Photosynthesis Question 62

62. In leaves of $C_4$ plants malic acid synthesis during $CO_2$ fixation occurs in

[2008]

(a) epidermal cells

(b) mesophyll cells

(c) bundle sheath

(d) guard cells

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Answer : b

Hints & Solution

(b) In leaves of $C_4$ plants, malic acid synthesis during $CO_2$ fixation occurs in mesophyll cells. The mesophyll cells perform $C_4$ cycle and the cells of bundle sheath perform $C_3$ cycle. $CO_2$ taken from the atmosphere is accepted by phosphoenol pyruvic acid (PEP) present in the chloroplasts of mesophyll cells of these leaves, leading to the formation of a 4-C compound, oxaloacetic acid (OAA). This acid is converted to another 4-C acid, the malic acid which enters into the chloroplast of bundle sheath cells and undergoes oxidative decarboxylation yielding pyruvic acid (3C - compound) and $CO_2$.