Revision: Plant Physiology >> Transpiration Biology (English Medium) ICSE Class 10 CISCE

The collapse of leaves and stems is frequently the result of excessive water loss through transpiration, which leads to wilting, the loss of turgidity in plant cells.

Loss of water vapour through the stomatal openings of the leaves of a plant is termed as transpiration.

Guttation is defined as the loss of water in the form of water droplets from the leaves of intact plants. It is also called exudation.

The largest amount of air that can be expelled following a maximum inspiration. It is the sum of TV, IRV, and ERV and ranges from 4100 to 4600 mL.

Transpiration is the process of loss of water in the form of water vapour from the leaves and other aerial parts of the plant.

A potometer is a device that measures the rate of water intake by a plant and this water intake is almost equal to the water lost through transpiration.

The epidermis secretes a viscous layer on the surfaces of leaves, which is known as the cuticle. Its primary function is to prevent excessive transpiration, thereby reducing water loss from the leaf surfaces.

Some plants may lose water or other fluids along with dissolved substances directly in liquid form and not as water vapour. This is known as exudation.

Hydathodes are specialised structures that facilitate the discharge of excess water from the tips of veins in the leaf. They facilitate the release of superfluous water in liquid form by alleviating hydrostatic pressure within the plant.

1. Stomatal transpiration is the loss of water vapour through minute openings (stomata) on the leaf surface, mainly for photosynthesis and cooling.
2. Process: Water evaporates from mesophyll cells → enters intercellular spaces → moves to sub-stomatal cavity → diffuses out through stomata.
3. Direction of Movement: Water vapour moves from a region of higher concentration inside the leaf to a lower concentration outside, by diffusion.
4. Transpirational Pull: Continuous evaporation creates a pull that draws water upwards from roots through xylem, even in tall trees.
5. Regulation: Opening and closing of stomata is regulated by turgidity of guard cells—open when turgid, close when flaccid. More transpiration occurs from the lower surface of dicot leaves.

1. Cuticular transpiration is the loss of water vapour through the waxy cuticle covering the leaf surface.
2. Factors: Thicker cuticle → less transpiration.
3. Adaptation: Desert plants have thick cuticles to reduce water loss.

1. Lenticular transpiration is the loss of water vapour through lenticels—small openings on the bark of older stems.
2. Structure: Lenticels are always open and not surrounded by guard cells.
3. Function: They allow gaseous exchange and minimal water loss by evaporation from exposed cell surfaces.
4. Comparison: The Least amount of transpiration occurs via lenticels compared to stomatal and cuticular transpiration.
5. Location: Found on woody stems, not leaves.

1. Guttation is the loss of water droplets through hydathodes at leaf margins in uninjured plants.
2. It occurs early in the morning or at night, especially in humid conditions when transpiration is low.
3. The exudate in guttation is mainly water with dissolved mineral salts.
4. Bleeding is the flow of plant sap (rich in sugars) from cut or injured parts.
5. Bleeding occurs in all plants after injury, aided by root pressure.