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Xylem Transport - Coggle Diagram
Xylem Transport
U1 Transpiration is the inevitable consequence of gas exchange in the leaf
Definition:
Transpiration is the loss of water and O2 from leaves and stem of plants
Gas Exchange:
When the stomata is opened and gas is exchange, water is lost from transpiration
Stomata:
Pores on the underside of the leaf which facilitate gas exchange
Regulation: Transpiration rate is regulated by the opening and closing of stomata
Guard cells
Opening caused by:
High luminous intensity (sunlight levels)
reduced CO2 concentration
Closing caused by
Water storage: hormone abscisic acid is produced, forcing closure to prevent dehydration
Darkness
Stomata open and close depending on the turgor pressure in the surrounding guard cells.
When guard cells take in water, turgor pressure increases, the cells swell causing them to bow outwards, thus opening the stoma
When the guard cells lose water, the turgor pressure decreases and the guard cells become flaccid, causing the stoma to close.
U2 Plants transport water from the roots to the leaves to replace losses from transpiration
Water is heated by the mesophyll in the sunlight and becomes vapour
Vapour leaves through the stomata
Loss of water generates negative pressure and a transpiration pull on water molecules in the xylem
higher rates of transpiration lead to a faster transpiration stream and higher rates of water uptake
cohesion tension theory
U4 The adhesive property of water and evaporation generate tension forces in leaf cell walls
The loss of water from the top of xylem vessels due to evaporatin lowers the pressure inside the xylem and pulls more water into it due to cohesion
Adhesion attracts water molecules to the walls of xylem and vice versa
Therefore as the water moving is moving upwards it pull inward on the walls of the xylem generating tension
U5 Active uptake of mineral ions in the roots causes absorption of water by osmosis
Mineral Uptake:
Water Uptake:
Water will follow the mineral ions into the root via osmosis – moving towards the region with a higher solute concentration
Inside the root, water will either move towards the xylem either via cytoplasm (symplastic) or via the cell wall (apoplastic)
Xerophytes: Plants that tolerate dry conditions
Adaptations: reduced, rolled leaves, thick+waxy cutivle,
U3 The cohesive property of water and the structure of the xylem vessels allow transport under tension
Lignin in the xylem helps it withstand pressure changes as water moves through the plant
