5/17/13Ch 10 HW Due: -- MasteringBiology: Create Assignment Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy Photosynthesis (1 of 3): Inputs, Outputs, and Chloroplast Structure (BioFlix tutorial) Description: (BioFlix tutorial) This tutorial (the first of three associated with the Photosynthesis BioFlix animation) focuses on the inputs and outputs of the light reactions and Calvin cycle, redox reactions in photosynthesis, and chloroplast structure and function. The reactions of photosynthesis can be divided into two main stages: the light reactions, which convert light energy into chemical energy the Calvin cycle (sometimes called the dark or carbon reactions), which uses the products of the light reactions to produce sugar In this tutorial, you will identify the inputs and outputs of each stage, describe the oxidationreduction (redox) reactions in the light reactions and Calvin cycle, and identify the cellular compartments in which these reactions occur. Before beginning this tutorial, watch the Photosynthesis animation. Pay close attention to the role of light, the formation of NADPH and ATP, and the use of NADPH and ATP in sugar production. Part A - Inputs and outputs of the light reactions From the following choices, identify those that are the inputs and outputs of the light reactions. (Recall that inputs to chemical reactions are modified over the course of the reaction as they are converted into products. In other words, if something is required for a reaction to occur, and it does not remain in its original form when the reaction is complete, it is an input.) Drag each item to the appropriate bin. If the item is not an input to or an output from the light reactions, drag it to the “not input or output” bin. Hint 1. Energy conversion from one form to another in the light reactions The light reactions convert one form of energy into the chemical energy of ATP molecules. Think about the source of this energy and about what is needed to make ATP molecules. Hint 2. Which energy sources produced in the light reactions will be used by the Calvin cycle? Which of the following transfer energy from the light reactions to the Calvin cycle? Select all that apply. ANSWER: light G3P ATP NADPH The Calvin cycle requires two forms of energy as inputs: chemical energy (stored in ATP)--to drive energy-requiring reactions a source of reducing power (in the form of NADPH)--to provide the electrons needed to reduce CO2 to sugar Both ATP and NADPH are produced in the light reactions and transfer the energy originally in sunlight to power the reactions of the Calvin cycle. Hint 3. What is the role of light in the light reactions? The term “light reactions” implies that light plays some role in this stage of photosynthesis. Which of the following statements correctly describes a role of light in the light reactions? Which of the following statements correctly describes light's role? ANSWER: session.masteringbiology.com/myct/assignmentCreateOrCopy 1/19 Light is a form of energy (electromagnetic radiation) that can be absorbed by chlorophyll molecules in the photosynthetic machinery of plants and transformed into other forms of energy. Drag each item to the appropriate bin. light is transformed into redox energy in the form of NADPH and chemical bond energy in the form of ATP.5/17/13 MasteringBiology: Create Assignment Light supplies the energy to remove electrons from water and to transport those electrons to NADP+. ANSWER: In the light reactions. If the item is not an input to or an output from the Calvin cycle. identify those that are the inputs and outputs of the Calvin cycle. The NADPH and ATP produced are subsequently used to power the sugarproducing Calvin cycle. Consider what this means about whether light plays a direct role in the Calvin cycle. the energy of sunlight is used to oxidize water (the electron donor) to O2 and pass these electrons to NADP+. Hint 1. Hint 2. drag it to the “not input or output” bin. producing NADPH. the Calvin cycle occurs only in the light because it requires an input of chemical energy and reducing power from the light reactions.Inputs and outputs of the Calvin cycle From the following choices. Light provides the atoms that are needed to convert ADP to ATP. What is the product of the Calvin cycle that contains “fixed” carbon? The Calvin cycle uses energy from the light reactions to “fix” inorganic carbon into sugar. if the compounds that shuttle this chemical energy and reducing power from the light reactions are artificially provided to a chloroplast. Light supplies the electrons that are needed to reduce NADP+ to NADPH. The