Practise limiting-factor questions by interpreting photosynthesis rate graphs, explaining light, carbon dioxide and temperature effects, and judging controls.
Fig. 8.1 shows how the rate of uptake of carbon dioxide by a plant varies with temperature, at an optimum intensity of light on a clear day.
rate of uptake of carbon dioxide / arbitrary units (au)
Fig. 8.1
Suggest why the rate of carbon dioxide uptake levels off and then decreases after .
On Fig. 8.1, draw a curve to show the uptake of carbon dioxide on a cloudy day.
Chloroplasts isolated from leaf palisade cells can still function if they are suspended in a buffer solution. The buffer solution has the same water potential as the chloroplasts.
The dye DCPIP is a hydrogen acceptor that changes colour from blue to colourless when it becomes reduced.
Three test tubes were set up as shown in Table 7.2 and left for 20 minutes to allow any colour change to occur. The results are also shown in Table 7.2.
Table 7.2
Explain the results for test-tube 2.
Test-tube 1 is a control tube. Explain why test-tube 1 was included in the investigation.
Fig. 4.1 shows a diagram of a stoma, its guard cells and adjacent epidermal cells.
Fig. 4.1
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 hydrogen carbonate 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 Fig. 4.2.
Fig. 4.2
State why sodium hydrogencarbonate solution was used.
Suggest what factor, which may have an effect on the rate of photosynthesis, was not taken into account in this experiment.