GCSE Biology · Edexcel 1BI0 · Topic 1C
Transport in cells
Key points
- Diffusion: the net movement of particles from a higher to a lower concentration. It is passive (no energy from respiration needed).
- Osmosis: the net movement of water across a partially permeable membrane from a dilute solution (more water) to a more concentrated solution.
- Active transport moves substances against a concentration gradient, using energy from respiration and carrier proteins, e.g. root hair cells taking in mineral ions.
- Rate of diffusion increases with a steeper concentration gradient, higher temperature and larger surface area.
- Osmosis practical: put potato pieces in sugar or salt solutions of different concentrations, then find the percentage change in mass: .
- Plot % change against concentration; where the line crosses zero, the solution has the same concentration as the cells' contents.
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Cells constantly swap substances with their surroundings. This sub-topic covers the three ways things cross cell membranes, what controls how fast they move, and the classic practical with potato pieces in sugar solutions.
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