If the climate of a region is completely cloudy, what will be the effect on the transpiration rate of plants there?

Correct answer: The rate will become very slow

Direct answer: B. Transpiration is the loss of water vapour mainly through stomata in leaves. Cloud cover usually reduces incoming sunlight, so leaf temperature and the energy available for evaporation are lower. Cloudy conditions also commonly keep the surrounding air more humid. When air humidity is high, the difference in water-vapour concentration between the moist leaf interior and outside air becomes smaller, so diffusion of vapour slows. Reduced wind may further limit removal of moist air, although local weather can vary. A is wrong because strong sunlight usually promotes faster transpiration, not complete cloudiness. C is wrong because light and humidity are important controlling factors. D is an unjustified extreme; plants may continue photosynthesis and transpiration at lower rates. Memory cue: less light plus more humidity generally means slower transpiration.