Transpiration is the evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapour through the stomata.
Water moves through the xylem vessels in a continuous transpiration stream:
Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves. Water molecules are cohesive so water is pulled up through the plant.
The transpiration stream has several functions. These include:
- transporting mineral ions
- providing water to keep cells turgid in order to support the plant
- providing water to leaf cells for photosynthesis
- keeping the leaves cool by evaporation
Root hair cells
The root hairs are where most water absorption happens. They are long and thin so they can penetrate between soil particles, and they have a large surface area for absorption of water.
Water passes from the soil water to the root hair cell’s cytoplasm by osmosis. This happens because the soil water has a higher water potential than the root hair cell cytoplasm:
|Solution||Water potential||Concentration of dissolved solutes|
|Root hair cell cytoplasm||Low||High|