Science notesPSLE preparations 1 Body system The body system is made up of several different systems, including the digestive system, the respiratory system vice versa. They are all interdependent and our body would not be able to work properly without any one of them. The digestive system Processes There are four processes that will take place in our gut. Glands are also connected to parts of our guts to release enzymes. The four main processes are ingestion, digestion, absorption and egestion. Ingestion is the process whereby food is put into the mouth. Digestion is the process whereby food is broken down into smaller, soluble substances. Absorption is the process whereby digested food molecules move through the walls the walls of the small intestine into the bloodstream where they are transported to different parts of the body. Egestion is the process whereby undigested food is passed out of the body through the anus. The Mouth When food is placed in my mouth, we will chew the food into smaller pieces with our teeth. The teeth will cut and grind the food into smaller pieces and speed up the process of digestion and aid in the swallowing process. The teeth are also made up of different types. The front ones, known as incisors, will cut and break the food into smaller pieces. Then, the grinding teeth at the back of our mouth cavity, known as molars, will mash the food up into pieces. The process does not involve any chemical change of food substances; hence, we can say that the teeth play a part in the mechanical digestion of the food we eat. The salivary glands will secrete saliva which serves to digest the cooked starch into maltose as saliva contains salivary amylase. However, the food usually does not stay in the mouth long enough for all the starch to be digested into maltose. Saliva will also soften the food and make it easier for us to swallow the food. The tongue then rolls the food into a ball and sends it to the back of the mouth cavity, so that we can swallow. The food then enters the oesophagus through the process of swallowing. 2 The oesophagus The oesophagus or the gullet joins the mouth to the stomach. Peristalsis then occurs in the gullet as the oesophagus move the down the alimentary canal. Peristalsis refers to the wave-like muscle contraction of the gut, to propel food forward. The gullet contains muscles. The contraction and relaxation of the muscles help to push the food substances through the systems. Hence, the alternate contraction and relaxation of the muscles along the wall of the oesophagus forces the food ball down towards the stomach. Although no digestion occurs on the oesophagus, digestion of the starch by the saliva amylase may still continue. The stomach The stomach is a muscular bag that contracts and relaxes. Peristalsis of the stomach will break the food down into smaller pieces to speed up the rate of digestion, and to mix the food substances with the gastric juices. The gastric juices in the stomach are secreted by the gastric glands found on the wall of the stomach. The gastric juice contains protease that will digest protein into polypeptides. Dilute hydrochloric acid which provides acidic medium for the proteases to function optimally. The acid also kills any harmful bacteria present in food. The stomach also contains water. The walls of the stomach will produce mucus which functions to lubricate the food and protect the walls of the stomach from being corroded by the acid produced. This is also why if we do not eat our meals regularly, the digestive juices and acids will be secreted on an empty stomach, leading to gastric ulcers on the walls of the stomach as the acid digests the stomach wall. The food will stay in the stomach for about two to six hours and will appear as a black liquid after some time. 3 The small intestine The small intestine is the main organ in the digestive system that is involved in the process of digestion. The small intestine is a long coiled tube of about six meters long. It is also connected to two other important glands, the liver and the pancreas, which secretes digestive juices into the small intestine. In the small intestine, food is mixed with intestinal juices secreted by glands found on the intestinal walls. Amylase, protease and lipase, from the pancreas can be found in the intestinal juices. Bile from the liver can also be found. Absorption of food through the walls of the alimentary canal into the bloodstream will occur in the small intestine. Digestion will be complete in the small intestine. However, not all the food that we eat can be digested in the small intestine. *Absorption The absorption of food takes place in the small intestine. Digested food, which exists as small soluble molecules, will pass through the walls of the small intestine into the bloodstream during absorption. Hence, the movement of food though the walls of the alimentary canal is called absorption. Only small, soluble and diffusible substances such as glucose and amino acids can pass through the walls of the small intestine. Larger particles like starch or protein cannot pass through and be absorbed. In the small intestine, finger-like projections, known as Villi are present. The diagram above shows a cross section of a single villus in the small intestine. There are thousands of Villi present n the small intestine. The Villi are highly convoluted or coiled up, and contain blood capillaries that will transport the absorbed nutrients to all parts of the body. The Villi bring blood closer to aid in absorption. It also increases the surface area to speed up the rate of absorption. 4 the complete digestion of maltose by pancreatic juices. The alkaline nature of the juice helps to neutralize the acid in the food from the stomach. rate of digestion will increase in the presence of bile. a protease and a lipase. Hence. the digestion of polypeptides to amino acids by protease and the digestion of fats to fatty acids and glycerol by lipases. some of the processes that will take place in the presence of the pancreatic juice includes. it plays an important role of breaking the fats down into smaller oil droplets. It is also necessary to have an alkaline medium for the enzymes secreted into the small intestine to function optimally. the digestion of maltose by maltase.The liver The liver is a large reddish gland that is responsible for the secretion of bile into the small intestine. 5 . will increase the area for lipase to act on. This the any The pancreas The pancreas is a gland that produces alkaline digestive juices. Bile is a yellowish-green liquid that is produced by the liver and stored in the gall bladder before being secreted into the small intestine via a bile duct. While bile does not contain digestive enzymes. Hence. The pancreatic juice contains an amylase. water is absorbed and mineral salts such as zinc. will enter the body. leaving behind an almost solid waste known as feaces. The Villi bring blood closer to aid in absorption. It also increases the surface area to speed up the rate of absorption. The feaces is then stored temporarily in the rectum and is excreted from our body through the anus. iron and calcium. In the large intestine. The large intestine is about 1. it can help too to satisfy our hunger and can help to control and maintain our weight. which are necessary for the development of the body. diffusible molecules so that they can be absorbed by the body. wheat. It is important to include fiber in our diet since it provides the bulk of the food masses passing through the alimentary canal.5 meters long and consists of colon. The fiber also absorbs the poisonous wastes. How do the Villi help in the absorption of food: The Villi finger-like projections in the small intestine and are highly convoluted or coiled up. Fiber can be obtained from whole meal bread. they contain blood capillaries that will transport the absorbed nutrients to all parts of the body. are also absorbed. 