(e) i. 22. (a) ii (b) iv (c) v (d) iii

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1 Chapter 5 Review, pages Knowledge 1. a 2. b 3. b 4. d 5. d 6. b 7. b 8. b 9. b 10. a 11. True 12. False. Chlorophyll a, when excited, becomes oxidized as it passes an electron to a primary electron acceptor. 13. False. One molecule required for photosynthesis is carbon dioxide (or water, or chlorophyll). 14. False. ATP synthesis takes place in the stroma of a chloroplast. 15. True 16. False. In photosynthesis, light is responsible for providing the energy to remove electrons from H 2 O. 17. False. Melvin Calvin determined that atmospheric CO 2 was incorporated indirectly into glucose during the Calvin cycle. 18. True 19. False. Most autotrophs and heterotrophs carry out cellular respiration. 20. False. ATP synthase generates ATP by oxidative phosphorylation. 21. (a) v (b) iv (c) i (d) iii (e) ii 22. (a) ii (b) iv (c) v (d) iii (e) i 23. An analogy to explain the role of accessory pigments in photosynthesis is accessory pigments are like radio antenna in that they receive many varied frequencies, but only react to specific ones by sending them to the receiver (chlorophyll a). 24. The net reaction of the Calvin cycle in redox terms: high-energy electrons and protons (H + ) reduce fixed CO 2 in order to manufacture carbohydrates and other metabolites. 25. The significance of the products of the light reactions of photosynthesis is that the light reactions produce oxygen, high-energy ATP, and NADPH. The Calvin cycle uses these ATP and NADPH molecules from the light reactions, along with carbon dioxide, to produce sugars. 26. No, the light-dependent reactions and the Calvin cycle do not occur in the same part of the chloroplasts. The light-dependent reactions occur in the thylakoid membranes, while the lightindependent reactions (Calvin cycle) occur in the stroma of the chloroplasts. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-2

2 27. The role of the non-protein organic groups in the light-dependent reactions of photosynthesis is to act as electron carriers and redox agents. 28. The sequence of the redox reactions that take place in the electron transport system of the light reactions of photosynthesis is as follows: Absorption of photon and oxidation of P680 by the primary electron acceptor of PSII P680 + oxidizes water Oxidation of the primary acceptor by plastoquinone Oxidation of plastoquinone by the cytochrome complex Oxidation of cytochrome complex by plastocyanin Oxidation of plastocyanin by P700 + (after it has been energized by a photon and oxidized by the primary electron acceptor of PSI) Oxidation of the PSI primary electron acceptor by ferredoxin Oxidation of ferredoxin by NADP Ferredoxin is an important molecule for the Calvin cycle and other energy-dependent reactions in the chloroplasts because it transfers electrons from PSI to either NADP + or to PQ. The transfer to PQ begins cyclic electron transport, which allows for the production of the additional ATP from photosystem I that is needed by the Calvin cycle and other energydependent reactions in the chloroplast. 30. The role of ATP synthase is exactly the same in mitochondria and in chloroplasts. ATP synthase in the thylakoid membrane or in the mitochondrial membrane captures the energy of protons moving through the channel formed by the ATP synthase to phosphorylate ADP, producing ATP. 31. (a) P680 + oxidizes water, producing oxygen and causing it to be released into the atmosphere. (b) When P680 + pulls the electron from the water, it releases the H + into the thylakoid lumen, helping to create a proton gradient. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-3

3 32. Answers may vary. Sample answer: 33. When the CO 2 :O 2 ratio drops, rubisco takes an O 2 into the Calvin cycle rather than a CO 2 molecule. This results in photorespiration. 34. Two ways photorespiration is detrimental to a plant are that photorespiration uses ATP and it results in the release of fixed carbon as CO 2 from the cell. 35. Photorespiration is a greater problem in warmer climates versus cooler climates because the solubility of carbon dioxide decreases more rapidly than that of oxygen as the temperature increases. This increases the availability of oxygen at the rubisco active site. In addition, plants may need to close their stomata in hot and dry weather to conserve water, but this also prevents gas exchange. As carbon dioxide is consumed during the Calvin cycle, its concentration drops and photorespiration increases. In high temperatures, as much as 50 % of the plant s energy can be wasted by photorespiration. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-4

