13.1. Photosynthesis as an energy transfer process
A subsection of Biology, 9700, through 13. Photosynthesis
Listing 10 of 108 questions
In flowering plants, the light-dependent reactions are carried out by photosynthetic pigments which fall into two categories: primary pigments and accessory pigments. Outline the role played by accessory pigments in the light-dependent reactions. Photosynthetic pigments are arranged in photosystems. There are two photosystems, PS I and PS II. PS I takes part in cyclic photophosphorylation but PS II does not. Outline the differences between cyclic and non-cyclic photophosphorylation. The rate of photosynthesis is affected by several environmental factors. shows the effect of temperature on the rate of photosynthesis. temperature / °C rate of photosynthesis / arbitrary units Explain why the rate of photosynthesis levels out at 30 °C. On continue the curve to indicate what would happen to the rate of photosynthesis if the temperature was increased to 70 °C. Explain why you have continued the curve in this way. A palisade mesophyll cell is adapted to carry out photosynthesis. The table below lists some of the adaptations of a palisade mesophyll cell. Complete the table to show how these adaptations help the cell to carry out photosynthesis. adaptation how the adaptation helps photosynthesis thin cell wall cylindrical shape large vacuole chloroplasts can be moved within the cell
9700_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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In plants such as rice, Oryza sativa, rubisco has a low rate of activity, which in turn affects the rate of photosynthesis. The cereal crop sorghum, Sorghum bicolor, has a high rate of activity of rubisco. A genetically modified (GM) variety of rice was produced. Parts of the quaternary structure of rubisco in rice were altered to be the same as the rubisco in sorghum. The rate of activity of rubisco in non-GM rice and GM rice was measured at different concentrations of atmospheric carbon dioxide (CO2). The results are shown in . rate of activity of rubisco / arbitrary units atmospheric CO2 concentration / mg dm–3 GM rice non-GM rice GM rice non-GM rice Compare the two curves shown in and explain why the curve for non-GM rice levels off. Suggest which part of the rubisco molecule was altered to produce the GM variety of rice. shows an outline of the Calvin cycle. CO2 GP RuBP TP other molecules ATP ADP + Pi ATP ADP + Pi NADP reduced NADP Name the process that involves the enzyme rubisco. State the type of reaction that occurs when GP is converted to TP. RuBP is regenerated from molecules of TP. State how many molecules of RuBP are produced from 10 molecules of TP. TP molecules that are not involved in the regeneration of RuBP can be used in the synthesis of other molecules. State two molecules that can be produced from these TP molecules.
9700_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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Grass crops such as maize, sorghum and sugarcane are C4 plants. They are common grass crops of tropical regions. Oats and wheat, commonly grown in temperate regions, are C3 plants. Most plants are C3 plants. They are termed ‘C3’ because the first product of photosynthesis is a three carbon compound. Outline how the biochemistry of C4 plants differs from that of C3 plants. The C4 pathway for fixing carbon dioxide was worked out in 1966 by Hatch and Slack. During their investigation they measured the rates of fixation of carbon dioxide at high light intensities in leaves removed from both temperate and tropical grasses. They also measured the rates of activity of two carboxylase enzymes in the leaves, ribulose bisphosphate carboxylase and PEP carboxylase. All rates were measured at 30 °C. Some of their results are shown in Table 2.1. Table 2.1 grass crop rate of fixation of carbon dioxide / arbitrary units rate of activity of rubisco / arbitrary units rate of activity of PEP carboxylase / arbitrary units maize 3.5 0.62 17.50 sorghum 3.1 0.35 15.80 sugarcane 2.9 0.30 18.50 oats 1.6 4.50 0.33 wheat 1.7 4.70 0.29 With reference to Table 2.1, compare the rates of fixation of carbon dioxide in C3 and C4 grasses. Describe the role of rubisco in the Calvin cycle. With reference to Table 2.1, suggest reasons for the differences in activity of the two carboxylase enzymes in C3 and C4 grasses. It has been calculated that, to produce one molecule of glucose, the C3 pathway uses 18 molecules of ATP and the C4 pathway uses 30 molecules of ATP. Suggest why C4 plants can afford this high cost of ATP.
9700_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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Grass crops such as maize, sorghum and sugarcane are C4 plants. They are common grass crops of tropical regions. Oats and wheat, commonly grown in temperate regions, are C3 plants. Most plants are C3 plants. They are termed ‘C3’ because the first product of photosynthesis is a three carbon compound. Outline how the biochemistry of C4 plants differs from that of C3 plants. The C4 pathway for fixing carbon dioxide was worked out in 1966 by Hatch and Slack. During their investigation they measured the rates of fixation of carbon dioxide at high light intensities in leaves removed from both temperate and tropical grasses. They also measured the rates of activity of two carboxylase enzymes in the leaves, ribulose bisphosphate carboxylase and PEP carboxylase. All rates were measured at 30 °C. Some of their results are shown in Table 2.1. Table 2.1 grass crop rate of fixation of carbon dioxide / arbitrary units rate of activity of rubisco / arbitrary units rate of activity of PEP carboxylase / arbitrary units maize 3.5 0.62 17.50 sorghum 3.1 0.35 15.80 sugarcane 2.9 0.30 18.50 oats 1.6 4.50 0.33 wheat 1.7 4.70 0.29 With reference to Table 2.1, compare the rates of fixation of carbon dioxide in C3 and C4 grasses. Describe the role of rubisco in the Calvin cycle. With reference to Table 2.1, suggest reasons for the differences in activity of the two carboxylase enzymes in C3 and C4 grasses. It has been calculated that, to produce one molecule of glucose, the C3 pathway uses 18 molecules of ATP and the C4 pathway uses 30 molecules of ATP. Suggest why C4 plants can afford this high cost of ATP.
9700_w16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
108