Some students investigate the effect of the surface area : volume ratio on the rate of diffusion. They use hydrochloric acid and gelatine cubes that have been stained blue using a pH indicator solution. The indicator turns red in acidic conditions. They put different sized cubes into three separate test tubes containing hydrochloric acid and time how long it takes for each cube to completely turn red. The table below shows the results of their investigation:
| Length of each side of the cube (mm) | Surface area : volume ratio | Time to completely change colour (seconds) |
|---|---|---|
| 3 | .................... | 45 |
| 6 | 1 : 1 | 150 |
| 9 | 2 : 3 | 380 |
Calculate the surface area : volume ratio for the cube with side length of 3 mm. Write your final ratio in its simplest integer form.
What conclusion can be made about the effect of surface area : volume ratio on the rate of diffusion?
17 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.