6 . Frequent questions*** Define digestion: Digestion is the process whereby large. the rectum and the anus.Large intestine The large intestine is where undigested food substances like fibers. insoluble food substances are broken down into smaller. fruits and vegetables. The absorption of water and minerals occur at the colon. Concept map (abstract) 7 . Our heart beat rate varies with our age and the type of activities that we carry out. a pressure wave passes along the blood vessel. Heart beat and pulse Each cycle of the contraction and relaxation of the heart is called a heartbeat. With each heart beat. It has two atria. the faster the pulse rate. More carbon dioxide is thus produced. and count the number of heartbeat per minute. Valves are located in the heart to prevent blood from flowing backwards. We can take out pulse rate by pressing our finger along the blood vessels in our wrist or neck. causing them to expand and relax. pushing the blood through them. blood is pumped through the blood vessels. The faster the heart beat. the chambers that pump blood out of the heart. while deoxygenated blood enters from the right atrium of the heart and into the right ventricle before exiting to the lungs. This is measured when a person is at rest. After each heartbeat. Oxygen rich blood from the lungs enters the left atrium of the heart and into the left ventricles of the heart before exiting to the rest of the body. The heart pumps faster so that the blood can supply more food and oxygen to the cells rapidly remove carbon dioxide produced. the chambers which receive blood returning to the heart and two ventricle. This is known as the pulse. 8 . The normal pulse rate of a healthy young male is 60 to 70 pulses per minute. The beats faster when we exercise as our bodies need more food and oxygen to release enough energy from the food for use.Circulatory system The Heart The heart is a ball of muscles that pumps blood to all parts of the body. The blood vessels There are three different types of blood vessels in our body. What makes the red blood cell 9 . They contain haemoglobin which allows oxygen from the lungs to bind loosely to them. Red blood cells are characterised by their biconcave disk shape and their bright red colour. The blood actually acts as a medium of transportation of substances around the body. The oxygen will eventually be given up to other cells. it connects the aqueous environment of all the body cells together. Blood cells There are all together three types of blood cells. The capillaries have a very thin. one cell thick. Through the circulatory system. they are also the ones that spread to cover all parts of our body. vein and the capillaries. The arteries have thick walls so that it can sustain the pressure at which the blood is pumped from the heart. permeable walls to allow exchange of materials between the blood and cells. plasma and the platelets. The red blood cells Red blood cells are the most numerous blood cells. Blood Blood is the circulating tissue composed of fluid plasma and cells. the artery is to transport the oxygenated blood to all parts of the body. artery. blood is pumped to all parts of our body. Its function is to transport diffused oxygen from the lungs to all the cells in our body for cellular respiration. the white blood cells. the red blood cells. the capillaries are for transporting both types of blood as it connects two main vessels. Lastly. Each vein has a different use. The veins have slightly thinner walls than arteries. The main components of the blood are the red blood cells. the white blood cells and the platelets. The vein is used to carry the de-oxygenated blood back to the heart. By transporting blood throughout the body. They do so by producing antibodies. They play an important role is our body. dissolved nutrients. When we bleed. The tissue fluid acts as a medium between cells and blood. 10 . hormones and ions can be found in plasma blood.different is that they do not have a nucleus. Plasma Majority of the blood volume consists of liquid plasma. red blood cells are actually produces by the bone marrow. It is now known as tissue fluid. thus they cannot self divide and. waste product together with antibodies. the platelets with gather at the point of the bleeding and form something like a plug and plug up the cut and clot up the blood. The exchange of waste substances for useful substances occurs between cells and the tissue fluids by osmosis. Platelets Platelets are small fragments of cells. blood protein. preventing excess blood loss White blood cells The main function of the white blood cells is to fight off infection. diffusion or active transport. The blood and other blood cells are suspended in the plasma along with many other substances. we would be prone to diseases and would not be able to fight them off. They help to clot the blood and stop bleeding. as without them. Carbon dioxide. it is possible for humans to live with only one lung. which makes it hospitable for bacteria. the two are not identical. As oxy gen requirements increase due to exercise. The cardiac notch is a concave impression moulded to accommodate the shape of the heart. In combination with other physiological measurements. it can be measured with a spirometer. The lobes are further divided into segments and then into lobules. having a much larger surface area in total than the outer surface area of the lung itself. Vital capacity is the maximum volume of air that a person can exhale after maximum inhalation. without it we will die. Many respiratory illnesses are the result of bacterial or viral infection of the lungs. due to the excess capacity. The connective tissue that divides lobules is often blackened in smokers and city dwellers. Human lungs are located in two cavities on either side of the heart.Respiratory system The respiratory system is very important to our body. hexagonal divisions of the lungs that are the smallest subdivision visible to the naked eye. Though similar in appearance. allowing the body to match its carbon dioxide or oxygen exchange requirements. in situations like these only a small portion of the lungs are actually perfuse with blood for gas exchange. Inflammation of the lungs is known as pneumonia. inflammation of the pleura surrounding the lungs is known as pleurisy. The medial border of the right lung is nearly vertical. The environment of the lung is very moist. the vital capacity can help make a diagnosis of underlying lung disease. with the other compensating for its loss. Lungs are to a certain extent 'overbuilt' and have a tremendous reserve volume as compared to the oxygen exchange requirements when at rest. while the left lung contains a cardiac notch. a greater volume of the lungs is perfusing. Both are separated into lobes by fissures. Lung The lungs of mammals have a spongy texture and are honeycombed with epithelium. 11 . It helps us to respire. with three lobes on the right and two on the left. The lungs of humans are a typical example of this type of lung. as respiration is a very important process. Such excess capacity is one of the reasons that individuals can smoke for years without having a noticeable decrease in lung function while still or moving slowly. Additionally. which lead to alveolar sacs. The oxygen binds to hemoglobin and the carbon dioxide is released. the hemoglobin in the red blood cells has carbon dioxide bound to it and very little oxygen. like individual grapes within a bunch. air is sucked into or expelled out of the lungs. through the action of other respiratory and accessory respiratory muscles. When you exhale. As a result. Contraction of the diaphragm pulls the bottom of the cavity in which the lung is enclosed downward. so carbon dioxide leaves the blood and passes across the alveolar membrane into the air sac. where oxygen diffuses into blood and is exchanged for carbon dioxide in the haemoglobin of the erythrocytes. it flows through the larynx and into the trachea. At the beginning of the pulmonary capillary. increasing volume and thus decreasing pressure. which branches out into the main bronchi and then subsequent divisions. The oxygen-rich blood returns to the heart via the pulmonary veins to be pumped back into systemic circulation. Air from the lungs (high pressure) then flows out of the airways to the outside air (low pressure). and after multiple divisions. The bronchial tree continues branching until it reaches the level of terminal bronchioles. Within each air sac. The carbon dioxide then 12 . so oxygen passes or diffuses across the alveolar membrane into the pulmonary capillary. the diaphragm and inter costal muscles (those are the muscles between your ribs) contract and expand the chest cavity. Air enters through the oral and nasal cavities. the trachea divides into the two main bronchi that enter the roots of the lungs. bronchioles are given rise. causing air to flow into the airways.When you inhale. This expansion lowers the pressure in the chest cavity below the outside air pressure. Air then flows in through the airways (from high pressure to low pressure) and inflates the lungs. Deoxygenated blood from the heart is pumped through the pulmonary artery to the lungs. the diaphragm and intercostal