Some students investigate the effect of the surface area to volume ratio on the rate of diffusion using agar cubes.
They use agar cubes stained with universal indicator and place them in an alkaline solution, timing how long it takes for each cube to completely change color.
The table below shows their results:
| Length of side of cube (mm) | Surface area : volume ratio | Time to completely change color (seconds) |
|---|---|---|
| 3 | .................... | 45 |
| 6 | 1:11 : 11:1 | 180 |
| 9 | 2:32 : 32:3 | 405 |
Calculate the surface area : volume ratio for the cube with sides of 3 mm3\text{ mm}3 mm.
State the relationship between the surface area : volume ratio of a cube and the rate of diffusion.
A medical condition causes the microscopic air sacs (alveoli) in the lungs to merge, forming larger but fewer air sacs. Explain the impact of this condition on the diffusion of oxygen into the blood, using the concepts demonstrated in this investigation.
Explain why animal cells, such as red blood cells, will swell and burst (undergo lysis) when placed in a solution with a very high water potential (such as pure water), whereas plant cells do not burst.
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.