Biology AQA 3.2.7 The passage of water through a plant

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The passage of water through a plant, AQA specification point 3.27 revision

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WHA

WHAT YOU NEED TO KNOW ABOUT A DICOT: cortex root hair xylem (red squashed square) phloem (yellow dots)

The casparian strip is a waterproof layer, which causes appoplastic pathways to go symplastic

Symplastic pathways are through the cytoplasm

appoplastic pathways are across cell walls.

This is the movement of water from the root hair cell to xylem through the process of transpiration

Th

The casparian strip is located at the endodermis

TRANSPIRATION.

The

The movement of water through a plant, and the process of evaporation from the leaves.

LIGHT: causes the stomata to open to allow gaseous exchange, this means more water is lost through them by evaporation, during the night stomata close. Carbon dioxide is needed for photosynthesis in the plant which creates glucose for energy.

TEMPERATURE: Temperature increases the rate of evaporation because heat creates kinetic energy in molecules, which makes them form a gas.

HUMIDITY: There is a higher water potential in the air if it is humid.So less evaporation occurs meaning the rate of transpiration is lowered.

AIR MOVEMENT: The more windier it is, the more difficult it is for water molecules to remain inside the stomata so they go with the wind, this means that root pressure and transpiration occurs at a quicker rate

roo

root pressure: Due to active transport moving water molecules into the roots, there is an increase number of molecules which build up the pressure, this forces water up the xylem, water molecules are joined together by hydrogen.

Cohesion Tension Theory used to explain the movement of water through the xylem from the bottom to the top of plants. When water evaporates from the surface of a cell, tension is created, pulling water molecules up towards that surface. Due to the cohesiveness of water molecules, this tension is transferred the entire way down the xylem, effectively pulling water to the top of the plant.

Adhesion: Where Water molecules are attached together by hydrogen bonds, and hydrogen bonds attach them to the walls of the xylem

structure

transpiration

root pressure and cohesion

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