Question

Define and explain the transpiration, its factors and importance?

Answer 1

• The loss of water in the form of vapour from aerial parts of the plants, especially

through stomata is called transpiration.

• Potometer is used to measure the rate of transpiration.

• The difference of osmotic pressure is present between lower and upper parts of

a plant. This difference produces a pull or tension, which pull the water form high

pressure to lower pressure. This pull or suction force is produced in xylem tissue

and is called transpiration pull.

• Due to transpiration pull of water molecules, water moves up in xylem as an

unbroken channel called transpiration stream. 

Factors affecting the transpiration:

Temperature: -

 i) High temperature increases the rate of transpiration.

 ii) Low temperature decreases the rate of transpiration.

Humidity: -

i) In dry conditions or low humidity the rate of transpiration increases.

ii) In wet conditions or high humidity the rate of transpiration decreases.

Light: -

i) In day time, in presence of light stomata remains open. They cause

increase in rate of transpiration.

ii) In night time, in darkness stomata remain closed. They cause decrease in

rate of transpiration.

Atmospheric Pressure: -

i) Low atmospheric pressure increases the rate of transpiration.

ii) High atmospheric pressure decreases the rate of transpiration.

Importance of transpiration:

• Transpiration is very important in the plant life as it provides the forces to pull the

sap up in the xylem vessels form root to the leaves.

• Transpiration also keeps the cell surface moist to facilitate the exchange of gases

in dissolved state.

• Tiny openings present on the lower side of leaves are called stomata. Each stoma

is surrounded by sausage shaped cells called guard cells.

 i) Stomata remain open when guard cells are turgid.

 ii) Stomata remain close when the guard cells loose their turgidity.