Answer»
- The mineral salts REMAIN in the soil solution in dissociated condition. The essential ions are ABSORBED in different amounts by the root hairs and are then trans-located through the xylem stream to the different parts of the plant body.
- Previously, it was assumed by plant physiologists that inorganic salts were passively absorbed en mass along with water. But at present it is consistent with the notion that ions are absorbed by different mechanisms. Time to time different theories have been proposed by different workers to explain the MECHANISM of ion absorption.
- Early workers continuously produced physical mechanisms and models to explain salt absorption. Finally, it has been shown that salt absorption is largely dependent on metabolic energy, i.e., the uptake of salt is predominantly active.
- There are two major mechanisms for ion uptake — non-mediated uptake and mediated uptake. An ion, like any other body, will move in a given DIRECTION only if driven by some force.
- If ion transport in and out of cells occurs spontaneously down a gradient of electrochemical potential energy, it is called PASSIVE uptake and when ion driven up such a gradient by some process directly coupled to metabolism, it is called metabolic or active uptake. Non-mediated transport is always passive whereas mediated transport may be either passive or active.
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