relationship of light to the Calvin cycle In most plants. However.masteringbiology. Some light energy is used to convert ADP to ATP. What is the product of the Calvin cycle that contains this fixed carbon? ANSWER: session. Part B . Light energy is used to fix CO2 into sugar. In the light reactions. the Calvin cycle can proceed in the dark.com/myct/assignmentCreateOrCopy 2/19 . Part C . ANSWER: In the Calvin cycle. As these compounds are used.Redox reactions of photosynthesis session. Hint 3. PGA is not the ultimate product of the Calvin cycle.5/17/13 G3P CO2 glucose RuBP MasteringBiology: Create Assignment Carbon enters the Calvin cycle as inorganic CO2 and is “fixed” during the first phase of the Calvin cycle into organic carbon in the form of PGA (phosphoglyceric acid). Which product or products of the Calvin cycle is/are returned as input(s) to the light reactions? Which of the following outputs from the Calvin cycle are also inputs to the light reactions? Select all that apply.masteringbiology. which are returned to the light reactions so that more ATP and NADPH can be formed. PGA is eventually converted into the three-carbon sugar G3P. As ATP and NADPH are used. It is G3P that exits the Calvin cycle to be used in the production of other organic molecules in the plant. Recall that ADP and NADP+ are required as inputs to the light reactions for the production of ATP and NADPH. ANSWER: G3P NADP+ NADPH ADP ATP ATP and NADPH are used in the Calvin cycle in the production of G3P.com/myct/assignmentCreateOrCopy 3/19 . Using the energy of ATP and NADPH. ADP and NADP+ are produced. they produce ADP and NADP+. respectively. the energy outputs from the light reactions (ATP and NADPH) are used to power the conversion of CO2 into the sugar G3P. However. Thus ATP/ADP and NADPH/NADP+ shuttle energy and reducing power (electrons) between the light reactions and the Calvin cycle. Drag the terms to the appropriate blanks to complete the following sentences summarizing the redox reactions of photosynthesis. Terms may be used once. Hint 3. Hint 2. In one reaction. Note that compounds A and B each exist in two forms: One form is reduced (it carries the extra electrons). session. forming NADPH. Review of redox reactions and terminology Under most circumstances. What is the original electron donor in photosynthesis? In photosynthesis. In the other reaction. as shown in this figure along with other components of photosynthesis.masteringbiology. Hint 1. redox reactions occur in pairs. a redox compound that is produced in the light reactions is required to drive other redox reactions in the Calvin cycle. Which of the following molecules shuttles electrons from the light reactions to the Calvin cycle? ANSWER: NADPH ADP NADP+ ATP In the light reactions. How is redox energy transferred from the light reactions to the Calvin cycle? In the light reactions. sunlight is the original source of the energy required to produce sugar. the other form is oxidized (it does not carry the extra electrons).com/myct/assignmentCreateOrCopy 4/19 . the energy of sunlight is converted to redox energy. These two reactions occur simultaneously. where they are used to reduce CO2 to sugar. A generic redox reaction showing the transfer of two electrons is illustrated here. NADPH then transfers electrons to the Calvin cycle. or not at all. In the reactions shown here. more than once. This redox energy is transferred to the Calvin cycle in the form of a reductant that provides electrons for reducing other compounds. the electron donor is oxidized (it loses electrons). the energy of light is used to oxidize (remove electrons from) water and pass those electrons to NADP+. the electron donor is the reduced form of compound A.5/17/13 MasteringBiology: Create Assignment In photosynthesis. and the electron acceptor is the oxidized form of compound B. the electron acceptor is reduced (it gains the electrons lost by the first compound). identify where the light reactions and Calvin cycle occur by dragging the pink labels to the pink targets. Identify the membranes or compartments of the chloroplast by dragging the blue labels to the blue targets. which carries the electrons to the Calvin cycle. Review of chloroplast structure session. Hint 1. and only pink labels should be placed in pink targets. The electron transport chain transfers the electrons to NADP+. which is oxidized in the light reactions. NADPH is oxidized back to NADP+ (which returns to the light reactions).5/17/13 MasteringBiology: Create Assignment What is the original source of the electrons that are eventually used to reduce CO2 to