Transport in Plants

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At night and early morning, evaporation is low. So

excess water collects in the form of droplets around

special openings of veins near the tip of grass

blades, and leaves of many herbaceous parts.

Such water loss in liquid phase is called guttation.

(NEET 2020)

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Root pressure can only provide a modest push

in the water transport. They have no major role

in water movement up tall trees. Root pressure

re-establish

the

continuous

chains

of

water

molecules

in

the

xylem

which

often

break

under

the

tensions

created

by

transpiration.

(AIPMT 2015)

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In most plants, majority of water transport

occurs by transpiration pull.

TRÅÑSPÏRÅTÏØÑ PÜLL

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In plants, the water flow upward through the xylem achieves fairly high

rates (up to 15 m/hr).

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Water is mainly ‘pulled’ through the plant, and that the driving force

for this process is transpiration. This is known as cohesion-tension-

transpiration pull model of water transport.

TRÅÑSPÏRÅTÏØÑ

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It is the evaporative loss of water by plants through the stomata in the

leaves.

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Less than 1% of the water reaching the leaves is used in photosynthesis

and plant growth. The remaining is lost by transpiration.

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Transpiration can be studied using cobalt chloride paper. It turns colour

on absorbing water.