4 36. The C 4 cycle and spatial separation of the Calvin cycle help plants avoid photorespiration by reducing the exposure of rubisco to oxygen. The C 4 cycle allows plants to sequester carbon dioxide in the form of malate and make it available to rubisco in high concentration in the bundle sheaths away from high concentrations of oxygen. 37. The steps in the C 4 cycle are: CO 2 first combines with three-carbon PEP to produce fourcarbon oxaloacetate, which is reduced to malate by electrons transferred from NADPH. Once it reaches the site of the Calvin cycle, the malate gets oxidized to pyruvate, releasing CO 2, and finally pyruvate is converted back to PEP in a reaction that uses ATP. 38. The advantage that C 4 plants have in an arid climate is that C 4 plants prevent photorespiration by sequestering carbon dioxide more efficiently. They do not need to keep their stomata open for as long as a C 3 plants, which conserves water. 39. Table 1 Structure Function Mitochondria ovoid shape have multiple membranes have own DNA have intermembrane space (matrix) cristae continuous with inner membrane generate ATP from glucose during cellular respiration consume O 2 and release CO 2 use electron transport chains generate ATP by chemiosmosis Chloroplasts ovoid shape have multiple membranes have own DNA have intermembrane space (stroma) thylakoids discontinuous with inner membrane generate ATP from light energy (via photosynthesis) to produce glucose for storage consume CO 2 and release O 2 use electron transport chains generate ATP by chemiosmosis Understanding 40. Although van Helmont s conclusions to his willow tree experiment were partially wrong (most of the tree s dry mass came from CO 2 and only a small portion came from water), his work laid the foundation of quantitative plant research and focused later experiments on the gases and liquids that the plant interacts with as a potential source of nutrients and, thereby, expanded our understanding of plant physiology. 41. A green plant would grow better under a red light because a green plant would reflect most of the green light it receives, and not be able to absorb and use the green light for photosynthesis. 42. Photosynthesis is an anabolic process that is the primary source of energy for most food webs on the planet. According to the second law of thermodynamics, some usable energy is lost with every energy conversion, and entropy increases. Therefore energy must be input (absorbed) into this system because this process causes entropy to decrease. The Sun supplies this energy, but it must be converted into chemical energy that organisms can use through the process of photosynthesis. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-5

5 43. Light energy is absorbed by the antenna complex and transferred to an electron in the chlorophyll a molecule, causing the electron to move progressively farther away from the nucleus of the original atom. Eventually, the electron is promoted to a high enough energy level that the attractive force of the nucleus is no longer able to hold the electron on to its original atom, and the electrons can now be sequestered by a nearby acceptor molecule. The electron is then further transported to other carriers in the chain. 44. The standard equation makes it appear that the formation of glucose is the result of water bonding directly to carbon dioxide and directly producing glucose and oxygen gas. This reaction does not account for the separate reactions of the electron transport chain and the Calvin cycle. It also does not account for the role of light energy, chemiosmosis, enzymes, other molecules, and intermediate reaction steps. 45. Photons drive the electron transport chain in photosystem I and photosystem II by exciting electrons in P680 and P Chemiosmosis is the process of protons moving through the ATP synthase channel across the thylakoid membrane, and down their electrochemical concentration gradient, which produces ATP via the ATP synthase complex. 47. The term dark reaction suggests that the Calvin cycle occurs in the dark, when, in reality, it never occurs in the dark. The Calvin cycle can only occur during the day or in the presence of an adequate light source. Although it does not use light directly, the cycle requires the ATP and NADPH that are being continuously produced/regenerated by the light-dependent reactions. In the absence of light, these molecules would be depleted and the Calvin cycle would stop. 48. Plants in arid climates have three adaptations that make it more difficult to obtain enough carbon dioxide to keep the Calvin cycle running: They have low surface-to-volume ratio (small leaf surface area). They have fewer leaf stomata to reduce water loss. They keep their stomata closed during the day to conserve water, which blocks CO 2 from entering. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-6

