Question

Describe the mechanism of water absorption by plants.
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Answer 1

There are two methods of absorption of water by plants. These are as follows:

$\bigstar \: \: \underline{ \red{\sf Active \: absorption \: of \: water:}}$

• In active absorption, the wall of root hair imbibes large amount of water which enters the root hair by the process of osmosis.
• This water moves from root hair to the cortical coils and from one cortical cell to another by the gradient of wer potential diffusion pressure deficit).
• Root hair and conical cells of the root possess higher O.P. than that of the soil. Due to which, water moves to cell to cell by ons. This is called gradient of water potential.
• When water enters the root halt cell by masis, it becomes fully turgid and its D.P.D. becomes zero.
• Temer cortical cell possess higher DPD therefore water moves into this cell by osmosis.
• Consequently the inner cortical cell becomes turgid and its D.P.D. becomes zero
• Water from the cell moves to the next inner cell. Hence, cach cell becomes alternately turgid and flaccid and water moves from cell to cell cortex.
• Metabolic energy is required to maintain high O.P. Hence, the process is called active absorption.

$\bigstar \: \: \underline{ \pink{\sf Passive \: absorption \: of \: water:}}$

• In passive absorption, living cells of root do not play any important role in water absorption.
• When the leaf looses water due to transpiration, it develops water deficit or suction pressure. To overcome this deficit,it draws water from the petiole.
• The petiole in turns draw from the stem and the stem draws from the root. The suction force is thus transmitted from veins to root hair.
• The root system behaves as a physical absorbing organ through which water is absorbed due to suction pressure developed in roots owing to transpiration.
• There is no penduare of metabolic energy. hence the process is considered as passive absorption.