Question

The example of facultative CAM plant which carries on C₃ metabolism under unstressed conditions is:

• A. Mesembryanthemum crystallinum
• B. Opuntia
• C. Chrysanthemum
• D. Amaranthus edulis

Hint:

Remember the key difference: "Obligate" means always, "Facultative" means having the option to switch. Cacti are obligate CAM plants. The ice plant ({Mesembryanthemum}) is the most common example of a facultative CAM plant.

Answer 1

The Correct Option is A

Step 1: Concept Overview:
The question requires identifying a facultative CAM plant. CAM (Crassulacean Acid Metabolism) is a photosynthetic adaptation for dry environments. Obligate CAM plants always use the CAM pathway. Facultative CAM plants can switch between C₃ and CAM photosynthesis based on environmental conditions like drought or salinity.
Step 2: Detailed Analysis:
Examining the photosynthetic pathways of the plants:

(A) {Mesembryanthemum crystallinum (Common ice plant):} A classic example of a facultative CAM plant. It uses C₃ photosynthesis when water is plentiful but switches to CAM under drought or salt stress.

(B) {Opuntia (Prickly pear cactus):} An obligate CAM plant adapted to arid conditions, consistently using the CAM pathway for water conservation.

(C) {Chrysanthemum:} A typical C₃ plant, not utilizing CAM photosynthesis.

(D) {Amaranthus edulis:} A C₄ plant with Kranz anatomy, not utilizing CAM photosynthesis.

Step 3: Conclusion:
{Mesembryanthemum crystallinum} is a facultative CAM plant, employing C₃ metabolism in unstressed conditions and CAM under stress.