6 49. The Earth s atmosphere is 21 % oxygen and approximately 0.04 % carbon dioxide. Since the amount of O 2 in the atmosphere is so much greater than the amount of CO 2, rubisco will bind with CO 2 only about 75 % of the time. The other 25% of the time, rubisco will bind with O 2, resulting in photorespiration. Therefore if the supply of CO 2 becomes reduced, the rate of photorespiration increases, which drains the resources of the cell. 50. You would expect to find the highest number of C 4 plants in southern Ontario versus northern Ontario. At higher temperatures, C 3 plants are much less efficient than C 4 plants because of increased photorespiration. If they are able to survive, they will grow and reproduce more slowly than C 4 plants in these conditions. Therefore, they are more likely to be outcompeted in southern Ontario. In cooler northern climates, the opposite is true. Photorespiration is not a problem, so the C 3 plants that don t need to use ATP for the extra C 4 cycle are more efficient than the C 4 plants; therefore, C 3 plants would be expected to grow and reproduce faster and outcompete the C 4 plants. 51. The reason that C 4 plants and CAM plants are not more successful than C 3 plants is because they are adapted for different environments. The C 3 plants are more efficient than C 4 and CAM plants under cool, moist conditions and under normal light. Both C 4 and CAM plants have adapted to drier environments, but require specialized cell structures and processes to be successful in these environments. Since most of the Earth s terrestrial environments are relatively moist, C 3 plants are most abundant because they have adapted to be the most efficient plant for that type of environment. 52. The advantage of PEP carboxylase in carbon dioxide fixation compared with rubisco is that it functions well regardless of the oxygen concentration in the environment. PEP carboxylase does not bind with oxygen like rubisco, so there is not a risk of photorespiration damage with PEP carboxylase. In addition, since PEP carboxylase allows C 4 plants to be more efficient at carbon dioxide fixation, they can still perform adequate photosynthesis even when their stomata cannot be opened for very long. 53. Artificial photosynthesis would use technological devices to model the actions of the photosystems in living cells. These would be used to split water molecules and use further reactions to form hydrogen gas a fuel that stores chemical energy. Solar panels generate electrical energy directly. They transform light energy into electrical energy. 54. Two ways in which the electron transport systems in photosynthesis and cellular respiration are different are 1) photosynthesis uses two continuous electron transport chains while respiration uses only one, and 2) both of the electron transport chains in photosynthesis require the input of additional energy (light) while the electron transport system in respiration does not require any additional energy input. 55. The key feature that scientists are trying to harness in their development of artificial photosynthesis is the ability of photosystems to oxidize water. They would like to be able to produce free energized electrons from water using light energy and transfer them to protons to produce hydrogen gas. Hydrogen is a clean-burning fuel and using light energy would be very environmentally friendly. 56. The light-dependent and light-independent reactions (Calvin cycle) are dependent on each other. The NADPH molecules produced during the light-dependent reaction deliver hydrogen and high-energy electrons to the Calvin cycle for use in carbohydrate synthesis. The Calvin cycle regenerates ADP and NADP +, which are used in the light-dependent reactions. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-7

