Water transport in plants
- Created by: adele_26
- Created on: 15-05-16 16:24
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- Water Transport in Plants
- Transpiration
- The loss of water vapour from the leaves and stems.
- O2 moves out of leaves down a concentration gradient by diffusion out the Stomata.
- Affected by Light, Temperature, Humidity, Wind.
- O2 moves out of leaves down a concentration gradient by diffusion out the Stomata.
- Roots - leaves
- enters roots via osmosis and is transported up xylem to leaves.
- Evaporates from mesophyll cells along diffusion gradient.
- Cohesion-tension theory
- Water is cohesive- attracted to other H2O molecules so pulled up Xylem.
- Water evaporated at leaves- creates tension, pulling water up column.
- Water is adhesive- attracted to walls of xylem vessels.
- The loss of water vapour from the leaves and stems.
- Translocation
- Transport of organic compounds in Phloem from source to sink.
- PHLOEM LOADING
- Symplast route
- Through cytoplasm into sieve tubes via diffusion through plasmodesmata.
- Water follows sucrose- creates pressure and moves sucrose through Phloem (mass flow).
- Through cytoplasm into sieve tubes via diffusion through plasmodesmata.
- Apoplast Route
- Sucrose travels through cell walls into companion cells and sieve elements.
- Water also moves in via osmosis = build up of turgor pressure.
- Water carrying assimilates moves into sieve-tube elements and molve up or down plant to areas of low pressure by mass flow.
- Water also moves in via osmosis = build up of turgor pressure.
- In companion cells, sucrose moved into cytoplasm in active process.
- Hydrogen ions pumped out using ATP and return down conc. gradient via co-transport protein.
- Sucrose travels through cell walls into companion cells and sieve elements.
- Symplast route
- PHLOEM UNLOADING
- Sucrose unloaded at any point into cells- diffusion.
- Concentration gradient maintained.
- Loss of solutes in Phloem = rise in water potential.
- Water moves out by osmosis- some used in transpiration stream.
- Sucrose unloaded at any point into cells- diffusion.
- Symplast pathway
- Through living parts of cell- Cytoplasm.
- Cytoplasms connect through plasmodesmata
- Water moves via Osmosis
- Apoplast Pathway
- Through non-living parts (Cell walls).
- Water diffuses through cell walls- can carry solutes.
- From area of high hydrostatic pressure to low (mass flow).
- When water gets to epidermis, it's pathway is blocked by the casparian ***** and enters symplast pathway.
- Transpiration
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