concentration to where it is in low concentration through a selectively permeable membrane the control of body water and salt levels tissue which transports products of photosynthesis (translocation) in ferns. in plants – roots. used up or the amount of product(s) formed in a given amount of time receptor sensory cell responding to some internal or external environmental variable (eg. it refers to the 'pulling' of water molecules from the roots to the leaves by negative pressure a group of cells. These pores are controlled by two guard cells which regulate the loss of water from the leaves (transpiration) difference in temperature. It is found in junket tablets used to make a dessert out of milk and flavouring (sort of yoghurt dessert) a special surface for gaseous exchange change in an organism produced by a change in its internal or external environment an environmental factor (inside or outside the body) which is detected by a receptor (eg. Heat energy flows from an area of higher temperature to one of lower temperature endocrine gland in the throat area which produces thyroid hormones hormones involved with regulating the level of body metabolism TSH. cells in the brain responding to CO2 level or temperature of the blood) the aretery bringing blood to the kidney the vein taking blood from the kidney an enzyme found in the stomachs of mammals (especially young). found in a multicellular organism having a specific renal artery renal vein rennin respiratory surface response stimulus salt gland stomates (stomata) temperature gradient thyroid gland thyroid hormones thyroid stimulating hormone tension tissue x Maintaining a balance . CO2 levels in the blood. hormone released by the pituitary gland which controls the functioning of the thyroid gland part of the transpiration-tension-cohesion theory of water movement in xylem tubes. which makes milk go solid (coagulate). usually of similar type. temperature of the blood) structure found in marine birds and turtles which permits excretion of excess salts holes (pores) in the leaves of plants. including the plants ferns. largely insoluble and excreted as a paste with little water a waste product containing 2% urea a group of phloem. reptiles and birds. diluted by water and excreted in urine main nitrogenous waste product of insects. gymnosperms and angiosperms. xylem and cambium tissue in a stem plants which have conducting vessels. which belong to the phylum Trachaeophyta increase in the diameter of blood vessels to increase blood flow decrease in the diameter of blood vessels to decrease blood flow blood vessel which returns blood to the heart tissue which transports water and minerals upwards from roots to leaves in ferns. blood. conebearing and flowering plants (Trachaeophyta) urine vascular bundle vascular plants vasodilation vasoconstriction vein xylem Introduction xi . phloem. bone) Trachaeophyta translocation transpiration transpiration stream urea uric acid vascular plants movement of products of photosynthesis in the phloem of plants evaporation of water from the leaf surfaces of plants movement of water in the xylem tissue breakdown (deamination) of excess amino acids. in plants – epidermis. in animals – epithelium. xylem. xylem and phloem.structure and function (eg. Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 1: Enzymes I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . Gill Sans Bold Contents Introduction ............................................................................... 2 Enzymes ................................................................................... 4 The role and chemical composition of enzymes.................................4 Enzyme models....................................................................................6 Enzymes and temperature...................................................................7 Enzymes and pH ..................................................................................9 Enzymes and substrate concentration ..............................................10 Some questions about enzymes ......................................................11 Investigating an enzyme’s activity ....................................................13 The enzyme catalase and hydrogen peroxide .................................18 Suggested answers................................................................ 21 Exercises – Part 1 ................................................................... 25 Part 1: Enzymes 1 Introduction During your study of the Preliminary you learnt that DNA is the genetic material of most living organisms. DNA makes up the chromosomes found in the nucleus of eucaryotic organisms and forms chromosomes not bound by a nuclear membrane in procaryotic cells. Genes are sections of specific DNA molecules making up the chromosomes that determine cell function, and therefore ultimately the functioning of whole organisms, by determining which proteins will be produced in cells. Some proteins form part of the structure of cells (for example, part of the cell membrane) but many are enzymes, which control the functioning of cells by speeding up chemical reactions that would not normally occur under conditions found in cells. This part of the module looks at the action of enzymes. You will need the following equipment for an experiment: • • • • • • • • • test tube-sized containers of the same size, made of glass or heat-resistant plastic glass or heat-resistant plastic containers into which two of the test tube-sized containers will fit 1 junket tablet (You will need to buy a packet.) 1 small container of full cream milk milk powder 1 tray of ice blocks 1 eye dropper or pipette 1 medicine measure 1–3 thermometers (0–100°C range). 2 Maintaining a balance Gill Sans Bold In this part you will have the opportunity to learn to: • identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates identify the pH as a way of describing the acidity of a substance • In this part you will have the opportunity to: • identify data sources, plan, choose equipment or resources and perform a first–hand investigation to test the effect of: – – – increased temperature change in pH change in substrate concentrations on the activity of a named enzymes. Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board’s website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html. This version October 2002. Part 1: Enzymes 3 An example of an enzyme – sucrase Sucrose. is normally extracted by crushing out the contents of the phloem tissue of sugarcane plants. where the sucrose molecule (the substrate or reactant) is digested to form glucose and fructose (the products). The reaction can be summarised as follows. This enzyme will only break down sucrose sugar. It is broken down in the small intestine into its two component sugars by an enzyme called sucrase. SUBSTRATE PRODUCTS sucrase enzyme present glucose + fructose sucrose molecule The sugar in your sugar bowl does not break down into glucose and fructose and will only do so when the enzyme sucrase is present. 4 Maintaining a balance . This carbohydrate consists of two simpler sugar molecules – one glucose and one fructose molecule. They cause chemical reactions to proceed which would not normally occur under the conditions found in most cells.Enzymes The role and composition of enzymes Enzymes are organic catalysts. Sucrose is too large to be absorbed directly into the bloodstream from the digestive system. which is the sugar used in sweets and cakes and to sweeten tea and coffee. The molecules of glucose and fructose are small enough to be directly absorbed through the membranes of the digestive system into the bloodstream. Part 1: Enzymes 5 . _____________________ Yes. The shape of each enzyme molecule makes it able to take part in a specific kind of chemical reaction. protein molecules also have a three-dimensional structure as well. maltase. which gives each protein molecule a particular shape. sheep and kangaroos digest the high fibre in their diets. Like sucrose. Here is the overall reaction for the breakdown of maltose: SUBSTRATE maltose molecule PRODUCTS glucose + glucose Predict the name of the enzyme that causes this to happen in the small intestine. Do Exercise 1. number and arrangement of the amino acids (their primary structure). As well as the type. is made up of two glucose units. The building blocks of proteins are amino acids. Cellulase enzymes in the stomachs of these species digest cellulose. Fibre is mainly a material called cellulose. Many enzyme names end in -ase. This means that there are many different enzymes within each organism to control all the reactions that are part of the organism’s metabolism. You might remember from the Patterns in Nature module that bacteria in the stomachs of cattle. also found in a lot of sweets. This demonstrates that enzymes are very specific.1 now. Each enzyme changes the rate of one kind of chemical reaction only. Chemical composition Enzymes are proteins.Gill Sans Bold Another example Maltose sugar. There are only 20 types of amino acids which make up proteins but they can be joined in various ways to produce different proteins. this sugar needs to be digested using an enzyme before it can be absorbed into the bloodstream. In normal chemistry. An induced fit model A more refined explanation or model for enzyme function is that the shape of the enzyme on its own does not quite fit the substrate molecule’s shape but the shape of the enzyme is changed so that it becomes an exact fit. causing a reaction to occur. substrate product enzyme enzyme-substrate complex enzyme resumes original configuration Induced fit model of enzyme function. of course. it won’t open the door! It is thought that the enzyme only fits particular molecules to cause them to react. this is not possible in cells. This model of enzyme function is sometimes called the lock and key model. This can be thought of as a key (the substrate) fitting the lock (the enzyme). A simple lock and key model At a molecular level. The enzyme is not used up in the reaction and can be used again. It is like a glove being roughly the shape of your hand but not fitting completely until it is pulled on. This is referred to as the induced fit model of enzyme function. It works a bit like this: substrate + enzyme enzyme/substrate complex products + enzyme The complex between the enzyme and the substrate (or substrates) molecules reduces the energy required to get the reaction to happen (activation energy). Unless a key is right for a particular lock. 6 Maintaining a balance . the shape of an enzyme permits it to bind at a particular site (active site) to the substrate molecule (or molecules). heating to high temperatures provides this energy but.Enzyme models Why is the shape of each enzyme important? Here are two models to explain how the shapes of enzymes are involved in speeding up reactions. Think about the white of an egg – it mainly consists of protein. The change brought about by cooling is reversible. they slow down in their activity and eventually they no longer make the specific reactions work. Because enzymes are proteins. If you cool enzymes down. The formation of the enzyme-substrate complex induces a change in the shape of the enzyme molecule so that it fits the substrate perfectly at the active site (middle picture). if you put the uncooked egg white into the freezer. they stop working. Enzymes and temperature Temperatures affect all proteins. • • The enzyme has an active site in its structure into which the substrate (or substrates) fit (left picture). But if you warm them up once more they work again until the temperature goes past their optimum.2 now. which shows a slow increase in enzyme activity as temperature increases to the optimum. Its properties have changed and this change is not reversible – even if you cool the egg white down again it remains a white solid! However. Once the substrate is broken down (or the substrates are joined) into the product. The fall occurs because the enzyme is said to be denatured irreversibly. If you cook it (raise it to high temperature). it changes from being a clear liquid to become a white solid.Gill Sans Bold Use the following explanation to interpret the diagram of the induced fit model. If you heat them above the temperature at which they work best (their optimum temperature). Part 1: Enzymes 7 . This can be represented in a graph. they are also affected by changes in temperature. the enzyme is released from the complex and resumes its original shape (right picture). • Do Exercise 1. The graph is on the following page. followed by a rapid fall in activity to zero above that temperature. it becomes solid and goes a little milky in colour but returns to being a clear liquid if you thaw it out. Above this optimum temperature the activity rapidly drops to zero. there are other species whose enzymes can function over a greater range of temperatures. 8 Maintaining a balance . Above the optimum. Your enzymes work best at around 37°C and are denatured above this temperature. Change with cooling occurs because the lower temperature changes the shape of the enzyme molecule. This shape change caused by heating damages the enzyme molecule permanently. So why does denaturing happen? Well. the change in shape of the enzyme is permanent – the enzyme is said to have become denatured. Cooling also changes the shape of the molecule but this change does not permanently stop the enzyme from functioning. the shape of the enzyme is changed rapidly so that it no longer fits the substrate. For an enzyme this means that its shape no longer fits the substrate and so the enzyme can no longer work. going back to the egg white example. At low temperatures there is little activity but this increases as the temperature is raised to the optimum (temperature at which the enzyme works best). You might realise now why having your body temperature above the normal of 37°C can be considered quite serious. type and sequence of amino acids does not change when you heat it but the three-dimensional shape of the molecule does change. The change brought about by cooling is reversible but that caused by excess heating is irreversible – that is.100 maximum activity at optimum temperature increasing activity as temperature increases enzyme denatured (damaged) by too high a temperature Percentage maximum activity 80 60 40 20 0 low activity at low temperature activity falls to zero because enzyme has been irreversibly changed 10 Temperature (!C) 20 30 40 50 60 The effect of temperature on enzyme activity. the number. However. which has very acid conditions. The following graph shows the relationship between pH and enzyme activity for two digestive enzymes. Relative activity pepsin trypsin 0 2 4 6 pH 8 10 12 The effect of pH on enzyme activity.4 and will die if it goes above 7. 1 What is optimum pH for pepsin and trypsin? _____________________________________________________ 2 Could pepsin continue to work when it moves with food from the stomach into the small intestine? Why? _____________________________________________________ _____________________________________________________ _____________________________________________________ Check your answers. while trypsin is found in the small intestine. where conditions are slightly alkaline.0 (more acid). Enzymes are denatured both above and below their optimum pH. This can be different for different enzymes. maintain their blood pH at 7.Gill Sans Bold Enzymes and pH Each enzyme also has a specific pH at which it works best (optimum pH) but enzymes are rapidly denatured either above or below that optimum. Humans. It should be remembered that many species have very narrow ranges of pH over which they function. for example. pepsin is an enzyme found in the stomach. Part 1: Enzymes 9 . An enzyme has a pH at which it works best (its optimum). For example. Use the graph to answer these questions.7 (less acid) or below 7. So what is pH? pH is a figure given for acidity or alkalinity of a solution. rain water detergent vinegar battery acid celery blood milk cloudy ammonia caustic soda Mr OVEN Cleaner lemon juice Top tea Glo MILK Pure DISTILLED pure water Cream Cleanser & Ammonia stomach BRASSO Metal Polish Water 1 2. Enzymes and substrate concentration In any chemical reaction. the rate of a reaction is controlled more by the concentration of enzyme available than by the concentration of substrate. a solution with a pH of 2 (such as stomach acid) is 10 times more acidic than one with a pH of 3 and 50 times more acidic than one with a pH of 7.9 6. A pH of seven is called neutral because it is neither acidic or alkaline.0 Complete Exercise 1.0 11. It rises in jumps of 10.6 5.8 5.4 8. However. in living organisms. increasing the concentration of substrate tends to make the reaction occur more quickly – the rate of reaction is increased.0 7.0 11. For example. human blood is very slightly alkaline.8 9. Here are some examples of substances along the pH scale. 10 Maintaining a balance .8 7.5 13.0 6. more substrate could be taken into the body as food or produced by other chemical reactions in cells.9 12.2 5.4.5 5.3 now. The graph on the next page shows a typical response in the rate of reaction to the increase in substrate concentration in a living organism. but only to a certain level. The graph shows that the rate of a reaction will increase as the substrate concentration is increased.0 2. for example.5 10. So you would expect that the rate of any reaction would keep on getting faster if more substrate is made available.9 3. With a pH 7. As a reaction proceeds. The concentration of substrate is increased but the amount of enzyme held constant. It speeds up the rate of a specific reaction.Gill Sans Bold Rate of reaction Substrate concentration The effect of substrate concentration on rate of reaction. enzymes released from their complex with substrate molecules are used again. the rate of reaction becomes constant. This tends to keep the rate of reaction constant unless the enzyme concentration changes or conditions of temperature or pH are modified. remember that the enzyme molecules can be reused. Part 1: Enzymes 11 . After an initial rise in the rate. It breaks down larger molecules into smaller ones only. However. The reaction rate slows then becomes constant because there are not enough enzyme molecules to combine with each substrate molecule to make the reaction work any faster. 1 Which statement below best describes the role of an enzyme in cells? A B C D It speeds up the rates of all reactions. Some questions about enzymes Answer the following questions to check your comprehension of the role of enzymes. It builds up small molecules into complex ones only. The rates of reactions in living organisms are therefore determined by: • • • • temperature pH substrate concentration the amount of enzyme available. The available active sites on the enzyme molecules become saturated. 2 Combination of a substrate with an enzyme is necessary to permit the enzyme to function. specific amounts unchanged proteins 3 Enzymes are affected by: A B C D 4 Fill in the missing words using the following word list – temperature pH speed up Enzymes: • • • • • • • • are chemicals called _________________________________ ___________________ the rate of chemical reactions in cells are involved in chemical reactions but are _______________ at the end of the reaction and can be reused are needed only in very small ____________ are _____________ to particular reactions or groups of reactions are affected by ________________ are affected by ________________ may need other chemicals as co–enzymes (often containing vitamins) or co–factors (often minerals) to help them function. 12 Maintaining a balance . This is because the enzyme-substrate complex: A B C D increases the energy of the reaction reduces the amount of energy produced by the reaction reduces the amount of energy necessary to start the reaction increases the amount of energy necessary to start the reaction. temperature but not pH and are not used up in the reaction pH but not temperature and are used up in the reaction temperature and pH and are not used up in the reaction temperature and pH and are used up in the reaction. in junket tablets. by making milk solid. especially young ones which consume a lot of milk. called rennin. a pH of 3 or a pH of 11? _______________ Check your answers. The effect of changing temperature Your task is to perform an experiment to demonstrate how changing temperature affects the activity of an enzyme. temperature and concentration of substrate and the accumulation of products can alter the rates of enzyme-mediated reactions. You can buy rennin. This enzyme.Gill Sans Bold 5 Draw a graph which represents the change in the activity of an enzyme from the stomach of a human as its temperature is changed from 0 to 45oC. People use junket tablets to make a sort of yoghurt dessert from milk. You can use an enzyme found in the stomachs of mammals. Investigating an enzyme’s activity The pH. Rennin naturally occurs in the stomach because. 100 80 60 40 20 0 10 20 30 40 50 60 6 Which is more acidic. from the grocery store or supermarket. Part 1: Enzymes 13 . causes milk to go solid. it slows the movement of milk through the animal’s digestive system. The easiest factor to manipulate outside a laboratory is temperature. if you’d like some help. 14 Maintaining a balance . e ice water 10 mL milk 0–5!C c e c e c 35–40!C water baths 75–80!C e = enzyme c = control Experimental set up for investigation of the effect of temperature on enzyme activity using the enzyme rennin. Be careful with this! Use safe working practices. Method: You will need the following: • • • • • • • • • 6 test tube-sized containers of the same size made of glass or heat-resistant plastic 3 glass or heat-resistant plastic containers into which 2 of the test tube-sized containers will fit 1 junket tablet (you will need to buy a packet) waterproof felt-tipped pen 1 small container of full cream milk 1 tray of ice blocks 1 eye dropper or pipette 1 medicine measure 1–3 thermometers (0–100°C range). Aim: To investigate the effect of changing temperature on enzyme activity.You can plan and perform your own investigation. You will also need access to boiling water from an electric jug or urn. Read the directions on the junket packet for some clues. wear covered footwear. follow the experimental plan below. Or. Grind up a junket tablet in about 10 mL of cold water. Now use the ice and water (hot/cold) to bring your water baths to the three different temperatures. Measure 10 mL of milk into each of the six test tube-sized containers. 35–40°C (body temperature) and 75–80°C (hot). You need to use the three larger containers as water baths. 5 6 7 8 9 Hypothesis: You need to have made a hypothesis for what you expected to happen. You will need to use it again in the next practical. which you maintain around 0–5°C (cold). Place 1 control and 1 enzyme container into each water bath container. When the milk is at the correct temperature. Ice in water should keep the cold bath within the temperature range but you will need to keep adding hot water from time to time to maintain the temperatures in the other water baths. you can assume the enzyme is not working. _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 1: Enzymes 15 . You probably expected the enzyme to make the milk go solid at body temperature (the temperature in the stomach where it normally works) but probably not to work at the cold or hot temperatures.Gill Sans Bold The diagram shows how you should set up the experiment. Use your thermometer(s) to determine when the milk in the containers has reached the temperatures in each water bath. If it has not gone solid within 15 minutes after adding the enzyme mixture. add 4–5 drops of the junket mixture to each of the enzyme containers (not the controls). Work through the rest of the practical exercise but do not clean up your experimental set up yet. Steps: 1 2 3 4 Label three test tube-sized containers as control and three as enzyme using a waterproof felt-tipped pen. Record the time immediately. Would this be a reasonable hypothesis? State what you expected to happen in your own words. Record the time it takes for the milk to go solid. while heating above the optimum usually denatures them. Temperature range Time for milk to set (minutes) Control 0–5°C 35–40°C 75–80°C Enzyme Discussion: Did your experiment support your hypothesis? _________________________________________________________ Did the milk go solid in any of the control tubes? Explain why you used the control containers. State what you would expect to happen if you put the containers of milk from the hot and the cold water baths into the 35–40°C bath? _________________________________________________________ _________________________________________________________ Make sure that your 35–40°C water bath is at the right temperature and then transfer the containers from the hot and the cold baths to it. 16 Maintaining a balance .4 as a conclusion to this experiment. _________________________________________________________ _________________________________________________________ You will remember that changes to enzymes by cooling them below their optimum temperatures are normally reversible. Were the results what you expected? _________________________________________________________ _________________________________________________________ Do Exercise 1. Describe the results.Results: Record your results in the table below. changed pH and variations in substrate concentrations affect an enzyme’s activity? Here is another example of an enzyme that you can use to check your understanding of enzymes. What hypothesis are you testing? _________________________________________________________ _________________________________________________________ Write your conclusion in Exercise 1. Are you confident that you can describe how increases in temperature. If you have powdered milk. but it is difficult to set exact levels of pH outside a laboratory. Plan and perform your own simple experiment to investigate how changing the pH of milk affects the ability of rennin to thicken milk. you can increase the concentrations of these substances by adding powdered milk to normal milk. you can alter the pH of the milk (substrate) in your experiment by adding a few drops of vinegar (acid) or a quarter of a teaspoon of bicarbonate of soda (alkali).) What hypothesis are you testing? (What do expect to happen?) _________________________________________________________ _________________________________________________________ Write your conclusion in Exercise 1.6. Part 1: Enzymes 17 .Gill Sans Bold The effect of changing pH You could have done an experiment similar to this one using different pH levels. You can reduce the concentrations of these substances by adding water to the milk.5. Plan and perform your own simple experiment to investigate how changing the concentration of milk substances affects the ability of rennin to thicken the milk. (Hint: Perform your tests at 35–40°C. However. The effect of changing substrate concentrations The substrate in your experiment is substances found in milk. where you have access to chemicals and equipment used to accurately change the pH and to measure its change. 