AQA GCSE Biology Key Definitions

Diffusion

• passive movement of particles from an area of high concentration to an area of low concentration
• the greater the difference in concentration, the faster the rate of diffusion
• example: oxygen required for respiration diffuses into cells and carbon dioxide produced by respiration diffuses out of cells

Osmosis

• the diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• (from an area where there's lots of water to where there is less)
• example: absorption of water by the root hair cells in plant roots

Active transport

• movement of particles from an area of low concentration to an area of high concentration using energy
• works against a concentration gradient
• a carrier protein molecule in a cell membrane transports the molecule and rotates around (using energy) to the other side of the membrane and releases the molecule
• needs energy from respiration (mitochondria release energy from respiration so active transport uses this energy)
• example: absorption of mineral ions by root hair cells in plant roots
• reabsorption of glucose in the nephron in the kidney