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A secondary school revision resource for OCR GCSE Additional Science about homeostasis and its importance

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Diffusion is the process by which useful materials and waste products move in and out of cells. Substances diffuse down a concentration gradient - from an area of high concentration to an area of low concentration.

Diffusion occurs in many living systems, for example the movement of carbon dioxide and oxygen in the lungs and in leaves.

Diffusion

Diffusion is a model that explains how material spreads in gases and liquids. It's an important idea in biology as it can explain how useful materials and waste products can move in and out of cells.

Diffusion occurs when molecules collide, causing them to spread out. This gives the effect that the substance is moving from an area of high concentration to an area of low concentration (or 'down a concentration gradient'). When the particles are evenly spread out diffusion appears to stop.

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Speeding up diffusion

Diffusion can be speeded up when:

particles move faster, eg when they're warmer

concentration difference is greater, eg by replacing air in the lungs with fresh air rich in oxygen

distance for diffusion is kept to a minimum, eg by having a thin layer of cells lining the lungs

the surface area for diffusion is increased eg by folding

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Diffusion is the process by which useful materials and waste products move in and out of cells. Substances diffuse down a concentration gradient - from an area of high concentration to an area of low concentration. Diffusion occurs in many living systems, for example the movement of carbon dioxide and oxygen in the lungs and in leaves.