A laboratory model of a fish gill was used to measure oxygen diffusing from water into a receiving fluid across an exchange surface.
| Test | Water temperature (°C) | Oxygen concentration in water (mg dm⁻³) | Oxygen concentration in receiving fluid (mg dm⁻³) | Oxygen diffusing in 1 minute (mg) |
|---|---|---|---|---|
| A | 15 | 8.0 | 4.0 | 0.40 |
| B | 25 | 8.0 | 4.0 | 0.60 |
The area and thickness of the exchange surface were the same in both tests.
Calculate how many times greater the rate of diffusion was in test B than in test A.
Another test, C, is carried out at 20 °C. The oxygen concentrations are the same as in tests A and B. All other conditions are unchanged.
Predict the mass of oxygen that would diffuse in 1 minute in test C. Explain your prediction.
A fourth test, D, is carried out at 25 °C. The oxygen concentration is 7.0 mg dm⁻³ in the water and 5.0 mg dm⁻³ in the receiving fluid. All other conditions are unchanged.
Explain whether the predicted rate of diffusion in test D is higher or lower than the rate in test A. Include a calculation of the predicted rate.
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.