A scientist studies two aquatic organisms. Organism P is single-celled and organism Q is multicellular. Both organisms use oxygen at the same rate per unit volume. The concentration of oxygen is higher in the surrounding water than inside either organism.
| Organism | Outer surface area in mm² | Volume in mm³ | Greatest diffusion distance from the outer surface in mm |
|---|---|---|---|
| P | 0.060 | 0.0010 | 0.050 |
| Q | 600 | 1000 | 5.0 |
A scientist claims that organism P can obtain enough oxygen by diffusion across its outer surface, but organism Q needs a specialised exchange surface and a transport system.
Use calculations based on the data to explain the scientist's claim.
The scientist compares two possible exchange surfaces for organism Q. The temperature and membrane thickness are the same for both exchange surfaces.
| Exchange surface | Total surface area in mm² | Oxygen concentration in the water next to the surface in mg/dm³ | Oxygen concentration just inside the surface in mg/dm³ |
|---|---|---|---|
| A | 2400 | 7.0 | 1.0 |
| B | 1200 | 3.0 | 1.0 |
Explain which exchange surface would allow oxygen to diffuse into organism Q faster.
140 exam-style questions on AQA GCSE Biology 1.3 Transport in cells, covering 1.3.1 Diffusion, 1.3.2 Osmosis, and 1.3.3 Active transport. Each one has a worked solution and a mark scheme showing where the marks go.