A scientist compares leaves from two types of plant.
The leaves have the same surface area. The plants are grown under the same conditions.
The scientist counts the stomata in a 1 mm2 sample from each surface of the leaves. The scientist also measures the mean mass of water lost by the leaves in one hour.
| Plant type | Stomata in upper-surface sample | Stomata in lower-surface sample | Mean mass of water lost in one hour in mg\text{mg}mg |
|---|---|---|---|
| P | 15 | 85 | 18 |
| Q | 10 | 40 | 9 |
Calculate the total number of stomata counted in the two samples from plant type Q.
Describe what happens to the rate of water loss when stomata close.
Explain why the leaves of plant type P lost water at a greater rate than the leaves of plant type Q.
114 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.