- cells are living things, they constantly have to replace substances which are used up (e.g. food and oxygen) and remove other substances which would accumulate (e.g. carbon dioxide, waste products)
- Diffusion takes place automatically without the need for energy.
- Diffusion is the spreading of the particles of gas which results in a net movement from ahigher concentrated area to a lower concentrated area.
- The greater the difference in concentration, the faster the rate of diffusion.
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