muscles relax and the chest cavity gets smaller. The rib cage itself is also able to expand and contract to some degree. In humans. Carbon dioxide is also released from sodium bicarbonate dissolved in the blood of the pulmonary capillary. The cycle then repeats with each breath. expiration is passive and no muscles are contracted (the diaphragm relaxes). This type of lung is known as bellow lungs as it resembles a blacksmith's bellows. This exchange of gases occurs rapidly (fractions of a second). During normal breathing. The decrease in volume of the cavity increases the pressure in the chest cavity above the outside air pressure. The individual alveoli are tightly wrapped in blood vessels and it is here that gas exchange actually occurs. The concentration of carbon dioxide is high in the pulmonary capillary. The bronchi continue to divide within the lung.Processes of breathing Breathing is largely driven by the muscular diaphragm at the bottom of the thorax. the oxygen concentration is high. Alveolar sacs are made up of clusters of alveoli. The nerve cells that live within these centers automatically send signals to the diaphragm and intercostal muscles to contract and relax at regular intervals. can be overridden by chemical factors (oxygen. as it does many other functions in your body. nerve cells in the hypothalamus and cortex also influence the activity of the respiratory centers. Coughing and sneezing cause air to be rapidly and violently exhaled from the lungs and airways. Their influence. Nerve centers in the cortex can voluntarily tell the respiratory center to speed up. Of these factors. carbon dioxide diffuses easily into the CSF from the blood. a central chemoreceptor in the medulla monitors the carbon dioxide concentration in the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. slow down or even stop (holding your breath). These cells then signal the respiratory centers to contract the respiratory muscles. then both types of chemoreceptor signal the respiratory centers to increase the rate and depth of breathing. specialized nerve cells within the aorta and carotid arteries called peripheral chemoreceptor monitor the oxygen concentration of the blood and feedback on the respiratory centers. removing the offending substance. If you try to hold your breath. During pain or strong emotions. the activity of the respiratory centers can be influenced by several factors. Signals from higher brain centers. peripheral chemoreceptor also monitor the carbon dioxide concentration in the blood. This mechanism prevents damage to the lungs that would be caused by over-inflation. they tell the respiratory centers to increase the rate and depth of breathing. they signal the respiratory centers to exhale and inhibit inspiration. the purpose of breathing is to keep the oxygen concentration high and the carbon dioxide concentration low in the alveoli so this gas exchange can occur! You don't have to think about breathing because your body's autonomic nervous system controls it.leaves the alveolus when you exhale and the oxygen-enriched blood returns to the heart. 13 . noxious fumes. Oxygen can affect the activities. and pH). However. the strongest influence is the carbon dioxide concentration in your blood and CSF followed by the oxygen concentration. causing you to sneeze or cough. Stretch receptors in the lungs and chest wall monitor the amount of stretch in these organs. or cigarette smoke. Carbon dioxide too. The respiratory centers that control your rate of breathing are in the brainstem or medulla. If the oxygen concentration in the blood decreases. Thus. If the lungs become over-inflated (stretch too much). If the carbon dioxide concentration gets too high. the hypothalamus will tell the respiratory centers to speed up. carbon dioxide. however. The increased rate of breathing returns the carbon dioxide concentration to normal and the breathing rate then slows down. dust. your body will override your action and force you to let out that breath and start breathing again. water. Nerve cells in the airways sense the presence of unwanted substances in the airways such as pollen. In addition. The mixture is then. 14 . These impulses cause unwanted contractions (hiccups). Their gills function such that it has many fine blood vessels on each gill to take in the dissolved oxygen from the water as it drinks the water and the water pass through. Fishes do not have lungs to respire. The same thing happens in unborn children. This is why when the sun is very hot. The stomata have two guard cells and help to control the size of the pore to regulate the amount of water lost to the surrounding through respiration. It seemingly acts like our nose and allow air in and out. Oxygen will be given out together will excess water in its gaseous state.Sometimes the respiratory centers go temporarily awry and send extra impulses to the diaphragm. used to release the energy in the food and carbon dioxide. This happens because the respiratory centers of the developing child's brain are working just like those of an adult even though they are not yet breathing air. it is different. As for plants. Fishes & plants) Respiration is the process in which oxygen is taken in and together with the glucose from the food that we eat. The plants respire by releasing air through the openings on the underside of the leaves called stomata. together with water are by products. the water is then released through the two flaps on the gills as they open and the process would repeat itself again. they have gills. many pregnant women often feel their babies hiccup. The energy meanwhile will be used by the cell at which cellular respiration took place. instead. They are then released from the body through the trachea. Respiration (Human. After the exchange of gases at the gill. the stomata will become smaller. ring. nickel or cobalt. plastic. 15 . The centre of the magnet is usually very weak.North) attract each other. we are reducing the strength of the magnet strip on the door. Electromagnet can be formed using two methods. The second method is usually used in factories to retrieve large pieces of metal from the pile of rubbish as it can be turned on and off and is stronger than the stroking method. strip.Magnet Notes A magnet is a special piece of metal that can attract other objects. Magnetic force can pass through non-magnetic substances like glass. But it cannot pass through magnetic substances. A freely suspended magnet will always hang in a North. Natural magnets are made of lodestones. bar. Magnetic strength of a magnet can be reduced by hitting it many times or by heating it continuously. So when we slam refrigerator doors often. rod. U-shaped and horseshoe shape. Like poles of a magnet (North-North) repels each other while the unlike poles (South. These materials are called magnetic materials. wood. the North and the South. A magnet can be natural or man-made. But it can only attract objects made of iron. Either by stroking a magnetic substance with a magnet or by twirling wires over it and connect it to batteries. Man-made magnets are made from materials such as iron or steel. steel. The most common shapes are button. The strongest parts of a magnet are its two poles. Magnets can also come in many different shapes and sizes.south position. Saturn. The Sun The sun is a huge star that gives off its own light. Scientific Research To observe the Earth·s upper atmosphere. Uranus and Neptune. Earth·s Observation To study the Earth·s land. Venus. It is made up of a huge ball of gases. the moon. It is also surrounded by a layer of gas which traps heat for within the earth and shield 16 . The planets can be seen because they reflect the light from the sun to our eyes. The earth is mostly made up of rock metal and water. The Earth It is the fifth largest planet in the solar system. so we are able to see them.Solar System The sun. our skin will become darker and we may have skin diseases. The sun rises in the east and sets in the west. stars. Earth and the other planets make up the solar system. Navigation To help ships and airplanes determine their exact location on Earth. The planets travel on their own orbit. If too much ultra-violet ray reach the Earth. winds and temperatures To find the amount and types of pollutant in the air. Direct staring at sun can cause us temporary blindness. Mars. It provides plans with light to perform photosynthesis as it cannot take place without light. Planets are objects that revolve around the sun and do not give off light on its own. atmosphere an life. oceans. It also allows us to see things around us. Jupiter. Man-made Satellite Man-made satellites are used in many different ways in space. Communications To provide long distance communication links To transmit data to various parts of the world. planets in the universe. Mercury. Defense To observe the activities of enemy nations. Heat energy is also given off by the sun to warm us up and prevent us from freezing. The names of the names of the planets from the nearest to the furthest are. which is a fixed path that an object takes around something else. Earth. Weather forecasting To study the weather pattern on the earth by obtaining the information of the clouds. The earth does not give off its own light. It is the earth·s one and only natural satellite. is visible when we look at it in space. instead. It does not give off its own light as it merely reflect the sun·s light allowing us to see it at night. The regular movement of the moon and the gravity of the moon give rise to the high and low tides. 