sugar in photosynthesis? ANSWER: NADPH O2 ATP H2O light The original electron donor in photosynthesis is H2O. producing O2 gas. all the reactions of photosynthesis occur in various membranes and compartments of the chloroplast. Note that only blue labels should be placed in blue targets.masteringbiology. ANSWER: In the light reactions. In the Calvin cycle.com/myct/assignmentCreateOrCopy 5/19 . Part D . The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P).Chloroplast structure and function In eukaryotes. forming NADPH. which then exits the Calvin cycle. producing O2. These electrons are ultimately used to reduce NADP+ to NADPH. Then. light energy is used to remove electrons from (oxidize) water. It catalyzes a reaction in ATP synthesis in the light reactions. Where are NADPH and ATP produced? ATP and NADPH are products of the light reactions and are also the energy inputs into the Calvin cycle. ANSWER: session.5/17/13 MasteringBiology: Create Assignment Hint 2. It catalyzes a reaction in electron transport in the light reactions. Where in the chloroplast are ATP and NADPH produced? ANSWER: thylakoid membrane thylakoid space stroma ATP and NADPH are produced as the photosystems and the electron transport chains of the light reactions harness light energy and oxidize water.masteringbiology. The photosystems and electron transport chains are located in the thylakoid membranes of the chloroplast. What does the location of the enzyme Rubisco reveal about where processes occur in the chloroplast? The enzyme Rubisco is found in the stroma of the chloroplast. Rubisco is an enzyme that functions in the first step of the Calvin cycle.com/myct/assignmentCreateOrCopy 6/19 . catalyzing the attachment of CO2 to RuBP. It is one of the products of the Calvin cycle. Hint 3. The fact that Rubisco is located in the stroma of the chloroplast indicates that the Calvin cycle reactions take place in the stroma. What is Rubisco’s role in photosynthesis? ANSWER: It catalyzes a reaction in the Calvin cycle. or both PS II and PS I. Before beginning this tutorial.com/myct/assignmentCreateOrCopy 7/19 . In the light reactions of photosynthesis. not the one that functions after PS I. Pay particular attention to the steps where light is involved.masteringbiology. Roles of chlorophylls in the light reactions Chlorophylls play two roles in the light reactions: absorption of light and reduction of a primary electron acceptor. which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space. Inside the chloroplast. watch the Light Reactions animation. This task is accomplished by two photosystems that power linear electron flow from water to NADP+. the energy requirements of electron transport. Drag each item into the appropriate bin depending on whether the process is associated with Photosystem II (PS II) only. where protons accumulate during ATP synthesis in the light reactions. Part A . Photosystem I (PS I) only. while generating a proton gradient that is used to make ATP. and the coupling of electron transport to the formation of a proton gradient and ATP synthesis.Functions of the photosystems The light reactions require the cooperation of two photosystems to power linear electron flow from water to NADP+. energy in sunlight is converted into chemical and redox energy in the form of ATP and NADPH. the pattern of electron flow. session.5/17/13 MasteringBiology: Create Assignment The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Photosynthesis (2 of 3): The Light Reactions (BioFlix tutorial) Description: (BioFlix tutorial) This tutorial (the second of three associated with the Photosynthesis BioFlix animation) examines the roles of the two photosystems. Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma. Hint 1. the chlorophyll-containing thylakoid membranes are the site of the light reactions. Consider where the chlorophylls are located among the various components of the light reactions. Note that “electron transport chain” here refers to the electron transport chain between the two photosystems. and the formation of a proton gradient. water is oxidized and its electrons are passed eventually to NADP+. What is the role of the reduced PS I primary electron acceptor in the light reactions? ANSWER: oxidation of water to O2 reduction of the electron transport chain between the photosystems reduction of NADP+ to NADPH oxidation of the electron transport chain between the photosystems In the overall scheme of photosynthetic electron transport. NADP+ does not readily accept electrons (it is difficult to reduce NADP+). Thus a very strong reductant is required to donate