Biology [2 Mark Question Answer]

Given below is an experimental set up to study a particular process :
(i) Name the process being studied.
(ii) Why is the pot covered with a Jar?

Transpiration takes place by the following three ways:-
(i) Stomatal Transpiration: Stomata are pores present in the epidermis of the leaves. These normally remain open during the day time to take in carbon dioxide for photosynthesis. Simultaneously, water vapour diffuses out of the stomata. Approximately, 80-90\% of transpiration takes place through stomata.
(ii) Cuticular Transpiration: Cuticle is a thin waxy layer on the surface of the leaf. Some amount of water vapour escapes through it.
(iii) Lenticular Transpiration: In woody plants, the stem has openings on their surface called lenticels which is composed of loose mass of cells. Water vapour easily escapes through them.

Significance of transpiration
(i) It helps in the absorption of water from the soil.
(ii) Produces cooling effect.
(iii) Maintains cell turgidity.
(iv) Controls opening and closing of stomata.
(v) Helps in absorption of minerals from the soil.

Anti-transpirants are chemical substances that reduce the rate of transpiration. They are generally used to improve the efficiency of water utilisation by plants, without affecting the carbon dioxide uptake. Example - Phenyl Mercuric Acetate (PMA).

Roots continuously absorb a very large quantity of water. Transpiration is an effective method of removing excess water from the plant body. Thus, water transpired is the water absorbed, obviously the excess water.

In some plants, e.g. balsam, the leaves of the plants wilt during the mid-day. In such cases, the rate of transpiration during mid-day exceeds the rate of absorption of water by the roots. The cells, therefore, lose turgidity and wilts.

Rate of transpiration is more on a windy day than calm day because wind velocity increases the rate of transpiration as it increases the pressure gradient.

Balsam plants wilt during midday even if the soil is well watered. This is because the rate of transpiration during mid day exceeds the rate of absorption of water by the roots. The cells therefore, lose turgidity.

Antitranspirants are chemical substances that are used to reduce the rate of transpiration. By doing so they check the water loss through the stomata, so that they remain fresh for a long time.

In some xerophytes like cacti, leaves are modified into spines to reduce surface area for transpiration.

Due to the excessive hot and dry weather, more water evaporates from the leaves of a plant and thus, the rate of transpiration increases.