18 Maintaining a balance . and make a froth on the surface. It is also the product of some reactions in cells. oxygen is released. very slowly. You could have investigated the effect of temperature on this reaction by comparing the amount of oxygen released at different temperatures. much as you did with the rennin experiment.The enzyme catalase and hydrogen peroxide Hydrogen peroxide solution is used as an antiseptic and as a bleach. It can also be used to show the effect of pH on the catalase enzyme. no reaction froth = evolution of oxygen froth hydrogen peroxide cube of potato cells (containing catalase enzyme) pH level 2 6 8 10 Catalase/hydrogen peroxide experiment. If small cubes of potato of the same size are placed into test tubes of hydrogen peroxide. It is poisonous and so living organisms have an enzyme in their cells which quickly break it down into oxygen and water. this reaction occurs but very. Look at the diagram below which shows such an experiment done by a student at four different pH levels. The reaction looks like this: 2H2O2 hydrogen peroxide catalase enzyme 2H2O water + O2 oxygen Without the enzyme catalase. since potato cells contain some of the catalase enzyme. The height of this froth can be measured as an indication of the amount of enzyme activity. both of which are harmless substances. Oxygen bubbles form in the liquid in the test tube. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 1: Enzymes 19 . Remember your design needs to contain a control and you need to indicate how you would measure the enzyme activity. Provide an explanation for your answer. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 4 Design an experiment to investigate the effect on enzyme activity of increasing the concentration of hydrogen peroxide (substrate concentration) – perhaps use 2. 10. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 The student did not use a control in the experiment. 20% hydrogen peroxide solutions. Predict the results for your experiment. Describe how you would have designed the experiment to include a control. 1 Describe the effect of pH changes on catalase enzyme function. 5.Gill Sans Bold Study the experiment then answer the following questions. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 State what the optimum pH for this enzyme might be. taking part in many different reactions to make up your metabolism. for example. As you have seen. enzymes operate optimally with very specific conditions. So how does this affect a living organism? Take you. You’ll learn about how this monitoring (measuring) and control occurs in Part 2.______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ Check your answers. There are many different enzymes within your body. The conditions inside your body have to be very carefully controlled for all these reactions to occur at their best. 20 Maintaining a balance . Any little change in conditions has to be noticed and put right to keep your body functioning normally. C is correct.9.Gill Sans Bold Suggested answers Enzymes and pH 1 2 The optimum pH for pepsin is approximately 2. the optimum pH for trypsin is approximately 8. 3 4 Part 1: Enzymes 21 . The enzyme-substrate complex reduces the amount of energy which is necessary to start the reaction (called the activation energy). Pepsin would be denatured as it was moved from the acidic stomach into the slightly alkaline small intestine. Some questions about enzymes 1 2 B is correct. Enzymes • • • • • • • • are chemicals called proteins speed up the rate of chemical reactions in cells are involved in chemical reactions but are unchanged at the end of the reaction and can be reused are needed only in very small amounts are specific to particular reactions or groups of reactions are affected by temperature are affected by pH may need other chemicals as co-enzymes (often vitamins) or co-factors (often minerals) to help them function. Enzymes are affected by both temperature and pH but are not used up in reactions. Any enzyme speeds up a specific reaction (or type of reaction) in a cell. C is correct. A control test tube with hydrogen peroxide (and acid or alkali added to produce the required pH level). record the height of the froth as a measure of enzyme activity. The optimum pH for the enzyme was between 8 and 10 – the height of the froth was highest at pH 8 but had declined markedly by pH 10. 5. Remember that decreasing pH equals increasing acidity. after which it declined to very little at pH 10. 2 3 4 22 Maintaining a balance . This would establish that the reaction only occurred in the presence of the potato (containing the enzyme). • • • • Set up two test tubes using each concentration of H2O2 (2. would need to be included for each pH level. After the same amount of time (say 2 minutes). Use the same volume in each test tube. 100 Percentage maximum activity 80 60 40 20 0 10 20 30 40 50 60 Temperature (!C) 6 A pH of 3 is more acid than one of 11. It should drop rapidly to no activity above 37°C. Insert a piece of potato of the same size into one tube (to supply the same amount of enzyme) of each pair of test tubes. 10. The enzyme catalase and hydrogen peroxide 1 The enzyme activity.5 The graph should show an increase in activity from low/no activity at 0°C to maximum activity around the normal body temperature of a human (37°C). Experiments at pH levels between these 8 and 10 would need to be done to find out the optimum more accurately. The tubes without the potato are the control experiments. Here is an example of suitable experiment. measured by the height of the froth produced by the oxygen given off. 20%). but with no potato. and increasing pH equals increasing alkalinity. was zero at a pH of 2 but increased up to a pH of 8. Part 1: Enzymes 23 . In that case. • Remember.Gill Sans Bold Hypothesis (what you expected) • There would be no reaction (no froth) in any of the control tubes. of course. indicating that the presence of the potato (containing the enzyme) caused the reaction. the level of activity (height of the froth) may have levelled off after a certain concentration. The highest level of activity (height of the froth) would be in the most concentrated solution. that your hypothesis may not have been supported as there may not have been enough catalase enzyme available for the reaction to keep increasing with increased substrate concentration (see ‘Enzymes and substrate concentration’ in this part of the module). 24 Maintaining a balance . Gill Sans Bold Exercises Part 1 Exercises 1.1 to 1.6 Name: _________________________________ Exercise 1.1: The role and chemical composition of enzymes a) What is the role of enzymes in the metabolism of an organism? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) What is the general chemical composition of enzymes? _____________________________________________________ _____________________________________________________ c) Give an example of an enzyme and outline the reaction in which it participates. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 1: Enzymes 25 . select the enzyme that would speed up the above reaction. Give reasons to justify your choice.3: Enzymes and pH Normal human urine has a pH of less than 6.Exercise 1. Why do enzymes have different shapes? ______________________________________________________ ______________________________________________________ Exercise 1. substrate products a) From the choices below. Is this acidic or alkaline? _________________________________________________________ 26 Maintaining a balance . A C B D ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ b) Each enzyme has an active site in its structure that fits into only one substrate.2: Enzyme models Look at the following model used to explain the action of enzymes. Gill Sans Bold Exercise 1. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 1: Enzymes 27 .5: The effect of changing pH Write a conclusion for your investigation.6: The effect of changing substrate concentrations Write a conclusion for your investigation. Conclusion: _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 1. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 1.4: The effect of changing temperature Write a couple of sentences stating what this experiment has shown you about the effects of temperature on enzyme function. Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 2: Homeostasis and temperature regulation I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . . ................................. 25 Exercises – Part 2 .....4 Homeostasis and feedback ............Gill Sans Bold Contents Introduction .............................................. 4 Collecting and using information ............................................. 8 Control of body heat production (heat gain) .12 Limitations to temperature regulation..........................................................20 Suggested answers...............................................20 Some questions about temperature regulation.................................................................................................................................. 17 Adaptations and responses to temperature regulation .................9 Control of heat loss ... 23 Additional resources...................... 2 Homeostasis ..............................................................................................5 Temperature regulation for endotherms .........................................................................................................15 Temperature regulation for ectotherms ...........................................................11 Summary .................................................. 20 Australian endotherms and ectotherms ..................................... 31 Part 2: Homeostasis and temperature regulation 1 .............................................................................................................................. All of these organ systems need to be controlled and coordinated in their functions.Introduction Multicellular organisms are made up of a number of organ systems. This control and coordination is brought about by two systems in mammals – the nervous system and the endocrine (or hormonal) system. and the cells that make up those tissues. Here are some examples: • • • • the muscles of the skeleton carry out support and movement the lungs bring about gaseous exchange the digestive system facilitates digestion and absorption of food substances and materials needed by the cells waste products formed in the cells are transported around the body by the blood system. are specialised to carry out specific tasks. The tissues in each system. In this part you will have the opportunity to learn to: • • • explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency describe homeostasis as the process by which organisms maintain a relatively stable internal environment explain that homeostasis consists of two stages: – – • • • detecting changes from the stable state counteracting changes from the stable state outline the role of the nervous system in detecting and responding to environmental changes identify the broad range of temperatures over which life is found compared with the narrow limits for individual species compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation 2 Maintaining a balance . process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism analyse information from secondary sources to describe adaptations and responses of Australian organisms that assist temperature regulation.edu. originally issued 1999.nsw. Part 2: Homeostasis and temperature regulation 3 .boardofstudies.au/syllabus_hsc/syllabus2000_lista.html This version October 2002. The most up-to-date version can be found on the Board's website at http://www. In this part you will have the opportunity to: • • gather. Extract from Biology Stage 6 Syllabus © Board of Studies NSW.Gill Sans Bold • identify some responses of plants to temperature change. If your hand comes too close to a fire. or both. For instance. are responsible for most control and coordination in animals. These stimuli normally result in some sort of response from a particular organ or number of organs. which gets rid of the extra CO2. Stimuli received from the environment make you aware of your surroundings. using the nervous and hormonal systems. the cells’ metabolism will be most efficient. Collecting and using information All organisms receive information from the various parts of their bodies and from their environment in the form of stimuli (singular is stimulus). during exercise. The stimulus often does not affect an organ directly but instead responses occur as a result of transmission through the nervous system. stimulates special cells in the skin of your hand resulting in nerve impulses being transmitted to the part of your brain that interprets these impulses as your hand getting hot. Stimuli also come from inside the body. for example. respiration in the muscle cells increases the carbon dioxide (CO2) level in the blood. plants do not have a nervous 4 Maintaining a balance . you respond by pulling it away. This stimulates an increased breathing rate. Plants have a hormonal system which controls and coordinates body processes. However.Homeostasis How do organisms maintain a balance within their tissues. As far as is known. Using information to maintain a balance Responses to stimuli. to keep conditions optimal for cellular processes? When conditions are optimal. the way this system works is less well understood in plants than in mammals. the endocrine (hormonal) system. The heat is the stimulus and using the muscles of your arm to pull your hand away is the response. Heat from a fire. Part 2: Homeostasis and temperature regulation 5 . You have already come across the idea of homeostasis. Homeostasis involves the systems of control and coordination. but their activities are controlled and coordinated so that homeostasis is maintained. the return to the normal temperature level is detected by the thermostat and the heater is turned off. Homeostasis and feedback The working of a typical household electric water heating system is a practical application of how homeostasis is maintained. or the process of keeping conditions inside the organism relatively constant. Follow around the cycle in the diagram below. you get water flowing from the hot water cylinder at about 70°C. Homeostasis consists of two stages: • • detecting changes from the stable state counteracting changes from the stable state. This water is replaced by colder water coming into the cylinder. or stable.Gill Sans Bold system. Once the water has heated back up to 70°C. Homeostasis is maintained and you have hot water when you need it. When you are not using hot water. the insulation surrounding the cylinder reduces the loss of heat. But heat will still gradually be lost and the temperature of the water in the cylinder will fall. The drop in water temperature is detected by the thermostat and it switches on the heater in the cylinder. beginning at the stimulus. STIMULUS reduction in cylinder water temperature FEEDBACK change in cylinder water temperature RESPONSE heater heats up water in cylinder RECEPTOR thermostat senses drop in water temperature EFFECTOR heater TRANSMISSION electric current in wires transmits information to the heater When you turn on the hot tap in the shower or the sink. Any change in temperature is again sensed by the thermostat and the heater is switched on and off during the day to maintain the temperature of the water inside the cylinder. When you are exercising. 6 Maintaining a balance . During exercise. your breathing will remain rapid. This rise is detected by a centre in your brain. the level of CO2 in your blood rises. the cells of your muscles are producing a lot of carbon dioxide (CO2) which needs to be removed from your body. The stimulus information has been done for you to get you started. It is sometimes referred to as the stimulus–response model. the rapid breathing will result in the CO2 level of the blood coming right back to normal. STIMULUS RECEPTOR FEEDBACK RESPONSE EFFECTOR TRANSMISSION You've seen that this model can be used to explain the hot water cylinder example mentioned above. The rapid breathing gets rid of excess CO2 through the lungs and the level in the blood falls back towards normal. as the level of CO2 in your blood will rise again almost immediately. If you keep exercising. If you stop exercising. so that they contract more often and you breathe more rapidly. Your breathing will slow down again.The diagram below represents a general model. which can be applied to many biological examples. Use the information you have just read (about how CO2 levels in your blood are controlled) to complete the diagram on the next page. It can also be used for biological feedback. such as the effect of exercise on breathing rate. which sends more frequent nerve impulses to the muscles of your chest and diaphragm. This will be detected by your brain which will then reduce the frequency of nerve impulses to your chest muscles and diaphragm. How did you go? In this example. which control and coordinate its functions. Part 2: Homeostasis and temperature regulation 7 . the breathing centre in the brain is the receptor and transmission of information to the muscles and diaphragm occurs as impulses passing through the nerves. and others you will deal with in this module further illustrate the concept of stimulus-response pathways to maintain homeostasis. It is turned on when the water in the cylinder decreases in temperature. Don’t worry too much if you didn’t get it all correct. or as the water cools slightly during the day. when you use more hot water. The term feedback appears in the diagrams of the models and it needs to be discussed. change often occurs to meet demands. the response (rapid breathing) is turned off once the high carbon dioxide level (stimulus) is reduced back to normal. as a result. the heating response is turned off as the temperature of water in the cylinder (stimulus) increases back to 70oC. The effectors are the chest muscles and the diaphragm which produce the response of rapid breathing. Control and coordination in mammals are normally maintained in a similar way because the response modifies the initial stimulus and. the raised blood CO2 is the stimulus.Gill Sans Bold STIMULUS increase of CO2 in blood FEEDBACK RECEPTOR RESPONSE EFFECTOR TRANSMISSION Check your answers. In the example of the hot water cylinder.1. Complete Exercise 2. A feedback occurs when the response changes the stimulus. for example. There are lots of systems like this in the body. In the example of breathing rate changing in response to exercise. the response itself is changed. In homeostasis. but the system ensures that normal levels are eventually re-established. How can these animals maintain a stable temperature? Heat is a form of energy Heat moves from where there is a lot of it (something which is hotter) to where there is less of it (something which is colder). If an animal is to maintain a constant body temperature: Heat gained must equal heat lost. The heat an organism loses or gains from the environment has to be balanced against the heat that it produces by its own cellular processes (metabolism). Something ‘feels’ cold because you are losing heat to it. which do not internally maintain a stable body temperature with changing environmental temperatures. (You also considered ectotherms. 8 Maintaining a balance . body temperatures are normally regulated 4–5°C higher than in placental mammals. In birds.Temperature regulation for endotherms Birds and mammals control their body temperatures at constant levels over the range of environmental temperatures in the places in which they live. Temperature is a measure of the amount of heat present in an object. For example. 36°C in the marsupials and 37°C in the placental mammals. a can of drink taken from the fridge ‘feels’ cold because heat is moving from your hand (which is hotter than the can) to the can (which is colder than your hand).) Body temperatures are maintained around 32°C in the monotreme mammals (platypus and echidnas). These groups are the endotherms or endothermic species which you considered earlier in the Preliminary course in the module called Evolution of Australian biota. There is no such thing as ‘cold’. On a cold day you are losing more heat from your body to the environment than you would on a warm day and so you ‘feel’ cold. especially cellular respiration. Any slight reduction of the temperature of the blood is detected by the hypothalamus in the brain. especially the liver and muscles. Minute to minute regulation of temperature is controlled by the nervous system. involving a number of feedback systems. This generation of heat is largely controlled by the endocrine system. shivering and dilation and constriction of blood vessels. Most metabolic processes. less secretion of thyroid hormones from the thyroid gland and therefore less heat being generated by metabolism of tissues. Except in cold environments. These are: • • by increasing the metabolic rate of cells throughout the body by shivering. In other words. This hormone stimulates the thyroid gland to produce its hormones. to increase the level of metabolism. In hotter conditions. Part 2: Homeostasis and temperature regulation 9 . less metabolic heat is lost to the environment. produce heat and this is used to regulate the body temperature of endothermic organisms. The secretion of these hormones into the bloodstream results in an increase in metabolism.Gill Sans Bold Endothermic animals gain heat from the environment but most of the heat used to control their body temperature is generated by their own metabolism. generating the extra heat needed to control body temperature under cold winter conditions. Control of body heat production (heat gain) Mammals (such as you) have two main ways of producing heat to keep the body temperature higher than the surroundings. especially cellular respiration. which stimulates the pituitary gland to secrete a hormone (thyroid stimulating hormone. In mammals and birds. the metabolism generates a great deal of heat. it is the interaction of both the endocrine and nervous systems that controls body temperature. resulting in the secretion of less TSH from the pituitary gland. Increasing the body’s metabolic rate The thyroid gland produces thyroid hormones which act on a number of organs. TSH) into the blood. including sweating. Any increase in blood temperature is detected by the hypothalamus. most endothermic animals produce more heat than they need for temperature regulation and this excess heat needs to be lost to the environment. the role of the hypothalamus and pituitary in governing the constancy of these is of great importance to the survival of many species. The diagram on the following page shows the positions of the hypothalamus and pituitary near the brain.So from winter to summer. generating lots of heat that is used only to maintain the body temperature. including regulation of body water levels and body temperature regulation. 10 Maintaining a balance . The pituitary produces some of its own hormones but others are produced in a part of the brain called the hypothalamus. However. But in this instance. ovaries and testes. which is connected to the pituitary by a series of nerve fibres. hormones released into the blood by the pituitary gland include hormones that stimulate the thyroid gland. Heat is produced by shivering. Considering that enzyme function is affected by both temperature and pH levels. the organism is able to turn up and turn down heat production so that a stable body temperature is maintained. the response is transmitted through the nervous system (the transmission) to the muscles (the effector). there is a more rapid response. This response is controlled by the nervous system. Shivering When environmental temperatures change quite quickly. where muscle fibres rapidly contract and relax. For example. like when a cold ‘southerly buster’ comes through and you have left your jumper at home. the change in blood temperature stimulating the shivering response is still detected by the hypothalamus (the receptor in the stimulus-response model). The hypothalamus is involved in the control of many body functions. The hypothalamus and pituitary The pituitary gland is often referred to as the ‘master gland’ as it secretes hormones which control the functioning of other glands. whereas it is lost more slowly in hot conditions. As environmental temperatures decrease. Part 2: Homeostasis and temperature regulation 11 . As mentioned above. the rate of heat loss speeds up but as it approaches body temperature. rapid shallow breathing (panting) may also be used in evaporative cooling of the body. Control of heat loss Heat is lost more quickly to the environment in cold conditions. Or. So how can the body lose heat to maintain a constant body temperature? Endotherms use the process of by evaporative cooling.Gill Sans Bold cerebral hemisphere hypothalamus pituitary medulla oblongata cerebellum spinal cord The human brain showing the position of the hypothalamus and the pituitary. Increasing heat loss When environmental temperatures increase above body temperature. Evaporative cooling works because heat is required to change liquid water into water vapour and this heat is drawn from the body. heat moves from the environment into the body. The rate of heat movement depends on the difference between the two temperatures (the temperature gradient). Water is evaporated from the skin or respiratory surfaces. in fact. Sweating from the skin is the most important method of evaporative cooling in humans. heat moves from an area of higher temperature to one of lower temperature. However. the heat loss slows down. in many mammals. may be gained in conditions which are hotter than the body temperature. Vasodilation is controlled by the hypothalamus via the nervous system. feet and ears. This air acts as better insulation. Heat loss to the environment is increased if small blood vessels (capillaries) at the skin surface are fully open. These evaporative cooling responses are controlled by the nervous system. Some species such as the red kangaroo lick their skin to spread saliva. The goose bump response is also controlled by the hypothalamus and the nervous system. These are received by the hypothalamus. Another area of the brain is also stimulated. or dilated. dogs lose most heat by panting. 