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| Gaseous Exchange in Plants |
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| In lower plants (and also protozoans) exchange of gases takes place through the general body surface as they are not highly modified or specialised. Also, the body surface allows the diffusion of gases. In higher plants the exchange of gases takes place through stomata. |
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| Stomata are openings generally present on the lower surface of the leaves through which the gases and water vapour diffuse in and out easily. The oxygen diffuses in through the stomata and then enters the leaf cells. Similarly, the carbon dioxide produced by the leaf cells diffuses out through the stomata. |
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| Gaseous Exchange in a Leaves |
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| In woody stems, the entire surface is covered by bark which is impervious to gases or water. However, there are certain openings or pores in the layer of bark. These are called the lenticels. They are visible slightly more raised than the general surface of the stem. At the base of the lenticels are loosely arranged cells which allow the diffused gases to pass through them. |
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| Lenticels on the Bark of a Tree Exchange Gases Between |
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| Outside Air and Tissues Underlying Bark |
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| Gases diffuse in and out of the general surface of the roots. The gases are found in the soil surrounding the roots. Plants which grow in salty water show specialised roots called the pneumatophores. These are roots growing out of the surface of water with numerous pores on their surface. |
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