13. Photosynthesis
A section of Biology, 9700
Listing 10 of 183 questions
Scientists are researching new ways to reduce the global atmospheric carbon dioxide (CO2) concentration. There are concerns that an increasing atmospheric CO2 concentration may lead to effects that decrease biodiversity. Give one example of a human activity, other than deforestation, that contributes greatly to the increase in global atmospheric CO2 concentration. Algae are aquatic photosynthetic protoctists. Some researchers genetically modified the unicellular alga, Chlorella vulgaris, to try to increase the rate of the light independent stage of photosynthesis. C. vulgaris was modified to increase the expression of the gene coding for aldolase. Aldolase is an enzyme that causes an increase in the concentration of rubisco. Two cultures of C. vulgaris, one that was not genetically modified and one genetically modified, were grown under controlled conditions for 14 days. Samples were taken from the cultures at regular intervals during the 14 days to obtain measurements of dry mass. The results are shown in . 0.0 0.4 0.8 1.2 1.6 2.0 time / days dry mass / g dm–3 unmodified Key genetically modified With reference to , describe the differences between the results for the two cultures. Explain how the Calvin cycle was affected by the genetic modification of C. vulgaris. Intermediate products of the Calvin cycle are needed to produce organic molecules for use by the cell. Describe how these organic molecules are used by cells. Planting large numbers of trees is one way to reduce global atmospheric CO2 concentration. Large scale culture of genetically modified C. vulgaris could also reduce global atmospheric CO2 concentration. Suggest one advantage of using genetically modified C. vulgaris instead of trees to reduce global atmospheric CO2 concentration.
9700_w21_qp_42
THEORY
2021
Paper 4, Variant 2
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An investigation was carried out to measure the rate of photosynthesis at different concentrations of carbon dioxide. Two different plants, barley and sugar cane, were tested at two different temperatures, 10 °C and 25 °C. The results are shown in . rate of photosynthesis / arbitrary units sugar cane at 25 °C carbon dioxide concentration / arbitrary units barley at 25 °C barley at 10 °C sugar cane at 10 °C Suggest why, in all four experiments, the rate of photosynthesis became constant as the carbon dioxide concentration increased. With reference to , describe the difference in the rate of photosynthesis, at 10 °C, between barley and sugar cane. Sugar cane is a C4 plant. Barley is not a C4 plant. Explain why, at 25 °C, sugar cane had a higher rate of photosynthesis than barley. Carbon dioxide for photosynthesis enters the leaves through open stomata. Stomata do not stay open all the time. Changes in environmental conditions can cause stomata to close. Describe these conditions and explain how stomatal closure benefits the plant.
9700_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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shows the effect of temperature on the rate of photosynthesis of a plant at a constant light intensity and a carbon dioxide concentration of 0.03%. temperature / °C rate of photosynthesis Suggest and explain why the rate of photosynthesis of the plant decreases to zero just above 40 °C. Draw, on , the likely curve if the same experiment were carried out on a C4 plant, such as sorghum. Give reasons to explain your curve. Experiments were carried out to determine the effect of light intensity on the rate of photosynthesis of a species of the unicellular protoctist, Chlorella. A cell suspension of Chlorella was used. • The suspension of Chlorella was illuminated at a light intensity of 5 lux for 20 seconds. • The carbon dioxide uptake by Chlorella was measured at the end of the 20 second period of illumination. • The experiment was repeated at 10, 13 and 15 lux. • The suspension was maintained at a temperature of 20 °C. Table 8.1 shows the results of the experiments. Table 8.1 light intensity / lux total CO2 uptake after 20 seconds / μmol rate of photosynthesis / μmol s–1 1.8 Complete Table 8.1. Use the data in the table to plot a graph on the grid below to show the effect of light intensity on the rate of photosynthesis. With reference to photosynthesis, state what is meant by a limiting factor. State the limiting factor in these four experiments.
9700_s12_qp_41
THEORY
2012
Paper 4, Variant 1
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shows the effect of temperature on the rate of photosynthesis of a plant at a constant light intensity and a carbon dioxide concentration of 0.03%. temperature / °C rate of photosynthesis Suggest and explain why the rate of photosynthesis of the plant decreases to zero just above 40 °C. Draw, on , the likely curve if the same experiment were carried out on a C4 plant, such as sorghum. Give reasons to explain your curve. Experiments were carried out to determine the effect of light intensity on the rate of photosynthesis of a species of the unicellular protoctist, Chlorella. A cell suspension of Chlorella was used. • The suspension of Chlorella was illuminated at a light intensity of 5 lux for 20 seconds. • The carbon dioxide uptake by Chlorella was measured at the end of the 20 second period of illumination. • The experiment was repeated at 10, 13 and 15 lux. • The suspension was maintained at a temperature of 20 °C. Table 8.1 shows the results of the experiments. Table 8.1 light intensity / lux total CO2 uptake after 20 seconds / μmol rate of photosynthesis / μmol s–1 1.8 Complete Table 8.1. Use the data in the table to plot a graph on the grid below to show the effect of light intensity on the rate of photosynthesis. With reference to photosynthesis, state what is meant by a limiting factor. State the limiting factor in these four experiments.