12 Maintaining a balance . Again.For example. This is called vasodilation. It should also be noted that heat and cold receptors in the skin also result in information being directed to the brain by the passage of impulses along nerves. in vasoconstriction. with feedback through minute temperature changes in the blood. again as a result of the temperature centre in the hypothalamus detecting small changes in blood temperature. Most heat loss is lost through skin at the extremities. in animals with a thick fur coat. or constricted. Another way of reducing heat loss also involves the skin. For example. which then evaporates and results in cooling. have you noticed how cold your hands. resulting in the ‘feeling’ of cold or hot. feet and ears can become when you are feeling cold? The capillaries are partially closed. Summary The diagrams on the following page summarise the regulation of responses in an endotherm to the body to day-to-day changes in environmental temperatures. hands. such as the legs. However. Have you noticed that you get ‘goose bumps’ when you are cold? This is caused by small muscles attached to the base of the hairs on your body contracting to make the hair stand up. this response increases the depth of the air layer trapped in the fur. These regulatory responses to minute changes in blood temperature are controlled by the nervous system using feedback through the hypothalamus. reducing the amount of heat loss from the body. this process is controlled by the hypothalamus. arms. Reducing heat loss Heat loss to the environment can be reduced by reducing the flow of blood through capillaries near the skin's surface. This does not do much good for you and is a hang over from your ancestry. Gill Sans Bold This diagram combines the ones from the previous page. Part 2: Homeostasis and temperature regulation 13 . Do Exercise 2. circles show endocrine involvement and triangles mark responses. 14 Maintaining a balance .SKIN cold receptors BLOOD TEMPERATURE decrease increase SKIN heat receptors cause changes in blood temperature skin surface cooler than surroundings skin surface warmer than surroundings THYROID STIMULATING HORMONE increased HYPOTHALAMUS HYPOTHALAMUS heat loss heat gain centre centre THYROID STIMULATING HORMONE decreased SHIVERING THYROID HORMONE increased VASOCONSTRICTION ERECTION OF HAIR SWEATING OR PANTING VASODILATION LOWERING OF HAIR THYROID HORMONE decreased METABOLISM increased more heat produced. less heat lost more heat produced METABOLISM decreased more heat produced less heat produced Note: Rectangles indicate involvement of the nervous system.2 now. For example. The range of temperatures over which an endothermic animal can regulate its body temperature varies between species but at some point for every species. but it quickly dies from heat stress at temperatures higher than 30°C. At temperatures below about –10°C. They can control their body temperatures independently of the external environmental temperature within the range over which their enzymes work best. The graph below shows this for a species such as the platypus which can tolerate cold temperatures but is poor at regulating its temperature in the heat. The red kangaroo can tolerate environmental temperatures well above its body temperature of 36°C but could not survive under such cold conditions as the platypus. there is an upper and lower limit to this regulation. But there is still a limit to the range of temperature over which each species can survive. this species is no longer able to regulate and its body temperature begins to fall. This species is unable to regulate its normal body temperature (32°C) below –10°C or above 35°C.Gill Sans Bold Limitations to temperature regulation Endothermic species can occupy areas with a much wider range of temperatures than most ectotherms. Above 30°C. The range of temperature over which a human can Part 2: Homeostasis and temperature regulation 15 . even when swimming around in water near 0°C. it begins to overheat and its body temperature rises. the enzyme-dependent reactions of the species’ metabolism will fail and the animal will die. the platypus can maintain its body temperature around its normal 32°C. In both instances. 50 45 Body temperature !C 40 35 30 25 20 15 10 5 –15 –10 –5 0 5 10 15 20 25 30 Ambient temperature !C 35 40 45 Body temperature regulation for a species that can tolerate cold but not hot conditions. 3 now. 16 Maintaining a balance . is much smaller than that of an animal such as a platypus! Do Exercise 2.regulate body temperature. without extra clothes. heating or air conditioning. Outside this range of temperatures. But most species have a limited range of temperature over which they can survive and reproduce.Gill Sans Bold Temperature regulation for ectotherms So why is temperature regulation important? Well. These species. organisms which do this are restricted to: • • living in places where the temperature of the environment is within the range of temperature over which their enzymes work only being active at times when the environmental temperature is close to the optimum temperature of their enzymes. are called ectotherms. for a lot of organisms. which do not regulate their body temperature at a constant level. or would be prevented from working by it being too cold. the enzymes would either be denatured. with some being able to tolerate temperatures below the freezing point of water and others surviving above 100°C. However. Although some heat is generated by their metabolisms it is not sufficient to regulate their temperatures and so they depend on heat from the environment to stay at temperatures at which their enzymes function. which occupy extremes of temperature. due to the temperature being too hot. There are living organisms (mainly extremophile bacteria). it isn’t that important and many simply let their body temperatures change with that of the environment. Part 2: Homeostasis and temperature regulation 17 . (These animals move into the shade during hot periods to prevent overheating. In many species a dark colour facilitates absorption of heat. For example. (Photo: J West) 18 Maintaining a balance . You may have seen lizards basking in the sun and snakes are renowned for it. ectothermic species can bask in the sun to absorb the heat energy it provides. Ectothermic animals Many ectothermic animals alter their body temperature using energy from the sun.) Dilation or constriction of blood vessels in the skin can increase or decrease the amount of heat which is taken up or lost to the environment. but many other species of animals also make use of the sun’s heat. They mainly do this by changing the amount of heat they take up from the environment.tolerance range zone of death or avoidance zone of stress optimum range zone of stress zone of death or avoidance number of organisms unavailable marginal too cold preferred temperature marginal unavailable too hot Many ectothermic animals and plants can change their body temperatures even when their physical surroundings are above or below the temperatures at which they function best. A dark coloured lizard basking in the sun. Many Eucalyptus species growing in hot areas of Australia can actually move their leaves so that the edges rather than the surface of their leaves are exposed to the sun at the hottest part of the day. Also. They can prevent becoming overheated by evaporative cooling through transpiration of water from their stomates. plants living in very hot areas tend to be species with less leaf surface area.Gill Sans Bold Ectothermic plants Plants often receive too much heat from the sun on the surface of their leaves. Part 2: Homeostasis and temperature regulation 19 . Some questions about temperature regulation Use information from this module to complete the following tasks. there was only one transmission and one effector. The stimulus has been filled in for you as a starting point. you can learn more about temperature regulation by reviewing materials from this module and from the Preliminary course. This material deals with adaptations and responses to extreme environments with respect to temperature regulation in some Australian species. 1 In the stimulus-response model that you considered near the beginning of this part. Use the diagram on the next page to complete a feedback loop showing the regulation of body temperature by varying heat production under hot conditions (such as in the summer). when one endocrine gland is controlling another. Australian ectotherms and endotherms You will find some revision material from the Preliminary course in the Additional Resources section. Do Exercise 2. there are two of each of these. However. 20 Maintaining a balance .Adaptations and responses to temperature regulation In this section. Use this material and any extra material from the Internet or books to complete the following exercise.4. Part 2: Homeostasis and temperature regulation 21 . _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 The constancy of body temperature in mammals and birds is maintained by the: A B C D endocrine system and the blood vessels of the skin nervous system and sweat glands endocrine and nervous systems nervous system and respiratory surfaces. pituitary and thyroid gland that would correct this organism's body temperature back to its ‘normal’ level.Gill Sans Bold STIMULUS slight decrease in blood temperature FEEDBACK RECEPTOR TRANSMISSION RESPONSE EFFECTOR TRANSMISSION EFFECTOR 2 An endotherm in a colder environment experiences a slight fall in blood temperature. Describe the feedback system through the hypothalamus. vasoconstriction of surface capillaries and erection of hairs (fur) sweating. Check your answers. The temperature of plants is always exactly the same as that of the external environment. 6 Which of the following statements applies most accurately to temperature regulation in plants? A B C D Plants have no control over their temperature. reduced metabolism and erection of hairs (fur).4 An ectotherm is best defined as an animal which: A B C D regulates its body temperature using heat generated by its metabolism controls its body temperature by using heat from the environment permits its body temperature to change exactly with that of the environment allows its body temperature to fluctuate depending on its activity. vasoconstriction of surface capillaries and decreased metabolism shivering. 22 Maintaining a balance . Plants can stand much higher temperatures than animals. 5 A response to a cold environmental temperature in an endothermic species is most likely to include: A B C D sweating. Transpiration and movement of their leaves can affect the temperature of some plant species. vasodilation of surface capillaries and increased metabolism shivering. Keep thinking about how feedback works. It is not an easy idea. Part 2: Homeostasis and temperature regulation 23 .Gill Sans Bold Suggested answers Homeostasis and feedback RECEPTOR breathing centre in brain senses increased carbon dioxide STIMULUS increase of carbon dioxide in blood FEEDBACK changes of carbon dioxide in blood RESPONSE increased breathing rate EFFECTOR chest muscles and diaphragm TRANSMISSION nerve impulses to chest and diaphragm Do not worry if you found this task difficult. Then try the problem again when you have learnt more about homeostasis. So why is temperature regulation important? 1 STIMULUS slight decrease in blood temperature FEEDBACK increase in blood temperature to normal TRANSMISSION thyroid stimulating hormone (TSH) RECEPTOR hypothalamus to pituitary RESPONSE heat production EFFECTOR muscles and liver TRANSMISSION thyroid hormones EFFECTOR thyroid gland 2 Any slight fall in blood temperature is detected by the hypothalamus. especially in the extremities (eg. many of these species can have some control over their temperature. Some plants. and erection of hairs to increase insulation of the fur. but by using heat from the environment. B is correct. 3 4 5 6 24 Maintaining a balance . such as are found in areas of Australia. C is correct. This in turn reduces the amount of thyroid hormones being released from the thyroid gland. ears). and heat loss to the cold environment is reduced by vasoconstriction of surface capillaries. particularly those living in very hot conditions. which reduces the release of thyroid stimulating hormone (TSH) from the pituitary. The blood temperature returns to normal. resulting in a reduction in heat production by metabolism. Shivering generates heat. feet. Ectothermic species may permit their body temperatures to follow that of the environment. The endocrine system is involved in maintaining metabolic heat production while the nervous system controls shivering and the mechanisms that help to reduce or increase heat loss from the body. Some plants can also move their leaves so that they get less heat from the sun in the middle of the day. C is correct. B is correct. can regulate their temperatures to some extent by evaporative cooling due to transpiration. the frogs burrow down into the soil. They can survive for many months. The water holding frog (ectothermic) The water holding frog (Cyclorana platycephala) is one of several Australian species of burrowing frogs which live in arid conditions – a rather unusual place for frogs to live. The Eastern Blue-tongue lizard (ectothermic) The Eastern blue-tongue lizard (Tiliqua scincoides) is a type of skink. When the temporary pools in which they live begin to dry up. As soon as water from new rains soaks down to them. away from the heat of the sun. which is lowered during their time underground. The frogs themselves survive for extended dry periods by living in a cocoon about 0. the frogs break out of their cocoons and make their way back to the surface to feed and mate in the pools.Gill Sans Bold Additional resources Some of the material below is extracted from the Preliminary course module called Evolution of Australian biota. Australian desert frogs can survive drought conditions by burrowing down into the clay soil and forming a layer of dead skin around their bodies.5 m underground. possibly even years. This cocoon is quite impermeable to water and so their water losses to the surroundings are low. which reduces water loss to the soil. between rainfall events. They avoid high Part 2: Homeostasis and temperature regulation 25 . you would expect! Frogs have external fertilisation and so must have water in which to mate and produce tadpoles. These frogs can tolerate some dehydration (loss of body fluids) and an increase in toxic waste products arising from their metabolism. and form cocoons around themselves made from dead skin and mucus secreted by the skin. There are over 200 species of skink in Australia. when standing up on its hind legs.5–0.temperatures by seeking shelter under rocks and in leaf litter in the heat of the day.8 m (female) 66 kg (male) 27 kg (female) You can see that males are much larger than females. 26 Maintaining a balance . they need to balance the water they use in this evaporative cooling against their water intake to maintain regulation of their body fluids (osmoregulation). it lives in an area where summer temperatures are very high and winter temperatures can be below freezing.0 m (male) 0.1 m (male) 1. while rainfall is very low at most times of the year. Regulating body temperature Once the external temperature is high enough to equal the body temperature of an animal. is also about the same height as a fairly tall human. You will remember that birds and mammals living in hot dry conditions keep their body temperature constant by evaporating water through sweating or panting. A large red kangaroo is about the weight of an adult human male and. In the morning they bask on a rock and rely on the warmth of their surroundings for their body temperature. They maintain a body temperature between 30 and 35 degrees centigrade.9 m (male) 0. The following table lists some characteristics of red kangaroos. the only way that the animal can get rid of heat produced by its own metabolic processes is to carry out evaporative cooling by sweating or panting. They become inactive during cold weather. The red kangaroo (endothermic) The red kangaroo(Macropus rufus) occupies the central and central western areas of Australia. Body dimensions of the red kangaroo Measurement range Head and body length 0.9–1. However.0 m (female) Tail length 0.7–1.9 m (female) Weight 22–85 kg 17–35 kg (male) (female) Measurement average 1.7–1. In other words.4 m (male) 0.0 m (female) 0. The animal gains heat from the environment (mainly heat from the sun) and from its own metabolism. Sweating is not as efficient a way of losing heat as panting. A kangaroo’s kidneys reabsorb a great deal of water. Increased blood flow in vessels supplying these membranes permits a great deal of heat to be lost by evaporation. Water balance This seems good so far – the kangaroo can get rid of excess heat by panting. This consists of shallow and rapid breathing passing air over the membranes of the nasal passages.Gill Sans Bold In central Australia in the hottest summer temperatures. so that its urine is very concentrated and it urinates quite infrequently during hot times. relating to the times when settlers and explorers moved around in the hottest parts of the day in tropical areas. when it only gets to drink every five days or so? The red kangaroo has other strategies to reduce water losses. including extra heat generated during exercise. The kangaroo spreads saliva on its forelimbs and evaporation results in heat loss from these blood vessels. but the red kangaroo also sweats to lose heat if it needs to exercise during the hot periods of the day. This means that after a couple of hours in the sun it would need to drink eight full litres of water just to keep its body water at a constant level. a red kangaroo lying in the direct sunlight in the middle of the day would need to evaporate around four litres of water per hour to regulate its body temperature. Let’s have a look at how it does it. water loss has to be balanced by water gain and heat loss to heat gain if the kangaroo is to keep its body temperature and body water levels constant. spreading saliva and by sweating if necessary – but what about the water it loses in these processes. You have possibly also heard the saying that mad dogs and Englishmen go out in the midday sun. Red kangaroos only usually need to drink about every five days and so the species obviously has adaptations which permit it to balance its heat loss and regulation of body water under such severe conditions. The red kangaroo does the same as these indigenous Part 2: Homeostasis and temperature regulation 27 . whereas most indigenous people avoided those parts of the day by seeking shade. The kangaroos also have a mass of small blood vessels under the skin on its forelimbs. As discussed before. resulting in very little water being lost in the dry faeces. Water is also very efficiently reabsorbed by the large intestine. Remember that heat loss is the same as cooling. When you pick up a can of drink out of the fridge it feels cold because your hand is losing heat to the cold can. At rest the red kangaroo loses heat by panting. 2 cm (female) 1.7 kg 0. the 28 Maintaining a balance .0–2. In Australia.9 kg (male) (female) 1. It also only moves around in the middle of the day if it really has to. small mammals and birds from dry areas have similar adaptations. females are around 1 kg in weight and males a bit heavier at around 1.7–1.5 cm (male) 11. and saliva spreading (at rest). On the mainland. it should be noted that these strategies are not just found in this species.. However. as do animals such as camels. Red kangaroos increase heat losses by evaporative cooling by: panting (at rest).4 kg (male) 0. The table following shows average body dimensions. other kangaroo and wallaby species.people. sweating (during exercise).5 kg. The platypus (endothermic) The platypus (Ornithorhynchus anatinus) is quite a small animal although the species seems to be much larger in Tasmania (with some individuals reaching 3 kg). Red kangaroos decrease in heat gain or heat production by: seeking shade and avoiding exercise. dry conditions. jack rabbits and prairie dogs living in desert conditions in other parts of the world. seeking out even the slightest shade provided by low shrubs or trees in its environment. Water conservation adaptations of red kangaroos include: concentrated urine and dried faeces. which must be got rid of by evaporating water.6 kg (female) The platypus is found over a range of different habitats from tropical areas in the north of Queensland to very cold areas in Tasmania. The red kangaroo then is very well adapted in these ways for living in hot. including tail 45–60 cm (male) 39–55 cm (female) 11–15 cm (male) 9–13 cm Weight (female) Measurement average 50 cm 43 cm (male) (female) Tail length 12. as exercise means the production of more body heat. Body dimensions of the platypus Measurement range Total length. 1995. This behaviour also helps the species survive in the hotter areas of its range as the burrow insulates against heat coming in from outside too. reducing heat loss through the rear feet. Adaptations of the platypus for cold conditions. Webbed front feet: large surfaces of the webs provide propulsion in the water but have restricted blood supply to conserve heat. What are some adaptations that permit platypuses living in these sorts of areas to survive such harsh conditions? The diagram following summarises some adaptations of the platypus. (From The Platypus.) Platypus fur has several layers. D. hats and gloves because the fur insulation was so good in air. The platypus also has behavioural adaptations to help it to survive cold conditions. Sydney. which fall well below freezing in winter. Counter-current heat exchange system: veins and arteries flowing in opposite directions exchange heat in the muscles of the pelvic area. Grant. In these cold areas. NSW University Press. and in the Snowy Mountains and Victorian alpine areas. which keeps it cool. A unique mammal. Even in water. Tail fat: fat stored in the tail acts as an energy source for body metabolism. which acts as a very good insulator. the platypus is often in the water. the platypus fur has about the same insulation as a wetsuit. The flat blades of the guard hairs and the wavy shape of the fine underfur layer trap air. which can drop to freezing. T. but also low water temperatures. which increases to regulate body temperature during the winter. Platypuses were hunted until around 1900 and their skins used for rugs. Fur: dense fur traps a layer of air acting as insulation. It lives in a burrow where the soil acts as insulation to prevent the burrow losing heat to the cold outside air. Fanning. Part 2: Homeostasis and temperature regulation 29 . When it is active in hotter areas.Gill Sans Bold tablelands of New South Wales and Victoria. the platypus experiences not only low air temperatures. beavers). they are poorly adapted to hot conditions when they are out of water or away from their burrows. The platypus’ body temperature is 32°C. mammals. or eutherian. have slightly lower body temperatures of around 36°C. 30 Maintaining a balance . humans have a body temperature of 37°C. the platypus has evolved adaptations which are quite similar to those of species from other parts of the world that also live in similar very cold environments (eg. including the red kangaroo. As noted with the red kangaroo.Season Summer (max) Winter (min) Water temperature 24°C Air temperature 34°C Burrow temperature 18°C 5°C -12°C 14°C Because platypuses have mainly evolved adaptations to survive the cold. while most marsupials. quite a bit lower than that of most other mammals but it maintains it at a constant level. Like most placental. musk rats. They quickly die of heat stress in temperatures above their body temperature. 1 to 2.Gill Sans Bold Exercises Part 2 Exercises 2.1: Using information to maintain a balance a) Define homeostasis.4 Name: _________________________________ Exercise 2. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Why is it important to maintain a constant internal environment? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ c) What are the two stages of homeostasis? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 2: Homeostasis and temperature regulation 31 . _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 2. Give an example of a named organism and the temperature range it is found over. For each named organism describe an adaptation and a response that assists temperature regulation.3: Limitation to temperature regulation a) Identify the broad range of temperatures over which life is found. identify two ectotherms and two endotherms.4: Australian ectotherms and endotherms a) Using named Australian examples.Exercise 2. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ Exercise 2.) ______________________________________________________ ______________________________________________________ ______________________________________________________ 32 Maintaining a balance . (Try to describe a different method of temperature regulation for each organism.2: Summary Outline the role of the nervous system in detecting and responding to changes in environmental temperature in a mammal. ______________________________________________________ ______________________________________________________ b) Individual species however cannot survive over such a broad range. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 2: Homeostasis and temperature regulation 33 .Gill Sans Bold _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Identify some responses of plants to temperature change. Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 3: Mammalian blood I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . . ............................................................................................................................................................. 2 Blood ............................ 35 Part 3: Mammalian blood 1 .......23 Finding out more .........................................................4 Composition of blood ................ 17 Comparing arteries........................19 pH of the blood.............................................................................................................................21 Keeping pH stable ..........................9 Learning more about red blood cells ........................................................................................6 Substances transported in blood........................................................17 What happens at capillaries? ........................22 Measuring pH .........................................................................................................................................................................................25 Suggested answers................. 21 Normal pH for body fluids ........................................................................... 31 Exercises – Part 3 .......... 