17 . It takes one year to rotate on complete round around the sun and each year is 365 days. whereas water also exist in liquid state. it reflects the light from the sun so. and this layer of gas form the atmosphere. The rotation of the earth on its own axis which takes 24 hours each round. gives rise to the day and night cycle.the earth from the sun·s harmful ultra-violet rays. The Moon There is no air or water on the moon so it does not support life. We are only able to live on earth as its position is just right from the sun and there is food for us to eat and air for us to breathe. but others cannot. Some forces can act at a distance. A force is a pull or a push. unlike poles attract It can act at a distance The strength of a magnet does not depend on its shape or size The strength of a natural magnet. Magnetic force may also be produced by ordinary electric current flowing through a coil of wire. Force of a magnet is strongest at the poles Like poles repel. Gravitational force) Energy is needed to produce force. We get energy from the food we eat. and change the speed of an object and change the direction an object moves in. dropping or heating it Temporary magnets can be created using the stroking and electromagnetism methods 18 . A force can change the shape of an object. A steel nail placed near a magnet. Many actions such as kicking a ball involve forces. stop a moving object. becomes magnetized and can attract a second nail. and certain other materials. cannot be increased Earth is the largest piece of magnet The strength of a magnet varies The strength of a magnet can be decreased by hammering. slow down a moving object. nickel. for example. it may pull magnets together or push them apart. move a stationary object. steel. Types of forces Magnetic force: Magnetism is the force that electric currents exert on other electric currents. Magnetism may be created by the motion of electrons in the atoms of certain materials. we cannot see a force but we can feel the effects of force after it interacts with another object or substance (ECT. The atoms with aligned electrons then act like tiny bar magnets. which are called magnets. Magnetization occurs because the magnet causes spinning particles called electrons in the atoms of the nail to align along the magnet's field lines. A force cannot be seen but we can see what a force can do.Simple Machine notes Force A force can be push or a pull. The attracted materials then become magnets themselves in a process called magnetization. The magnetic force may cause attraction or repulsion--that is. a lodestone. called an electromagnet. A magnet attracts iron. You could not walk without friction to keep your shoes from sliding on the pavement. An object's weight is largest if the object is on the surface of the planet. the top object can be lifted without any resistance except that of gravity. a man who weighs 91 kilograms on the earth would weigh only 15 kilograms on the moon. The weight of an object also depends on the mass of the planet. Friction has many important uses. If the mass of a planet is smaller than that of the earth. 82 kilograms on Venus. and 234 kilograms on Jupiter.Elastic spring force: It is the force founding the spring when it is compressed or stretched. Friction also has disadvantages. It produces heat that may cause objects to wear. The weight of the object stretches the elastic band or spring The heavier the object. This is why it is hard to walk on ice. The object has no weight in space where the gravitational force acting on it is too weak to be measured. the greater the extension Gravitational force: It is the force of attraction between the Earth and any object on Earth. If two objects with flat surfaces are placed one on top of the other. The weight becomes smaller if the object is moved away from the planet. the spring will in turn exert a force on whatever is stretching or compressing it. It allows a conveyor belt to turn on pulleys without slipping. It makes the wheels of a locomotive grip the rails of the track. But if one object is pushed or pulled along the surface of the other. For example. the gravitational force there is smaller. He would weigh 34 kilograms on Mars. Gravity is a force that prevents things from falling out of the Earth Gravity causes falling objects to fall downwards Gravity causes a spring to stretch or extend A very strong force is needed to resist the pull of gravity There is zero gravity in space Weight is the gravitational force put forth on an object by the planet on which the object is located. This is why oil and other 19 . there is a resistance caused by friction. When this force is exerted on a spring. The weight of any object depends on the distance from the object to the centre of the planet and the mass of the object. Friction is the property that objects have which makes them resist being moved across one another. The smooth surface of the ice produces less friction than a pavement and allows shoes to slip. Laws of friction: The basic law of friction says that the force needed to overcome friction is proportional to the total normal. depends on the type of surfaces moving against each other. = F/P.F. when the weight of a box being pulled across a floor is doubled. When the box weighs four times as much. This can be written C. or perpendicular. The advantages of friction It lets people walk without slipping It enables car wheels to stop spinning and thus stop a moving vehicle It starts movements without slipping It enables us to hold on to things It produces heat The disadvantages of friction It slows down movement It causes wear and tear It forces us to use more energy Friction can be reduced by using: Rollers Wheels Ball bearings Lubricants Water 20 .).F. That is.lubricating liquids are used to fill spaces between moving machinery parts. The ratio between the weight being moved and the force pressing the surfaces together is called the coefficient of friction (C. four times as much force must be used to pull it. The value of the C.F. The coefficient of friction equals the force needed to move an object divided by the force pressing the surface together. the force necessary to pull it must be doubled. The liquid reduces friction and makes the parts move more easily and produce less heat. force pressing one surface against the other. The load is tied to a rope that winds around the wheel. Lever A lever enables us to use a smaller force to overcome a larger force. Pulleys A pulley has a wheel that rotates freely. Simple machines also help us to do work easily by reducing the distance travelled by the load. A force is needed to operate these machines. quickly and efficiently. distance the effort needs to travel. moveable and fixed pulley. place the fulcrum as near to the load as possible. by reducing the effort needed to lift the load. less effort is used to lift the load. more than one simple machine is used in one object it is complex machine. 