GCSE Biology - AQA

3.2.2 - Factors That Affect the Rate of Diffusion

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The term 'rate of diffusion' means how quickly a substance is diffusing (moving by diffusion) from one area to another.

The main factors that affect the rate of diffusion are:

- The size of the concentration gradient
- The temperature
- The surface area of the membrane (in situations where a substance is diffusing across a membrane)

Diffusion always occurs down a concentration gradient, meaning that the substance diffuses from the area of higher concentration to the area of lower concentration.

The rate at which diffusion occurs depends on the size of the concentration gradient - in other words it depends on how big the difference in concentration between the two areas is.

The larger the concentration gradient, the higher the rate of diffusion will be. In other words, the larger the difference in concentration between the two areas, the more quickly the substance will diffuse.

The larger the concentration gradient (the difference in concentration between the two areas), the higher the rate of diffusion.

Increasing the temperature means that the particles of the substance that is diffusing move around more quickly (they have more kinetic energy). Therefore, the rate of diffusion increases.

The higher the temperature, the higher the rate of diffusion.

In biology, we often have situations where a substance is diffusing across a membrane - from an area of higher concentration on one side of the membrane to an area of lower concentration on the other side.

In these situations, the surface area of the membrane has a big effect on the rate of diffusion. Increasing the surface area means that there is more space for particles of the substance to diffuse across. Therefore, the higher the surface area of the membrane, the higher the rate of diffusion.

The higher the surface area of the membrane, the higher the rate of diffusion.

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

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Which factors affect the rate of diffusion?

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How does the size of the concentration gradient affect the rate of diffusion?

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How does the temperature affect the rate of diffusion?

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How does the surface area of the membrane affect the rate of diffusion?

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