13.2. Investigation of limiting factors
A subsection of Biology, 9700, through 13. Photosynthesis
Listing 10 of 75 questions
Photosynthesis is a process that results in the synthesis of complex organic molecules. Respiration is a process that involves the breakdown of complex organic molecules. The light dependent stage of photosynthesis involves cyclic and non‑cyclic photophosphorylation. Describe two differences between cyclic and non‑cyclic photophosphorylation. Biochemical processes involving carbon dioxide change the external environment of the aquatic plant, Elodea canadensis, and the pond snail, Lymnaea stagnalis. Carbon dioxide dissolves in water to form carbonic acid. A student set up 8 test‑tubes. Each test‑tube contained 30 cm3 of distilled water containing a pH indicator, bromothymol blue. shows the experimental set up for these 8 test‑tubes. The test‑tubes were left for 12 hours. high light intensity aquatic plant Key: pond snail dark shows how the colour of bromothymol blue changes with pH. blue green yellow increasing pH neutral pH decreasing pH All tubes were green at the start of the experiment. The results of the experiment are shown in Table 5.1. Table 5.1 test‑tube colour after 12 hours green blue yellow green green yellow‑green yellow yellow Explain the purpose of test‑tube 1 and test‑tube 5. Explain the results of test‑tubes 2, 3 and 4. test‑tube 2 test‑tube 3 test‑tube 4 Explain the colour change in test‑tube 6.
9700_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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Photosynthesis is an energy transfer process that results in the production of carbohydrate. It has two stages: the light-dependent stage and the light-independent stage. Cyclic photophosphorylation and non-cyclic photophosphorylation are essential pathways in photosynthesis that occur in the light-dependent stage. Describe the similarities and differences between cyclic photophosphorylation and non-cyclic photophosphorylation. Explain why herbicides that prevent cyclic photophosphorylation and non-cyclic photophosphorylation stop carbohydrate being produced in the chloroplast. The rate of regeneration of RuBP in the Calvin cycle is known to limit the rate of photosynthesis. Sedoheptulose-1,7-bisphosphatase (SBPase) is an enzyme in the Calvin cycle that controls the rate of regeneration of RuBP. SBPase is coded for by the gene SBPase. In an experiment, wheat plants were genetically modified to make more SBPase by introducing the SBPase gene from another grass species, Brachypodium distachyon. The resulting GM wheat plants were named Sox4. • Wild type plants (not GM) and Sox4 plants were grown. • A leaf from the wild type plant was placed in a sealed glass vessel. • The carbon dioxide (CO2) concentration in the vessel was increased so that the intercellular air spaces also had an increase in CO2 concentration. • The other environmental conditions were kept constant. • The rate of fixation of CO2 was measured for the leaf. • The experiment was repeated with a leaf from a Sox4 plant. shows the rate of fixation of CO2 by the leaves of wild type plants and Sox4 plants when the intercellular air space CO2 concentration was increased. 800 1000 CO2 concentration / mg m–3 Sox4 wild type CO2 fixation rate / μmol CO2 m–2 s–1 1200 1400 1600 1800 2000 With reference to , describe and explain the results shown by the wild type plants. With reference to , describe and suggest explanations for the differences in the rate of fixation of CO2 between wild type plants and Sox4 plants.
