GCSE Biology - AQA

3.2.2 - Factors That Affect the Rate of Diffusion

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Factors That Affect the Rate of Diffusion

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)

The larger the concentration gradient, the higher the rate of diffusion

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.

Diagram illustrating the relationship between concentration gradient and rate of diffusion. At the top of the diagram there is a box. In the left half of the box there are many small circles, representing particles. In the right half there are only a few particles. There is a large arrow pointing from the left half to the right half of the box. This part of the diagram is labelled, "Large concentration gradient. High rate of diffusion". Beneath this, there is another box. This time, the left side only has slightly more particles than the right side. There is a small arrow pointing from the left side to the right side. This part of the diagram is labelled, "Small concentration gradient. Low rate of diffusion".

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

The higher the temperature, 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.

Diagram illustrating the relationship between temperature and rate of diffusion. At the top of the diagram is a box containing some particles (small circles). There are more particles in the left half of the box than in the right half. The box is red to illustrate that it is hot. There is a large arrow, representing diffusion, pointing from the left half of the box to the right half. This part of the diagram is labelled, "High temperature. High rate of diffusion". Below this is the same box again with the same distribution of particles, but this time the box is blue to illustrate that it is cold. The diffusion arrow is much smaller this time. This part of the diagram is labelled, "Low temperature. Low rate of diffusion".

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

The higher the surface area of the membrane, 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.

Diagram illustrating the relationship between the surface area of the membrane and the rate of diffusion. At the top is a drawing of a cell with many particles (represented by small circles) inside it and a few circles outside it. The cell membrane of the cell is highly folded, giving it a large surface area. There is a large arrow representing diffusion of particles out of the cell. This part of the diagram is labelled, "High surface area. High rate of diffusion". Below this is a drawing of a cell in a similar situation, but this cell's membrane is much less folded, and therefore has a much smaller surface area. The diffusion arrow is much smaller. This part of the diagram is labelled, "Low surface area. Low rate of diffusion".

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

Flashcards

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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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