A fish absorbs oxygen from the water that flows over its gills.
Two changes are described in the table.
| Change | Description |
|---|---|
| R | The fish pumps water over its gills more quickly. |
| S | The barrier between the water and the blood in the gills becomes thinner. |
Which statement explains how each change increases the rate at which oxygen diffuses into the blood?
R maintains a steeper oxygen concentration gradient; S shortens the diffusion distance.
R gives the oxygen particles more kinetic energy; S shortens the diffusion distance.
R maintains a steeper oxygen concentration gradient; S increases the surface area for diffusion.
R gives the oxygen particles more kinetic energy; S increases the surface area for diffusion.
102 exam-style questions on Edexcel GCSE Biology 8.1 Exchange surfaces and diffusion, covering 8.1.1 Introduction to exchange and transport, 8.1.2 Alveoli adapted for gas exchange, 8.1.3 Factors affecting rate of diffusion, and 8.1.4 Rate of diffusion using Fick's law. Each one has a worked solution and a mark scheme showing where the marks go.