A researcher measured the mean concentration of substance X in blood entering and leaving two organs of a mammal.
| Sampling site | Mean concentration of substance X in blood (mmol dm⁻³) |
|---|---|
| entering the liver | 4.7 |
| leaving the liver | 5.9 |
| entering the kidneys | 5.6 |
| leaving the kidneys | 4.8 |
Suggest the identity of substance X. Use the results and the role of transport in mammals to explain your answer.
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.