4 Optional review of the circulatory system ..................................... veins and capillaries ...............................................................................Gill Sans Bold Contents Introduction ........................................10 Blood vessels ...................... usually blood or lymph. This occurs in a watery medium.Introduction Transport in multicellular animals is necessary to move nutrients and wastes around the body. capillaries and veins in relation to their function describe the main changes in the chemical composition of the blood as it moves around the body and identify tissues in which these changes occur outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential • In this part you will have the opportunity to: • • perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water perform a first-hand investigation using the light microscope and prepared slides to gather information to estimate the size of red and white blood cells and draw scaled diagrams of each 2 Maintaining a balance . In this part you will have the opportunity to learn to: • identify the form(s) in which each of the following is carried in mammalian blood: – – – – – – – • • • carbon dioxide oxygen water salts lipids nitrogenous waste other products of digestion explain the adaptive advantage of haemoglobin compare the structure of arteries. • • Extract from Biology Stage 6 Syllabus © Board of Studies NSW.Gill Sans Bold • analyse information from secondary sources to identify current technologies that allow measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and explain the conditions under which these technologies are used analyse information from secondary sources to identify and describe the products extracted from donated blood and discuss the uses of these products analyse and present information from secondary sources to report on progress in the production of artificial blood and use available evidence to propose reasons why such research is needed. The most up-to-date version can be found on the Board's website at http://www.au/syllabus_hsc/syllabus2000_lista. originally issued 1999.nsw.html This version October 2002.edu. Part 3: Mammalian blood 3 .boardofstudies. Blood You have seen the importance of the temperature of the blood in maintaining a stable body temperature in an endotherm (such as a mammal). 4 Maintaining a balance . diamonds and circles in the diagram on the next page. Here is an optional activity for you to do to familiarise yourself again with the circulatory system. the watery liquid called blood transfers materials from where they are absorbed or produced to other places in the body where they are needed or removed. As the main transport system of the body. Optional review of the circulatory system You will probably remember the general circulation of blood in the body of a mammal. Use two different colours of pen: • • one for blood with high oxygen concentration (oxygenated blood) one for blood with low oxygen concentration (deoxygenated blood). The blood has an important role in distributing heat throughout the body. Draw in the blood flow between the parts of the body represented by the boxes. blood vessels and heart – make up the circulatory system. Together. The blood has a vital role in distributing other substances too. from the Preliminary course. The blood travels through blood vessels due to the ceaseless beating of a strong muscular heart. these things – blood. Gill Sans Bold A diagram of the human circulatory system head and arms lungs heart liver digestive system kidneys abdomen and legs Check your answer. Part 3: Mammalian blood 5 . Here is a table of information to remind you about the cells and cell fragments (formed elements) in blood. head and arms lung right atrium right ventricle left atrium left ventricle intestine kidney legs oxygenated blood deoxygenated blood Blood circulation in a human. say. a human and a giraffe but the circulation in all mammals has the same basic plan. A less diagrammatic (but harder to draw!) scheme of circulation in the human body is shown below. The exact positions of the organs and the lengths of the vessels may change a bit between.The diagram in the Suggested answers is fairly simple. 6 Maintaining a balance . Composition of blood In the Preliminary course you looked briefly at the cells which are found in the blood – the red and white blood cells. clear liquid fraction (55% plasma) cell fraction (45% red cells. Part 3: Mammalian blood 7 .Gill Sans Bold Types of blood cells and fragments Formed elements (43–47% of blood) red cells white cells platelets (cell fragments) % of formed elements 99% <1% <1% Function in body transport oxygen combat infection blood clotting These cells make up less than 50% (43–47%) of the blood in humans. The diagram below shows this separation of blood components due to centrifugation. The rest of the blood is a liquid called plasma. leaving the plasma floating on the top as a pale yellow liquid. white cells and platelets) Composition of blood. If you were to spin a tube of blood in an instrument called a centrifuge. the spinning would force the solid elements (cells and cell fragments) to the bottom of the tube. membranes) mainly energy eliminated. ions. no function solvent for many substances Check your answers.Blood plasma Here is a pie graph showing the main components of blood plasma. Use information from the graph to complete the table below. all the other main substances are dissolved in plasma. You can see that plasma is very important for transporting substances around the body. building structures (eg. involved in many metabolic activities ions nutrients such as: – amino acid – lipids – carbohydrates wastes water building structural proteins and enzymes provide energy. wastes and nutrients (about 1%) proteins water (about 92%) Components in blood plasma Plasma (53–57% of blood) proteins % composition of plasma Function in body osmotic balance of blood. 8 Maintaining a balance . Apart from oxygen (which is carried by red blood cells). blood clotting osmotic balance of body fluids. enzymes. carrying essential materials to cells throughout the body and removing their wastes.Gill Sans Bold Substances transported in blood The circulatory system is the main transport system of the body. The table below summarises the materials carried in blood. Part 3: Mammalian blood 9 . Wastes (such as carbon dioxide and urea) are eliminated (removed) from the body through the excretory and respiratory systems. Essential materials (such as oxygen and digested food) are brought into the body from outside through the respiratory and digestive systems. their source and where they are used or eliminated.1 now. Summary about substances carried in the blood Materials in blood Form in which material is carried mainly attached to haemoglobin in red cells mainly dissolved as bicarbonate ions Material enters blood respiratory system Material leaves blood used by all cells oxygen carbon dioxide from all cells respiratory system products of digestion – lipids (fats) – amino acids – simple sugars – vitamins salts (ions) water nitrogenous wastes (mainly urea) as particles called chylomicrons dissolved dissolved dissolved dissolved water molecules dissolved digestive system digestive system digestive system digestive system digestive system digestive system liver used by cells used by cells used by cells used by cells urinary system used by all cells urinary system Do Exercise 3. depending on what is being used or added by cells or which body system it is passing through. So the substances present in blood vary around the body. haemoglobin releases the oxygen: So haemoglobin is used over and over. not so well adapted to low oxygen conditions. However. Each haemoglobin molecule combines with four molecules of oxygen. haemoglobin + oxygen Hb + 4O2 oxyhaemoglobin Hb(O2)4 oxyhaemoglobin Hb(O2)4 haemoglobin + oxygen Hb + 4O2 At the tissues. This is why red blood cells release oxygen to cells throughout the body. Haemoglobin has a very strong affinity for (great ability to pick up) oxygen. The larvae of some biting midges (sandflies) also live in the mud. but haemoglobin changes back to a dark purple once it has given up its oxygen. when it is taken from a vein into the syringe. 10 Maintaining a balance . to carry oxygen from the lungs to cells. Other worms and insects. tubifex or bloodworms are found in places where oxygen has been used up by bacteria breaking down dead organic material (such as in sewage treatment ponds and the muddy bottoms of lakes). Remember that the blood in the veins is being returned to the heart. But if you have had a blood test. For example. Quite a few invertebrate animals that are adapted to living in places where oxygen is in very low concentrations also have haemoglobin in their blood. each one assembled around an atom of iron. the blood looks really red because it rapidly picks up oxygen from the air. which is made up of four long amino acid chains (polypeptides). when oxygen is in higher concentration than it is in the blood. Why does the colour change? The red colour of the blood of most vertebrate animals is due to the presence of a complex protein molecule called haemoglobin. This happens at the lungs. but colourless. which will then pump it to the lungs to be reoxygenated. have blood which is not red. When you cut yourself. rather than red. When haemoglobin picks up oxygen it becomes bright red in colour. you may have noticed that blood looks very dark purple. Oxygen combines chemically with haemoglobin (Hb) at the lungs to form a molecule called oxyhaemoglobin.Learning more about red blood cells Blood normally looks red because of the many red blood cells it contains. They have haemoglobin in their blood to help them absorb oxygen. blood which is collected from a vein looks purple because it is low in oxygen (deoxygenated). Haemoglobin can also release oxygen in an area where oxygen is in lower concentration than it is in the blood. which is 21% oxygen. They all mean the same and it is best for you to stick to using one name. Do Exercise 3. then you will see a whole lot of cells under the microscope.Gill Sans Bold Animals living normally at high altitudes have evolved adaptations. which have nuclei. It looks a bit like a doughnut where the hole does not go all the way through. Part 3: Mammalian blood 11 . including humans. will be stained. By the time they enter the bloodstream after being formed in the bone marrow. If you treat a smear of blood on a microscope slide with a stain which colours the nucleus (usually dark purple). It is made even more efficient by the shape of the red blood cell – it is flattened and both sides are concave so that it is thicker at the edges than in the middle. For example. which makes movement of oxygen across the cell membrane very efficient. This shape is shown below.2 now. they have more haemoglobin packed into each red blood cell and their haemoglobin itself is even more efficient at picking up oxygen than is human haemoglobin. So you can see that haemoglobin is an extremely important molecule when it comes to the survival of many animals. but you need to recognise the other names just in case you see them in something you are reading. each red blood cell in mammals. has lost its nucleus. The structure of red blood cells You may hear the word erythrocyte or red blood corpuscle being used instead of red blood cell. Their small size gives them a very large surface area to volume ratio. but only the white blood cells. 7 mm red blood cell cut in half Shape of a red blood cell. However. the llamas of the high Andes Mountains in South America have fewer red blood cells in their blood than humans. especially if it is an examination paper! Red blood cells are very small cells indeed and you will look at their actual size in a later exercise. University of Colorado) 12 Maintaining a balance .Look at the following photographs of blood smears. as seen through a microscope. Human blood smear under a light microscope at x400 magnification. (Photograph Jane West) white blood cells red blood cells Red and white blood cells taken with an electron microscope (Courtesy K R Porter and Gin Fonte. You will probably remember from using a microscope before. from reading the Science Resource Book for the Preliminary course or from working on the website (http://www.au/science) that magnification by the microscope depends on two sets of lenses. remember that red cells make up a bit less than 50% of blood and the white cells and platelets together make up less than 1%. on most microscopes normally magnifies x10 and the objective lenses can be changed between x10. You can estimate or measure the sizes of these images. only the size of its image through the microscope.lmpc. The size of red blood cells How could you measure the size of a red blood cell? A microscope makes objects that you look at seem larger. there appears to be as many white blood cells as there are red blood cells. x40 and x100. When you know the magnification of the microscope you are using. Note the location of the eyepiece (ocular lens) and objective lenses. Part 3: Mammalian blood 13 .Gill Sans Bold In the electromicrograph (phototograph from an electron microscope). The ocular. However. But this does not tell you the size of the object.edu. or eyepiece lens. eyepiece coarse adjustment fine adjustment arm body tube objectives stage clip stage base mirror Parts of an older style of light microscope. you can calculate the sizes of objects from measurements of images that you see through the microscope. Finding total magnification for a light microscope The total magnification of the microscope is calculated by multiplying the two lens magnifications together as is shown in the table below. This is the actual diameter of the circle you look at when you see down the microscope with the particular lens combination. How many micrometres (µm) is that? Yes. 14 Maintaining a balance .6 mm ÷ 1 000).000 001 m) Or you can say.001 mm) = 1 millionth of a metre (0. The unit usually chosen is called a micrometre.6 mm). micron or just µm (the Greek letter µ and the abbreviation for metre). It is a drawing of what you would see if you looked at a piece of graph paper with 1 mm divisions through a microscope at x100 total magnification. 0.3 mm say. 1 micrometre (µm) = 1 thousandth of a millimetre (0. headed ‘field of view’. Before you can calculate the size of these fields of view (or often just called the fields ) you need to have a unit of measurement which is small enough to use. Look at the diagram below.3 mm + 0. 1 600 µm (1. Lens combinations and magnification for a light microscope Eyepiece (ocular) lens x10 x10 x10 Objective lens Total magnification x100 x400 x1000 Field of view x10 x40 x100 Making measurements in a field of view There is another column in the table on the previous page. You can see one full division across (1 mm) plus a bit more on each side (0. So you have measured the full field as being 1. 1 millimetre (mm) = 1 000 micrometres (µm) or 1 metre (m) = 1 000 000 microns (µm) Now you can work out some field diameters.6 mm across. (You have to measure the field of view for each microscope.0 mm 0. it is 800 µm (It takes up half of the field of view.3 mm Measured field of view at x100 magnification.Gill Sans Bold diameter of field of view grid lines on graph paper 0.) How wide is the paramecium? ________________________________ It fits six times across the field of view so it is 1600 ÷ 6 = 267 µm Part 3: Mammalian blood 15 . You now know that anything you look at under x100 magnification on this microscope which completely fits across the field is 1600 µm in length.3 mm 1. There is an object called a paramecium that fits half way across the field. diameter of field of view 1600 µm Object measured in field of view at x100 magnification.) Now look at the next diagram. How long is the paramecium? Yes. 1600 ÷ 2. Do Exercise 3.If you had an organism under the microscope which you estimated fitted across the field four times. 400 µm or 1600 ÷ 4 = 400 µm. Here it how it is done. So you can estimate the approximate size of anything you look at under that power of the microscope because: size of an object = diameter of the field of view of microscope ( mm ) number of times the object fits across the field Did you wonder about fields of view under other magnifications? Well. 16 Maintaining a balance . Now do the calculations for the field under x1000 magnification. _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answers. Show your working then put the answer into the table. you can calculate these using the x100 field that you have measured using the graph paper. measured diameter of the field of view (in mm ) number of times magnification has been increased Since x100 field = 1600 mm size of field = then x400 field = 1600 = 4 mm Complete the calculation and put your answer (in micrometres) into the earlier table comparing total magnification and field of view.3 now. how big would it be?______ Correct. The return of blood against gravity is aided by body muscles contracting and helping to squeeze the veins. veins and capillaries outer layer muscle layer inner layer layer one cell thick artery vein capillary Arteries Arteries take blood away from the heart.Gill Sans Bold Blood vessels Blood travels throughout the body via interconnecting blood vessels. Part 3: Mammalian blood 17 . Comparing arteries. Blood in the arteries is always under high pressure and so always flows in the one direction. veins return blood to the heart from all parts of the body. veins and capillaries. particularly for blood from the outer and lower parts (arms and legs). They have thick muscular walls to withstand the pressure of the blood resulting from the pumping of the heart muscles. The pressure of blood in the veins can be quite low. These are arteries. away from the heart. Veins On the other hand. These muscular walls also even out the flow of blood by expanding and contracting themselves. direction of blood flow artery connective tissue elastic fibres and smooth muscle endothelium capillary connective tissue elastic fibres and smooth muscle endothelium (one cell thick) endothelium vein A capillary network and the structure of arteries. Capillaries In each organ of the body. veins and capillaries. valves prevent blood from flowing backward in areas where the pressure may be quite low. Standing in one place for a long time can cause a person to become dizzy or even faint because insufficient blood returns the heart from the lower parts of the body. 18 Maintaining a balance . the main arteries subdivide to form smaller and smaller vessels until the network of tiny microscopic vessels (capillaries) supply individual cells or groups of cells. These capillaries rejoin into larger vessels. This is because the leg muscles are not contracting to move the blood in the veins back up to the heart. so the brain does not get quite enough blood to function properly. The diagram on the next page shows this happening. As well. taking blood out of the organ and empties it into the largest veins that return blood to the heart. but the muscle layers are not as well developed as they are in arteries. muscle tendon valve closes and prevents backflow of vein squeezed by muscle valve opens and blood flows towards heart Movement of blood in veins due to skeletal muscle contraction.The walls of veins are also muscular. Gill Sans Bold The capillaries are extremely small and so have a large surface area through which to unload some materials (oxygen and nutrients) and to receive others (carbon dioxide and other wastes). Organ System Lungs • • • • oxygen carbon dioxide urea glucose more less no change more less more no change less Blood entering organ Blood leaving organ Kidney • • • • oxygen carbon dioxide urea glucose Leg muscle • • • • oxygen carbon dioxide urea glucose Small intestine • • • • oxygen carbon dioxide urea glucose Check your answers. Do Exercise 3. The first row has been done for you. What happens at capillaries? Complete the following table to show the exchange of substances between blood in capillaries and the surrounding tissues.4 now. as an example. Part 3: Mammalian blood 19 . Urea is produced in the liver. 20 Maintaining a balance .How did you go? Remember that all cells use up oxygen and glucose in their cellular respiration. The kidney (and to a very small extent. the skin) is the only other organ which changes the concentration of urea in the blood. Normal pH for body fluids Normally. a weak acid that breaks up into H+ ions and hydrogen carbonate ions (bicarbonate. then called lymph. the acidity of blood can be described using the pH scale. These fluids can also be made more acidic by the presence of carbon dioxide. especially those of the nervous system.Gill Sans Bold pH of the blood Like all substances. blood in arteries has a pH of 7. Part 3: Mammalian blood 21 . is moved only by pressure from surrounding muscles (in the same way that blood moves in veins). while in the veins it is 7. For proper functioning of the cells. The fluid does not accumulate in tissues but drains into the thin walled vessels of the lymphatic system. This fluid is constantly leaking from the blood plasma into tissue due to blood pressure. That doesn’t seem much of a difference but having a blood pH outside this range quickly leads to death in humans. HCO3–) when it dissolves in water.40. So lymph travels through the body and empties into the veins of the neck. Changes in pH Acids in food and a variety of acids produced by a range of metabolic reactions have the capacity to change the pH of the body fluids. a constant pH level must be maintained in the blood and the fluid which surrounds cells. The fluid.35. Most carbon dioxide carried by the blood forms carbonic acid. which is transported away from cells carrying out cellular respiration. including blood and lymph. The presence of H+ ions in plasma increases the acidity (reduces the pH) of blood and lymph. if a buffer is present in the water. A carbon dioxide CO2 B carbonic acid H2CO3 C bicarbonate ion HCO3 – + water + H2 O carbonic acid H2CO3 hydrogen ion attached to water (H2O)H + + water + H2 O + bicarbonate ion + HCO3 – + water + H2 O hydrogen ion attached to water (H2O)H + + carbonate ion + CO3 2– In equation B and equation C. Buffers in body fluids A buffer is a solution of two or more chemicals which prevents marked changes in H+ ion concentration (pH) when either an acid or alkali (base) is added to the system. the buffer takes up most of the H+ ions and the pH changes only very slightly.7). kidney function and variations in breathing rate. However. D carbonate ion CO3 E 2– + + hydrogen ion H + bicarbonate ion HCO3 – bicarbonate ion HCO3 – + + hydrogen ion H + carbonic acid H2CO3 22 Maintaining a balance . However.0–7. For example. study these equations. the pH falls quickly. These include: buffers in body fluids. hydrogen ions are added to the solution so it becomes more acidic (lower pH). these reactions can also happen in reverse.Keeping pH stable There are a number of homeostatic mechanisms which prevent the pH range of body fluids from exceeding or going below the levels necessary for survival (7. If a few drops of concentrated acid are added to water. that act as buffers to maintain the acid balance of blood. it can also be found using an indicator. During exercise. Variations in breathing rate Increased breathing flushes excess CO2 from the blood and reduces the level of carbonic acid in the blood and therefore the acidity (H+ ion concentration). carbonate and bicarbonate ions will take up + H ions and raise the pH. carbon dioxide dissolved in plasma is a buffer in the blood. This test only indicates acid or alkali. Otherwise the pH of the blood could be lowered to dangerous levels. it is essential that breathing rate increases to get rid of the extra CO2 produced by muscle cells. However. bicarbonate ions + and carbonic acid will give out H ions and lower the pH. Kidney function The nephrons of the kidney are capable of excreting more acidic or more alkaline urine depending on the level of H+ ions in the blood passing through the kidney. Blood also contains other chemicals. You probably used litmus paper at school and saw that blue litmus paper went red in acidic conditions and red litmus paper turned blue in alkaline conditions. If the solution is too alkaline. blood contains enzymes (such as carbonic anhydrase) to speed up these reactions so that the pH of blood remains stable. when carbon dioxide dissolves in water it acts as a buffer. An indicator is a chemical that has a different colour depending on whether the conditions are acidic or alkaline. However.Gill Sans Bold In equation D and equation E. So the concentration of H+ ions (pH) can be varied by the kidneys. Measuring pH The pH of a liquid can be measured using an electronic pH meter. hydrogen ions are removed from the solution so it becomes less acidic (higher pH). In other words. including proteins like haemoglobin. Part 3: Mammalian blood 23 . If the solution is too acidic. The feedback system you considered in Part 1 (stimulus-response model) plays an important part in ensuring that this normally does not happen. In the same way. 5 3 2 light orange dark orange red You can look at the LMP science website to see a colour version of the universal indicator scale. hydrangea flowers for example are blue if the plant grows in acidic soils and pink in alkaline soil.au/science You may be able to get some universal indicator to use from your local school or TAFE. www. The table below shows some colours of universal indicator at different pH. Once the water is a good purple colour tip it into a container and let it cool. You now have your indicator. Making your own indicator Finely chop about a handful of red cabbage (or flower petals). you can make your own.lmpc. Universal indicator paper is one of these. Then boil the cabbage in a small saucepan (or microwave container) with just enough water to cover it. However. A lot of plants have coloured pigments which change colour depending on the acid level of the soil in which they grow. You can test it with some of the substances in the table above to see the changes in colour at various pH levels. 