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Plants have a special exchange surface in the soil called root hairs to absorb and
transport water.

Root hairs
are the
exchange surfaces in plants that are responsible for the
absorption of water and mineral ions. Plants constantly lose water by
the process of transpiration.…

Page 2

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As water is drawn into epidermal cell, it pulls more water along behind it due
to the cohesive properties of the water molecules. That creates a

Cohesion is the mutual attraction of molecules for one another. It is the
ability of water…

Page 3

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Casparian strip
Endodermal cells control substances passing from root to plant. Each endodermal
cell has A WATERPROOF LAYER (casparian strip). They are impermeable to
water and mineral ions and it blocks apoplast pathway. All substances must pass
through cell surface membrane of endodermal cells.

Passage of water into the xylem…

Page 4

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Mineral salts are actively transported to the xylem and this
requires energy. It takes place along carrier proteins in the cell surface
membrane. When mineral ions are actively transported into the xylem there is a
low water potential in the xylem, this creates a concentration gradient and water
moves into…

Page 5

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Mesophyll cells lose water to the air spaces
These cells now have a low water potential
than its neighbour and water moves
in by osmosis
The loss of water from neighbours lowers its
water potential and they in turn take in
water from their neighbours

In this way, a water…

Page 6

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the xylem and this causes the trunk to shrink in diameter. When transpiration
rate of low (during night), there is less tension in the xylem and so the diameter
of the tree trunk increases
If a xylem vessel is broken and air enters it, the tree can no
longer draw…


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