ZIMSEC O-Level Biology (4025)

Movement of Substances In and Out of Cells: notes

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Diffusion: net movement of particles from high to low concentration, down a gradient. Needs no energy. Oxygen entering a cell is an example.
Osmosis: net movement of water through a partially permeable membrane from a dilute solution to a more concentrated one.
Active transport: movement against a concentration gradient using energy from respiration. Root hairs take up mineral ions this way.
Rate of diffusion rises with a steeper gradient, higher temperature and larger surface area.
Turgid cell: full of water and firm. Plasmolysed cell: lost water, membrane pulled from the wall.
Potato test: strips in strong sugar solution lose mass; in pure water they gain mass.