13.2. Investigation of limiting factors
A subsection of Biology, 9700, through 13. Photosynthesis
Listing 10 of 75 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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Environmental conditions such as light intensity affect plant physiology. Use the letter X to identify a point on the sketch graph in where light intensity is acting as a limiting factor on the rate of photosynthesis. light intensity / arbitrary units rate of photosynthesis / arbitrary units An experiment investigated how light intensity affected gene expression in kale, Brassica oleracea sabellica. • Two groups of kale plants were grown, with one group in high light intensity and one group in low light intensity. All other conditions were standardised. • After the same period of time, messenger RNA (mRNA) was extracted from each group of kale plants. • The mRNA was used to produce cDNA. • The cDNA was hybridised with probes for 89 621 kale genes on a microarray. • The microarrays showed which genes were switched on in each set of conditions. The results showed that expression of 18% of the genes was affected by light intensity. • 14% of the genes were switched on only in high light intensity. • 4% were switched on only in low light intensity. State the name of the enzyme that produces cDNA from an mRNA template. State the name of the type of proteins that control gene expression in plants. Suggest why more genes were switched on only in plants growing in high light intensity compared to fewer genes that were switched on only in plants growing in low light intensity.
9700_w23_qp_41
THEORY
2023
Paper 4, Variant 1
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Environmental conditions such as light intensity affect plant physiology. Use the letter X to identify a point on the sketch graph in where light intensity is acting as a limiting factor on the rate of photosynthesis. light intensity / arbitrary units rate of photosynthesis / arbitrary units An experiment investigated how light intensity affected gene expression in kale, Brassica oleracea sabellica. • Two groups of kale plants were grown, with one group in high light intensity and one group in low light intensity. All other conditions were standardised. • After the same period of time, messenger RNA (mRNA) was extracted from each group of kale plants. • The mRNA was used to produce cDNA. • The cDNA was hybridised with probes for 89 621 kale genes on a microarray. • The microarrays showed which genes were switched on in each set of conditions. The results showed that expression of 18% of the genes was affected by light intensity. • 14% of the genes were switched on only in high light intensity. • 4% were switched on only in low light intensity. State the name of the enzyme that produces cDNA from an mRNA template. State the name of the type of proteins that control gene expression in plants. Suggest why more genes were switched on only in plants growing in high light intensity compared to fewer genes that were switched on only in plants growing in low light intensity.
9700_w23_qp_43
THEORY
2023
Paper 4, Variant 3
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The effect of light intensity on the rate of photosynthesis can be investigated using a cut shoot of a pond plant. The apparatus used in the investigation is shown in . gas collects here test-tube water containing sodium hydrogencarbonate pond plant syringe air bubble in capillary tube scale in cm lamp X The light intensity can be changed by placing the lamp at different distances from the pond plant. Apparatus X, shown in , is a thin glass container filled with water. Explain the function of apparatus X. Before completing the assembly of the apparatus shown in , sodium hydrogencarbonate is added to the water surrounding the pond plant in the test-tube. Explain why sodium hydrogencarbonate is added to the water surrounding the pond plant in the test-tube. Name the gas collected in the test-tube. The investigation was carried out with the lamp at distances of 10, 20, 30, 40 and 50 cm from the pond plant. For each of these distances, the air bubble in the capillary tube was initially positioned at 0 cm on the scale and, after 5 minutes, the distance moved by the air bubble was measured. The rate of movement of the air bubble was then calculated. The results are shown in . rate of movement of air bubble / cm min–1 0.0 0.5 1.0 1.5 2.0 distance of lamp from pond plant / cm With reference to , describe the relationship between the rate of photosynthesis and light intensity. Further investigations showed that at distances of less than 10 cm, the rate of movement of the air bubble was the same as at 10 cm. Explain why there was no change in the rate of movement of the air bubble at distances less than 10 cm. Some of the light energy absorbed by the pond plant is used in cyclic photophosphorylation. Outline the process of cyclic photophosphorylation.
9700_m19_qp_42
THEORY
2019
Paper 4, Variant 2
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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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Questions Discovered
75