Question

CAM helps the plants in-
A) Reproduction
B) Secondary growth
C) Conserving water
D) Disease resistance

Answer 1

Hint: Certain plants, especially succulents which grow under extremely xeric conditions, fix atmospheric $C{O_2}$ in dark. Since the process was first observed in plants belonging to the family crassulaceae, it was termed crassulacean acid metabolism (CAM).

Complete Answer:
– Plants which carry out crassulacean acid metabolism are referred to as CAM plants.
– The most characteristic feature of these plants is that their stomata remain open at night (in dark) but closed during the day (in light). Thus, CAM is a kind of adaptation in succulents to carry out photosynthesis without much loss of water.
The Metabolic pathway of CAM –
In Dark (During night), when stomata are open, $C{O_2}$ combines with phosphoenol pyruvic acid (PEA) to form oxalo acetic acid (OAA) in the presence of enzyme PEP – carboxylase.
– Phosphoenol pyruvic acid \[ + \,C{O_2} + {H_2}O \to Oxalo\;acetic\;acid + {H_3}P{O_4}\]
– Oxalo acetic acid is converted into malic acid by enzyme malic dehydrogenase. NADH is required for this reaction.
$Oxalo\;acetic\;acid + \;NADH\; \to \;Malic\;acid + NA{D^ + }$
– Malic acid is stored in vacuole.
– During night organic acid content of CAM plants increases and the pH of their cell sap decreases.
In light (During the day) – When stomata are closed, the malic acid is decarboxylated to produce pyruvic acid and evolve $C{O_2}$.
$Malic\;acid\; + \;NA{D^ + } \to Pyurvic\;acid\; + \;NADH + C{O_2}$
– Pyruvic acid may be oxidized to $C{O_2}$ by krebs cycle.
– $C{O_2}$released is again fixed through the Calvin cycle with the help of RuBP and RuBisCo.
– Crassulacean plants have developed a unique mechanism to perform photosynthesis without much loss of water, therefore helps plants in conserving water.

The correct option is C. Conserving water.

Note: Examples of CAM plants are – Bryophyllum, Kalanchoe, Sedum, Cactus, Orchid, Pineapple families etc.
– CAM plants have scotoactive stomata.