Question:

Read the following statements about adaptations in desert plants and select the correct ones. (i) They have a thick cuticle on their leaf surfaces. (ii) They have stomata present in deep sunken pits. (iii) They use $CAM$ pathway for photosynthesis. (iv) They have flattened stems and large sized leaves. (v) Their stomata remain closed during the day.

Updated On: Jul 7, 2022

(i), (ii) and (iii)
(ii), (iii) and (v)
(i), (ii) and (iv)
(i), (ii), (iii) and (v)

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The Correct Option is D

Solution and Explanation

Xerophytes can withstand a prolonged period of drought, for this purpose they have certain peculiar adaptations. Thick cuticle is present in these plants. Stomata are generally sunken (deep seated) and open during night only. They have $CAM$ pathway for photosynthesis. Leaves are generally small and scaly. Sometimes leaves are modified into spines to reduce water loss through transpiration. They generally have an extensive root system and a smaller shoot system. Stems may be modified to phyllodades or dadodes to carry out the function of photosynthesis.

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Concepts Used:

C4 Pathway

Every photosynthetic plant moves according to the Calvin cycle, but in some plants, there is a primary stage to the Calvin Cycle called the C4 pathway. Plants in tropical desert regions commonly move accordingly to the C4 pathway. Here, a 4-carbon compound called oxaloacetic acid (OAA) is the first product of carbon fixation. Such plants are special and have specific adaptations as well.
The C4 pathway commences with a molecule called phosphoenolpyruvate (PEP) which is a three-carbon molecule. This is the primary CO₂ acceptor and the carboxylation, that takes place with the help of an enzyme called PEP carboxylase. They yield a 4-C molecule known as oxaloacetic acid (OAA).
In due course, it is converted into another 4-carbon compound called malic acid. Later, they are shifted from mesophyll cells to bundle sheath cells. Here, OAA is crumbled to yield carbon dioxide and a 3-C molecule.
The CO₂ thus formed, is utilized in the Calvin cycle, whereas the 3-C molecule is shifted back to mesophyll cells for regeneration of PEP.
Sugarcane, corn, and shrubs are some examples of plants that follow the C4 pathway. Calvin pathway is a very common pathway in both C3 plants and C4 plants, but it takes place only in the mesophyll cells of the C3 Plants and not in the C4 Plants.