Question

In CAM plants, $C{O_2}$ required for photosynthesis enters the plant during –
A) Day time when stomata are open
B) Night when stomata are open
C) Night when hydathodes are open
D) Day time through lenticels.

Answer 1

Hint: CAM plants belong to family crassulaceae i.e. why they are termed as crassulacean acid metabolism. Examples of CAM plants are – Bryophyllum, Kalanchoe, Sedum, Cactus, Orchid, Portulaca and Pineapple etc.

Complete Answer:
- The most characteristic feature of these plants is that their stomata open at night and colored during light.
- CAM is a kind of adaptation in succulents to carry out photosynthesis without much loss of water.
- In night, stomata are open, the $C{O_2}$ combines with phosphoenol pyruvic acid (PEP) to form Oxalo acetic acid (OAA) in the presence of enzyme PEP-Carboxylase.
Phosphoenol pyruvic acid $C{O_2} + H_2^{}O \to \;Oxalo\;acetic{\text{ }}acid + {H_3}P{O_4}$
- Oxalo acetic acid is converted into malic acid by enzyme malic dehydrogenase. This reaction occurs in the presence of NADH.
$Oxalo\;acetic\;acid + \;NADH\; \to \;Malic\;acid\; + \;NA{D^ + }$
- The correct option is B. Night when stomata are open.

Note: CAM plants grow under extremely xeric conditions, fix atmospheric $C{O_2}$ in dark.