electrons to NADP+: This reductant is the reduced PS I primary electron acceptor.5/17/13 MasteringBiology: Create Assignment Hint 2.masteringbiology. The resulting reduced primary electron acceptor in PS I is one of the strongest known biological reductants (electron donors). not in the order in which they function in electron transport. Electrons flow from PS II to PS I.com/myct/assignmentCreateOrCopy 8/19 . and its electrons are passed eventually to NADP+. Thus a very strong oxidant is required to take electrons from water: This oxidant is the P680+ produced in Photosystem II. What is the role of P680+ in the light reactions? ANSWER: reduction of the electron transport chain between the photosystems oxidation of water to O2 reduction of NADP+ to NADPH oxidation of the electron transport chain between the photosystems In the overall scheme of photosynthetic electron transport. Hint 4. The resulting positively charged P680+ is the strongest known biological oxidant (electron acceptor). Water does not give up its electrons easily (it is difficult to oxidize). Electron movement between the two photosystems Photosystem I and Photosystem II were named in the order they were discovered. Hint 3. water is oxidized. What redox reactions occur in Photosystem II? In Photosystem II (PS II). What redox reactions occur in Photosystem I? In Photosystem I (PS I). ANSWER: session. the excited state of P680 chlorophyll transfers an electron to the PS II primary electron acceptor. the excited state of P700 chlorophyll transfers an electron to the PS I primary electron acceptor. Consider what this means in terms of the roles of PS II and PS I in either the reduction or oxidation of the electron transport chain between the photosystems. In PS I. which drives electron transport. session. Part B . P680 is oxidized (which in turn oxidizes water). the PS I primary electron acceptor is reduced (which in turn reduces other compounds that ultimately reduce NADP+ to NADPH). and P700 is oxidized (which in turn oxidizes the electron transport chain between the photosystems). In PS II (the first photosystem in the sequence).masteringbiology.Energetics of electron transport This diagram shows the basic pattern of electron transport through the four major protein complexes in the thylakoid membrane of a chloroplast. and the PS II primary electron acceptor is reduced (which in turn reduces the electron transport chain between the photosystems).com/myct/assignmentCreateOrCopy 9/19 .5/17/13 MasteringBiology: Create Assignment The key function of each of the two photosystems is to absorb light and convert the energy of the absorbed light into redox energy. but cannot donate its electrons directly to NADP+. The excited state of P680 donates an electron to the PS II primary electron acceptor. Which of the following must also occur when compound X is added to chloroplasts in order to account for the observed reduction of NADP+ to NADPH in the dark? ANSWER: In PS I.masteringbiology. Of all the electron carriers in photosynthetic electron transport. Recall that in a mitochondrion. no reduction of NADP+ to NADPH occurs. In other words. the only components that can reduce NADP+ without light are those between the primary electron acceptor of PS I and NADP+. The primary electron acceptor of PS I must be reduced. However. Thus the only possible answer is that the mystery compound reduces the PS I primary electron acceptor.com/myct/assignmentCreateOrCopy 10/19 . causes the reduction of NADP+ to NADPH in the dark. This form is called the excited state of the chlorophyll. must reduce some other component of photosynthetic electron transport that can pass its electrons on to NADP+. the excited state of P680 chlorophyll (the result of light absorption in PS II) is a better electron donor than the non-excited (ground) state. In Photosystem II (PS II). Hint 2. The loss of an electron from P680 produces P680+ (the oxidized form of P680). How is light energy used in Photosystem II? When light energy is absorbed by a chlorophyll molecule. when added to a solution of functioning chloroplasts. Water must be oxidized and O2 must be formed. drag the appropriate label to indicate whether or not that step requires an input of energy. Hint 3. an electron in the chlorophyll is boosted to a higher energy level. The excited state of P680 donates an electron to the primary electron acceptor. ANSWER: session. Think about how this similarity applies to the energy requirements of the photosynthetic electron transport chain. What is the effect of artificially (without light) reducing NADP+ to NADPH? Suppose that a