24 Maintaining a balance .edu. For example.There are other indicators that change colour depending on the actual pH of the liquid. Substance domestic cleaner window cleaning liquid baking soda (NaHCO3) dissolved in water saliva vinegar lemon juice pH 14 10 9 Colour of universal indicator dark blue dark green green 6. • Blowing into a drinking straw is a good way to get CO2 into some water. Soda water is produced by bubbling CO2 into water under pressure.edu. identifying why you are doing the experiment. If it has potassium bicarbonate in it. You should gather information about these areas and then analyse the information. the results of your experiment will be poor as the bicarbonate acts as a buffer. Here are a few things that might help. read the label on the bottle before you buy it.au/Science Part 3: Mammalian blood 25 . Remember you need a control in your experiment. Use the Internet. You will need one which simply says ‘carbonated water’. You need to be able to show that any change in your indicator colour is caused by dissolving carbon dioxide and not by something else.lmpc. there are three research areas that deal with advances in technology in the study of blood. In Exercise 3. write a brief introduction. your local library and/or a Biology textbook Some useful websites can be found at: http://www. You already have made an indicator that changes colour when pH changes.Gill Sans Bold Observing the effect of dissolved carbon dioxide on the pH of water Design a simple experiment which shows that dissolving carbon dioxide in water makes the water more acidic. reduces the change in acidity. which as was discussed earlier.5. but it will take several minutes to get enough dissolved to affect your indicator. Finding out more On the next page. • • If you are going to use soda water. followed by a description of your methods and a presentation of your results. A discussion of your results should include consideration of how the results relate to carbon dioxide being carried in the blood and how these concentrations are maintained in balance. the blood becomes bright red when more oxygen is attached to the haemoglobin (forming oxyhaemoglobin) and becomes a dark purple when less oxygen is present. Maximum saturation is 100% and blood in the arteries is normally 95–100% saturated. The instrument then uses this value to calculate the amount of oxygen in the blood flowing through the arterial capillaries of the skin.1 Measurement of gases dissolved in the blood Current technology allows the measurement of oxygen concentration (called oxygen saturation) and carbon dioxide concentration in the blood. As you will remember. This instrument is used to monitor the amount of oxygen in the blood of patients who are undergoing surgery or who have abnormal breathing or circulation. 26 Maintaining a balance . Additional oxygen can be supplied to these patients if the oxygen saturation falls too low. The pulse oximeter looks like a clothes peg which fits over the finger. This difference in colour can be responsible for a sick person looking ‘blue’ in colour. Pulse oximeter. The result is displayed as the percent saturation of the blood with oxygen. Light (red and infrared) is emitted from the top part of the ‘peg’ and the amount of light passing through the skin is determined by an electronic sensor on the bottom part. Pulse oximeter This device senses the change in colour of the blood as it circulates through the skin. Two of these new techniques involve: • • a pulse oximeter arterial blood gas analysis. which was then quickly treated with intravenous antibiotics. For example. the following blood gas analysis came back from a patient who was admitted to a hospital casualty department with ‘bluish’ skin colour and who was breathing quickly.4 normal range 7. 2 Blood – the vital factor You or someone in your family may have donated blood in the past. mm Hg. These measurements are very useful in monitoring patient progress during treatment or surgery and in diagnosis of disease. The movement of oxygen molecules through a membrane from the blood produces an electrical current which is converted by the machine to a digital reading of the amount (partial pressure*) of oxygen in the blood. Part 3: Mammalian blood 27 . In Exercise 3. • Blood gases are often expressed in terms of pressure that the gas exerts and have the units.44 normal range 35–45 mmHg* normal range 90–100mmHg* carbon dioxide concentration 30mmHg oxygen concentration 50mmHg This suggested a respiratory illness and a chest x–ray later showed that the patient had pneumonia. The diffusion of carbon dioxide through another membrane changes the pH of the solution inside the membrane and this is used by the instrument as a measure of the amount of carbon dioxide present in the blood. Often the blood is separated into different products that have different uses. pH 7.36–7.6.Gill Sans Bold Arterial blood gas analysis Modern blood gas analysis machines can measure the amount of oxygen and carbon dioxide in a sample of blood by using the diffusion of these gases through artificial membranes which are permeable to these gases. describe why oxygen and carbon dioxide concentrations are of interest to doctors and write a summary about each of the new techniques listed above. A barometer measures air pressure in the same units. 3 Artificial blood Donated blood supplies in Australia often run low during holiday times. describe the products extracted from donated blood and the uses of these products. haemophilia) Serum albumin for illnesses resulting in low plasma protein levels (eg.7. Concentrated clotting factors for illness involving reduced blood clotting (eg. These shortages would be less important if artificial blood could be developed and produced.Less than half of all blood donations are used as whole blood in transfusions. The diagram below shows the major fractions and how they are normally used. Most is separated into its components (fractions) and is often used separately. 28 Maintaining a balance . some liver diseases) Unprocessed blood for some transfusions Whole blood Immunoglobulins (concentrated antibodies) for passive immunity and immune deficiency illnesses Packed red cells for transfusion after blood loss to increase oxygen carrying capacity Stable protein plasma for transfusion after blood loss and/or shockin an emergency before blood is available Source: Australian Red Cross Society Blood Transfusion Service 1985 In Exercise 3. when there is a major accident or when an unusually high number of surgical operations are performed. Gill Sans Bold Artificial blood The first blood transfusion was carried out in 1665 between dogs. Later animal blood was transfused into humans, usually with fatal results. Even when human-to-human transfusion began in 1818 it was often fatal. The reason for this was not discovered until 1900, when it was found that antibodies produced by the cells of different blood groups caused the clumping together of the red blood cells of another blood group. For that reason blood has to be ‘cross matched’ so that it is compatible with the blood group of the recipient before transfusion takes place. This can be a great disadvantage in emergency situations and so it would be great if artificial blood could be developed. Of course this would be very difficult, considering the complexity of this ‘living tissue’ which is the blood. No suitable fluid has yet been researched that would replace blood but a number of short-term substitutes can be used in emergency situations involving blood loss. Here are some examples. • stable protein plasma solution – there are no red cells in this solution so that it does not have to be cross-matched. It does not help the loss of oxygen-carrying capacity of the remaining blood but does replace the volume of fluid lost and aids in restoring blood pressure. It is often used after fluid loss as a result of burn injuries. Dextrose solution (4% glucose solution in a fluid with the same salinity as blood) can be used to restore blood pressure after blood loss. Haemoglobin can now be extracted from donor blood and administered to treat accident victims. Because there are no red cells cross matching is not necessary. Haemoglobin can be stored for long periods and can be sterilised. • • In Exercise 3.8, report on the progress towards the production of artificial blood and use available evidence to propose reasons why such research is needed. So, as you have seen, blood plays an important role in the transport of material and the maintenance of homeostasis in the body. In the next part you will be looking at the transport of materials in plants. Part 3: Mammalian blood 29 30 Maintaining a balance Gill Sans Bold Suggested answers A review of the circulatory system head and arms lungs heart liver digestive system kidneys abdomen and legs oxygenated blood deoxygenated blood Part 3: Mammalian blood 31 Blood plasma Plasma (53–57% of blood) proteins % composition of plasma 7% Function in body osmotic balance of blood, enzymes, blood clotting osmotic balance of body fluids; involved in many metabolic activities ions <1% nutrients such as: – amino acid – lipids – carbohydrates wastes water <1% building structural proteins and enzymes provide energy, building structures (eg. membranes) mainly energy <1% 92% eliminated, no function solvent for many substances Finding total magnification for a light microscope Eyepiece (ocular) lens x10 x10 x10 Objective lens Total magnification x100 x400 x1000 Field of view x10 x40 x100 1 600 400 1.6 32 Maintaining a balance Gill Sans Bold What happens at capillaries? Organ System Lungs • • • • oxygen carbon dioxide urea glucose more less no change more less more no change less Blood entering organ Blood leaving organ Kidney • • • • oxygen carbon dioxide urea glucose* more less more more less more less less Leg muscle • • • • oxygen carbon dioxide urea glucose more less no change more less more no change less Small intestine • • • • oxygen carbon dioxide urea glucose more less no change less less more no change more *Note: The kidney reabsorbs any glucose lost into the nephron but some glucose is used up in respiration in the kidney cells. Part 3: Mammalian blood 33 . 34 Maintaining a balance . 8 Name: _________________________________ Exercise 3.Gill Sans Bold Exercises Part 3 Exercises 3.1: Blood Identify the form(s) in which each of the following is carried in mammalian blood: a) carbon dioxide _________________________________________ _____________________________________________________ b) oxygen _______________________________________________ _____________________________________________________ c) water_________________________________________________ _____________________________________________________ d) salts _________________________________________________ _____________________________________________________ e) lipids_________________________________________________ _____________________________________________________ f) nitrogenous wastes______________________________________ _____________________________________________________ g) other products of digestion. _______________________________ _____________________________________________________ Part 3: Mammalian blood 35 .1 to 3. At this magnification. six red blood cells fit across the field of view. six red blood cells fit across the field of view. a) What special features of the haemoglobin molecule enable it to move oxygen around the body? ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ Exercise 3.2: Learning more about red blood cells Haemoglobin occurs in the blood and gives it a red colour.3: The size of red blood cells Here is a diagram of a blood smear viewed under a microscope. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 36 Maintaining a balance . 7 microns a) At this magnification. What is the diameter of a red blood cell? Show your working.Exercise 3. What is the diameter of a red blood cell? Show your working. The field of view is 75 µm. Gill Sans Bold b) The diagram (which is drawn to scale) in the notes shows that white blood cells are quite a bit larger than red cells. Then draw a large diagram. Put them side by side so that it is easy to compare their sizes. (Hint: A reasonable scale to use would be 1µm = 0.) Part 3: Mammalian blood 37 . _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ c) Look back at the photographs and diagrams of red and white blood cells in Part 3. at the same scale. Use this information to calculate the size of the white blood cells from the diagram. Show your working. of these two kinds of cells. You have calculated the size of a red blood cell above.5 cm on the drawing. Diagram arteries Suitability of structure for function veins Capillaries Red blood cells moving through a capillary 38 Maintaining a balance . In the second column.Exercise 3. describe how the structure of each blood vessel suits its function. veins and capillaries Compare the structure of arteries. In the first column.4: Comparing arteries. capillaries and veins by completing the table below. draw a simple labelled diagram of each type of blood vessel. Gill Sans Bold Exercise 3.5: Observing the effect of dissolved carbon dioxide on the pH of water Introduction _________________________________________________________ _________________________________________________________ Method _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Results _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Discussion _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 3: Mammalian blood 39 . 6: Measurement of gases dissolved in the blood a) Why is the amount of oxygen in blood important? ______________________________________________________ ______________________________________________________ ______________________________________________________ b) Why is the amount of carbon dioxide in blood important? ______________________________________________________ ______________________________________________________ ______________________________________________________ c) Summary about a pulse oximeter ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ d) Summary about arterial blood gas analysis ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 40 Maintaining a balance .Exercise 3. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 3.7: Blood – the vital factor Describe the products extracted from donated blood and the uses of these products. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 3: Mammalian blood 41 .8: Artificial blood Report on the progress on the production of artificial blood and use available evidence to propose reasons why such research is needed.Gill Sans Bold Exercise 3. Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 4: Transport in plants I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . . ........................................................................................................................5 A different look at vascular tissue................................... 2 Movement of materials in plants.......................................................................... 17 Additional resources........................................................... 19 Exercises – Part 4 ....................12 Suggested answers............10 Movement of substances through xylem and phloem tissue .................. 3 Investigating vascular tissue.....................................................................Gill Sans Bold Contents Introduction ....... 23 Part 4: Transport in plants 1 ....................................... 2 Maintaining a balance . In this part you will have the opportunity to learn to: • describe current theories about processes responsible for the movement of materials through plants in xylem and phloem tissue.Introduction So far you have been concentrating on the transportation of materials in animals.boardofstudies.au/syllabus_hsc/syllabus2000_lista.edu. The most up-to-date version can be found on the Board's website at http://www. In this part you will have the opportunity to: • choose equipment or resources to perform a first-hand investigation to gather first-hand data to draw transverse and longitudinal sections of phloem and xylem tissue Extract from Biology Stage 6 Syllabus © Board of Studies NSW. originally issued 1999. To study the vessels that carry the materials you will need to purchase some celery.nsw. In this part you will look at the movement of materials in plants. a single sided razor blade and some food dye.html This version October 2002. which are responsible for the uptake of carbon dioxide from the atmosphere and for transpiration. Lignin is the major component of wood. and with phloem. which transports water and minerals in the plant. These form the vascular system of ferns. Part 4: Transport in plants 3 . through which the products of photosynthesis are transported within the plant. including the roots. You also need to know about the stomates or stomata (singular stomate or stoma). In woody plants.Gill Sans Bold Movement of materials in plants The native Tasmanian ‘oak’ tree (Eucalyptus regnans) grows to a height of over 120 metres – approximately the height of an 8–10 storey building! Water must reach the leaves of this tree to be used in its photosynthesis and the products of photosynthesis need to be transported from the leaves to other parts of the tree. which are called the vascular plants and they belong to the phylum Trachaeophyta. The cells of the xylem grow to maturity and then die but are kept open by a material called lignin. old xylem cells form growth rings in the stem as the plant grows. gymnosperms and angiosperms. How is this possible? You should be familiar with xylem tissue. (See the Additional Resources section for revision material. bark operative xylem and phloem woody growth rings Tree rings are formed from old xylem cells.) Xylem tissue Xylem tissue is made up of long tubular cells which join into ‘pipes’. These provide support to keep the plant erect. phloem vascular bundle Three-dimensional section of a stem from a flowering plant. They contain sieve plates at the ends of the cells so that fluids can move through the cells but cell components remain within each living cell. Vascular tissue In young stems of woody plants and the stems of all herbaceous plants (soft herbs). In the roots of plants. xylem and phloem occur in bundles (vascular bundles). epidermis pith cortex xylem cambium FIBRES – dead cells with walls thickly coated with lignin are also found around and within the vascular tissue. xylem and phloem form a cylinder.Phloem tissue Phloem tissue is also made up of long tubular cells but these cells are living and not thickened with lignin. Here is a three-dimensional diagram of a stem showing the position of the xylem and phloem tissues. 4 Maintaining a balance . Gill Sans Bold Investigating vascular tissue A section can be cut across a plant stem or root and this is called a transverse section (TS) or cross-section (XS). The photograph below shows the same cuts through a celery stalk. (Photo: J West) Part 4: Transport in plants longitudinal section (LS) 5 . If you cut down from top to bottom the section is called a longitudinal section (LS). A transverse section and a longitudinal section of a celery stalk. transverse section (TS) or cross-section (XS) Diagram showing both transverse and longitudinal sections. The other tissues shown in the photographs are of less concern to you and have a variety of functions. (Photograph J West) 6 Maintaining a balance . The photographs below show vascular bundles in a transverse section from a stem. starch) epidermis – the outer layer of cells all over the plant pith – larger cells similar to the cortex but in the middle of the stem. which slices the tissue so thinly that light can pass through and it can be viewed using a microscope. Cross-section of a stem.Very thin sections can be cut by a machine called a microtome. They include: • • • • cambium – produces new xylem and phloem cells as the stem grows cortex – sometimes called ‘packing cells’ which have a range of functions but mostly are involved in storing materials (eg. However. Part 4: Transport in plants 7 . Close-up of a vascular bundle. it is difficult to study these tissues in detail.Gill Sans Bold This photograph is a larger magnification of one vascular bundle. Preparing and observing your tissue sections You will need: • • • • a fresh stick of celery a single sided razor a glass or container with water food dye (red works well). (© Jane West) Without a microscope. you will be able to observe xylem and phloem tissues in a longitudinal section and a transverse section from a soft plant (non-woody or herbaceous) such as celery. 8 Maintaining a balance . into a container containing a strong solution of food dye.(Photos: J West) What to do: Place an end of a freshly cut stick of celery. Leave it overnight. with its leaves still attached. You should see the vascular tissue (xylem and phloem) as bundles. which will have moved up through the xylem cells. will highlight the bundles.Gill Sans Bold For a transverse section Take a piece of the celery stalk and use a hard-backed razor blade to cut across it. Part 4: Transport in plants 9 . either with the unaided eye or using a hand lens. The red dye.) Cutting a transverse section through the celery stick. (Photo: J West) Look at the cut end. The darker regions are the vascular bundles. (Photo: J West) If you have a powerful hand lens you may be able to distinguish separate xylem cells. This makes a transverse section. You will see what looks like the ends of very small tubes. put some tape over one side to make it safer to use. (Be careful not to cut yourself! If you do use a double-sided blade. showing the positions of the xylem and phloem in the vascular bundles. In Exercise 4.If you do have access to a microscope (and know how to use it or can get someone to show you). A different look at vascular tissue In your investigation. making sure that you are cutting through at least one vascular bundle. Cut a longitudinal section down through the piece. draw a simple diagram of your longitudinal section showing the position of the xylem and phloem in the vascular bundle. you will be able to identify the different types of cells present in the root cross-section. In Exercise 4. to look closely at the long tubes. draw a simple diagram of your transverse section of the celery. It is hard to distinguish the phloem unless you stain it. the x10 eyepiece lens and x10 objective lens.) The image you see will not be as clear as shown in the photographs here. Your observations (and diagrams) would be slightly different if you had prepared a transverse section and longitudinal section of a root instead. if you have one.) 10 Maintaining a balance . The following photograph shows a transverse section of a root. you have studied vascular tissue from a stem.1. as has been done in the slides used for the photographs. but you should see that the xylem cells are very large with thick walls. For a longitudinal section Cut off a piece of celery about 2 cm long. Label the cells that you have identified. Compare it with the photograph of the transverse section of a stem earlier in this part. you can cut fine transverse sections of the celery using the razor blade. (Do not attempt to draw all the cells! Draw an outline and label the areas of different cell types. Then draw a simplified diagram of the transverse section of the root in the space below its photograph. By comparing the photographs. Place a thin slice on a slide in a drop of water. cover it with a coverslip then view it under the microscope with x100 total magnification.2. (Can you remember which lenses you need to use? Yes. Use your hand lens. Check your answer. Part 4: Transport in plants 11 .Gill Sans Bold Cross-section of a root (Photograph Jane West). 12 Maintaining a balance . Close-up of the vascular bundle of a root (Photograph Jane West).Did you notice that the xylem vessels in the root are arranged in a cross or star shape at the centre of the root? The phloem vessels are in bundles around the xylem cells. Here is a close-up of the vascular bundle at the centre of a transverse section of a root. where it is usually in a higher concentration than in the plant. Movement of water in plants Water moves into the plant through the large surface area of the root hairs. minerals and the products of photosynthesis. These materials include water. This process is called osmosis. Movement of substances through xylem and phloem tissue The xylem and phloem tissues in the plant are responsible for the transport of materials around the plant. Water moves from cell to cell within the plant by osmosis until it reaches the xylem cells. It moves from the soil. ) • Originally biologists thought that the pressure created by osmosis in the roots ‘pushed’ water up through the xylem. indeed some good evidence. So is there evidence for this theory? Yes. • Very accurate measurements of the stems of plants show that the stems actually shrink very slightly while the plant is transpiring. This movement is called capillarity but again it was worked out that this movement would still not move water to the top of a tall tree. they cannot carry out cellular respiration to produce the required energy. indicating ‘pulling’ from the top. • • • In this way. It was also suggested that water crept up the very fine tubes of the xylem. another molecule of water moves by osmosis into the bottom of the xylem to replace the one that has moved up. being essentially ‘pulled’ up from the leaves (transpiration-cohesion-tension theory) rather than being ‘pushed’ up from the roots (root pressure. there is. The movement of water from the roots through the xylem to the leaves is referred to as the transpiration stream. A continuous column of water molecules occurs in the xylem. Since xylem cells are dead. As one water molecule evaporates (in transpiration) from the leaf surface through the stomate. a bit like ink moving through the fibres of blotting paper. microscopic columns of water continue to move up the xylem vessels. • • So how is it done? The theory which has most support is called the transpiration-tension-cohesion theory. In turn. where the positive end of one water molecule is attracted to the negative end of the next one in the xylem cells. This is how it appears to work. once it was possible to calculate pressures inside plants it was concluded that this pressure was not strong enough to push water up to reach the leaves of tall trees like the Tasmanian ‘oak’ tree. If water were being pushed from Part 4: Transport in plants 13 .Gill Sans Bold Several theories arose for how water moved in the xylem once it reached this tissue. Water molecules stick together by a process called cohesion. to replace it. The suggestion that the water was ‘pumped’ by the cells using energy from cellular respiration (active transport) was quickly abandoned. • Water enters the roots by osmosis and reaches the xylem by the same process (by moving from an area of higher concentration to an area of lower concentration). (Refer also to the Additional resources. capillarity and active transport theories). another one is ‘pulled’ up the column of water in the xylem by the negative pressure (tension) created. However. • The figure below summarises the theory of the functioning of the transpiration stream. you would expect a slight expansion of the stem as a result of that positive pressure.3. water enters xylem in root Do Exercise 4. leaf water moves along xylem into leaf water evaporates into air spaces in spongy mesophyll water vapour escapes through stomata water drawn up xylem in the stem stem water around soil particles water enters root hairs by osmosis Movement of water in plants. cut flowers).the bottom. you might expect the removal of the roots to significantly reduce water movement. • Water continues to move through a plant whose roots have been cut off (eg. If root pressure were the mechanism for water movement. This rules out active transport as a mechanism of water transport. Plants which have been chilled or poisoned to kill all living cells continue to conduct water. 