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Transport in cells

Diffusion, osmosis and active transport: how substances move into and out of cells.

41 exam questions · 105 marks

1.13 Diffusion What diffusion is, why it needs no energy, examples in the body (oxygen, carbon dioxide, urea), and the factors that change the rate: concentration gradient, temperature and surface area. AQA Edexcel OCR 1.14 Surface area to volume ratio and exchange surfaces How to calculate surface area to volume ratio, why large organisms need exchange surfaces and transport systems, and how the small intestine, lungs, gills, roots and leaves are adapted for exchange. AQA Edexcel OCR 1.15 Fick's law Fick's law: the rate of diffusion is proportional to surface area times concentration difference, divided by the thickness of the membrane, and how it explains the adaptations of alveoli, villi and gills. Separate only Edexcel 1.16 Osmosis What osmosis is, its effects on animal and plant cells (swelling, bursting, turgid, flaccid, plasmolysed), how to calculate percentage change in mass, and water potential (OCR). AQA Edexcel OCR 1.17 Required practical: osmosis in plant tissue How to investigate the effect of different concentrations of sugar solution on the mass of potato cylinders: method, variables, percentage change in mass, plotting the graph and finding the concentration of the cell sap. AQA Edexcel OCR 1.18 Active transport How active transport moves substances against a concentration gradient using energy from respiration: mineral ions in root hair cells and glucose in the gut, why mitochondria matter, and a comparison with diffusion and osmosis. AQA Edexcel OCR