particular compound X. P700 must be oxidized to P700+. The excited state of P680 removes an electron from water. no additional input of energy is needed to power electron flow to O2. Electron carriers between PS II and PS I (such as plastoquinone) must be reduced. once electrons enter the electron transport chain from NADH. A compound that causes NADP+ to be reduced to NADPH in the dark. How is the energy of the excited state of P680 chlorophyll used in Photosystem II? ANSWER: The excited state of P680 removes an electron from the primary electron acceptor. compound X cannot directly reduce NADP+ to NADPH.5/17/13 MasteringBiology: Create Assignment For each step of photosynthetic electron flow from water to NADP+. when X is mixed with NADP+ in the absence of chloroplasts. Comparing the energy requirements of chloroplast and mitochondrial electron transport chains In a chloroplast. photosynthetic electron transport between Pq (plastoquinone) and Pc (plastocyanin) via the cytochrome complex is nearly identical to the central portion of the electron transport chain in a mitochondrion. Hint 1. The energy in this proton gradient is then used to power ATP synthesis. This proton transport is accomplished by one of the small electron carrier molecules that shuttles electrons between the major electron transport complexes. these protons are released into the thylakoid space. and only the pink labels for the pink targets. The result in each case is a reductant (the reduced primary electron acceptor) and an oxidant (P680+ in PS II and P700+ in PS I) that are able to power the rest of the electron transfer reactions without further energy input. Hint 2. Drag the labels to the appropriate locations on the diagram of the thylakoid membrane.Proton gradient formation and ATP synthesis ATP synthesis in chloroplasts is very similar to that in mitochondria: Electron transport is coupled to the formation of a proton (H+) gradient across a membrane. Use only the blue labels for the blue targets. In each photosystem. this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem’s primary electron acceptor. the oxidation of water to O2 produces protons as a byproduct. How does the oxidation of water by PS II contribute to the proton gradient? In Photosystem II (PS II). As the carrier transports protons across the thylakoid membrane. Note: One blue target and one pink target should be left empty. releasing protons in the thylakoid space.com/myct/assignmentCreateOrCopy 11/19 . light energy is used to produce an electron acceptor that is strong enough to oxidize water.masteringbiology. Two types of processes that contribute to the formation of the proton gradient are: processes that release H+ from compounds that contain hydrogen. Electron transport through the PS II complex pumps protons across the thylakoid membrane. The oxidation of water by PS II releases protons in the thylakoid space. Where does proton pumping across the thylakoid membrane occur? The transport of protons across the thylakoid membrane contributes to the proton gradient that drives ATP synthesis. light energy is used to drive a redox reaction that would not otherwise occur. Hint 1. Because this reaction occurs on the thylakoid space side of PS II. it also shuttles electrons across the membrane. and processes that transport H+ across the thylakoid membrane. Part C . session.5/17/13 MasteringBiology: Create Assignment In both PS II and PS I. How does the oxidation of water contribute to the proton gradient across the thylakoid membrane? ANSWER: Water molecules pick up protons from the stroma and transport them to the thylakoid space. where the water is oxidized. In PS II. Oxygen molecules produced by PS II react with water. Pq picks up two protons from the stroma.masteringbiology. the thylakoid space becomes more acidic (by about 3 pH units) than it is when the chloroplast is in the dark. The formation of a proton gradient across the thylakoid membrane When a chloroplast is exposed to light. When it is reduced by PS II. it releases the two protons in the thylakoid space. Hint 3. The net result is pumping of protons from the stroma to the thylakoid space as electrons flow from PS II to the cytochrome complex.5/17/13 MasteringBiology: Create Assignment Which component of the light reactions is involved in pumping protons across the thylakoid membrane? ANSWER: Fd (ferredoxin) as it transfers electrons from PS I to NADP+ reductase Pq (plastoquinone) as it transfers electrons from PS II to the cytochrome complex Pc (plastocyanin) as it transfers electrons from the cytochrome complex to PS I the PS I complex as it