14 Maintaining a balance . when they are in high concentration in the soil but are in lower concentration inside the plant roots. The following diagram is a summary of the current theory for how translocation of sugars works. Some observations include that: • • • their movement in the phloem is very rapid (as quickly as 1 metre per hour) the direction of movement can be reversed movement of materials can be in different directions in different parts of the same vascular bundle. Obviously. This suggests that the translocation of products of photosynthesis through phloem tissue is an active process that demands the use of energy. However. However. it has been shown that radioactively marked phosphorus is transported from old leaves that are dying to new leaves which require this mineral for their growth. For example. Movement of products of photosynthesis Biologists studied the ways that radioactively marked sugars move throughout plants. Part 4: Transport in plants 15 . These observations need to be explained by any theory of movement of products of photosynthesis in the phloem (usually called translocation). Unlike xylem cells.Gill Sans Bold Movement of minerals in plants Most minerals (ions) are dissolved in water in the soil. They move into the plant through root hairs and then travel through xylem tissue. the movement of materials in phloem is different from that in xylem. phloem cells are living so material stops moving through them when phloem cells die. Some mineral ions enter the plant by diffusion. other minerals do not seem to be recycled (eg. calcium). This theory is called the pressure flow theory. These minerals need to be constantly taken up from the soil. Some minerals are recirculated within the plant through the phloem. most are moved from the soil into the root by active transport. site of sugar production in leaves Sugars are ‘pumped’ into the phloem cell due to active transport. This results in a higher sugar concentration inside the phloem cells. HIGH osmotic pressure Water moves into the phloem cells due to osmosis as a result of the higher sugar concentration. movement of sugar and water through the phloem along an osmotic pressure gradient Sugars are ‘pumped’ out of phloem cells by active transport. Water moves out of phloem cells by osmosis due to more sugars in the surrounding cells. LOW osmotic pressure site of use of sugars in fruit, flowers, root and stem Diagram representing the pressure flow theory for the translocation of sugars in vascular plants. 16 Maintaining a balance Gill Sans Bold Suggested answers A different look at vascular tissue epidermis small cells in cortex large cells in cortex xylem phloem Part 4: Transport in plants 17 18 Maintaining a balance Gill Sans Bold Additional resources This information comes from the Preliminary module, Patterns in Nature. Vascular bundles This is the term used to describe the groups of conducting tissue in a stem. Each bundle contains three types of tissue: xylem, phloem and cambium. Xylem Xylem forms long tubes up to 1 m in length. They are made up of dead cells, thickened with woody material, with cross walls that have broken down. They are known as xylem vessels. Xylem gives support, strength and rigidity to the stem, and transports water and mineral ions upwards from the roots to the leaves. Note: Water and mineral ions travel only in one direction in the xylem – upwards. Phloem Phloem consists of living sieve-tube cells forming long columns. There are perforations in the cell walls so that the cytoplasm of the cells connects along the tubes. Associated with the sieve-tube cells are companion cells and other supporting tissue. Organic materials including sugars, amino acids and hormones are transported by the living sieve-tube cells of phloem tissue. This movement is called translocation. Materials move both up and down the plant through phloem tissue. The movement is too fast to be caused by diffusion only. There are several theories suggesting possible forces involved but the exact mechanism remains unknown. Part 4: Transport in plants 19 Cambium Cambium cells are capable of cell division. They divide to form cells which become new xylem and phloem tissue. In older stems, division of cambium cells results in a continuous ring of vascular tissue. How water travels up plant stems Why does water move upwards in plants? Some of Australia’s tallest trees, such as the Mountain Ash in Victoria and Tasmania, are more than 100 metres tall. How does water move to this height, defying gravity? Several processes seem to be involved in the upward movement of water. The processes include: • • • • • adhesion capillarity root pressure transpiration-cohesion guttation. Adhesion Adhesion refers to the forces of attraction which exist between different types of particles. Using tissues or a cloth to mop up water works because of the force of attraction between dissimilar particles, the cloth particles and the water particles, or the tissue particles and the water particles. A piece of plastic would not be used to soak up water because the forces of attraction between the plastic particles and water particles are very weak while those between cloth and water are much stronger. In plants, cellulose acts like blotting paper or a cloth. Cell walls are made of cellulose. They help the plant to absorb water from the soil. Capillarity Capillarity is the name given to the action by which the surface of a liquid (usually water) is elevated when in contact with a solid surface by attraction of molecules between the liquid and solid surfaces. The water particles at the top of a column of water help to pull up the water particles beneath them. When the liquid is in a narrow vessel, the level of water will rise quickly, but capillarity can also occur in structures such as soils, causing a rise in the water table. 20 Maintaining a balance It is thought that high root pressure may cause guttation. such as a Monstera deliciosa commonly called Monsteria (mon-stear-e-ah) or fruit salad plant. Generally. because of forces of cohesion (attraction) between water particles. there is this continual stream of water molecules upwards in plants. Water is continually leaving the plant via the leaves. water can be seen to come out of the plant from the severed xylem vessels. they may lose water as drops of liquid water. So. when humidity is high and plants are well watered. Transpiration-cohesion At the moment. water would be seen to rise up the glass tube. This rise is said to be caused by root pressure. is called transpiration. water in the form of a gas. as each water molecule passes out of the leaf. the whole chain of beads (water molecules) is pulled up a little. They are extremely minute tubes or capillaries and water rises up them partly by a process of capillarity. more water is drawn up. It can rise from several centimetres to more than one metre. As one bead (water molecule) is pulled out of the leaf. Root pressure is caused by the intake of water due to osmosis. Guttation You may have noticed. As more beads (water molecules) are pulled out of the plant. Root pressure If the stem of a well-watered plant is cut off. drops of water (not dew) on certain outdoor plants and indoor plants. Part 4: Transport in plants 21 . plants lose water in the form of water vapour. the best theory which attempts to explain the upward movement of water in plants is the transpiration-cohesion theory. in the form of water vapour from the leaves. that is. If a glass tube were attached to the cut stem with a piece of rubber tubing. This process is called guttation. This loss of water. The columns of water in plants can be likened to chains of beads. Now. Scientists have found that root pressure is too small to account for the rise of water upward in plants which are taller than several metres. Many plants have special openings through which drops of water are forced out. However. more enter the plant in the root region. occasionally.Gill Sans Bold The xylem vessels in plants extend from the roots to the leaves. These special openings may be found along the edges of leaves or near the ends of their veins. 22 Maintaining a balance . The root hairs are single celled extensions of the root epidermis (surface or outer layer of the root). root hair soil particles water Water moves into the plant from the soil through the root hairs. which consist of xylem and phloem. that carry materials between the shoot and root systems. The cellulose cell walls in plants soak up water by this process. One of the main functions of stems is transport of substances around the plant. transpiration) results in the upward movement of more water molecules since these molecules are attracted to each other by forces of cohesion guttation – the loss of water in the form of a liquid from openings on the leaves. The conducting tissue can be arranged in a ring or scattered throughout the stem tissue cortex. • • • • Water enters the plant through the roots. The roots are covered by fine root hairs which increase the surface area for absorption of water. Internally. in much the same way as a blotter soaks up water capillarity – the rise of water in thin tubes by forces of adhesion and cohesion. Water will move from an area of high water concentration (in the soil) to an area/region of low water concentration (within the root hair cells). Water enters the root hair by diffusion since the concentration of solutes in the soil water is lower than their concentration inside root hair cells. They include: • adhesion – forces of attraction between different particles are called forces of adhesion. Water rises up thin tubes because of attraction between the particles of the plant and water particles (adhesion) and because of the attraction between the water particles themselves (cohesion) root pressure – the upward movement of water caused by the pressure from water moving into the root as a result of osmosis transpiration-cohesion – the loss of water molecules from the leaves (that is.Summary Several processes appear to be involved in the upward movement of water in plants. stems contain tubes of conducting tissue or vascular bundles. 1: For a transverse section Draw a transverse section of a celery stem in the space below.Gill Sans Bold Exercises Part 4 Exercises 4. including the xylem and phloem. including the xylem and phloem.3 Name: _________________________________ Exercise 4. Part 4: Transport in plants 23 . Exercise 4.2: For a longitudinal section Draw a longitudinal section of a celery stem in the space below. Remember to carefully label the diagram. Carefully label the diagram.1 to 4. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ What is the accepted theory today and what evidence is there for this theory? _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ 24 Maintaining a balance .3: Movement of water in plants Outline three theories that have been used to explain the movement of water through xylem tissue.Exercise 4. Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 5: Excretion I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . . ....................................................................................................................................................6 Excretory systems ................................................................. 2 Water and wastes................................................... 3 Water balance .........Gill Sans Bold Contents Introduction ............................................................................................................................................ 9 Dissection of a mammalian kidney...9 What can be done when kidneys don’t function? ......................................................................................................................................................... 23 Part 5: Excretion 1 ...............18 Suggested answers.................. 21 Exercises – Part 5 ......3 Wastes .......... au/syllabus_hsc/syllabus2000_lista. The most up-to-date version can be found on the Board's website at http://www.edu. In this part you will look at the structure and function of a kidney and what happens when kidneys fail. During this part you will need to purchase a sheep’s kidney from your local butcher.html This version October 2002. 2 Maintaining a balance . process and analyse information from secondary sources to compare the process of renal dialysis with the function of the kidney. • Extract from Biology Stage 6 Syllabus © Board of Studies NSW.nsw.Introduction The kidneys play a vital part in maintaining the internal balance of animals.boardofstudies. use of a model or visual resource and identify the regions involved in the excretion of waste products gather. In this part you will have the opportunity to learn to: • • • • • explain why the concentration of water in cells should be maintained within a narrow range for optimal function explain why the removal of wastes is essential for continued metabolic activity explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes in some organisms distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition. originally issued 1999. In this part you will have the opportunity to: • perform a first-hand investigation of the structure of a mammalian kidney by dissection. especially salts. organisms must match their water gains with their water losses. cellular respiration) and required by others (for example. in the fluids surrounding cells and in the blood must be maintained within very narrow limits to prevent loss or uptake of water which could result in damage to cells. In many animals the concentration of water and dissolved substances. these substances are usually transported in blood whereas in vascular plants they are carried in xylem and phloem sap. If water is not readily available. Some reactions involving water Water is produced by some reactions in the bodies of organisms (for example.Gill Sans Bold Water and wastes Water is an extremely important substance as it acts as a solvent for many substances in organisms. excess water may need to be quickly removed from organisms to maintain osmotic balance. organisms may die as a result of not having enough. To maintain their water balance. For revision. These dissolved substances can be involved in chemical reactions within cells and can be transported within organisms. Water balance Many of these dissolved substances also determine the movement of water within organisms and between cells due to osmosis. write an equation for each of these examples. photosynthesis). Within animals. On the other hand. Cellular respiration Photosynthesis Check your answers. Part 5: Excretion 3 . A reminder about osmosis Osmosis is the movement of water from where it is in higher concentration to where it is in lower concentration through a selectively permeable (sometimes called semi-permeable) membrane. movement of water A concentrated solution has a higher concentration of solute (dissolved substance) but a lower concentration of water. Remember that the adjective osmotic always describes a situation where water is moving from where water is in higher concentration (a more dilute solution) to where water is in lower concentration (a more concentrated solution) and where that movement is through a selectively permeable membrane. Movement of water from one cell to another. In summary. osmotic pressure is exerted by water when it moves into cells. So for example. In a single-celled organism this surrounding fluid is usually water. In multicellular organisms the surrounding fluid is usually the interstitial fluid found between cells. selectively permeable membrane Cells that are isotonic (same concentration inside the cell as in the surrounding fluid) function well. A dilute solution has a lower concentration of solute but a higher concentration of water. If the cell is not isotonic with its surroundings then water may be lost or gained and this may lead to death. Osmotic is the word which describes things (an adjective) related to osmosis. or between organisms and their external environment due to concentration differences. water needs to be maintained within a narrow range because: • • water is involved in many of the essential chemical reactions that occur in cells such as respiration and photosynthesis it acts as a solvent for many substances 4 Maintaining a balance . can be called osmotic movement. 1 now. Do Exercise 5.Gill Sans Bold • • it is important for the transport of materials around the organism cells may be damaged if there is too much or not enough water. Part 5: Excretion 5 . Organs which remove these wastes are known as excretory organs. Many products of metabolic reactions are wastes. which are normally eliminated from the body. Cellular respiration is one metabolic pathway with which you are familiar. which is called a metabolic pathway. It is produced in tadpoles and in most fish and aquatic invertebrates that have access to plenty of water to dilute it. Ammonia is a very soluble and very poisonous nitrogenous waste. due to enzymatic breakdown of potentially harmful substances taken into the body or produced by metabolism. particularly proteins. Some products of reactions in the body are in fact poisonous (toxic) and must be broken down to less toxic substances or be very quickly eliminated from the body. These nitrogenous wastes are formed from the breakdown of materials which contain nitrogen. These reactions normally occur as a series of chemical reactions. sharks and rays. Each step in a metabolic pathway is governed by a specific enzyme. adult amphibians. Urea is excreted by most mammals. Some examples of waste products The respiratory surfaces excrete the carbon dioxide formed during cellular respiration (the final metabolic process in the breakdown of fats and carbohydrates). urine is a source of water loss for these species. Since it needs to be diluted in water to reduce its toxicity. 6 Maintaining a balance . gills) and the kidneys. The kidneys get rid of other metabolic wastes including water and nitrogenous wastes. for example. Both of these wastes are less toxic than ammonia. In most vertebrate species the liver is responsible for producing many waste products.Wastes Do you recall what metabolism means? The definition in the glossary tells you that metabolism is all of the biochemical reactions occurring in the cells of the body. Urea is fairly soluble in water. The two main excretory organs in vertebrate animals are the respiratory surfaces (lungs. Terrestrial species produce nitrogenous wastes in the form of either urea or uric acid. it is a major waste in urine. an accumulation of carbon dioxide would lead to changes in pH inside cells. It is very insoluble (and the least toxic form of nitrogenous waste) and so needs little water to get rid of it. such as urea. too much or too little salt can result in cell damage or the malfunctioning of organ systems. urea and lactic acid in sweat) and a few are got rid of through the digestive system (for example.2 now. Waste products (such as carbon dioxide. You read earlier about the importance of respiratory surfaces and kidneys for removing wastes. some are essential to cell functioning. For example. The table below compares some properties of the nitrogenous wastes produced by terrestrial and aquatic organisms. However. some wastes are eliminated by the skin (for example. birds and insects excrete a material called uric acid. the breakdown products of haemoglobin are added into faeces). altering the water balance. Do Exercise 5. For example. Some metabolic products are not necessarily directly detrimental. You will recall that changes in pH can bring metabolic processes to a standstill by denaturing enzymes. some wastes. water and nitrogenous wastes) must be removed from living cells to enable them to continue to function normally. However. these are not the only excretory organs. are toxic and so must be removed. Part 5: Excretion 7 . Finally. For example. in mammals.Gill Sans Bold Reptiles. Accumulation of other wastes would cause water to move into cells by osmosis. salts. Indeed. the concentrations of these substances must also be closely regulated as they may produce conditions that also result in cell death. 8 Maintaining a balance .The diagram below summarises processes that produce wastes and how these can be removed. urea and lactic acid) other metabolic wastes large intestine (for example. products of haemoglobin breakdown) Summary of modes of excretion. Cellular respiration CO2 respiratory surface (gills or lungs) water Other metabolic pathways kidney nitrogenous wastes skin (for example. Now complete Exercise 5. Ask the butcher to give you some idea of the weight of the sheep from which the kidney was taken. However. except that a sheep’s kidney is smaller. You can use a model or a video if you have access to one but it is not much trouble to buy a sheep’s kidney from the local butcher and dissect it yourself. waste products are quickly lost into the environment through the cell membrane by diffusion. Dissection of a mammalian kidney If you dissected a kidney during the Preliminary module called Patterns in Nature.) If you know the local butcher.. When the kidney is removed at the abattoir or when the fat is trimmed away. you can carefully pick the fat away and you are more likely to see the ureter and blood vessels. if you did not do the dissection then. in multicellular organisms. the ureter and blood vessels are usually cut off too. This can occur because each cell has a large surface area to volume ratio. In unicellular organisms. The kidney is embedded in fat to hold it in place in the body and this also acts to protect it.Gill Sans Bold Excretory systems Different organisms have different kinds of excretory mechanisms for removing their wastes. If you can get a kidney that has not been trimmed. you really need to do it here. you could ask for a kidney ‘in the fat’. complex excretory organs (such as kidneys) are needed to provide the necessary surface area for the elimination of wastes. you need only to refer back to that module. (A sheep’s kidney is very similar to a human kidney. However. How heavy is a kidney? Although kidneys Part 5: Excretion 9 .3. You will notice a funnel-shaped structure with a hole in the centre. This hole leads into the ureter. they are quite small compared with the size of the animal.are very important organs. 6 10 Maintaining a balance . The three tubes are: a) the ureter. Discover where the ureter leaves the kidney. Make sure you are wearing suitable covered footwear and dispose of all waste materials carefully wrapped in newspaper. These are not easy to see because they are all connected together with tissue and may have been cut off the kidney you have. there is a lot of fat where they are connected to the kidney. called the capsule. which has a thick wall c) the renal vein. Continue cutting down to open up the kidney as shown in the photograph below. which is the large tube in the centre b) the renal artery. Observe the protective outer layer of skin. When using animal tissue you should wear rubber gloves if available. Also. What to do: 1 2 3 Observe the shape of the kidney. Now look inside. Materials required: • • • • • • sheep’s kidney small kitchen knife cutting board or plate knitting needle or similar rubber gloves if available newspaper. which has a thinner wall. 4 5 To observe the internal structure of the kidney. Risk assessment You will be using sharp instruments so take care that you do not cut yourself. Take an object like a knitting needle and push it gently through the opening. carefully cutting away from your fingers. Identify the three tubes which enter the kidney. cut through the kidney lengthwise. 7 Find the following structures: • the brown outer layer. This is where the waste substances are squeezed out through the membranes of the glomeruli into the Bowman’s capsules an inner pink layer of medulla. Part 5: Excretion 11 . draw a fully labelled diagram of the dissected kidney. • • 8 On the following page.Gill Sans Bold capsule cortex medulla pelvis ureter The internal structure of a sheep’s kidney. water and some salts are reabsorbed into the blood from the tubules of the nephrons a hollow whitish region. Here. This is the pelvis of the kidney where large collecting tubes empty urine into the funnel-shaped beginning of the ureter. or cortex. this is called active transport. diffusion and active transport Since particles in matter are constantly moving. If the diffusion of water occurs through a selectively permeable membrane.Diagram of a dissected kidney Complete Exercise 5. osmosis and active transport – are very important in the functioning of the kidney. all of these processes – diffusion. Active transport may also involve changes in the structure of the membranes. materials move from where they are more concentrated to where they are less concentrated. the process is called osmosis.4. As you will see. However. A review of osmosis. this is diffusion. living cells can make substances move from where they are less concentrated to where they are more concentrated by using energy. 12 Maintaining a balance . thus permitting materials to be moved against the concentration gradient. gases and solutions liquids and solutions only liquids and gases only. Diffusion occurs in: The energy necessary for osmosis and diffusion is due to the: Active transport occurs in: Check your answers. the information below about the functioning of the kidney should be much easier to follow. Part 5: Excretion 13 . liquids. size of the particles involved process of cellular respiration number of particles present movement of the particles involved.Gill Sans Bold Try this short quiz to test your knowledge of these substance-moving processes. liquids and gases all cells living cells animal cells but not in plant cells. gases and solids liquids. How did you go? Now that you are familiar with the structure of the kidney and the mechanisms responsible for movement of particles in organisms. 1 Osmosis is a special case of diffusion because it: a b c d 2 a b c d 3 a b c d 4 a b c d involves the movement of water only involves the movement of water only and always occurs through a membrane occurs in plants only where the cell wall prevents cells from bursting occurs in plants and animals but not in microorganisms. solutions. The functional units of the kidney – nephrons The diagram below shows the structure of the kidney and its blood supply. 