Question

Give suitable explanations for the following: [5 MARKS]
(a) A higher rate of transpiration is recorded on a windy day rather than on a calm day
(b) Excessive transpiration results in the wilting of the leaves.
(c) Water transpired is the water absorbed.
(d) More transpiration occurs from the lower surface of a dorsiventral leaf.
(e) Cork and bark of trees help in preventing loss of water.

Answer 1

Each Part: 1 Mark

(a) A higher rate of transpiration is recorded on a windy day rather than on a calm day because on a windy day, the water vapour released during transpiration is removed faster and the area outside the leaf does not get saturated with water vapour. Consequently, the rate of transpiration increases.

(b) Excessive transpiration results in the wilting of the leaves because the rate of transpiration exceeds the rate of absorption of water by the roots. Consequently, the cells lose turgidity.

(c) All plants continuously absorb water through their roots. This water is conducted upward through the stem and is distributed to all the aerial parts including the leaves. Only a small quantity of this water (about 2%) is used by the plant in photosynthesis and other activities. The rest of it is almost lost to the atmosphere as water vapour. This loss of water as water vapour from the aerial parts of the plant is called transpiration. Thus, water transpired is the water absorbed.

(d) In a dorsiventral leaf, more stomata are present on the lower surface as compared to the upper surface. Therefore, more transpiration occurs from the lower surface of these leaves.

(e) Cork and bark are a homogeneous mass of flattened dead cells with a fatty substance that makes it almost impermeable to water and thereby help in preventing loss of water.