13. Photosynthesis
A section of Biology, 9700
Listing 10 of 183 questions
The banana plant, Musa acuminata, is a tall herbaceous plant with very large leaves. shows a banana plant. An investigation was carried out to measure the net carbon dioxide uptake by a banana plant at different light intensities. shows the results of the investigation. – 4 – 2 – 0 light intensity / lux mean net carbon dioxide uptake / μmol m–2 s–1 10 000 12 000 With reference to , describe and explain the results at a light intensity of 1000 lux. With reference to , describe and explain what can be concluded from the graph at light intensities of between 2000 lux and 7000 lux. Explain why the rate of carbon dioxide uptake levels off as light intensity increases above 10 000 lux. Pitcher plants are carnivorous plants that trap and digest insects in a large modified leaf called a pitcher. shows a pale pitcher plant, Sarracenia alata. pitcher Unlike the Venus fly trap, pitcher plants have no moving parts to trap insects. Insects are attracted to scent produced at the top of the pitcher. Once inside the pitcher, the insect slides down to the bottom and into a liquid containing digestive enzymes. Suggest a type of enzyme found in the pitcher plant that is used to digest insects. Pitcher plants grow in bogs and wet grassland where the soil has a low concentration of minerals such as nitrates. The plants obtain nitrates from the digestion of insects. Calvin cycle intermediates are used to synthesise more complex compounds, some of which need nitrogen from nitrates. Name one compound that needs nitrogen from nitrates and name the Calvin cycle intermediate from which it is synthesised. compound that needs nitrogen Calvin cycle intermediate
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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is a photomicrograph of a transverse section through the leaf of a C4 plant. J K L Identify structures J to L. J K L Outline how this leaf anatomy adapts the plant for high rates of carbon fixation at high temperatures. Sorghum is a C4 plant and Sorghum bicolor is a major food crop in dry tropical regions. The leaves of S. bicolor are covered with a layer of wax made up of a mixture of esters and free fatty acids, with a melting point of 77– 85 °C. Waxes from the leaves of non- tropical plants tend to have melting points lower than this. For example, wax from the bayberry, Myrica sp., has a melting point of 45 °C. Suggest how the wax on sorghum leaves helps the plant to survive in dry, tropical regions. An investigation was carried out into the response of sorghum to being kept at a low temperature for a short period of time. Soybean plants, which are better adapted than sorghum for growth in subtropical and temperate climates, were used for comparison. Plants of sorghum and soybean were kept at 25 °C for several weeks and then at 10 °C for three days. The temperature was then increased to 25 °C again for seven days. Day length, light intensity and carbon dioxide concentration were kept constant throughout. The uptake of carbon dioxide, as mg CO2 absorbed per gram of leaf dry mass, was measured • at 25 °C before cooling • on each of the three days at 10 °C • for seven days at 25 °C. The results are shown in Table 4.1. Table 4.1 plant carbon dioxide uptake / mg CO2 g–1 at 25 °C, before cooling at 10 °C at 25 °C (mean over days 4 to 10) day 1 day 2 day 3 sorghum 48.2 5.5 2.9 1.2 1.5 soybean 23.2 5.2 3.1 1.6 6.4 Compare the changes in carbon dioxide uptake in sorghum and soybean during the three days at 10 °C. During the cooling period, the ultrastructure of the sorghum chloroplasts changed. The membranes of the thylakoids moved closer together, eliminating the spaces between them. The size and number of grana became reduced. Explain how these changes could be responsible for the low rate of carbon dioxide uptake by sorghum even when returned to a temperature of 25 °C.
9700_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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Leaves of tobacco plants, Nicotiana spp, have a high concentration of nicotine, the addictive component of tobacco smoke. Scientists are continually seeking ways to produce tobacco plants that have reduced nicotine content. Describe and explain the effects of nicotine on the cardiovascular system that can contribute to a person developing coronary heart disease. The production of low-nicotine cigarettes and cigars is considered a strategy that may reduce the harmful effects of smoking. Explain whether or not you agree with this statement.
9700_s11_qp_22
THEORY
2011
Paper 2, Variant 2
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shows a diagram of a stoma, its guard cells and adjacent epidermal cells. stoma epidermal cell guard cells nucleus cytoplasm nucleus Guard cells have chloroplasts while epidermal cells do not have chloroplasts. State one other difference, visible in , between guard cells and epidermal cells. During stomatal closure: state precisely where abscisic acid (ABA) binds identify the ion that diffuses from the guard cells to epidermal cells compare the relative water potential of the guard cells with that of epidermal cells describe the change in volume of the guard cells. The following experiment was carried out to investigate the effect of light intensity on the rate of photosynthesis of a water plant, Elodea. • Elodea was cut into three pieces, each 10 cm long. • Each piece of Elodea was placed in a glass tube, containing 0.5% sodium hydrogencarbonate solution, which was then sealed with a bung. • Tube A was placed 10 cm away from a lamp. • Tube B was placed 5 cm away from a lamp. • Tube C was placed in a dark room. • An oxygen sensor was used to measure the percentage of oxygen in the solutions at the start of the experiment and again at 5, 10 and 20 minutes. The results are shown in . time / minutes percentage of oxygen in solution A B C State why sodium hydrogencarbonate solution was used. Calculate the mean rate of oxygen production for tube A for the 20 minutes of the experiment. Show your working. answer Compare the results for tubes A and B. Explain the results for tube C. Suggest what factor, which may have an effect on the rate of photosynthesis, was not taken into account in this experiment. shows the relationship between the light-dependent and light-independent reactions in a chloroplast. Calvin cycle light-dependent reactions X H2O CO2 O2 sugar Y Name the substances X and Y in . X Y
9700_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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Questions Discovered
183