Sea lettuce is an alga. A sample of sea lettuce is kept in seawater at a constant light intensity and temperature. At 0 minutes, the concentration of dissolved carbon dioxide in the seawater is increased. The volume of oxygen produced in successive two-minute periods is recorded.
| Time after the carbon dioxide concentration was increased in minutes | Volume of oxygen produced in cm³ |
|---|---|
| 0–2 | 0.7 |
| 2–4 | 1.1 |
| 4–6 | 1.5 |
| 6–8 | 1.5 |
A student says that the volumes for 0–2 minutes and 2–4 minutes should not be used to estimate the rate of photosynthesis at the higher carbon dioxide concentration.
Which statement gives the best reason?
Light intensity was the limiting factor during these periods.
The rate of oxygen production had not yet become steady.
The alga had not yet started to photosynthesise.
These two volumes are anomalous results caused by measurement errors.
87 exam-style questions on Edexcel GCSE Biology 6.1 Photosynthesis, covering 6.1.1 Photosynthetic organisms as producers, 6.1.2a Limiting factors on the rate of photosynthesis, 6.1.2b Interactions of limiting factors on photosynthesis, and 6.1.3 Inverse square law and light intensity. Each one has a worked solution and a mark scheme showing where the marks go.