A scientist treats one area of a leaf with solution Q. Solution Q affects only the guard cells. Another area of the same leaf is left untreated.
The results are shown in the table.
| Leaf area | Number of open stomata per 100 stomata examined | Rate of gas exchange (mm3 cm−2 min−1\text{mm}^3\ \text{cm}^{-2}\ \text{min}^{-1}mm3 cm−2 min−1) |
|---|---|---|
| Untreated | 80 | 1.6 |
| Treated with solution Q | 25 | 0.5 |
Use the results to explain how solution Q affects the function of the guard cells.
The solution is washed off. The number of open stomata increases to 60 per 100 stomata examined.
Assume that the rate of gas exchange is directly proportional to the number of open stomata.
Calculate the predicted rate of gas exchange.
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.