Two small multicellular organisms, P and Q, have the same volume. Each organism is modelled as a cuboid, and all six faces are exposed to the surroundings. Oxygen enters each organism across its outer surface.
| Organism | Length in mm | Width in mm | Height in mm |
|---|---|---|---|
| P | 6.0 | 2.0 | 1.0 |
| Q | 3.0 | 2.0 | 2.0 |
Calculate how many times as large the surface area : volume ratio of organism P is compared with organism Q.
Show your working.
Suggest which organism is more likely to rely on diffusion across its outer surface without a transport system.
Use the dimensions and your answer to part (a) to explain your answer.
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.