transfers electrons from Pc to Fd the PS II complex as it transfers electrons from water to Pq Plastoquinone (Pq) is found in the interior of the thylakoid membrane.com/myct/assignmentCreateOrCopy 12/19 . When Pq is oxidized by the cytochrome complex. The proton gradient results in part from the electron transport chain pumping protons across the membrane against their concentration gradient. This means that the H+ concentration is higher in the thylakoid space than in the stroma. ANSWER: session. This proton-motive force then drives the synthesis of ATP as the protons diffuse back across the membrane through ATP synthase. Before beginning this tutorial. In each of the three key phases of the Calvin cycle (carbon fixation. with one CO2 entering at each turn of the cycle. Part A . and the coupling between the Calvin cycle and the light reactions. carbon skeletons are modified in reactions that lead to the final products (see diagram below). carbon dioxide (CO2). Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space.com/myct/assignmentCreateOrCopy 13/19 . and regeneration).5/17/13 MasteringBiology: Create Assignment Photosynthetic electron transport contributes to the formation of a proton (H+) gradient across the thylakoid membrane in two places. reduction. which enters the leaf as a gas. Along the way. watch the Calvin Cycle segment of the Photosynthesis animation.masteringbiology. is converted into the simple sugar glyceraldehyde-3-phosphate (G3P).Following carbon atoms around the Calvin cycle The net reaction of the Calvin cycle is the conversion of CO2 into the three-carbon sugar G3P. In PS II. Pay particular attention to the flow of carbon atoms through the cycle and the places in the cycle where ATP and NADPH are used. The resulting proton gradient is used by the ATP synthase complex to convert ADP to ATP in the stroma. the oxidation of water releases protons into the thylakoid space. the use of ATP and NADPH from the light reactions. This process uses ATP and NADPH produced by the light reactions. Photosynthesis (3 of 3): The Calvin Cycle (BioFlix tutorial) Description: (BioFlix tutorial) This tutorial (the third of three associated with the Photosynthesis BioFlix animation) examines the reactions of the Calvin cycle: the flow of carbon atoms. reactions rearrange carbon atoms session. The net production (output) of one molecule of G3P requires three complete turns of the Calvin cycle. In the Calvin cycle. For each intermediate compound in the Calvin cycle. Over the course of 3 turns of the cycle. identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. In this exercise.5/17/13 MasteringBiology: Create Assignment among intermediate compounds and use the ATP and NADPH produced by the light reactions. For each molecule of CO2 that enters the Calvin cycle. thus enabling the Calvin cycle to continue. the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms. the enzyme Rubisco catalyzes the addition of CO2 (1 carbon atom) to RuBP (5 carbon atoms). The G3Ps are needed for reactions that use up the extra ATP and NADPH produced by the light reactions.com/myct/assignmentCreateOrCopy 14/19 . ANSWER: session. or not at all. The result is a short-lived 6-carbon compound that immediately breaks down into 2 molecules of 3-phosphoglycerate (PGA). Phase 3 of the Calvin cycle converts 5 molecules of G3P into 3 molecules of RuBP. which equation correctly represents what happens to its carbon (C) as the next intermediate is produced? ANSWER: 1C+2C→3C 1C+5C→3C+3C 1C+1C→2C 3 C + 15 C → 18 C 3C+3C→6C In Phase 1 of the Calvin cycle. Carbon atoms enter the Calvin cycle as individual CO2 molecules (1 carbon atom per molecule) and exit the cycle in the 3-carbon sugar glyceraldehyde-3-phosphate (G3P). the total number of carbon atoms is conserved: There is no net gain or loss of carbon atoms. each containing 3 carbon atoms. What happens to all of the G3P produced in Phase 2 of the Calvin cycle? Only 1 of the G3P molecules produced in Phase 2 of the Calvin cycle is exported from the cycle. keeping these molecules from accumulating in the cell. you will track carbon atoms through the Calvin cycle as required for the net production of one molecule of G3P. Hint 3. more than once. Hint 1. The remaining G3P molecules are used in Phase 3.masteringbiology. Within the Calvin cycle. What happens to a CO2 molecule in Phase 1 of the Calvin cycle? Phase 1 of the Calvin cycle (carbon fixation) consists of a reaction between a molecule of CO2 and a molecule of RuBP. catalyzed by the enzyme Rubisco. Hint 2. Labels may be used once. Changes to carbon skeletons in the Calvin