Worksheets 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, with answers. Print them, or work through one on screen. Write your working straight onto the paper and Genie marks it question by question against the mark scheme.