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What is transpiration?

Plant needs water for carrying out all the important functions. The route of water is from the soil up to the leaves . Certain processes are involved and transpiration is the major one accounting for more than 90% to the transport of water. The process is basically defined as the movement of water from the roots to the aerial parts of the plants from  where it evaporates and creates a cooling effect.
Roots are widely spread into the soil and diffuse the water into it from that soil. There is an extensive channel of xylem tubes in the roots which extend up till the stem and then the leaves. Water absorbed through the roots is taken up to the leaves through this xylem channel.
All the water requirements of the plants are fulfilled by the water brought up by the transpiration pull, for example photosynthesis where water is one of the important reactants. Water molecules have special affinity with each other and with the walls of the xylem vessels which are referred as the cohesion and adhesion forces, which binds them with each other so they can flow in a stream
There are a number of factors that influence the rate of transpiration. These include humidity, if the humidity is higher the transpiration rate will decrease , as it is a relative process, water tends to transpire better in dryer conditions . second temperature, if the outside temperature is high water will transpire at a faster rate. Basically dry conditions establish a water concentration gradient that favors more movement of water into the dry environment from the plant. Similarly soil moisture is another factor, only if there is enough moisture content in the soil then the water can be absorbed from the soil through the roots and made a part of the transpiration stream
The major site or gate through which water enters and leaves the plant cell is stomata. The opening of the guard cell of the stomata itself is controlled by the water In them. The guard cells are open only when there is enough water inside them .Also note that transpiration can occur from any of the aerial parts of the plants be it the stem or the leaves.

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