Transpiration

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Biology
Transpiration: The evaporation of water from a plant
· Soil > root > xylem
· Root hairs > increased surface area
· Root cortex > endodermis > xylem
· Drawn into the roots via a water potential gradient
· High water potential > low water potential
Symplastic Pathway: The water goes through the cytoplasm, as all neighbouring cells are
connected through small gaps in the cell walls called plasmodesmata.
Apoplastic Pathway: The water goes through the cell walls which are very absobant, and
the water can simply diffuse through them and pass through the spaces between them,
too. This pathway provides the least resistance.
Casparian Strip: When the water reaches the endodermis if travelling along the
apoplastic pathway, its path is blocked by a waxy strip (the casparian strip), meaning the
water then has to take the symplastic pathway. This is useful, because it means the
water has to go through a cell membrane, which can control whether or not to let
substances dissolved in the water can pass through into the xylem.
Xylem Vessels: Transport water all around the plant. When it reaches the leaves, water
leaves the xylem and moves into the cells usually by the apoplastic pathway. The water
evaporates from the cell walls and into the spaces between the cells in the leaf. When
the stomata open, the water moves along the water potential gradient and into the air.
The loss of water from the plant is called transpiration.

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