Question

Stomata of CAM plants:
A. Are always open
B. Open during the day and close at night
C. Open during night and close during the day
D. Never open

Answer 1

Hint: CAM plants are the plants that grow in xeric conditions. In order to prevent needless loss of water through evapotranspiration, the stomata of CAM plants are sunken and open during the night.

Complete answer:
CAM plants are so named because they employ Crassulacean Acid Metabolism for carbon dioxide fixation as an adaptation to their arid habitat. CAM pathway was first observed in family Crassulaceae. Plants such as xerophytes and succulents exhibit characteristic traits like fleshy leaves with thick cuticle coverings and reduced surface area and sunken stomata. A major physiological adaptation is the closing of stomata to cut the rate of transpiration.
CAM plants show reverse opening and closing of stomata. During the day time, when the water stress is high and the rate of transpiration is at its peak, the stomata of CAM plants remain closed.
As the temperature lowers down at night and the atmosphere becomes misty, stomatal opening is observed. This entire phenomenon helps in the conservation of water and sustain periods of prolonged dryness.
In Crassulacean Acid Metabolism, carbon dioxide is absorbed and fixed during the dark time, i.e. at night and phosphoenol pyruvic acid (PEP) is carboxylated and organic compounds are synthesised and in the light, i.e. during the day decarboxylation takes place and carbon dioxide is evolved. CAM pathway is of utmost significance for succulents, their growth and survival.

The correct option is C.

Note: CAM plants display sunken pitted closed stomata for water retention but also, the carbon dioxide supply for the process of photosynthesis is lost which is why it is necessary for the plants to open the stomata at least once so that the plant metabolism is not affected.