7 57. The statement The development of photosynthetic organisms on Earth had a profound effect on Earth s atmosphere is true because photosynthetic organisms released large amounts of oxygen into Earth s early atmosphere, dramatically changing the composition of Earth s atmosphere. Analysis and Application 58. The fact that a green grass stain on clothing will eventually fade away even if not washed suggests that the chlorophyll pigment molecule is more chemically and physically stable when it is within a living cell and/or it degrades slowly within living cells (but is being continuously replaced). 59. (a) Answers may vary. Sample answers: Measure and document all the water added to plant. Dry out the tree before measuring mass (like the earth) to compare dry masses. Grow the tree indoors under controlled conditions. (b) Answers may vary. Sample answers: Grow the tree in water so water is the only variable. Measure and record all water added to plant. Use only distilled water (no unknown variables in water). 60. Answers may vary. Press briefings should include suggestions that the plants may have evolved to contain large amounts of chlorophyll b, which uses blue/green light. Since no red light reaches the planet s surface, plants that could use blue or green light for photosynthesis would have a competitive advantage. The plants would likely appear very dark in colour on their home planet, because red light does not reach them and they absorb the blue and green light. They would likely appear red if they were brought to Earth, because they do not contain chlorophyll a, which absorbs red light, so they would reflect it. 61. Answers may vary. Experiments should include: Grow several identical plants under identical conditions other than the colour/wavelength of the light they are exposed to. Take careful measurements of the growth of each plant for several months to determine which colour/wavelength results in the best growth. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-8

8 62. (a) (b) Violet-blue light would be the least useful light for viewing spinach because it absorbs those colours. Green-yellow light would be the most useful because it is reflected back to the eye. (c) (d) There are no peaks in the 500 to 620 nm range because spinach leaves do not absorb light in this range (green-yellow). (e) Chlorophyll a and chlorophyll b are primarily responsible for the absorption in the 400 to 480 nm range. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-9

9 63. Since diuron (DCMU) is a photosystem II inhibitor, it prevents electrons from being transferred from photosystem II through plastoquinone and on to the rest of the electron transport carriers. The non-cyclic electron transport chain is blocked. This means that diuron essentially stops photosynthesis, killing the plant. 64. Answers may vary. Sample answer: The high concentration of ATP and little NADPH may be due to a problem/defect with photosystem II (i.e., the cyclic pathway is operating properly, but the non-cyclic pathway is not). 65. (a) The plants are kept in the dark to keep the sugar content at a common baseline. (b) Bean plants grown under high light conditions produce more sugar than plants grown under low light conditions at different temperatures. The higher light provides more light energy for photosynthesis. The positive effect on photosynthesis with increasing temperature is only seen at high light levels. At low light, increasing the temperature has little effect. The lower the light, the less energy is available for carbon dioxide fixation. (c) The plants in low light stopped manufacturing sugar before the plants in high light because the plants in low light had less carbon dioxide fixation occurring. The high temperature may have also caused the plants to close their stomata in an effort to conserve water, which would also decrease their available CO Answers may vary. Sample answers: I could use grow lights in a greenhouse so that I can alter day length, which increases the time for photosynthesis. I could increase the intensity of the light by installing more powerful lights. I could increase the temperature of the environment by using a heater, which has a positive effect on photosystem II. I could increase the CO 2 concentration, which reduces the amount of O 2 that binds to rubisco and increases the efficiency of photosynthesis, by filtering out excess oxygen and/or introducing extra CO 2 using tanks of CO 2. The lower O 2 concentration may also help minimize respiration. 67. Answers may vary. Answers should include: Apparatus Tests performed C 3 C 4 CAM equipment for Calvin s experiment greenhouse magnifying glass and nail polish Use a light and dark regime to determine the presence of fixed malic acid. Vary temperature, humidity, and CO 2 levels and look for best growth compared to the other plants under the same conditions. Paint nail polish on underside of leaf; peel off polish when dry; use magnifying glass to count number of stomata. no malic acid in dark best growth: low temperature, high humidity, high CO 2 numerous stomata malic acid in dark best growth: high temperature, normal CO 2, high humidity fewer stomata malic acid in dark best growth: high temperature, normal CO 2, low humidity very few stomata Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-10

