Question

Dry weight of leaf is maximum during
(a)Morning
(b)Noon
(c)Afternoon
(d)Night

Answer 1

Hint: The time during the day when the sun shines the most, at that time of the day, most of the transpiration (loss of water from aerial parts) happens in the plant and so, the least amount of water is found in the leaves.

Complete answer:
The dry weight of the leaf is maximum during the afternoon. During the afternoon, i.e. after 12 p.m. the sun is generally at the equator and during this time most of the water transpiration occurs in the plant. Since a high amount of water is evaporated from the leaf of the plant; it will have the maximum dry weight during this time of the day.

Additional Information: -The dry weight of the plant or leaf of the plant has its importance in many experimental works.
-Transpiration occurs mainly through the stomata of the leaves.
-It has been proposed that transpiration provides the energy to transport water in the plant through a mechanism known as transpirational pull.
-Excessive transpiration can be very injurious to a plant. It can lead to retardation of the plant growth and ultimately lead to death by dehydration.
-Stephen Hales, an English botanist, and physiologist were the first to measure transpiration.
-Due to darkness and internal water deficit, the stomata close and transpiration decreases.
So, the correct answer is, ‘Afternoon’.

Note: Transpiration is generally considered to be merely an unavoidable phenomenon because the openings of the stomata are necessary to admit carbon dioxide to the leaf interior and to allow oxygen to escape during photosynthesis. Hence, during such a process the water escapes in the form of water vapors from the leaves of the plant.