Water transport in plants
- Created by: Natasha Granville
- Created on: 19-03-18 18:47
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- Water transport in plants
- Water moves into the root hair cells
- by osmosis
- because soil water has a high water potential and cytoplasm of root hair cells has a low water potential
- evidence for the role of active transport in root pressure
- some poisons, e.g. cyanide, prevent production of ATP
- if cyanide is applied to root cells, root pressure disappears
- temperature affects root pressure
- suggests that chemical reactions are involved
- some poisons, e.g. cyanide, prevent production of ATP
- by osmosis
- Water moves across the root and into the xylem
- Symplastic pathway
- Apoplastic pathway
- through apoplast - cell walls and intercellular spaces
- by osmosis
- because root hair cell has higher water potential than adjacent cell
- water moves into adjacent cell, then this cell has higher water potential than next cell, so water moves to next cell etc.
- water moves out of root hair cell, water potential of root hair cell drops, more water is taken up by osmosis - maintains steep concentration gradient
- because root hair cell has higher water potential than adjacent cell
- when water reaches the endodermal cells, movement os water is stopped by the waxy casparian *****
- apoplastic pathway is inhibited and water is forced to move through the symplastic patyhway
- by osmosis
- through apoplast - cell walls and intercellular spaces
- Water moves up the xylem
- Capillary action
- water adheres to xylem
- water moves upwards
- water adheres to xylem
- Root Pressure
- minerals are actively pumped into the xylem
- this produces movement of water by osmosis (because it lowers the water potential of the xylem)
- this increase in water is called root pressure
- this produces movement of water by osmosis (because it lowers the water potential of the xylem)
- minerals are actively pumped into the xylem
- Transpiration stream (cohesion- tension theory)
- water evaporates from leaves, out through stomata
- lowers water potential in cell, water moves into cell from adjacent cell by osmosis
- this is repeated - water is drawn up the xylem in a continuous stream to replace the water that is lost - this is known as transpiration pull
- water molecules move by adhesion and COHESION
- this results in TENSION in the xylem, helping to move the water up
- water molecules move by adhesion and COHESION
- this is repeated - water is drawn up the xylem in a continuous stream to replace the water that is lost - this is known as transpiration pull
- lowers water potential in cell, water moves into cell from adjacent cell by osmosis
- Evidence for the cohesion tension theory
- changes in the diameter of trees at different times of the day
- high transpiration rate during the day,
- high tension in xylem
- tree shrinks in diameter
- high tension in xylem
- high transpiration rate during the day,
- if a xylem vessel is broken
- air is pulled into the xylem
- the plant can no longer move water up the stem as a continuous stream
- because the cohesive forces between water molecules have been broken
- the plant can no longer move water up the stem as a continuous stream
- air is pulled into the xylem
- changes in the diameter of trees at different times of the day
- Transpiration
- the loss of water vapour from the plant as it evaporates from inside the leaf and diffuses down a concentration gradient out through stomata
- Factors affecting transpiration
- increase temperature
- increase rate of photosynthesis
- increase co2 demans
- stomata open
- increase co2 demans
- increase KE of water molesules
- faster evaporation
- increase rate of photosynthesis
- increase light intensity
- increase numbers of stomata open
- increases rate of water vapour diffusing out of leaf
- increase numbers of stomata open
- increase water availability
- greater root pressure
- increase numbers/ size of stomata
- more water vapour can evaporate
- increase wind
- carries water vapour away
- decreases water potential outside of plant
- increases water vapour potential gradient
- increase rate of transpiration
- more water vapour can evaporate
- greater root pressure
- increases rate of water vapour diffusing out of leaf
- faster evaporation
- stomata open
- increase rate of transpiration
- increases water vapour potential gradient
- decreases water potential outside of plant
- carries water vapour away
- increase humidity
- decrease water vapour potential gradient
- decrease rate of transpiration
- decrease water vapour potential gradient
- increase temperature
- water evaporates from leaves, out through stomata
- Capillary action
- Water moves into the root hair cells
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