A scientist places a culture of green algae in a sealed transparent chamber containing water. A carbon dioxide sensor records the concentration of dissolved carbon dioxide.
A second, identical chamber contains the same volume of water but no algae. This is the control.
Both chambers are kept in the light for 2 hours, in darkness for 2 hours and then in the light for another 2 hours.
| Time in hours | Conditions during the previous 2 hours | Carbon dioxide concentration in chamber with algae in mg dm−3\text{mg dm}^{-3}mg dm−3 | Carbon dioxide concentration in control chamber in mg dm−3\text{mg dm}^{-3}mg dm−3 |
|---|---|---|---|
| 0 | – | 12.0 | 12.0 |
| 2 | light | 7.0 | 12.0 |
| 4 | dark | 10.0 | 12.0 |
| 6 | light | 5.0 | 12.0 |
Calculate the net rate at which the carbon dioxide concentration decreased in the chamber with algae during the first 2 hours. Give your answer in mg dm−3 h−1\text{mg dm}^{-3}\text{ h}^{-1}mg dm−3 h−1.
A student concludes that the answer to part (a) is the rate at which photosynthesis used carbon dioxide.
Evaluate the student's conclusion.
Calculate the net rate of change in carbon dioxide concentration in the chamber with algae during each of the intervals from 2 to 4 hours and from 4 to 6 hours. Compare the rates and use them to draw a conclusion about the processes in the algae.
A student suggests that light alone causes the carbon dioxide concentration to decrease. Evaluate this suggestion using the control results.
117 exam-style questions on OCR GCSE Biology 1.4 Photosynthesis, covering 1.4.1 Photosynthesisers as biomass producers, 1.4.2 Factors affecting the rate of photosynthesis, and 1.4.3 Limiting factors in photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.