10 68. (a) The knocking out of the gene responsible for NADP + reductase enzyme would have a negative effect on non-cyclic ATP synthesis. Non-cyclic ATP synthesis would cease since the electron normally donated from ferredoxin to NADP + via NADP + reductase would not occur; therefore, it would force the plant to undergo only cyclic ATP synthesis. (b) The effect on cyclic ATP synthesis would be positive as the only route for high-energy electrons from ferredoxin would now be plastoquinone. This would cause protons to be shuttled across the membrane without photosystem II; therefore, only ATP would be produced and no NADP + could be reduced. (c) The Calvin cycle would be shut off as it requires the NADPH produced using the NADP+ reductase during non-cyclic electron transport to reduce 3-phosphoglycerate to G3P, two molecules of which combine to form glucose. 69. The arid environment of the lowland areas of the Galapagos is an environment that CAM plants would thrive in. That is why there are more cacti and other succulents. These plants open their stomata to release O 2 and sequester CO 2 only at night. During the day, CAM plants close their stomata to conserve water and the sequestered CO 2 is released, reducing photorespiration. The highlands are cool and moist so C 3 plants can grow without risk of water loss, so they can keep their stomata open to allow gas exchange, which reduces photorespiration. 70. Since the control plants show the presence of malic acid but not G3P, you can infer that these plants must undergo crassulacean acid metabolism (CAM) since the leaves incorporated CO 2 into malate in the dark (stomata opened in the dark). 71. (a) The CO 2 compensation point for the C 3 plant is higher than the CO 2 compensation point for the C 4 plant because C 3 plants require higher CO 2 concentrations to outcompete O 2 for the active site of rubisco. (b) The rate of C 4 plant photosynthesis rises faster than the rate of C 3 photosynthesis as the CO 2 concentration increases because the PEP carboxylase enzyme in C 4 plants is more efficient at fixing CO 2 than rubisco. (c) In an environment where the CO 2 concentration is increasing, C 4 plants will gain an immediate advantage, but at the higher concentration levels, C 3 plants have higher rates of CO 2 uptake because they are more efficient (require no intermediate molecule to fix CO 2 ). That is, at higher CO 2 concentrations photorespiration is reduced so it is more efficient for rubisco to fix CO 2 directly. 72. Assuming that the herbicide was able to get into the plants, the weeds should all be dead or dying in the field sprayed with rubisco inhibitor, since all these plants have rubisco, which is needed in photosynthesis. In the field sprayed with PEP carboxylase inhibitor, the C 4 and CAM plants should be dead or dying while the C 3 plants should be healthy since only the first two types of plants have PEP carboxylase. 73. Even under ideal growing conditions, CAM plants grow much more slowly than C 3 plants because, although they can grow in higher temperatures and with less water than C 3 plants, they can only store a limited amount of CO 2 during the night. During the day when this is used up they can t obtain any more because if they opened their stomata they would desiccate. C 3 plants under ideal settings can continuously take in CO 2 and perform the reactions of the Calvin cycle whenever there is adequate light. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-11

11 74. (a) Table 3 Type of plant Store Greenhouse C 3 healthier no change C 4 no change no change (but appear healthier than C 3 plants) (b) As temperatures increase, C 3 plants begin to photorespire as carbon dioxide solubility decreases. They also transpire more water in response to the high temperature. Reducing the temperature in the store created better conditions for the C 3 plants by reducing photorespiration and water loss, so they appeared healthier. C 4 plants reduce transpiration by closing their stomata during hot, dry days to conserve water. The high affinity of PEP carboxylase for carbon dioxide, even at low CO 2 :O 2 concentration ratios, allows C 4 plants to be more efficient at photosynthesis when temperatures are higher. Evaluation Plants evolved to contain chlorophyll b and accessory pigments to increase the plants ability to absorb the energy of wavelengths of light beyond that which chlorophyll a can absorb. This increases the plants action spectrum beyond the absorption spectrum of chlorophyll a. 77. Answers may vary. Sample answer: Rubisco can be considered the most important enzyme in the biosphere because it is the enzyme that catalyzes the first reaction of the Calvin cycle. Without rubisco, plants could not make carbohydrates. Without plants, consumers would not survive. Therefore, rubisco is the primary method by which solar energy enters into the food chain on which many organisms depend on for survival. 78. (a) Photosystem II does not function during cyclic electron transport, and cyclic electron transport generates ATP by proton pumping, but does not produce NADPH. In addition, noncyclic electron transport consumes water and produces oxygen, while cyclic electron transport does not. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-12