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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Use Wheat, maize and sorghum are three of the most important cereal crops in the world. shows the effect of temperature on the rate of photosynthesis of wheat plants. CO2 used per dm2 of leaf per hour / mg temperature / °C With reference to , describe the effect of temperature on the rate of photosynthesis of wheat plants. Suggest why temperature affects the rate of photosynthesis in the way you have described in . Examiner’s Use The conditions in which young plants of wheat and maize are grown affects their ability to photosynthesise at high and low temperatures when they are mature. Young maize and wheat plants were grown to maturity at high and low temperatures. When they were mature, their rate of photosynthesis was measured at different temperatures. The results are shown in . CO2 used per dm2 of leaf per hour / mg maize grown at high temperature wheat grown at low temperature wheat grown at high temperature maize grown at low temperature temperature / °C Examiner’s Use With reference to , compare the effect of temperature on the rate of photosynthesis of maize plants and wheat plants that were grown at a high temperature when they were young. Maize is a C4 plant. Explain how the structure of the leaves of maize plants enables them to photosynthesise more effectively at high temperatures than wheat plants. Low temperatures slow down the formation of the membranes inside chloroplasts in maize leaves, but not in wheat leaves. Use this information to explain the differences between the results for maize and wheat grown at low temperatures, shown in . Examiner’s Use Cereal crops frequently form the staple diet of human populations. Table 5.1 shows the oil and starch content of maize and sorghum grains. Table 5.1 percentage of dry mass maize sorghum oil 4.7 3.8 starch 62.2 70.1 Name the part of the maize grain in which oil and starch are stored. With reference to Table 5.1, compare the energy values of maize and sorghum grains when the oil and starch they contain are used as respiratory substrates.
9700_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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Use In the majority of plants the leaf is the main photosynthetic organ. List four ways in which the structure of a dicotyledonous leaf is adapted for gas exchange. In an experiment to investigate the effect of light intensity on the rate of photosynthesis, the following procedure was carried out. ● Discs were cut, using a cork borer, from the photosynthetic tissue of the brown alga, Fucus serratus, a common seaweed of rocky shores. ● Ten discs were placed in each of four beakers containing 50 cm3 of sea water. The discs are denser than sea water and therefore initially sink to the bottom of the beaker. ● Each beaker was illuminated with a bench lamp placed at different distances, d, from the beaker. ● With time the discs began to rise to the surface of the water. ● The time, t, in minutes, at which the fifth disc from each batch reached the surface was recorded. ● The rate of photosynthesis was determined by calculating 1000 / t. A student’s set of results is shown in Table 8.1. Table 8.1 distance of beaker from lamp, d / cm light intensity 1 / d 2 time for fifth disc to reach the surface t / min rate of photosynthesis 1000 / t 0.04 43.5 0.01 27.8 0.004 19.2 11.4 Examiner’s Use Calculate the value for light intensity when the distance between beaker and lamp was 20 cm. Record the value in the space in Table 8.1. Explain why the discs rise to the surface after being illuminated for a length of time. Using the data in Table 8.1, describe the relationship between light intensity and the rate of photosynthesis. The student found that there was no increase in the rate of photosynthesis when two lamps were placed 5 cm from the beaker. Suggest why there was no increase in the rate of photosynthesis.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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shows the male and female flowers of maize. With reference to suggest how the flowering habit of maize encourages wind pollination. In a maize plant, the anthers normally ripen and release pollen before the stigmas are mature and ready to receive pollen. This encourages cross-pollination. Explain two potential advantages of cross-pollination to a plant species. The conditions in which wheat and maize are grown affect their ability to photosynthesise. compares the rate of photosynthesis of wheat and maize at different temperatures. temperature / ° C rate of photosynthesis / arbitrary units Key wheat maize With reference to : compare the effect of temperature on the rates of photosynthesis of wheat and maize explain the difference between the rates of photosynthesis of wheat and maize at 28 °C. Cereal grains are a major component of the human diet. Table 4.1 shows some of the nutrient contents of 100 g samples of grains of wheat, white rice and maize. Table 4.1 wheat white rice maize protein / g 12.3 7.5 8.9 fat / g 2.0 2.8 4.7 carbohydrate / g 75.0 77.0 74.0 fibre / g 2.3 0.9 2.0 calcium / mg 34.0 28.0 7.0 iron / mg 5.4 1.6 2.7 sodium / mg 2.0 6.0 35.0 With reference to Table 4.1 suggest reasons for the difference in protein content between wheat and white rice. State, giving a reason, which type of grain would be beneficial for a person with anaemia.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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Questions Discovered
75