B3 1.8 Exchange in plants

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Animals aren't the only living organisms that need the exchange materials. Plants rely heavily on diffusion to get the carbon dioxide they need for photosynthesis. They use osmosis to take water from the soil and active transport to obtain mineral ions from the soil. Plants have adaptations that make these exchanges as efficient as possible.

Gas exchange in plants

Plants need carbon dioxide and water for photosynthesis to take place. They get the carbon dioxide they need by diffusion through their leaves. The flattened shape of the leaves increase the surface area for diffusion. Most plants have thin leaves. This means the distance the carbon dioxide has to diffuse from the outside air to the photosynthesising cells is kept as short as possible. 

What's more, leaves have many air spaces in their structure. These allow carbon dioxide to come into contact with lots of cells and give a large surface area for diffusion.

However, there is a problem. Leaf cells constantly lose water by evaporation. If carbon dioxide could diffuse freely in and out of the leaves, water vapour would also be lost very quickly. Then the leaves - and the plant - would die.

The leaf cells do not need carbon dioxide all the time. When it is dark, they don;t need carbon dioxide because they are not photosynthesising. Sometimes light is a limiting factor on the


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