Waste products of catabolism are used by green plants in their anabolic process Green plants do not excrete nitrogenous wastes, on the contrary they recycle breakdown products of nitrogen metabolism. Metabolism of plants is mostly carbohydrate based and its end products CO2 and water and far less harmful than the nitrogenous wastes produced by proteins metabolism in animals.
Certain substances which accumlate to levels in excess of plants need, such as water, carbon dioxide, oxygen and certain ions, are to be eliminated. Plants get rid of surplus water by losing it in vapour form which diffuse out through stomata.
This process is known as transpiration some land plants exude water from points called hydathodes found at the margins and tip of leaves. This loss of water in liquid form is known as Guttation. It is common in plants growing in tropical rain forests. Green plants in light release oxygen because rate of photosynthesis is much higher than the rate of respiration. In dark plants release carbon dioxide.
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