14 Maintaining a balance . The great surface area created by so many nephrons in the kidney makes it efficient in carrying out its two important functions.) medulla renal vein cortex renal artery ureter The following diagram shows the position of tiny structures.2 million of these nephrons in each of your kidneys. called nephrons. The kidneys also have some role in regulating blood pH by the secretion of H+ ions into the nephron by active transport. which make it up the kidney. position of nephon There are around 1. (Turn back to check that you correctly labelled your diagram of a dissected kidney. These are: • • excretion – the elimination of harmful and unwanted products of metabolism osmoregulation – the control of body water and salt levels. making a surface area of approximately 12 m2 in humans. water. Substances are forced out of the blood in this knot of capillaries into Bowman’s capsule. proximal tubule glomerulus distal tubule branch of renal artery Bowman’s capsule branch of renal vein collecting tubule loop of Henle capillaries A mammalian nephron.Gill Sans Bold An individual nephron is shown below. where the parts are named and the complex blood capillary network associated with each nephron is shown. The loop of Henle and the collecting tubule (or collecting duct) protrude down into the medulla. The Bowman’s capsule and the proximal and distal tubules are found in the cortex. which let small molecules and ions through but prevent the movement of larger molecules (such as large proteins) and blood cells. glucose and amino acids to the kidney glomerulus – blood passing through the glomerulus is under high pressure. Each part of the nephron has an important role in the filtration of blood and the osmoregulation of the animal. Bowman’s capsule – a cup-shaped structure surrounding the glomerulus that collects materials forced out of the blood Part 5: Excretion 15 . salts. including nitrogenous wastes (especially urea). The process is largely governed by the size of the pores in the membranes of the capillaries and Bowman’s capsule. renal artery – brings blood containing small particles. which is the lighter-coloured part towards the centre of the kidney. which you will remember from your dissection is the outer dark brown-coloured layer of the kidney. This process is controlled by the endocrine system and will be discussed later. more water is taken back into the bloodstream from the tubule. the body can determine the amount of each substance that is reabsorbed. The process of reabsorption involves both the movement of materials.proximal tubule. once the concentration difference between the blood and various parts of the nephron is balanced. especially ions. because there is a lower concentration of them in the blood and a higher concentration in the tubule. Urine is produced by: • • filtration of many substances. Diffusion. The waste in the collecting tubule is urine. But why do substances move from the tubules back into the blood? Some substances can move by diffusion. both wastes and useful ones. This involves active transport. In this way. osmosis and active transport in a nephron Substances move from the blood into the Bowman’s capsule because of the high pressure of the blood through the glomerulus. very thin tube. making a long. loop of Henle and distal tubule join together into the renal vein. Most of the glucose and amino acids are reabsorbed in this way. However. This blood vessel carries blood that has been cleaned by the nephron back into the body’s circulation. back into the blood. So. the amount of substances including salt and water reabsorbed is precisely controlled to balance water and salt intake and losses. by active transport and the movement of water by osmosis collecting tubule (or collecting duct) – materials remaining after reabsorption are the wastes that move into the collecting tubule. such as glucose and amino acids. For example. all glucose will be reabsorbed but only some salt. which is passed down into the pelvis of the kidney renal vein – capillaries that surround the proximal tubule. energy must be used to move useful substances. Water and salts are reabsorbed in these parts of the nephron. osmoregulation and excretion by nephrons in the kidney are accomplished by the production and elimination of urine. Since active transport is used. 16 Maintaining a balance . from the blood (at the glomerulus/Bowman’s capsule) reabsorption of useful substances into the blood (at the tubules and loop of Henle). useful substances are reabsorbed back into the blood in the capillaries surrounding the tube. As the substances filtered from the blood travel through this tube. As these wastes move through the tubule. loop of Henle and distal tubule – these structures are joined together. so that the composition of blood and fluid surrounding cells is maintained at a constant level. in summary. This shows that. Check your answers. Material Bowman’s capsule (filtrate) yes Renal pelvis (urine) yes nitrogenous wastes (mainly urea) glucose amino acids salts (ions) water large proteins blood cells yes yes yes yes no no no no variable amount variable amount no no Turn back to the diagram of the nephron in this section and label: • • • where filtration and reabsorption occur some substances that are reabsorbed from the tubules into the blood the wastes that leave the collecting tubule as urine. Complete Exercise 5. active transport is used to pump useful materials back into the bloodstream. Part 5: Excretion 17 . for the most part. rather than specifically pumping undesirable substances into the nephron.5.Gill Sans Bold A summary of filtration and reabsorption in a nephron The following table summarises the functioning of the kidney by indicating the general composition of the fluid which enters Bowman’s capsule (sometimes called the filtrate) and the fluid which eventually drains out of the collecting tubules into the renal pelvis (the urine). a saline solution is passed into the body cavity (peritoneum) of the patient by a catheter (fine tube). In this instance.What can be done when kidneys don’t function? In people who have impaired kidney function. waste products can be removed from their blood using a process called renal dialysis. This process avoids the necessity to circulate the blood from the patient’s body. especially urea. The blood of the patient is passed through a coil separated by a membrane from a salt (saline) solution which has the same concentration as the blood (called a dialysing solution). the blood of the patient is circulated through the haemodialysis machine depicted in the diagram below. 18 Maintaining a balance . artery to dialyser superficial vein from dialyser dialyser membrane bubble trap fresh dialysing solution Haemodialysis machine. For 4–5 hours about three times a week. constant temperature bath used dialysing solution Dialysis can also be carried out within the body by a process known as peritoneal dialysis. The dialysis membrane is permeable to water and to nitrogenous and other waste products of metabolism. with the possible risk of blood clotting and infection. which is then drained out by another catheter. Wastes diffuse from the body fluids and pass through the membrane that lines the peritoneum into the saline solution. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 Explain why the dialysing solution has the same salt concentration as blood. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Check your answers. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 The membrane in the haemodialysis machine is equivalent to which part of the nephron of the kidney? A B C D the membrane of the tubule the membrane of Bowman’s capsule the capillaries surrounding the nephron the walls of the collecting tubules State a reason for your selected answer. Part 5: Excretion 19 . 1 Explain the reason for the constant temperature bath in the machine.Gill Sans Bold Comparing renal dialysis with normal kidney function Refer to the diagram of the haemodialysis machine and use your knowledge from throughout this module to deduce answers to the following. 20 Maintaining a balance . Gill Sans Bold Suggested answers Some reactions involving water Cellular respiration glucose + oxygen 6O2 many enzyme controlled steps carbon + water + energy dioxide 6CO2 + 6H2O + energy C6H12O6 + many enzyme controlled steps Photosynthesis carbon dioxide 6CO2 + + water + light energy many enzyme controlled steps glucose + oxygen controlled steps 6H2O + light C6H12O6 + 6O2 energy or to show that the source of the oxygen gas is water and not carbon dioxide many enzyme 6CO2 + 12H2O + light energy many enzyme controlled steps C6H12O6 + 6O2 + 6H2O A review of osmosis. diffusion and active transport 1 2 3 B B D The energy of movement of the particles is responsible for the movement. It is not supplied by the cells themselves through respiration. This energy (kinetic energy) increases with temperature. 4 C Part 5: Excretion 21 . If it were less concentrated.nutrients and water urine (water. 2 3 22 Maintaining a balance .A summary of filtration and reabsorption in a nephron Here is a sample answer. Remember that reabsorption occurs in the other parts of the nephron. the patient would lose water into the solution by osmosis. If the solution had a higher salt concentration than blood. salts (such as NaCl. HCO3– and K+) nutrients and water many substances from blood salts. where filtration occurs. urea and salts) REABSORPTION Comparing renal dialysis with normal kidney function 1 If the constant temperature bath were not used to keep the solution at body temperature. nutrients and water H+ (to balance pH) FILTRATION salts. The membrane of Bowman’s capsule is the equivalent structure in the nephron. B is correct. water would pass into the patient’s blood by osmosis through the membrane. the blood would lose heat to the solution in the core and the patient could become hypothermic (have a body temperature below normal). 2: Some examples of waste products a) Metabolic processes constantly produce wastes such as carbon dioxide. Why is it essential for continued metabolic activity that these wastes are removed from cells? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 5: Excretion 23 .Gill Sans Bold Exercises Part 5 Exercises 5.5 Name: _________________________________ Exercise 5.1: Water balance What is the solvent for metabolic reactions in living cells? _________ Why is it important that the concentration of this solvent remains constant in living cells? (What might happen if it did not?) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 5.1 to 5. nitrogenous wastes and water. Exercise 5.5: A summary of filtration and reabsorption in a nephron a) Why do substances move out of the blood into Bowman’s capsule at the glomerulus? ______________________________________________________ ______________________________________________________ 24 Maintaining a balance . are able to rely on diffusion and osmosis to remove wastes such as nitrogenous wastes and water. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 5. multicellular organisms. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 5. such as mammals. However. such as unicellular animals. Explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes from multicellular organisms.3: A review of respiratory and excretory systems Simple organisms.4: Dissection of a mammalian kidney Outline the safe working practices that you used during the dissection of the mammalian kidney. require complex organs and body systems for excretion. ) _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ c) List five substances that are filtered from the blood at the nephron. _____________________________________________________ _____________________________________________________ _____________________________________________________ d) Explain how filtering then reabsorbing some substances enables the kidney to control the composition of body fluids. Then circle the ones that are reabsorbed. such as blood.Gill Sans Bold b) Why do substances move out of the tubules and loop of Henle into the blood in the surrounding capillaries? (Discuss osmosis and active transport in your answer. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 5: Excretion 25 . Gill Sans Bold Biology HSC Course Stage 6 Maintaining a balance Part 6: Maintaining water balance I er b to T S c O EN g in D M t a r EN o p or AM c n 0 20 2 . . ...............................................................................................................................................................................................................Gill Sans Bold Contents Introduction ................................................................................. 29 Part 6: Maintaining water balance 1 ... 23 Exercises – Part 6 ................7 Adaptations for demanding environments ................................. 7 In other animals...................3 Aldosterone ........................................................12 Adaptations for changing environments......5 Osmoregulation ........................................................................................ 3 Anti-diuretic hormone ....16 Suggested answers..................................................................................................................................................... 19 Additional resources. 2 Hormonal control of body fluid composition.................................................. The most up-to-date version can be found on the Board's website at http://www.Introduction So far in this module. aldosterone and ADH (anti-diuretic hormone).boardofstudies.au/syllabus_hsc/syllabus2000_lista. you have been studying the internal mechanisms that are responsible for maintaining the balance in organisms. In this part you will have the opportunity to: • present information to outline the general use of hormone replacement therapy in people who cannot secrete aldosterone • perform a first-hand investigation to gather information about structures in plants that assist in the conservation of water • analyse information from secondary sources to compare and explain the differences in urine concentration of terrestrial mammals.html 2 Maintaining a balance . marine fish and freshwater fish • use available evidence to explain the relationship between the conservation of water and the production and excretion of concentrated nitrogenous wastes in a range of Australian insects and terrestrial mammals • process and analyse information from secondary sources and use available evidence to discuss processes used by different plants for salt regulation in saline environments Extract from Biology Stage 6 Syllabus © Board of Studies NSW.nsw. originally issued 1999. in the regulation of water and salt levels in blood • define enantiostasis as the maintenance of metabolic and physiological functions in response to variations in the environment and discuss its importance to estuarine organisms in maintaining appropriate salt concentrations • describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss. to look at some adaptations they have evolved to sustain life in different ecosystems. In this part you will move out into the external environment of organisms. In this part you will have the opportunity to learn to: • identify the role of the kidney in the excretory system of fish and mammals • outline the role of the hormones.edu. since it contains less water but the same amount of urea. If the water level in the blood is higher than normal. If the water level in the blood is lower than normal. These are: • • anti-diuretic hormone (ADH) and aldosterone. In this part you will learn about how osmoregulation occurs due to coordination by the endocrine system (hormonal system). the hypothalamus inhibits secretion of ADH. Two hormones are involved in the regulation of the levels of salt and water in the body. this is detected by the hypothalamus in the brain. you learnt about the functioning of the kidneys to control excretion of wastes and osmosregulation. The result of ADH is to make urine more concentrated. It makes these tubules more permeable to water so that more water is reabsorbed back into the bloodstream meaning that less is lost in the urine. This is a feedback system which regulates body water levels in response to water intake and loss. Part 6: Maintaining water balance 3 . which in turn stimulates the secretion of ADH.Gill Sans Bold Hormonal control of body fluid composition In Part 5. Anti-diuretic hormone Anti-diuretic hormone (ADH) is secreted by the posterior pituitary gland and acts mainly on the collecting tubules (collecting ducts) of the kidneys. The diagram below shows the feedback system controlling the regulation of body fluid concentration by anti-diuretic hormone. stimulate posterior pituitary to secrete ADH receptor cells in hypothalamus RESPONSE TO WATER LOSS increased reabsorption of water by collecting ducts in kidneys lowered blood water level increased blood water level homeostasis of blood fluid level increased blood water level RESPONSE TO WATER INTAKE receptor cells in hypothalamus decreased blood water level decreased reabsorption of water by collecting ducts in kidneys inhibit secretion of ADH by pituitary Hormonal regulation of body fluid levels by ADH. 4 Maintaining a balance . However. while the medulla secretes adrenalin. including the secretion of hormones from the pituitary. This increases the blood volume and so maintains blood pressure. often through the action of the pituitary. if Na+ ions are in lower than normal concentration in the blood.Gill Sans Bold Aldosterone Aldosterone is secreted by the adrenal gland. For example. Aldosterone is a steroid hormone from the cortex of the adrenal gland and its primary function is to increase the reabsorption of sodium ions (Na+) or potassium ions (K+) in the loop of Henle and distal tubules of the nephron. This gland consists of two parts – the cortex and the medulla. but this system is complicated by a number of influences on the action of the adrenal cortex.1. Blood pressure determines the filtration rate from the glomerulus into the Bowman’s capsule of the nephrons of the kidney. Maintenance of blood pressure is essential to the efficient transport of materials around the body and in the functioning of many organs. Do Exercise 6. The system is much more complex than the regulation of body water involving ADH. Conditions which affect the adrenal cortex directly are relatively uncommon and functioning of this part of the adrenal gland is more often impaired by diseases or medications which affect the adrenal cortex indirectly. as well as the sodium ion levels of the body fluids. Aldosterone secretion is also controlled by a feedback system. less sodium is excreted as these ions are moved from the nephron into the surrounding capillaries by active transport and water also moves as a result of osmosis. changed secretion rates of aldosterone in response to changes in the ionic composition of the blood and/or in blood pressure act to maintain homeostatic control of blood pressure and ionic composition of the body fluids. which is a small structure on top of each kidney. in general terms. Adrenal cortex hormone replacement therapy Although their incidence is not high. The pituitary produces a hormone Part 6: Maintaining water balance 5 . including the kidneys themselves. a number of medical conditions can affect the normal functioning of the part of the adrenal gland (the adrenal cortex) which produces the hormone aldosterone. Steroid hormones with a variety of functions are secreted by the cortex. the former president of the United States who was assassinated in 1963. Do Exercise 6. but often appears to have an autoimmune basis. John F. Addison’s disease is a disease affecting the adrenal cortex. in the form of a summary of the information given above. People suffering from this disease produce insufficient levels of all adrenal cortex hormones and require multiple hormone replacement therapy. to outline the general use of hormone replacement therapy in people who cannot secrete aldosterone.that influences the secretion of hormones from the adrenal cortex. They include: • hormones which are involved with the metabolism of fats and protein to increase blood sugars and liver glycogen. All of the hormones secreted by the adrenal cortex are steroids and are produced from cholesterol. including aldosterone. including a synthetic form of aldosterone (fludrocortisone). • • Present information.2 now. You now know a lot about the processes of excretion and osmoregulation in mammals. They appear to be involved in coping with long-term stress in animals hormones involved in the control of blood pressure and body fluid composition. such as body hair in males. Kennedy. but are probably involved in the development of secondary sexual characteristics. but what about other organisms? 6 Maintaining a balance . It can be caused as a result of tuberculosis. especially aldosterone certain sex hormones whose exact functions are unknown. had Addison’s disease. and some specialised adaptations of Australian animals for conserving water.Gill Sans Bold Osmoregulation Both plants and animals need adaptations and mechanisms for maintaining stable concentrations of water and salts. but fish avoid poisoning because they have access to plenty of water in which to dilute the ammonia and they get rid of urine very quickly from their bodies. Part 6: Maintaining water balance 7 . They have no bladder to store urine and so urinate continuously. They excrete urea by continuous urination. You will remember that bony fish excrete mainly ammonia from their kidneys as a nitrogenous waste product. if you think harder about it. you will realise that fish need to osmoregulate because their body tissues contain substances in different concentrations from their surroundings. In other animals Consider osmoregulation in fish and other animals. Because they live in water. However. Ammonia is very soluble and very toxic. Sharks and rays are fish that have a skeleton made of cartilage rather than bone. Osmoregulation and excretion in fish Fish use lots of water to remove wastes. you would think that fish would have no problem in regulating the level of water in their body fluids. The fish ‘drinks’ and takes in water with its food to replace this water loss. It returns to the estuaries of these rivers in winter to breed. but as a result this area also permits osmosis to occur very efficiently. they constantly lose water to their surroundings due to osmosis. Fish that move between salt and fresh water A number of fish species which live in Australian rivers move freely between salt and fresh water. this movement against the concentration gradient is brought about by active transport in specialised cells in their gills. You probably know that humans should not drink salt water to replace their water losses because their kidneys would not be able to get rid of the salts quickly enough to maintain normal salt balance. fish have special cells in the gills that can excrete excess salt back into the water by active transport. Being a fish in freshwater is a bit like being in a ‘leaky boat’. 8 Maintaining a balance . Their kidneys also excrete quite concentrated urine. What is the process involved? Yes. In the sea. Freshwater fish Freshwater fish have the opposite problem – water is constantly taken up from the surrounding water. and unless you keep bailing it out you are in trouble. especially through the membranes of the gills. but is able to take these up. However. have a higher concentration of water in their bodies than occurs in the water around them. that is. It loses some salts in its urine in this way. Bailing it out is exactly what the fish does. water keeps coming in. even although they are in very lower concentration in the surrounding water. the native bass (Macquaria novemaculeata) lives mainly in the freshwater sections of the coastal rivers of eastern Australia. where the concentration of water is much higher than in the body fluids of the fish. from Fraser Island in Queensland to Wilson’s Promontory in Victoria. Its kidneys work very efficiently to constantly produce large quantities of very dilute urine. For example. they excrete urine with a low water content. in the sea or estuaries. Fish have the added disadvantage that their gills have a huge surface area in contact with the water to carry out gaseous exchange.Saltwater fish Fish living in salt water. water rapidly leaves the body of a fish by osmosis. Part 6: Maintaining water balance 9 . scales and mucus secretion make skin fairly impervious to water loss water taken by ‘drinking’ salt water Saltwater Sea mullet (Mulgil cephalus) water lost through the gills by osmosis concentrated urine salts excreted by active transport scales and mucus secretion make skin fairly impervious to water some water taken with food Freshwater Bass (Macquaria novemaculeata) salts taken up by active transport continuous production of dilute urine water uptake through the gills by osmosis Osmoregulation in fish. So how do these species cope with the osmotic changes they encounter in these different environments? The eels and bass. The figure below summarises the responses of fish species living in freshwater (Australian bass) and in saltwater (sea mullet.Gill Sans Bold The two native eel species also migrate between fresh and marine waters. are capable of changing their responses to their changing environments. which move between fresh and salt environments. Mugil cephalus) to enable them to cope with their osmotic environment. Check your answers.Now complete these tasks. 10 Maintaining a balance . 1 What organ in fish and mammals is responsible for removing almost all nitrogenous wastes? _____________________________________________________ 2 In the space below. freshwater fish and marine (saltwater) fish. construct a table to compare and explain the differences in urine concentration of terrestrial mammals. This is not very toxic to them because it does not dissolve well in water. which also helps species living in arid areas to reduce their water losses through their urine. This is an advantage in arid regions. Next time you see a fresh bird dropping on something. The brown material is faeces and the white the urine. the digestive system (producing the faeces) and urinary system (producing urine) exit through a single opening to the outside of the body. Many species of Australian insects. Insects also produce uric acid as their major nitrogenous waste. which is mainly uric acid. Marine birds and reptiles can get rid of excess salts. The uric acid is concentrated and excreted into the digestive system by finger-like structures called Malpighian tubules. In birds. which have some similar functions to the livers of vertebrates. Bull ants (Myrmecia sp) excrete uric acid. It is produced in structures called fat bodies. Reptiles and birds produce their nitrogenous wastes mainly as uric acid. (Photo: J West) Part 6: Maintaining water balance 11 . such as a car windscreen. such as Bull ants (Myrmecia sp) and the sand grasshopper (Urnisa guttulua) live in arid regions where reduced water loss due to the excretion of uric acid is a distinct advantage for their survival. taken in by drinking and with their food. have a closer look at it! It will often be a mixture of white and brown material. It is excreted as a soft paste. called the cloaca. by excreting it through active transport from salt glands situated just below their eyes.Gill Sans Bold Osmoregulation in other animals All vertebrate animals produce metabolic wastes in their livers and excrete them through the kidneys. Some plant adaptations You looked at some plant adaptations to arid environments in the Preliminary course in Evolution of Australian biota and Adaptations to the Australian environment. plants and animals need to carefully balance their water gains and losses in order to maintain the level of water and salts in their tissues.Adaptations for demanding environments Over half of the Australian continent is considered to be arid. Many Australian plants. Some animal adaptations How are Australian insects and terrestrial mammals adapted to survive in arid environments? One important adaptation for conserving water is the production and excretion of concentrated nitrogenous wastes. 