Transpiration - this an important process for a plant!


This process of 'sucking up' of minerals and water by the xylem is called transpiration. It is just like sucking up a straw.  

Water and dissolved minerals are transported, through the Xylem, from the root to the leaves.



The transpiration ('sucking up') is caused by the evaporation of water inside the leaves to the surrounding air.

The water vapour passes out of stomata by diffusion.

This leads to a lack of water in the spongy mesophyll cells of the leaves.

The lost water is then replaced by more water from the xylem which in turn draws up more from the roots.

Transpiration benefits the plants in two ways:

  • Replaces lost minerals from the soil.
  • It has cooling effect on the plant -just like animals sweating.






Transpiration Stream


Factors affecting the speed of transpiration.

Amount of light - more light will increase transpiration as rate of photosynthesis increase.

Temperature - increased temperature increases both evaporation and photosynthesis, thus increasing transpiration.

Extent of air movement - increased air movement increases evaporation, thus increasing transpiration.

Humidity of the surrounding air - decreased humidity increases evaporation, thus increasing transpiration.

The condition of stomata - Turgid stomata allows more water to escape by diffusion, hence increasing transpiration.



From the above information, it is quite apparent that the highest rate of transpiration occurs during sunny, hot, dry and windy conditions.

Perfect conditions for putting your washing out!washing


Remember: The TURGIDITY (fluid pressure) of the cells help a  plant to stay upright and keep leaves firm.

When plants have ample supply of water, all their cells 'suck up' water into themselves by osmosis and turn turgid.

The 'watery' content of vacuoles in the cells start to press against the cell wall, just like tire tube against the tire, and so gives support to the plant tissue.

Turgor pressure also help the leaves to stay 'stiff'.  You have probably seen this with potted plant, if you don't water it for some weeks, the plant starts to 'wilt' and the leaves 'droop'.  This is due to the fact that cells start to lose water and thereby lose their turgor pressure.


Transport System in Plants


Tags:Photosynthesis, Turgidity, Osmosis, Turgor, Stomata, Transpiration



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