An interactive Year 7 Biology lesson exploring how substances move into and out of cells. Students develop the idea of diffusion using animated particle models, investigate the spread of a smell, and carry out a virtual coloured-agar diffusion experiment with timed observations. The lesson then applies these ideas to plants, including gas exchange, osmosis and an animated explanation of how water loss causes wilting. Activities follow pages 19–23 of the accompanying Cells lesson booklet and include retrieval, guided explanations, practical observation, checking and application tasks. simopsis