CAIE A Level Biology 9700 · Homeostasis
Table 1 shows the mean stomatal aperture of a plant species measured at different times of day under well-watered and water-stressed conditions.
| Time of day | Well-watered | Water-stressed |
|---|---|---|
| 06:00 | 2.1 | 1.2 |
| 12:00 | 8.7 | 2.8 |
| 18:00 | 6.3 | 2.0 |
Outline the mechanism by which guard cells regulate stomatal aperture. Use the data to explain the differences in stomatal aperture between well-watered and water-stressed plants.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.