cycle The Calvin cycle is essentially a sequence of reactions that shuffle carbon atoms among different molecules. As an example. The G3Ps are needed to absorb the CO2 that was taken up in Phase 1. These 3 RuBP molecules are needed to replace the 3 molecules of RuBP that were consumed during the carbon fixation reactions of Phase 1. What happens to the remainder of the G3P produced in Phase 2 of the Calvin cycle? ANSWER: The G3Ps are used in Phase 3 to regenerate the RuBP molecules used in Phase 1. In glycolysis. or not at all. and (c). for each molecule of G3P that is converted to PGA. Hint 2. Parallels between glycolysis and Phase 2 of the Calvin cycle The reactions of Phase 2 of the Calvin cycle are identical to several of the reactions in glycolysis (the first stage of cellular respiration). In reducing 3-PGA to G3P (Phase 2). In this exercise. For the net conversion of 3 molecules of CO2 into 1 molecule of G3P by the Calvin cycle. At the end of Phase 2. 1 of the 6 G3P molecules is output from the cycle. except that the reactions occur in the reverse direction. 1 Pi is taken up. Finally. NADPH/NADP+. more than once.masteringbiology. (b). Part B . How many Pi are released in Phase 3? In the first part of Phase 3. and 1 ADP is converted to ATP. The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3. and Pi (inorganic phosphate groups) that are input to or output from the Calvin cycle. there is no addition or removal of carbon atoms. consider the net conversion of 3 molecules of CO2 into 1 molecule of G3P. Hint 1. the R5P is converted to RuBP without the addition or loss of carbon atoms. Labels can be used once. The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms). removing 3 of the 18 carbons.com/myct/assignmentCreateOrCopy 15/19 . the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). next producing 6 molecules of 3PGA (18 total carbon atoms). To produce 1 molecule of G3P (which contains 3 carbons). where they are converted to 3 molecules of R5P. 1 NAD+ is converted to NADH. Drag the labels to the appropriate targets to indicate the numbers of molecules of ATP/ADP. which of the following equations correctly accounts for the inputs and outputs of phosphate groups in Phase 3? ANSWER: 5 P (in G3P) → 3 P (in R5P) + 2 Pi 6 P (in G3P) → 3 P (in R5P) + 3 Pi 15 P (in G3P) → 12 P (in R5P) + 3 Pi 3 P (in G3P) → 2 P (in R5P) + 1 Pi session.5/17/13 MasteringBiology: Create Assignment Counting carbons—keeping track of where the carbon atoms go in each reaction—is a simple way to help understand what is happening in the Calvin cycle. the G3P molecules left over from Phase 2 are converted to R5P with the release of Pi. Consider the analogous reactions in the Calvin cycle to help you label targets (a).Quantifying the inputs of ATP and NADPH and output of Pi The Calvin cycle depends on inputs of chemical energy (ATP) and reductant (NADPH) from the light reactions to power the conversion of CO2 into G3P. In the first part of Phase 3. the output of 1 G3P per turn of the Calvin cycle.com/myct/assignmentCreateOrCopy 16/19 . Can you trace the net movement of phosphate groups in the Calvin cycle? Phosphates are conserved in the Calvin cycle: For each turn of the Calvin cycle. In Phase 2. 8 of the 9 phosphate groups are released as Pi. In Phase 3. Hint 3. the output of 5 G3P from Phase 2 to Phase 3 of the Calvin cycle.5/17/13 MasteringBiology: Create Assignment In the first part of Phase 3. 5 molecules of G3P (1 phosphate group each) are converted to 3 molecules of R5P (also 1 phosphate group each). Phosphate is output from the Calvin cycle in all of the following ways except ANSWER: the output of Pi in Phase 2. Thus a net of two inorganic phosphate groups (Pi) are released. and the ninth phosphate appears in the G3P output from the cycle. ANSWER: The Calvin cycle requires a total of 9 ATP and 6 NADPH molecules per G3P output from the cycle (per 3 CO2 fixed).masteringbiology. The ninth phosphate group is output in the G3P produced by the Calvin cycle.Do the light reactions of photosynthesis depend on the Calvin cycle? session. six of the ATP and all of the NADPH are used in Phase 2 to convert 6 molecules of PGA to 6 molecules of G3P. Thus there is a net release of 2 Pi. the 6 phosphate groups that were attached to 3-PGA are output as Pi as NADPH reduces the 3-PGA to G3P. The transfer of 5 molecules of G3P from Phase 2 to Phase 3 does not represent an output of phosphate from the Calvin cycle. Six phosphate groups are also released in Phase 2 (derived from the 6 ATP used). In Phase 2. In the second part of Phase 3. 