Marine ecologists investigate photosynthesis by microscopic algae in seawater.
They fill equal-volume chambers from the same well-mixed seawater sample. One chamber is transparent. The other is covered with a light-proof material. The closed chambers are held side by side at the same depth and temperature for six hours of daylight.
The ecologists assume that the amount of oxygen used in respiration is the same in both chambers. The table shows the mean results from repeated chambers.
| Chamber | Light entering chamber | Initial dissolved oxygen concentration (mg dm−3\text{mg dm}^{-3}mg dm−3) | Final dissolved oxygen concentration (mg dm−3\text{mg dm}^{-3}mg dm−3) |
|---|---|---|---|
| transparent | daylight | 7.2 | 9.0 |
| light-proof | none | 7.2 | 6.3 |
Explain the difference between the final dissolved oxygen concentrations in the transparent and light-proof chambers.
Calculate the amount of oxygen produced by photosynthesis per dm3\text{dm}^3dm3 of seawater during the six hours. Use the results from both chambers.
During a repeat of the investigation, part of the light-proof covering slips and light reaches the algae in that chamber. The chamber remains closed.
Suggest how this would affect the calculated amount of oxygen produced by photosynthesis. Explain your answer.
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.