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Question

Which of the following statements are true and which ones are false? Give reason in support of your answer.

(a) Potometer is an instrument used for demonstration of transpiration occurring from the lower surface of a leaf.

(b) Hydathodes are similar to stomata in plant physiology.

(c) Atmospheric humidity promotes transpiration from a green plant.

(d) Some desert plants have sunken stomata on their leaves.

(e) Most transpiration occurs during midday.


Solution

(a)
False
Reason: Potometer is used to measure the rate of transpiration in a plant. Demonstration of transpiration occurring from the lower surface of a leaf is done by analyzing the changes in colour of pieces of dry cobalt chloride paper attached (and held in place) to the two surfaces of a leaf.

(b)
False
Reason: Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets exude out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water vapour. Stomatal openings are  regulated by guard cells.

(c)
False
Reason: Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.

(d)
True
Reason: Desert plants need to reduce transpiration as much as possible so as to survive in
the hot and dry environment. Hence some of them have sunken stomata as an adaptation to curtail
transpiration.

(e)
True
Reason: During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. During mid-day, the outside temperature is higher, due to which there is more evaporation of water from the leaves. Therefore more transpiration occurs during mid-day.


Biology
Concise Biology
Standard X

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