9 ATP are hydrolyzed to ADP. 3 ATP molecules are used to convert the 3 R5P into 3 RuBP. the output of Pi in Phase 3. the number of phosphate groups that enter the cycle from ATP is equal to the number of phosphate groups that are output from the cycle. 5 molecules of G3P (a total of 5 phosphate groups) are converted to 3 molecules of R5P (a total of 3 phosphate groups). Note that in the entire cycle. Part C . A total of 9 ATP are hydrolyzed to ADP in the Calvin cycle: an input of 9 total phosphate groups. 2 phosphate groups are output as Pi when 5 molecules of G3P (containing a total of 5 phosphate groups) are converted to 3 molecules of R5P (containing a total of 3 phosphate groups). Phosphates are conserved in the Calvin cycle. the vast majority of the ATP and NADPH produced by the light reactions is used in the Calvin cycle for CO2 fixation. This diagram shows the role that ATP. do the light reactions require from the Calvin cycle? Select all that apply. and NADP+. The Calvin cycle and the products of the light reactions Although many other processes in the chloroplast require ATP and/or NADPH from the light reactions. Think about all the inputs to the light reactions that could affect its rate. Hint 3. In addition. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. lower light levels generally mean a lower rate of O2 production. and NADP+ play in connecting the light reactions and the Calvin cycle (in both directions).masteringbiology. ANSWER: session. How the supply of inputs to a reaction is related to the rate of the reaction For most chemical reactions. ANSWER: RuBP ADP CO2 G3P NADP+ None The outputs from the Calvin cycle are G3P. Of these outputs. Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change. the rate of the reaction also tends to decrease. Are any outputs of the Calvin cycle also inputs for the light reactions? The Calvin cycle is dependent on the light reactions for ATP and NADPH that are required to power the conversion of CO2 to G3P. lower light levels also affect the rate of CO2 uptake by the Calvin cycle. What compounds. ADP. Thus. Hint 2. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water).) Hint 1. Consider what this may mean in terms of whether any outputs from the Calvin cycle are used as inputs to the light reactions. In this way. ADP (and Pi).com/myct/assignmentCreateOrCopy 17/19 . if any. NADPH. including reactions catalyzed by enzymes. only ADP (and Pi) and NADP+ are inputs to the light reactions. If the supply of an input decreases. the Calvin cycle depends on the light reactions.5/17/13 MasteringBiology: Create Assignment The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. the reaction rate (amount of product produced per unit of time) depends on the supply of substrates (inputs) for the reaction. 5/17/13 MasteringBiology: Create Assignment The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. A reaction or process is dependent on another if the output of the second is an input to the first. the light reactions are dependent on the Calvin cycle because the NADP+ and ADP produced by the Calvin cycle are inputs to the light reactions. if the Calvin cycle slows (because of a decrease in the amount of available CO2). The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease. ANSWER: photosynthesis photorespiration the opening of stomata the light reactions a shift to C4 photosynthesis Conserving water simultaneously reduces the amount of carbon dioxide available to the plant. Thus. the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced. Then answer the questions. Activity: Photosynthesis in Dry Climates Click here to complete this activity. The rate of O2 production would remain the same because the light intensity did not change.com/myct/assignmentCreateOrCopy 18/19 .masteringbiology. The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle. Part A In C3 plants the conservation of water promotes _____. session. For example. session.5/17/13 MasteringBiology: Create Assignment Part B In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells.masteringbiology. Part C C4 plants differ from C3 and CAM plants in that C4 plants _____.com/myct/assignmentCreateOrCopy 19/19 . ANSWER: open their stomata only at night use malic acid to transfer carbon dioxide to the Calvin cycle use PEP carboxylase to fix carbon dioxide are better adapted to wet conditions transfer fixed carbon dioxide to cells in which the Calvin cycle occurs In C3 and CAM plants carbon dioxide fixation and the Calvin cycle occur in the same cells. ANSWER: cytoplasm stoma stroma thylakoids grana In C4 and CAM plants carbon dioxide fixation occurs in the cytoplasm.