Transport in Plants

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1

It is a type of diffusion in which water is absorbed by

solids (colloids) causing them to increase in volume.

E.g. absorption of water by seeds and dry wood.

2

The pressure due to the swelling of wood can split

rocks.

3

Seedlings are emerged out of the soil due to the

imbibition pressure.

4

Imbibition

is

also

diffusion

because

water

movement is along the concentration gradient.

ÏMBÏBÏTÏØÑ RËQÜÏRËS

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Difference in concentration gradient.

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Water potential gradient between the absorbent and the liquid imbibed.

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Affinity between the adsorbent and the liquid.

LØÑG DÏSTÅÑÇË TRÅÑSPØRT ØF WÅTËR

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Diffusion is a slow process. It accounts for only short distance movement.

E.g. movement of molecules across a typical plant cell (about 50 mm)

takes about 2.5 s.

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Long distance transport systems are necessary to move substances

faster across long distances.

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Movement of substances in bulk (en masse) from one point to another

due to pressure differences between two points is called mass (bulk)

flow. Water, minerals and food are generally moved by a mass flow

system.

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In mass flow, substances (in solution or in suspension) are swept along at

the same pace as in a flowing river. But in diffusion, different substances

move independently depending on their concentration gradients.