A technician prepares two similar plants, P and Q. One plant is left in darkness for 48 hours. The other plant remains in normal light, but the technician loses the labels.
A student covers part of one leaf on each plant with aluminium foil so that no light can reach the covered area. Both plants are then placed in bright light for 12 hours. The student tests the covered and uncovered areas of each leaf with iodine solution.
| Plant | Area covered with foil | Uncovered area |
|---|---|---|
| P | orange-brown | blue-black |
| Q | blue-black | blue-black |
The student concludes that the results for plant Q show that light is not needed for photosynthesis.
Explain which plant was left in darkness before the investigation and why the student's conclusion is not valid.
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.