A technician places microscopic algae in an apparatus that collects the oxygen released in five minutes. The carbon dioxide concentration is kept high and constant, and the temperature is kept at 10 ∘C10\ ^\circ\text{C}10 ∘C.
The technician changes the light intensity. The table shows the results.
| Light intensity in arbitrary units | 100 | 200 | 300 | 400 | 500 | 600 |
|---|---|---|---|---|---|---|
| Volume of oxygen released in five minutes in cm3\text{cm}^3cm3 | 0.8 | 1.6 | 2.4 | 3.0 | 3.2 | 3.2 |
Which statement explains why the volume of oxygen released is the same at light intensities of 500 and 600 arbitrary units?
The low temperature is now limiting the rate of photosynthesis.
The oxygen has become a limiting reactant for photosynthesis.
The algae have stopped respiring at the higher light intensity.
The light intensity is still limiting the rate of photosynthesis.
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.