13.2. Investigation of limiting factors
A subsection of Biology, 9700, through 13. Photosynthesis
Listing 10 of 75 questions
Photosynthesis is a complex process involving the transfer of light energy into chemical energy. Describe the role of photosynthetic pigments. Name the precise location in a chloroplast of photosynthetic pigments. Name a practical technique to separate photosynthetic pigments. The rate of photosynthesis is affected by many environmental factors. A student carried out an experiment to investigate the relationship between the concentration of carbon dioxide available to an aquatic plant, Cabomba caroliniana, and its rate of photosynthesis. shows the experimental set-up for this investigation. sodium hydrogencarbonate (NaHCO3) solution 15 cm length of C. caroliniana sealed container LED lamp at fixed distance • Sodium hydrogencarbonate solution was used as a source of carbon dioxide. • The concentration of carbon dioxide was varied using six different concentrations of sodium hydrogencarbonate solution. • All C. caroliniana plants were kept in the dark before the light was switched on at the start of the experiment. • Five replicates were carried out at each concentration. • The rate of photosynthesis was obtained by calculating the percentage change in dissolved oxygen concentration in the solution over five minutes. shows the results of the investigation. percentage change in dissolved oxygen –15 –10 –5 0.25 0.00 0.50 0.75 1.00 1.25 concentration of sodium hydrogencarbonate solution / mol dm–3 With reference to , explain the pattern of results obtained between 0.25 mol dm–3 and 1.25 mol dm–3 of sodium hydrogencarbonate solution. The percentage change in dissolved oxygen for C. caroliniana at 0.00 mol dm–3 of sodium hydrogencarbonate solution is negative. Suggest reasons for this negative value. To minimise temperature changes, the student decided to use an LED lamp as a light source. LED lamps release very little heat energy. Explain the importance of minimising temperature changes in this experiment.
9700_s21_qp_41
THEORY
2021
Paper 4, Variant 1
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Photosynthesis is a complex process involving a light dependent stage and a light independent stage. Name the products of the light dependent stage that are needed in the light independent stage. Describe the role of chlorophyll b in photosynthesis. A student carried out an experiment to investigate the effect of light intensity and light wavelength on the rate of photosynthesis. • An aquatic plant, Elodea canadensis, was put into a beaker containing sodium hydrogencarbonate solution as a source of carbon dioxide. • To minimise changes in temperature, an LED lamp was used as a source of light. • The lamp was switched on and the number of bubbles released by the aquatic plant in 1 minute was counted. • The lamp was placed at seven different distances from the beaker to change light intensity. • Five replicates were carried out at each lamp distance. • All other variables were controlled. The student calculated the light intensity for each distance using 1 d 2. Table 5.1 shows the calculated light intensities for each distance. Table 5.1 distance between plant and lamp / m light intensity / 1 d 2 0.025 0.050 0.100 0.150 0.200 0.250 0.300 Complete Table 5.1 by calculating the light intensity for distance 0.100 m. At each distance from the lamp, the experiment was repeated using a red filter in front of the lamp to give a different wavelength of light. The experiment was repeated using a blue filter and then using a green filter. Each filter transmitted the same light intensity. The student calculated the mean rate of bubble production as a measure of the rate of photosynthesis. shows a graph of the results. 800 1000 1200 1400 1600 rate of photosynthesis / bubbles min–1 light intensity green light blue light red light white light Key: With reference to : • state the range over which light intensity is the limiting factor • explain why light intensity above this range is not limiting the rate of photosynthesis. At a light intensity of 1600, explain why different colour filters result in different rates of photosynthesis.
9700_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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Photosynthesis is affected by many environmental factors. Explain why light intensity can be a limiting factor in photosynthesis. The concentration of carbon dioxide (CO2) can also be a limiting factor. It has an effect on the Calvin cycle in the light-independent stage of photosynthesis. Ribulose bisphosphate (RuBP), triose phosphate (TP) and glycerate 3-phosphate (GP) are three important molecules in the Calvin cycle. shows how the concentration of GP changes when the concentration of CO2 is reduced from 0.04% to 0.008%. Complete by sketching the lines for RuBP and TP when the concentration of CO2 is reduced from 0.04% to 0.008%. time GP GP TP RuBP relative concentration of Calvin cycle molecules atmospheric CO2 0.04% reduced CO2 concentration 0.008% In very dry conditions, CO2 concentration can become the main limiting factor of photosynthesis in plants. Explain how very dry conditions cause CO2 concentration to become the main limiting factor of photosynthesis in plants. A factor that can limit the rate of photosynthesis is the rate of regeneration of RuBP. 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 in a greenhouse. • Light intensity, CO2 concentration and temperature were kept constant. • Mature plants were removed and dried to measure the biomass. shows the mean plant biomass for the wild type plants and GM Sox4 plants. mean plant biomass / g wheat plants wild type Sox4 Calculate the percentage change in mean plant biomass when Sox4 plants are grown compared to wild type plants. Show your working. percentage change = % Suggest and explain why Sox4 plants have a different mean plant biomass than wild type plants. Some soils may be deficient in nitrates. Suggest how nitrate deficiency could limit the quantity of SBPase made by Sox4 plants.
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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Use shows the results from two experiments carried out to investigate the effect of light intensity and carbon dioxide concentration on the rate of photosynthesis. light intensity / arbitrary units rate of photosynthesis /arbitrary units experiment 1 (25 °C 0.04% CO2) experiment 2 (25 °C 0.4% CO2) Describe and explain the results shown in for experiment 1. Describe and explain the difference between the results for experiment 1 and experiment 2. Examiner’s Use The optimum temperature for many plants living in temperate regions is approximately 25 °C. Explain why the rate of photosynthesis in these plants decreases at temperatures above 25 °C.
9700_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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The rate of photosynthesis at different wavelengths of light can be measured and plotted as a graph. This is called an action spectrum and is shown on . rate of photosynthesis wavelength of light / nm Describe and explain the effects of different wavelengths of light on the rate of photosynthesis. Name two products of the light-dependent stage of photosynthesis that are used in the light-independent stage. 1. 2. Describe how these two products are used in the light-independent stage of photosynthesis. The rate of photosynthesis is affected by factors other than the wavelength of light. These factors may act as limiting factors. Explain what is meant by the term limiting factor. Carbon dioxide concentration in the atmosphere may be a limiting factor in photosynthesis. Describe how carbon dioxide reaches the photosynthetic cells in a leaf.
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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Questions Discovered
75