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Gas Exchange
Inplants, carbon dioxide is a raw material for photosynthesis, and oxygen is given off as a by-product. Therefore, you may think of gas exchange in plants as an inward movement of carbon dioxind and an outward flow of oxygen. This exchange occurs only in photosynthetic tissues rhen light is present. However, all plant tissues, both photosynthetic and nonphotosynthetic, take in oxygen for cellular respiration and give off carbon dioxide.
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As photosynthesis occurs in leaves, carbon dioxide enters and oxygen is given off. The photosynthetic cells are surrounded by a thin film of moisture.
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Carbon dioxide in the air enters a leaf through stomata. The carbon dioxide enters air spaces, dissolves in thethin film of moisture, and then diffuses into the cells. Oxygen, a air space, and leaves through stomata. There are great many palisade and spongy cells within each leaf. Taken together, these cells provide an enormous amount of surface area for gas exchange. Thus, photosynthsis occurs very efficiently.
แหล่งข้อมูล : Biology living systems. Page 457
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