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A Handbook of Biology

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The water movement through the root layers is ultimately symplastic

in the endodermis. This is the only way water and solutes can enter the

vascular cylinder.

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In young roots, water enters directly into the xylem vessels and tracheids.

These are non-living conduits and so are parts of the apoplast.

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Some plants have additional structures for water and mineral absorption.

E.g. Mycorrhiza is a symbiotic association of a fungus with a root system.

The fungal filaments form a network around the young root or they

penetrate root cells. The hyphae absorb mineral ions & water from soil.

The roots provide sugars and N-containing compounds to mycorrhizae.

Some plants have an obligate association with the mycorrhizae. E.g. Pinus

seeds cannot germinate and establish without mycorrhizae.

WÅTËR MØVËMËÑT ÜP Å PLÅÑT

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Water moves up a stem against gravity. So it needs energy.

RØØT PRËSSÜRË

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As various ions from the soil are actively transported into the vascular

tissues of the roots, water follows (its potential gradient) and increases

the pressure inside the xylem. This positive pressure is called root pres-

sure.

(AIPMT 2015)

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It helps to push up water to small heights in the stem.

(AIPMT 2015 cancelled)

ËXPËRÏMËÑT TØ PRØVË ËXÏSTËÑÇË ØF RØØT PRËSSÜRË:

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During early morning, having atmospheric moisture,

cut a soft plant stem horizontally near the base. Drops

of solution ooze out of the cut stem. This is due to the

positive root pressure.

(AIPMT MAINS 2011)