21 .Simple Machines Machines help us to do work more easily. apply effort as far from the fulcrum as possible. hen an effort moves a greater distance than the load. When. There are many types of simple machine. When we want to lift a heavy load with the least effort. There are two types of pulley. Examples: Screwdriver Doorknob Steering wheel Pencil sharpener Cross spanner 22 . Factors that affect the amount of effort needed: The angle of inclination The weight of the load The steepness of the inclined plane The roughness of the inclined plane Gears Gears are wheels with teeth that can interlock one another. Gears are usually placed together with other gears so that the tooth of one gear fits into the notches of the other. It changes the direction of a force and also reduces the effort needed to lift a load. It is commonly used in lifts and cranes. Wheel and Axle A wheel and axle is made up of a large wheel connected to a rod called axle.Pulley System It which consists of a fixed and a movable pulley is often used to raise heavy loads. It makes us to use a smaller force to overcome a bigger force at the axle. It helps us to do work by reducing effort to move heavier load from a lower level to a higher level. They help us do work by changing the direction of rotation or applied force or changing the speed at which an object moves. Gears move in the opposite directions of the next gear interlocked with it. Examples are eggbeaters and bicycles. The load and effort move in opposite directions. Gears can be connected by a chain. The longer the slope. the lesser the effort needed to travel up but the effort has to travel a longer distance. Inclined plane An inclined plane is a sloping surface. It is actually a lever. the fulcrum is at the centre of the rod. If the wheel is bigger than the axle. 23 .Faucets A key A simple machine is made of a small rod stuck to a big wheel. less effort is required. the distance moved by the effort is greater than the distance moved by the load. However. It will be given out by the plant for us to respire and give out carbon dioxide for the plants. hairy. There are two different types of veins. A good example would be plant left in a dark box with only a small hole at the other end of the box. but they still contain chlorophyll as it is hidden under the color pigments of the leaf. they are able to move and respond to changes. the network vein and parallel vein. stem or roots. they play a very important role in maintaining the amount of oxygen and controlling the amount of carbon dioxide in the atmosphere for us to respire. However. A mushroom is definitely not a plant. The chlorophyll absorbs sunlight and together with water from the roots and the carbon dioxide that it gets. lobbed edges. A plant is usually immobile and functions on the spot. Leaves help the plant to make food and are also called. These are a few of the most common ones. it cannot make its own food. A few weeks later.Plants Plants are living things. Some leaves may also appear yellow or orange. stem and roots. you will find that the plant is growing towards the hole. The plants can also be classified by the veins. The leaf contains chlorophyll which causes the leaf to appear green. The plant·s leaves have special ¶designs·. Doesn·t that show that plants are able to move and respond to changes? A plant is basically made up of leaves. A plant is generally considered as a living organism that manufactures its own food (autotrophic). Leaves The leaf of a plant can have many textures. Moreover. The network vein is like a network 24 . waxy and rough. The plant has veins on the leaves that will transport water from the roots to all parts of the leaf and also collects the food at the stalk of the leaf and wait to be transported to other parts of the plant. It is a fungus as it does not have leaves. and entire edges. There are toothed edged. smooth. it photosynthesizes and makes food and oxygen is a byproduct of photosynthesis. the plant·s ¶kitchen·. When the plant photosynthesizes. Fibrous root It is a cluster of roots growing. it plays a vital role in ensuring that the plant survives.just as its names states and branches to all parts of the leaf. The root takes in water and the water is transported to the leaves. they are all about the same size and it can reach widely and reach further across the soil. It is mostly located at the underside of the leaf to prevent too much water loss as the sun might dry the leaf up. Prop roots penetrate the soil deeply Creeping roots It grows on the stem of other plants and this stem anchors them 25 . It acts like our nose and allow air in and out. but actually. The two most common types of root are the fibrous root and the tap root Other types of root Storage Root It stores food in the roots Breathing Root It is able to take in air with its roots Aerial Root It is able to respire with its roots Clasping Root It can clasp on other plants and ¶steal· minerals and water from them. The cactus has adapted to have needle-like leaves to minimize water lose through transpiration. Buttress root It can keep a heavy trunk erected. The parallel veins are positioned in a parallel position. It also releases excess water as water vapor. It also anchors the plant firm in the ground and prevents it from flying out of the soil at the slightest wind. Tap root It has a long thick main root and has smaller roots growing from it. Roots The root may look plain and useless. The plant respires and gets carbon dioxide for photosynthesis from this small opening found on the underside side of the leaf. the water that is needed comes from the root. It is good at anchoring and can reach deep into the soil. But this method is only workable for flowers with large droopy and feathery 26 . are arranged in a ring beneath the cortex. that transport water and dissolved minerals absorbed by the roots. Stems have a circular layer of cells called the cortex under the epidermis. a thin. Insects like bees and butterflies lands on flowers to such the nectar and the pollen grain will stick to their legs and will drop off when they land on the next plant. Pollination is the process whereby the pollen lands on the stigma. stigma. fertilizing it. The basic part of a flower is the petal. so they cannot stand up on their own. The stigma is the female part of the plant where the pollen sacs will land on.The Stem The stem is a very important part of the plant. The style is the passage that leads to the ovary and the ovules are female reproductive cells that will fuse with the male reproductive cells to form seeds. Another way is for the wind to blow the pollen and the pollen will land on the flower. It also helps to keep a plant upright. The anther. The xylem lies towards the inside of the bundle. The pollen can be transferred through several ways. Flower The flower is a very interesting part of a plant. they cling on to supports or other plants for support. and Phloem tubes. Dicotyledonous stems also have a band of cells called the cambium. ovary. skin-like layer of cells lying in seeds. It grows when a plant matures. Not all types of plant have both the male and female parts in one flower. plants and ferns which will protect he plant parts. and the phloem tube is towards the outside. anther and sepal. Bundles of Xylem tubes. the petals will drop off. ovule. where the male reproductive cells are. which lies between the Xylem tube and the Phloem tube within the bundle. The flower is made up of two parts. style. After the flower is fertilized. that transports food made by the leaf. is supported by the filament. The sepal is the part that protects the plant when it is still a bud. the ovary will start to swell and a fruit is formed over time. the male and female parts. filament. Some plants have weak stems. leaving the fruit to grow. The fruit will contain and protect the seeds that are needed to ensure the continuity of the species of plant. The seeds dispersed by wind are small and light. They may also have special structures like umbrella structures or wing-like structures that enable them to float for a longer distance away from the adult plant. Seed dispersal Different plant can have different methods of seed dispersal. The disadvantage is that if the adult plant has a disease of is prone to a disease. The advantages of cross pollination are that the plants may get good points of both the plant that fertilized it and the plant that is fertilized. 