9700_s12_qp_43
THEORY
2012
Paper 4, Variant 3
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The concentration of carbon dioxide in the atmosphere and the light intensity often limit the rate of photosynthesis. Explain what is meant by a limiting factor in relation to photosynthesis. Investigations were carried out in Florida, USA, into the effect of different concentrations of atmospheric carbon dioxide and of light intensity on the rate of photosynthesis of soybean plants. Plants were grown from seed in outdoor, computer-controlled growth chambers at different concentrations of carbon dioxide. The upper parts of the chambers were transparent so that the plants received natural sunlight. After the seedlings emerged, the air in the soil was separated from the air around the leaves by a gas-tight seal in each chamber. Suggest why the air in the soil and the air around the leaves of the plants were separated. In one investigation, two sets of plants, A and B, were grown from seed at different concentrations of carbon dioxide: • A – normal atmospheric concentration of carbon dioxide (0.033%) • B – normal atmospheric concentration of carbon dioxide ×2 (0.066%). Then, keeping each set of plants in its particular concentration of carbon dioxide, measurements were made of their rates of photosynthesis at different light intensities. The results are shown in on page 5. mean rate of photosynthesis per unit area of leaf / arbitrary units light intensity / arbitrary units set B set A With reference to : describe and explain, in terms of limiting factors, the results from the plants in set A explain the difference between the results of set A and set B at high light intensities. In a second investigation, two sets of plants, C and D, were grown from seed, as before, in different carbon dioxide concentrations: • C – normal atmospheric concentration of carbon dioxide (0.033%) • D – normal atmospheric concentration of carbon dioxide ×2 (0.066%). When the plants matured, conditions in the growth chambers were changed to investigate the rate of photosynthesis of each set of plants in different concentrations of carbon dioxide. The results are shown in . mean rate of photosynthesis per unit area of leaf / arbitrary units concentration of carbon dioxide / arbitrary units set D set C
9700_s16_qp_41
THEORY
2016
Paper 4, Variant 1
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The concentration of carbon dioxide in the atmosphere and the light intensity often limit the rate of photosynthesis. Explain what is meant by a limiting factor in relation to photosynthesis. Investigations were carried out in Florida, USA, into the effect of different concentrations of atmospheric carbon dioxide and of light intensity on the rate of photosynthesis of soybean plants. Plants were grown from seed in outdoor, computer-controlled growth chambers at different concentrations of carbon dioxide. The upper parts of the chambers were transparent so that the plants received natural sunlight. After the seedlings emerged, the air in the soil was separated from the air around the leaves by a gas-tight seal in each chamber. Suggest why the air in the soil and the air around the leaves of the plants were separated. In one investigation, two sets of plants, A and B, were grown from seed at different concentrations of carbon dioxide: • A – normal atmospheric concentration of carbon dioxide (0.033%) • B – normal atmospheric concentration of carbon dioxide ×2 (0.066%). Then, keeping each set of plants in its particular concentration of carbon dioxide, measurements were made of their rates of photosynthesis at different light intensities. The results are shown in on page 5. mean rate of photosynthesis per unit area of leaf / arbitrary units light intensity / arbitrary units set B set A With reference to : describe and explain, in terms of limiting factors, the results from the plants in set A explain the difference between the results of set A and set B at high light intensities. In a second investigation, two sets of plants, C and D, were grown from seed, as before, in different carbon dioxide concentrations: • C – normal atmospheric concentration of carbon dioxide (0.033%) • D – normal atmospheric concentration of carbon dioxide ×2 (0.066%). When the plants matured, conditions in the growth chambers were changed to investigate the rate of photosynthesis of each set of plants in different concentrations of carbon dioxide. The results are shown in . mean rate of photosynthesis per unit area of leaf / arbitrary units concentration of carbon dioxide / arbitrary units set D set C
9700_s16_qp_43
THEORY
2016
Paper 4, Variant 3
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Questions Discovered
183