12 Maintaining a balance . Under such dry conditions. Plant adaptations to reduce water loss Plants have many adaptations to enable them to conserve water. Then present your information in Exercise 6.3 is to explain why this adaptation is valuable for a range of Australian insects and mammal species. have evolved features that permit them to survive under dry conditions. The relevant pages are included in the Additional resources section at the end of this part. in particular. You will find some information in the sections you have already read within this part. The relevant pages are included in the Additional resources section at the end of this part. Your task in Exercise 6. You also looked at some animal adaptations to arid environments in the Preliminary course in Adaptations to the Australian environment.3. Read through the information provided and highlight any information that will help you to explain examples where producing and excreting concentrated nitrogenous wastes helps Australian animals to conserve water. Read through these before continuing. Your own investigation of plant adaptations Investigate your local environment. your own garden or even a local garden centre to find two species of plants which are able to grow under conditions where water is not readily available. Some of these features are shown in the diagram below.Gill Sans Bold Some plant structures that may be specially adapted for conserving water include: • • • • • • • • leaf surface area positioning of stomates shape of leaves depth and nature of roots arrangement of leaves thickness of cuticle number of stomates colour of leaf surface. flattened petioles flattened stem flattened succulent stem axillary bud leaflets of compound leaf stem small leaf spines tap root Some plant adaptations for arid conditions.4. Part 6: Maintaining water balance 13 . the nearest botanical garden. Use information from within this part and from the Additional materials to complete Exercise 6. Cacti are obvious examples. Or. Collect as much information as you can for the plants you have chosen to investigate about their adaptations for water conservation. Present your information about the two plant species you study as a table in Exercise 6. If you have a microscope. like the prickly pear (Opuntia species). although some. as a considerable amount of the continent was under the sea during the high sea levels between the various ice ages in the Pleistocene Period (2 million to 10 000 years ago). Prickly pear. There are no native cacti. but if possible you should try to find native species.Common plants such as casuarinas (she-oak) and eucalypts (gum trees) are good examples. you could count the number of stomates on the upper and lower surfaces of the leaves and compare them. 14 Maintaining a balance . Both have waxy coverings. do occur in the wild. leaves with reduced surface area and extensive root systems. (Photo: J West). you could count stomates on these species and compare the number with other species not adapted to dry areas. or access a microscope at your local school or TAFE college. thick cuticles. Some features that you could observe are listed and shown on the previous page.5. Plant adaptations to saline environments Saline soils occur naturally in Australia. some farmers have been able to switch their crops. These leaves drop off with age and therefore the plant gets rid of the accumulated salt. such as fruit trees and lucerne (alfalfa). For example. such as the leaves. but in other areas conditions are so salty that no plants have adaptations to cope with it. For example: • • • most species in New South Wales exclude salt from entering the plant some species. including the river mangrove. • • As saline water reaches the root zones of crop plants and pasture grasses. causing the water table to rise poor drainage. These trees previously extracted water from the water table and kept its level lower than it is today irrigation water draining into the saline artesian groundwater. These salt concentrations can vary depending on the tide and the amount of fresh water coming in from the river at the head of the estuary. are able to excrete salt through special glands in their leaves other species accumulate salt in various parts of the plant. The area affected and the extent of soil salinity has increased dramatically since European occupation of the continent for a variety of reasons. This is exactly the same reason that you can use salt as a weed killer around courtyards and paths. Different species of mangroves have different adaptations. some species such as saltbushes can excrete the excess salts which they take up from the soil using special glands in their leaves. Some crop plants. they die as they lose water from the roots by osmosis to the more saline soil (since there is a lower concentration of water outside the plant roots than inside). In areas where soil salinity is a problem. which also raises the level of the saline water table. like cotton and barley. Not only do they need adaptations to survive in a highly saline environment. In the Preliminary course you considered some adaptations in mangroves to regulate their internal salt concentrations.Gill Sans Bold A number of native species of plants can cope with high levels of salt in the soil. including: • a rise in the saline water table (artesian groundwater) brought about by clearing of native salt-tolerant trees. Part 6: Maintaining water balance 15 . can tolerate more salty conditions than others. Salt crystals on the leaves of the river mangrove. This is the process called 16 Maintaining a balance . Environments also change as a result of human activity. These changes may be natural variations. Many organisms are able to maintain a stable internal environment despite changes in external conditions. such as the changing salt concentrations in estuaries that you considered when you read about adaptations of estuarine fish and mangroves. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Adaptations for changing environments Organisms need adaptations to be able to survive in a changing environment. (Photo: J West) Write your own outline about processes used by different plants for salt regulation in saline environments. L. But not all organisms can do this completely. particularly invertebrate animals and many plants.T. Extract from Biology Stage 6 Syllabus 1999 © Board of Studies NSW. 1996. Most of the adaptations you have examined have been in organisms that closely regulate their internal environments with respect to their external surroundings. W. You should learn the definitions of both homeostasis and enantiostasis and understand that all organisms respond to changes in their external environment (that is. Norton. which tend not to maintain their internal environment at a different level from that of their external environment. These organisms are often referred to as conformers rather than regulators. You are right! However. In other words. J. These organisms are often called regulators and the processes they use to maintain stable internal conditions are collectively known as homeostasis: ‘the tendency in an organism towards maintenance of physiological stability’ Extract from Gould. that is.Gill Sans Bold homeostasis. The internal environments of these organisms vary pretty much in line with changes in their surroundings. Biological Science. 6th ed. Part 6: Maintaining water balance 17 . enantiostasis seems to embrace the whole range of adaptations that you have already considered. It is a fine distinction. originally issued 1999. You may think that there does not seem to be much difference between homeostasis and enantiostasis. and Keeton. New York. What is enantiostasis? Although you will have trouble finding the word enantiostasis in any dictionary of biology or first year university textbook. there are a large number of organisms. carry out enantiostasis) but some organisms do not necessarily tend to maintain stability in their internal environments. it is used in the syllabus and is defined as: ‘the maintenance of metabolic and physiological functions in response to variations in the environment’. but presumably enantiostasis has been included in the biology syllabus to include these organisms which do not maintain complete homeostasis. by which organisms control their internal environments. not all organisms carry out homeostasis. The process in such organisms is called enantiostasis. complete Exercise 6.So why is the effect of urban development on estuarine communities important? Could Australia do without mangrove ‘swamps’. You have now reached the end of the module. 18 Maintaining a balance .6. ‘squishy’ salt marshes and muddy estuaries? Finally. revise some of the concepts before going on. There are many difficult concepts covered in this topic and if you have time. urine released continuously to reduce toxic effect of ammonia mammal freshwater fish ammonia.Gill Sans Bold Suggested answers Osmoregulation and excretion in fish 1 2 kidneys Here is an example of a suitable table. water is needed to wash wastes out of body urine very dilute because of large amounts of water being excreted urine must be concentrated to reduce water loss. water dilute urine saltwater fish ammonia. Organism Main wastes in urine urea. salts and water Concentration of urine dilute to relatively concentrated Reason(s) for urine concentration urea is not very toxic. salt glands in gills remove most salt Part 6: Maintaining water balance 19 . salts concentrated urine. 20 Maintaining a balance . Terrestrial animals also rapidly lose water to their surrounding environment. glucose + oxygen carbon dioxide + water + energy There are many ways in which water losses can be minimised. You should remember the overall equation for respiration. especially in arid areas and in places where high temperatures and wind greatly increase evaporation. The regulation of water and salts in the body is called osmoregulation. Reabsorption of water by the kidneys produces more concentrated urine. which must take up CO2 through their stomates for photosynthesis. Introduction The concentrations of salts and water within the cells and bodies of many living organisms is regulated very precisely. water loss can be a severe problem. This is a problem in birds and mammals which normally use evaporation of water to keep their body temperatures constant in hot environments. Part 6: Maintaining water balance 21 . Drinking water is the main way that species gain water. On land the air is very dry. Changes brought about by dehydration or an imbalance of salts (ions) within the cells can quickly lead to the death of an organism. but they can also obtain water in their food (eg. Mammals and birds closely control the losses and gains of water by utilising a variety of adaptations.Gill Sans Bold Additional resources This section contains extracts from the Preliminary modules called Evolution of Australian biota and Adaptations to the Australian environment. For plants. including seeking shade to reduce the need to evaporate water for cooling. so that less water is excreted from the body. fleshy fruits) and some can use metabolic water which is produced during cellular respiration. Some species. This means that after a couple of hours in the sun it would need to drink eight full litres of water just to keep its body water at a constant level. such as the camel. Red kangaroos only usually need to drink about every five days and so the species obviously has adaptations which permit it to balance its heat 22 Maintaining a balance . In central Australia in the hottest summer temperatures. Regulating body temperature Once the external temperature is high enough to equal the body temperature of an animal. which. does not have to be dissolved in water. they need to balance the water they use in this evaporative cooling against their water intake to maintain regulation of their body fluids (osmoregulation).Birds. a red kangaroo lying in the direct sunlight in the middle of the day would need to evaporate around four litres of water per hour to regulate its body temperature. the only way that the animal can get rid of heat produced by its own metabolic processes is to carry out evaporative cooling by sweating or panting. normally lost when breathing out. reptiles and insects reduce the amount of water they lose in their urine by excreting a waste product called uric acid. red kangaroo and desert rats and mice. to condense and be reabsorbed back into the bloodstream. The red kangaroo The red kangaroo (Macropus rufus) occupies the central and central western areas of Australia. unlike the urea excreted by mammals. These cause some of the moisture. Some animal adaptations for maintaining water balance Here is information about adaptations of a common Australian mammal. However. also have cooling structures in their nasal passages. You will remember that birds and mammals living in hot dry conditions keep their body temperature constant by evaporating water through sweating or panting. it lives in an area where summer temperatures are very high and winter temperatures can be below freezing. In other words. while rainfall is very low at most times of the year. whereas most indigenous people avoided those parts of the day by seeking shade. However. The kangaroos also have a mass of small blood vessels under the skin on its forelimbs. Water balance This seems good so far – the kangaroo can get rid of excess heat by panting. water loss has to be balanced by water gain and heat loss to heat gain if the kangaroo is to keep its body temperature and body water levels constant. when it only gets to drink every five days or so? The red kangaroo has other strategies to reduce water losses. It also only moves around in the middle of the day if it really has to. In Australia. spreading saliva and by sweating if necessary – but what about the water it loses in these processes. dry conditions. The kangaroo spreads saliva on its forelimbs and evaporation results in heat loss from these blood vessels. The animal gains heat from the environment (mainly heat from the sun) and from its own metabolism. Let’s have a look at how it does it. other kangaroo and wallaby species. seeking out even the slightest shade provided by low shrubs or trees in its environment. This consists of shallow and rapid breathing passing air over the membranes of the nasal passages. Increased blood flow in vessels supplying these membranes permits a great deal of heat to be lost by evaporation. The red kangaroo does the same as these indigenous people. A kangaroo’s kidneys reabsorb a great deal of water. Remember that heat loss is the same as cooling. as exercise means the production of more body heat.Gill Sans Bold loss and regulation of body water under such severe conditions. The red kangaroo then is very well adapted in these ways for living in hot. it should be noted that these strategies are not just found in this species. As discussed before. Water is also very efficiently reabsorbed by the large intestine. At rest the red kangaroo loses heat by panting. which must be got rid of by evaporating water. but the red kangaroo also sweats to lose heat if it needs to exercise during the hot periods of the day. Sweating is not as efficient a way of losing heat as panting. so that its urine is very concentrated and it urinates quite infrequently during hot times. You have possibly also heard the saying that mad dogs and Englishmen go out in the midday sun. When you pick up a can of drink out of the fridge it feels cold because your hand is losing heat to the cold can. small mammals and birds from dry areas have similar Part 6: Maintaining water balance 23 . including extra heat generated during exercise. relating to the times when settlers and explorers moved around in the hottest parts of the day in tropical areas. resulting in very little water being lost in the dry faeces. Water is at premium and free water is rarely available. Red kangaroos increase heat losses by evaporative cooling by: panting (at rest). Mothers produce concentrated milk and even consume the urine of their babies. Its waste products are extremely concentrated. There are many different species of animals that use the same techniques as the Spinifex hopping mouse including the Bilby and the Mulgara (Dasycercus cristicauda). plants must also balance their loss of water against that which they take up through their roots. His animal conserves water in many ways and this includes the excretion of concentrated nitrogenous wastes. Australian plant adaptations Like animals. and saliva spreading (at rest). jack rabbits and prairie dogs living in desert conditions in other parts of the world.adaptations. Below are descriptions of two examples of native Australian species which are adapted to living in arid conditions. sweating (during exercise). there are a number of strategies which plants adopt to conserve water. As discussed earlier. It gets water from the breakdown of starch in its food. It makes use of any rain which may fall by having its leaves 24 Maintaining a balance . Mulga – a shrubland survivor Mulga is a type of tall shrub which is found in the shrubland areas of Australia. Red kangaroos decrease in heat gain or heat production by: seeking shade and avoiding exercise. Water conservation adaptations of red kangaroos include: concentrated urine and dried faeces. as do animals such as camels. so that they have to take up less from the environment to maintain their body water levels. Rainfall is sporadic in the region but the hopping mouse has many adaptations for survival. They must evaporate water in hot conditions to keep their leaves cool and to keep water flowing in the xylem so that it can be transported to the leaves to be used in photosynthesis. The Spinifex hopping mouse The Spinifex hopping-mouse (Notomys alexis) lives in the deserts of Central Australia. The faeces are dry and the urine is the most concentrated of any mammal. The Spinifex hopping mouse never drinks and does not have sweat glands. As well as this adaptation. Its leaves have an extremely thick cuticle to reduce the loss of water from the leaf surfaces and its stomates close for longer periods of time each day. but the plant also has strategies for conserving this scarce water. permitting the absorption of as much available water as possible. narrow leaves of the grass are rolled and the stomates are found at the bottom of pits inside the rolled surface.Gill Sans Bold arranged so that they catch the falling rain and direct it to the base of the tree. The long. Part 6: Maintaining water balance 25 . but this aspect of the biology of the species has not been investigated. where there are plenty of roots to absorb it. Obviously it must have its stomates open long enough to collect enough carbon dioxide for its photosynthesis. especially in the middle of the day when it is hotter. Porcupine grass – a desert grass As this native tussock grass often grows in sandy soils. very little water is lost from the species during drought periods. it also has shallow and widely spread roots near the surface to quickly absorb any available rainfall. as drought conditions increase. shallow and spreading. As a result of this. The diagram following shows the arrangement of these. the roots of the mulga are very long. These two adaptations increase water gain. but at least it is conserving water.) The rolling of leaves and sinking of stomates in pits means that a high humidity is maintained around the openings of the stomates and the effects of wind around the stomates is reduced. Maintaining humidity around the openings of the stomates reduces water loss in this way. Its light. You probably remember that high humidity reduces evaporation. The water in your sweat is not evaporating as quickly as it would on a dry day and so your evaporative cooling is not working as well as it should. Academy of Science. It probably means that the porcupine grass also is a bit hotter than it would have been if it hadn’t rolled its leaves. You need to note once more that similar adaptations are also found in dry area grasses and shrubs in other parts of the world. (from Web of Life. permitting them to survive under arid conditions in the grassland areas of Australia. 26 Maintaining a balance . 3rd Ed. 1981. The table below summarises the adaptations which have occurred during evolution of these two native Australian species. shiny leaf surfaces also help here as they reflect a lot of the heat from the sun.stomatal grooves (A) Leaf open junction of leaf edges (B) Leaf rolled stomatal grooves Cross sections through the rolled leaf of porcupine grass. This is the main reason that you feel uncomfortable on a hot humid day. Part 6: Maintaining water balance 27 .Gill Sans Bold Summary of adaptations of mulga and porcupine grass plants to hot arid conditions Adaptation to: Porcupine grass Mulga shrub Increase water gain • • wide expanse of roots leaves direct rainfall to the base of the plant + – + + Decrease water loss • • • • • impermeable thick waxy cuticle light coloured surface reflects heat leaves rolled reduce evaporation stomates sunk in pits reduce evaporation reduce stomate opening during drought periods + + + + – + – – – + + indicates adaptation present – indicates adaptation either not found or not identified. 28 Maintaining a balance . Gill Sans Bold Exercises Part 6 Exercises 6. Sam is working in the garden on a hot dry summer’s day.1: Anti-diuretic hormone and aldosterone Outline the role of the hormones aldosterone and ADH in the regulation of water and salt levels in blood.6 Name: _________________________________ Exercise 6.1 to 6. She is sweating a lot. which is regulating her body temperature. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 6. Part 6: Maintaining water balance 29 . but she notices that she is also losing water and salts from her body in sweat.2: Adrenal cortex hormone replacement therapy Consider the following chain of events in terms of your understanding of the involvement of the kidneys and hormonal system in the regulation of salt and water balance in a mammal. Although she has been drinking some water. she notices that her urine is quite dark in colour. When she finally urinates at the end of the day. she has not had to urinate (go to the toilet to release urine) all day. __________________________________________________ ii How would she obtain this hormone? __________________________________________________ iii Discuss why treatment with this hormone is important for Sam. i Name the hormone that Sam would need to treat her disease.) __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ 30 Maintaining a balance . ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ d) Now imagine that Sam has the disease called Addison’s disease. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ b) Why is Sam’s urine a darker colour when eventually she urinates? ______________________________________________________ ______________________________________________________ ______________________________________________________ c) Describe what could be the result of such heavy work in the heat over a number of days and if Sam does not drink much water in that time. if it does any harm.a) Explain why Sam has not needed to urinate during the day. (How does it help her? Find out. if you can. ) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 6: Maintaining water balance 31 .3: Animal adaptations Explain the relationship between the conservation of water and the production and excretion of concentrated nitrogenous wastes in a range of Australian insects and terrestrial mammals.Gill Sans Bold Exercise 6. (You do not have to use all the lines provided. 4: Plant adaptations to reduce water loss Describe some adaptations of a range of terrestrial Australian plants that assist in minimising water loss.Exercise 6. (You do not have to use all the lines provided.) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ 32 Maintaining a balance . 6: Adaptations for changing environments a) Define enantiostasis. Use the list of features in the materials. _____________________________________________________ _____________________________________________________ b) Why does a mangrove need to carry out enantiostasis? _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 6: Maintaining water balance 33 . Consider any risks that you may encounter while doing this first hand investigation and let your teacher know how you would overcome these. Exercise 6.5: Your own investigation of plant adaptations Construct a table to present information you have collected about some structures of two plants that assist in the conservation of water.Gill Sans Bold Exercise 6. scientific equipment.Student evaluation of the module Name: ________________________ Location: ______________________ We need your input! Can you please complete this short evaluation to provide us with information about this module.) _____________________________________________________ _____________________________________________________ 5 Do you have access to the appropriate resources? eg a computer. chemicals. people that can provide information and help with understanding science _____________________________________________________ _____________________________________________________ Please return this information to your teacher. BIOHSC43204 Maintaining a balance . the internet. 1 Did you find the information in the module clear and easy to understand? _____________________________________________________ 2 What did you most like learning about? Why? _____________________________________________________ _____________________________________________________ 3 Which sort of learning activity did you enjoy the most? Why? _____________________________________________________ _____________________________________________________ 4 Did you complete the module within 30 hours? (Please indicate the approximate length of time spent on the module. This information will help us to improve the design of these materials for future publications. who will pass it along to the materials developers at OTEN – DE. Learning Materials Production Open Training and Education Network – Distance Education NSW Department of Education and Training .