Question

Wilting of leaves in hot weather is due to
(a) Excessive transpiration.
(b) Excess of transpiration as compared to water absorption.
(c) Excessive water absorption by roots.
(d) None of the above.

Answer 1

Transpiration causes water loss from leaves through stomata, 99 % of absorbed water evaporates out through stomata, and the remaining 1% used in photosynthesis and plant growth. It gets influenced by light, pH, Carbon dioxide, and hormones.

Complete answer:
Water is very essential for plant growth because photosynthesis takes place in the presence of water. Transpiration helps to contribute to the cooling of leaves and also protects leaves from heat injury under high temperatures and intense light. Wilting of leaves and other plant parts are caused due to excess water loss in hot weather as compared to absorption. Due to this reason transpiration is also considered a necessary evil.

Additional Information: Stomata are tiny pores present in the epidermis of leaves and other soft aerial parts aid for gaseous exchange and transpiration. The lower surface of the dorsiventral leaf has a greater number of stomata while the isobilateral leaf number of stomata is equal on both sides. Cellulose microfibrils in the stomach help to open the stomata. In monocot guard cell is dumb-bell shaped while in dicot guard cell is bean-shaped. It is a photoactive type because normally it opens in the day and closes at night. Turgidity helps to create the pore with the absorption of water and with loss of water pore get closed. Some plants show rhythmic opening and closing of stomata which does not depend upon the environmental condition. Drought stress and solar radiation cause the production of abscisic acid by the closure of stomata.
So, the correct answer is Excess of transpiration as compared to water absorption.

Note: Antitranspirants are used to improve the efficiency of plants for water use because there are several disadvantages of transpiration in the plant due to water loss. Antitranspiratant is generally a chemical substance like phenylmercuric acetate, abscisic acid, silicon emulsion, plastic resins, and low viscosity waxes. Antitranspirants improve plant productivity under limited water supply.