12 (b) Cyclic electron transport only photosystem I electron comes from chlorophyll and returns to chlorophyll Non-cyclic electron transport in both photosystem I and photosystem II source of electron is water (NADP + is the final acceptor) and electron goes out of system oxygen not produced oxygen is produced as by-product generates ATP generates ATP and NADPH 79. (a) Fructose and glucose (6-carbon sugars) and sucrose (12-carbon sugar) are seen on the chromatogram after 30 s (Figure 5 (b)) but not on the chromatogram after 5 s, (Figure 5 (a)) which suggests that they are not immediately produced. (b) Evidence suggesting PGA may be one of the first intermediate compounds in the Calvin cycle is that PGA was in abundance after only a few seconds of exposure to light and continued to increase in abundance as the experiment progressed. (c) There is a small amount of labeled G3P (triose phosphate) on the 5-s chromatogram but none labeled on the 30-s chromatogram, which suggests that it is produced rapidly during photosynthesis but quickly converted to larger carbohydrates. 80. Autotrophs also need heterotrophs to survive because when the autotrophs die, their carbon is trapped. Autotrophs need heterotrophic decomposers to recycle the carbon needed for photosynthesis. 81. Increasing temperatures and CO 2 levels due to climate change could have different effects on C 3, C 4, and CAM plants. As CO 2 and temperatures increase, C 3 plants would benefit by the increased concentration of CO 2, which would tend to reduce photorespiration. However, the increase in temperature would increase water loss and, therefore, might be a detriment to these same plants that are not well suited to dry environments. The increase in temperature also reduces the solubility of CO 2, so the increase in atmospheric concentrations might not actually result in an increase in available CO 2. CAM plants are the plants best suited for this type of environment, and would likely thrive. Water will play an important role. If water is in short supply, then C 4 and CAM plants will be best adapted for the new conditions. In regions where water is abundant, C 3 plants may be best adapted. Reflect on Your Learning 82. Alternative pathways for carbon fixation likely evolved over time because the C 3 pathway is not very efficient, and plants growing in hot and arid climates cannot afford to keep their stomata open all day. Each pathway has certain advantages in addition to its disadvantages. 83. Answers may vary. Sample answer: Artificial photosynthesis should be explored further and implemented, if possible, because this form of energy production would not pollute the environment, it is renewable, the raw materials needed for this type of energy production are readily available, and artificial photosynthesis would not produce much waste. 84. Answers may vary. Sample answer: I learned that carbon dioxide fixation and the splitting of water to produce oxygen occur in different reactions, so the process of gas consumption and production in photosynthesis is more complicated than I thought. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-13

13 85. Answers may vary. Sample answer: I learned about the important role plants play in providing humans and other heterotrophs with food. Without plants and other photoautotrophs acting as primary producers to convert light energy into chemical energy, we would not survive. To help promote plants, I could recycle paper to reduce the need for cutting down trees. Research 86. (a) Answers may vary. Students should research how bioscrubber technology is used to control CO 2 emissions, and consider how it can be implemented on a small scale. (b) Presentations may vary but should include key points from Section 5.4 along with appropriate graphics. 87. Answers may vary. Answers should include growing conditions and plant type. 88. (a) Answers may vary. Sample answers: Broadening the wavelengths absorbed over a wider range of the solar spectrum Storing unused solar energy more efficiently Decreasing oxygen affinity (or increasing carbon dioxide affinity) of rubisco (b) Answers may vary. Sample answers: Plants could play a larger role as an alternative renewable fuel source. Less land will be needed to grow the same amount of food. (c) Answers may vary. Sample answers: Plants could be genetically engineered to contain pigments that absorb light at different wavelengths. Rubisco could be genetically engineered to improve its CO 2 binding efficiency. Plants could be genetically engineered to become biological voltaic cells. Copyright 2012 Nelson Education Ltd. Chapter 5: Photosynthesis: The Energy of Life 5-14