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Biology X - Transpiration Cheat Sheet by

Important Notes On the Chapter- Transpiration for Exams

Important Defini­tions

The process of loss of water in the form of water vapour from the leaves and other aerial parts of plant is called Transp­ira­tion.
Ganong's Potometer is a device which measures the rate of water intake by a plant.
Stomatal Transp­iration is a type of transp­iration which occurs from the leaves through stomata
Cuticular Transp­iration is a type of transp­iration which occurs directly from the surface of the leaves and stems
Lenticular Transp­iration is a type of transp­iration which occurs from the lenticels which are the minute openings on the surface of the old woody stems
Special pore-b­earing structures present on the margins of leave to allow exudation are called Hydathodes
Guttation is the loss of water as droplets along the margin of leaves through hydathodes
Bleeding is the direct flowing out of plant sap from any cut surfaces in case of injury.

Adapta­tions To Reduce Excessive Transp­iration

Sunken Stomata- The stomata may be sunken or covered by hairs. Eg: Nerium
Fewer Stomata- No. of stomata may be reduced
Narrow Leaves- Leaves may become narrower to reduce surface area. Eg: Nerium
Reduced Exposed Surfaces- Leaves may get wavy, rolled or folded to reduce exposed surface.
Loss of Leaves- Leaves may be dropped or absent or changed into spines. Eg: Cacti
Thick Cuticle- Leaves may be covered by thick cuticle. Eg: Banyan & most evergreen trees.

Ganong's Potomenter

Precau­tions in use of Potometer:
Limita­tions in the use of Potometer:
1. The potometer should be made completely water-­tight
1. Introd­uction of air bubble is not very easy
2. The twig should be cut obliquely so that it allows larger surface for water intake and avoid suction of air bubble into the twig under water which will stop the absorption of water into the xylem
2. Twig may not remain fully alive for a long time
3. Any changes in the outside air temper­ature may affect the position of air bubble in the capillary tube.

Ganong's Potomenter

Signif­icance Of Transp­iration

Cooling Effect
Evapor­ation causes cooling. Hence, transp­iration helps plants in hot sunny days to cool.
Suction Force
Provides Transp­iration Pull which is respon­sible for the upward movement of water in tall plants
Distri­bution of Water & Mineral Salts
Since leaves are present at the tips of all branches, transp­iration helps to draw water or minerals towards them and thus helps in their distri­bution throughout the plant's body.

Factors Affecting Transp­iration

Intensity Of Sunlight
Since during the day, stomata are open to facilitate inward diffusion of CO2 for photos­ynt­hesis & are closed at night. Therefore more transp­iration occurs during the day
Increase of temper­ature allows more water to evaporate. Higher the temper­ature, more is the transp­ira­tion.
Velocity of Wind
Transp­iration increases with the velocity of wind. The faster the wind blows, more is the the transp­iration from the surface of leaves.
Transp­iration is reduced if the air outside is humid since high humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transp­ira­tion.
Carbon Dioxide
Increase in CO2 level over normal 0.03% causes stomatal closure, resulting in decrease of transp­irt­ation
Atmosp­heric Pressure
Rate of Transp­iration increases with the decrease in atmosp­heric pressure.


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