Question

What is passive absorbtion

Answer 1

Answer:

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What is passive absorbtion__?

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Passive absorption of water: In actively transpiring plants, absorption of water takes place due to the forces developed at the transpiring surface of the plant (i.e., transpiration pull). In this type, the cells of the root do not play any part, and it does not consume energy, hence it is known as passive absorption. Thus in passive absorption, water is just pulled through the roots. This is the most common (96%) and rapid method.

Generally, water is absorbed by the root hairs when the osmotic concentration of their sap is high. This is made possible by transpiration taking place in the aerial parts of the plant. It continously removes water from the sap of the root hairs which, in turn, are in contact with the soil water.

In actively transpiring plants, water loss from mesophyll cells occurs and increases their osmotic concentration. It also results in the increase of their DPD. As a result, water from neighbouring cells enters in them by osmosis. These cells in turn, have now increased their osmotic concentration or lowered their water potential . Hence, water enters into them by osmosis from other adjacent cells. In this way mesophyll cells draw water from one another along the suction pressure gradient or DPD till it reaches the xylem of the leaf. Once water is drawn from xylem of the leaf, the entire water column in the xylem of the leaf, stem and the root is lifted. The movement of water is apoplastic.

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In this way, water is absorbed by the root hair due to diffusion pressure deficit gradient produced by transpiration that develops in the leaf. Root simply acts as a passage or channel for water movement.