27 . After the ovule is fertilized the ovary becomes the fruit and the other parts of the flower outside the ovary wilts and dies. the young plant would also be diseased or prone to that disease. They also grow just beside rivers or seaside so that their seeds can be carried away by water. Flowers pollinated this way does not need to have colorful petals as they do not need to attract insects. Pollination can also be grouped into two types. when their kernel. The disadvantage is that the plant that fertilizes the plant may have some unknown disease and pass it on to the young plant. The pollen rain that lands on the stigma makes a pollen tube and travels to the ovary where its nucleus will fuse with the nucleus of the female reproductive cell of the flower. The seed is dispersed so as to prevent the young plant from growing too near to the adult plant and to prevent overcrowding and the competition for water and nutrients. A common type of dispersal is by wind. Fruits that disperse its seeds by water can float on water and have a fibrous husk that can trap air. The advantage of self pollination is that the good points of one plant will continue to be present in the young plant. promoting healthy growth of the young plant. self pollination and cross pollination. Self pollination is the pollen of the same plant fertilizing the flowers of the same plant. Although fruit like coconut which is dispersed by water is heavy. Fertilization occurs after pollination. which contains water dries up. The wind can also carry away seeds that have a fluffy covering. the ovule. they simultaneously lose a lot of weight. while cross pollination is the pollen of one plant fertilizing the flowers of another plant.stigma to catch the pollen in the air. Photosynthesis & Respiration All green plants can photosynthesize. All organisms depend on sugar as an energy source. The method is by digging the stem out. But that only applies for ferns. the new fern grow. Plants can also reproduce in many other ways. There are two types of animal dispersal. Ferns do not flower. There are also other types which just split open. The advantage of this is that the adult plant will provide it food and ensures that the young plant grows healthily. Human and other animals are unable to produce it on their own and must rely ultimately on the sugar produced by plants in the process called photosynthesis. they seed flies in all directions at high speed. Some fruit disperse seeds with the help of animals. a young plant will grow from it. The young plant will get nutrients directly from the adult plant and as the young plant grows larger.Fruits which are dispersed by splitting must be dry and can open with explosive force. However green plants like algae and certain bacteria can trap sunlight to make food. The leaves of plants that can make food are usually green as they contain chlorophyll which aids in 28 . the adult plant dies. glucose is a carbohydrate that is the basic fuel and basic building material for life. but with no explosive force as the wind will carry the seeds away. The food produced is glucose. Another ways is by using underground stem. Some plants also can use their roots to reproduce by cutting the ¶head· of the root and planting it. Another type is that the seeds have stiff hooks and cling onto the fur of passing animals and drop off after a while as the plant moves. The adult plant matures and a sucker will grow from its stem and that will be the young plant. cutting the part of the stem that has the bud and growing it. the first type is the animal eats the whole fruit and the hard indigestible seeds will pass out as feaces and the plant will grow. When the seed is dispersed. Humans or other living things are unable to make their own food. One of them is by suckers. They reproduce by spores which are carried by the wind and when the spores land. As time passes. thus they do not need pollination or flowers. Plants get energy from the food the produce through photosynthesis. But these only apply for special plants that have specially adapted roots and underground stem. Plants also can reproduce from spores. Plants dispersing seed in this way has nice smelling and nice tasting fruit to lure animals to eat them. Each fern has a lot of spore so as to ensure that some of the spore will develop into adult ferns as it is not confirmed that the spores would land on a spot which is suitable for the growth of the young fern. In a starch test. These stored reserves are used by plants for extra energy or building materials. they are called food producers. and oxygen. the plant cannot make its food. on photosynthesis as a source of food. Plants produce sugar in glucose for many uses. energy. Animals and other organisms do not have the ability to make food so they depend on other organisms and are called food consumers. fruits and seeds. seeds or stem. Without chlorophyll. It can be used to build leaves. The storage part of the plant can be either the roots. croton and copper leaf plants are plants with colorful leaves. There are several types of food consumers: Herbivores: Plant eaters Carnivores: Meat Eaters Omnivores: Plants and meat eater Insectivore*: Insect eaters Frujitivore*: fruit eater 29 . making it one of the most important biochemical processes known. An extremely important product of photosynthesis is oxygen. it can also be converted cellulose in building of their cell wall. there is iodine in a substance if the iodine turns dark blue. The oxygen that the plants give off is what we breathe in for respiration and the carbon dioxide that we breathe out is taken in by the plants for photosynthesis. The excess sugar is converted into starch and stored in different parts of the plants. Food Source & Energy Source of Animals All life on Earth depends. Iodine is used to test for starch. They also have chlorophyll that is hidden under the red and yellow pigments of the leaves. Coleus. flowers. Glucose and oxygen are products of photosynthesis. Plants usually make more sugar than they need. Some plants not only carry out photosynthesis but also trap insects to get more nutrients. directly on directly. As plants can make their own food.trapping sunlight for sunlight for photosynthesis. The chlorophyll is embedded in the chloroplast. glucose is converted to energy used to do work. Unlike photosynthesis which only takes place in the presence of light. It will turn chalky when comes into contact with carbon dioxide. respiration takes place all the time. Germination Germination can only occur under certain conditions. And remain clear if there is no presence of carbon dioxide. Without any one of these. Limewater is used to test the presence. glucose and oxygen are converted into energy for work. carbon dioxide and water. the plant would not require light since it does not make its own food and would get food from the seed leaves (cotyledons).Respiration All living things respire. the seed would not be able to germinate without any one of these conditions. the presence of water and warmth. at the germination stage. These conditions include the availability of air. However. When they breathe in oxygen. 30 . Living things take in oxygen and give out carbon dioxide during respiration. During respiration. It is very airy there and the temperature fluctuates from day to night. The fennec fox is another example as it has large ears to reduce heat gained. Rotting log The rotting log community always contains a rotting log as its name states and the log has to be in the process of decomposing. The rotting log is softened when it is decomposing thus easier for the organisms in it to digest it. The air there is quite stale. 31 . It is well ventilated there and the temperature is very much the same there all the time. The cactus has needle-like leaves to reduce water loss through transpiration and it has a storage stem to store the water in its stem. thus it is called the rotting log. The organisms that can be found there include the millipede. The animals there include crabs. fungus or bacteria to decompose the log. Others have adaptations to reduce water loss like the camel which sweats very little and give little urine. Some animals only come out during the night to avoid the high temperatures in the day. the centipede and spiders. Seaside The seaside community contains sandy soil and can retain little water thus the plants there have to have roots that can absorb water fast enough for photosynthesis.Conditions of habitat Desert The desert is very hot during the day and is very dry. starfishes. The decomposing log provides accommodation and food for the animals living in it. Thus some animals have special adaptations to survive in such conditions. The rotting log community must contain decomposers like the termite. The most common plant there is the cactus. Basically. called the leaf litter community. hydrilla and many others. Leaf litter The leaf litter community is rather damp and stuffy. The soil there is thus the most optimum for the growth of the plants. these plants can be classified into three groups. caterpillar and all types of animals that we usually see along the road.Garden The garden community is very common to most of as most of us have a garden. There are also many plants that live around or in the pond like the arrowhead. The animals found there include butterflies. like the dragonfly nymph. The garden