Which statement explains how the moist lining of an alveolus helps gas exchange?
It allows respiratory gases to react before crossing cell membranes.
It causes respiratory gases to move against their concentration gradients.
It causes respiratory gases to release energy for their own transport.
It allows respiratory gases to dissolve before crossing cell membranes.
42 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.