GCSE Biology · AQA 8461 · Topic 4.1.3
Transport in cells
Key points
- Diffusion is the net movement of particles from a higher to a lower concentration. It is faster with a steeper concentration gradient, a higher temperature and a larger surface area.
- Oxygen, carbon dioxide and urea all diffuse across cell membranes.
- Osmosis is the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
- In osmosis practicals, potato pieces gain mass in dilute solutions and lose mass in concentrated ones; use percentage change in mass to compare.
- Active transport moves substances against a concentration gradient and needs energy from respiration (e.g. root hairs taking in mineral ions, the gut absorbing sugar).
- Single-celled organisms have a large surface area to volume ratio, so diffusion is enough. Larger organisms need exchange surfaces: alveoli, villi, gills and leaves, which are thin, large and well supplied.
Topic notesPremium
Cells must constantly take in what they need and get rid of waste. This sub-topic covers the three ways substances cross membranes and explains why large organisms need special exchange surfaces and transport systems.
Unlock the full notes with Premium
Premium includes full topic notes, the paper generator, self-quizzes and progress tracking.
Practise this topicPremium
Premium members can generate an exam-style paper with a mark scheme, or take a quick quiz, on Transport in cells.