community has garden soil that contains many dead organisms to be decomposed and be simplified into simple substances and return to the soil as nutrients for the plant. Pond The pond community unlike other habitats has a lot of water and fishes live there. The leaves are decomposing and many insects live in them and feed on them. There are also many insects living around there. The air there is very airy and the temperature maintains at around the same range. The air there is stuffy and the area of the community is not very large. The air there is also very airy and the temperature is very much the same. Field Community 32 . partially submerged and fully submerged. floating. the water spider and many others. There is bound to be many trees around as the dead leaves would fall and create a heap. Pollutions Pollutions Pollutions occur when substances which can make the environment dirty or unhealthy are released into the environment. Air pollution 33 . In the recent years. the ozone layer has been depleted by humans as they release chlorofluorocarbon (CFCs) into the environment.CFCs and the ozone layer Ozone is a thin layer of gas in the atmosphere which shields the earth from most of the harmful ultraviolet (UV) rays from the Sun. Water Pollution 34 . Non-biodegradable products cannot be broken down by decomposers and will not decay. causing buildings to corrode Land Pollution Biodegradable products are able to be broken down into simpler forms by decomposers and can be recycled in nature. Negative impacts Destruction of trees in the environment Organisms that live in the rivers or lakes are harmed. 35 .Acid rain Acid rain often occurs when rainwater dissolves harmful gases in the air to form a weak acid. Our water supply is contaminated. Acid rain can react with stones and metals. The cutting of tree prevents the trees from getting a grip on the soil and the will also is soil erosion. 36 . When part of a forest is removed. The water cycle is also affected by deforestation. the trees no longer evaporate away this water. are cut down. Trees extract groundwater through their roots and release it into the atmosphere.Noise Pollution Deforestation Deforestation is the clearing of forest. resulting in a much drier climate. Then the carbon dioxide that we breathe out would be accumulated and there will be global warming. This affects our environment a lot as the trees which take in the carbon dioxide that we breathe out and turns them into oxygen. That causes the carbon dioxide and oxygen to be unbalanced. field. many of the organisms that can live in the pond would not be able to live in the forest community. A habitat provides the living thing with everything that it needs to stay alive. All these habitats are for various organisms. The population size is the total number of live organisms in a population. Adults and young must be when counting the population size. Thus. pollination and nutrients. or for competing with one another for food. There are many different types of habitats. the types of organisms found in different from the types of organisms found in another habitat. shelter and oxygen. Populations of several kinds are interdependent on each other.Environment Living organisms are also known as organisms. garden and many others. The place where a population lives is its habitat. For example. Populations living together in a habitat form a community together. Organisms are often found in groups with other organisms of its same species. 37 . Aquatic means anything relate to water. They depend on each other for survival. A population consists of all the organisms of the same kind that live and reproduce in a particular place. Pond Community A pond community is aquatic. are dependent on animals for seed dispersal. While the plants on the other hand. The animals depend on the plants for food. For example. all the duckweeds plant in pond is considered as a population. like forest. The living conditions are different habitats. The leaf litter is food for bacteria. Many populations of organisms can be in a leaf litter habitat. Other animal population in the leaf litter community feeds on each other.Leaf litter community Leaf litter forms from fallen leaves. fungi and some other animal population. bits of bark and dead plant matter. 38 . A leaf litter habitat is made up of leaf litter and the soil below the leaves is dark and warm. It s usually found wherever there are a lot of plants. with little air movements. It may be damp. 39 . The nucleus is involved in cell division and carries out instructions for protein synthesis. Cells can also group together to form a larger organism. It is bound by the nuclear membrane and isolates the genetic materials of the cell from there rest of the cell. It is involved in chemical energy conversion during metabolic activities of the cell. that allows certain substances in and others out and it is very flexible and appears in most cells. Cells structure Plasma Membranes The plasma membrane is a thin layer of semi-permeable covering of the cell made of protein and fats. In the cell. There is also nucleoplasm in the cell that acts like cytoplasm and fills up the nucleus. there is one or more of a small.Cells Cells are the smallest building block of life and can be large or small relative to a regular cell. The cell membrane is also there to separate one cell from an adjacent cell. it also prevents larger molecules like starch and protein from leaving the cell so that certain substances can be prevented from leaving the cell. Cytoplasm The cytoplasm is what fills up the cell apart from the organelles and is a median for cellular activities to occur. Nucleus The nucleus is the most prominent organelle in the cell and is the control center of the cell where all the commands are given out. It increases the surface area for absorption of nutrients and disposal of wastes. Mitochondria The mitochondria often appear in a rod or cylindrical shape. however. It is jelly-like and metabolism takes place. it contains chromatin which is made up of DNA. The nuclear pores on the membrane allow certain molecules to enter or leave the nucleus. It can also be said to be the power house of the cell and it is where aerobic respiration occurs to generate energy from the glucose molecules in the cell. The nuclear membrane has many perforations and it is scattered all over the nuclear membrane. It is a permanent structure in the cell. It is usually spherical in shape and found near the center of the animal cell. spherical structure called nucleolus which is not bound by a membrane and is in charge or forming ribosome. they can also live as individual organisms. the rough ER (RER) and the smooth ER (SER). the vacuoles appear as one large section of the cell in the middle. In plants. At the opposite side of the stack. a special form of SER is at the site of storage of calcium ions which have an important role in the contraction of muscle fibers. which are then 40 . Rough endoplasmic reticulum has ribosomes attached to it and vesicles are formed from swelling at the margins that get pinched off. including hormones and polysaccharide macromolecules. in animal cells. The cytoplasm of metabolically active cells is usually packed with endoplasmic reticulum. In the cytoplasm of voluntary muscle fibers. a watery solution of sugar. tubes or sacs. The SER is also responsible for the manufacturing of lipids. Smooth Endoplasmic Reticulum has no ribosomes attached to it and is the site of synthesis for substances needed by the cell. they appear as tiny granules. For example.Vacuole Vacuoles are sacs filled with sap. which is used to store and transport substances around the cell. but is especially prominent in metabolically active cells such as secretary cells. The structure originates from the outer membrane of the nucleus. Vesicles are formed from swellings at the margins that become pinched off. Many types of cell have vast numbers of ribosome and they also construct a type of acid known as nucleic acid. RER is the site of synthesis for protein such as digestive enzymes. The Golgi apparatus is present in all cells. to which they may stay attached to. There are two distinct types of endoplasmic reticulum. forming interconnected sheets. Ribosome Ribosome is made up of two sub units that aids in protein synthesis and is the biological catalysts and makes reactions of metabolisms. One side of the stack of membranes is formed by the fusion of membranes of vesicles from ER. and pigments. It is the site of synthesis for certain chemicals. These are ¶packaged· in the vesicles and are discharged from the cells. A vesicle is a small spherical organelle bounded by a single membrane. however. Golgi apparatus The Golgi apparatus consists of a stack-like structure that is a collection of flattened membranous sacs. salts. Endoplasmic Reticulum The endoplasmic reticulum consists of a network of folded membranes. These are the excess food stored in the cell after digestion. Diffusion & Osmosis Osmosis is generally the net movement of water molecules across a partially permeable layer from a substance of higher water potential to a substance of lower water potential.packages into vesicles. cell specialization in the division of labor is very important. Cell wall The cell wall in plant cells is a firm and turgid layer of cellulose that gives the cell its shape and it does not interfere with the cell membrane·s work of regulating entry and exit of substances as the perforations in it is large enough for almost all substances to go through. which are produced by either the Golgi apparatus or by the ER. Lysosomes are involved in the breakdown of contents of imported food vacuoles. there is another unique cell part. For example. Division of Labour Division of labour is needed since each cell has specified jobs and not any other cell is able to take over the job of a specified type of cell. Lysosomes may also fuse with and digest any broken-down organelles in the cytoplasm. Without the chloroplast. When a 41 . Lysosomes Lysosomes are small spherical vesicles bound by a single membrane. It is then broken down. An example might be a harmful bacterium that has invaded the body and been engulfed by one of the body·s defense cell. the chloropast which is the part in the cell that contains chlorophyll and trap sunlight to make food. and the products of digestion escape into the liquid of the cytoplasm. while those in plant cells my contain polysaccharide for cell wall formation. This allows multiple processes to go on concurrently. In animal cells these vesicles may form lysosome. the hydrolytic enzymes in the lysosome of the cells escape into the cytoplasm and cause self digestion. the plant cells would not appear green and would not be able to photosynthesize. The water would move across from the substrate of higher water potential until both sides have an equal water potential. When an organism dies. They contain a concentrated mixture of hydrolytic enzymes. a cheek cell is definitely not able to replace a brain cell thus. Water potential is the density of water molecules in a certain area. Chloroplast In plant cells. When the substrate has an equal water potential as the average water potential in you cell. it is said that the substance is hypotonic and water moves into the cell and a plant cell would become turgid while an animal cell would lyse. or the diffusion of blue paint in a beaker of water. Diffusion is affected by many different factors like the temperature of the substance since it affects the movement of molecule.substrate has a higher water potential than the average water potential in your cell. it is said that the substance is hypertonic and water would move out of the cell. 42 . When the substance has a lower water potential than the average water potential in your cell. Diffusion is quite the same thing as osmosis except that it involves a substance that can move and travel across in natural. the thickness of the barrier separating the two substances and the size of the molecule these factors all can affect the rate of diffusion and osmosis. for example. it is called isotonic and there is no net movement of water in and out of the cell. causing it to be flaccid. the diffusion of gas in the or air. The hydrochloric acid also helps to loosen the bonds in the meat. The pyloric sphincter controls the entry of food to the duodenum. Gullet The gullet or the esophagus is a passage way which connects the mouth to the stomach. The tongue then rolls the chewed up food into a ball called bolus and it is rolled to the back of the tongue so that it can go down into the throat. Due to its acidic environment. Alcohol and glucose are also absorbed here. pepsin. this is the action of the muscles contracting and relaxing. various enzymes are secreted. The teeth start helping by chewing and tearing the food up into smaller pieces (mastication) so that digestion can occur over a larger surface area for enzyme reaction and digestion can happen faster. The gullet itself is just a long tube of muscles. The tongue secretes enzyme amylase which helps to catalyse the digestion of starch into maltose in the food. This is an involuntary action. pushing the ball of food down. The food that has been churned by the stomach is called chime. 43 .Digestive System The process of digestion Mouth The mouth is the place where digestion starts. This acidic environment allows many of the processes in the stomach to go on and also kills the bacteria in the food. rennin and peptides. The food from the mouth is pushed down this tube by peristalsis. The food is kept in the stomach for about 2-4 hours and remains there until mostly digested. to render easy absorption of calcium and iron at a later stage in the process of digestion. the stomach has to secrete mucus in order to prevent the hydrochloric acid from digesting the walls of the stomach. In the stomach. It is also to soften the food. The hydrochloric acid in the stomach is highly acidic and thus the average pH of the stomach is about 2. The saliva also contains mucus that helps to make food more slippery and allows it to go down the esophagus more easily. The pepsin aids in breaking down the protein into peptides and the rennin converts protein into insoluble curds for hydrolysis of pepsin. No chemical reaction occurs here apart from the digestion of starch into maltose. Stomach The stomach is a muscular bag that contains hydrochloric acid and it is also where most of the digestion takes place. Liver The liver is one of the crucial parts of the digestive system and it is where green bile that is needed for emulsification of fats is formed and sent to the gall bladder to be stored and transferred to the small intestine to emulsify the fats and allow a larger area for reaction of lipase. into the lymphatic system to the liver. Just to name a few of the reactions that occur. the peptides are digested into amino acids. trypsin. and the bile helps to emulsify the fats so that the digestion of fats into fatty acid and glycerol can occur at a faster rate. The pH here is relatively normal as it is pH7 since the pancreatic juice is alkaline and thus the hydrochloric acid from the stomach may be neutralized so that the acids in the pancreatic juice can be activated. Small Intestine The small intestine is where the final stages of digestion take place. the walls of the small intestine are covered with tiny protrusions called micro-villi. there are millions of micro-villi. Pancreas The pancreas is one of the main secretor of alkaline enzymes in the digestive system. lactose is digested into glucose and galactose. In the duodenum. The other nutrients however. making it easier for the digestion of fats and lipids in the food. lipase and even water as it helps in hydrolysis of food. and there is the lacteal which is linked to the lymphatic system of the body. The villi are present to aid in the absorption of nutrients into the bloodstream as the surface area for absorption is increased and is more efficient. 44 . On the villi. the last stages of digestion take place and are completed and the food moves on to the duodenum. it is also where bile is secreted into the digestive system. each villus has blood capillaries linked to the hepatic system and in the middle of the main villi. In the ileum. are absorbed into the blood capillaries and transported to all parts of the body. The pancreas is a feathery like structure that secretes enzymes like amylase. sucrose is digested into glucose and fructose and the maltose is digested into sucrose. The fats and lipids are absorbed into the lacteal. It also secretes insulin to convert excess glucose to glycogen in the liver. Since there are no chemical to neutralize the enzymes from the small intestine. the walls of the large intestine secretes mucus to prevent the enzymes from harming the walls of the large intestine. water is absorbed from the food into the body The large intestine pushes the digested food through the large intestine by peristalsis. the colon is the part where no enzyme activity takes place. however.Large Intestine The large intestine is the alimentary canal and is mainly made up of the colon. 45 .