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: Understanding the Concept:
The question asks to identify a facultative CAM plant. Crassulacean Acid Metabolism (CAM) is a photosynthetic adaptation to arid conditions. Obligate CAM plants use this pathway all the time. Facultative CAM plants, however, can switch between C₃ photosynthesis and CAM photosynthesis in response to environmental cues like drought or salinity.
Step 2: Detailed Explanation:
Let's analyze the photosynthetic pathways of the given plants:

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

(B) {Opuntia (Prickly pear cactus):} This is an obligate CAM plant. It is a succulent that lives in arid environments and always uses the CAM pathway to conserve water.

(C) {Chrysanthemum:} This is a typical C₃ plant. It does not perform CAM photosynthesis.

(D) {Amaranthus edulis:} This is a C₄ plant, characterized by Kranz anatomy. It does not perform CAM photosynthesis.

Step 3: Final Answer:
{Mesembryanthemum crystallinum} is a known facultative CAM plant that uses C₃ metabolism in unstressed conditions and switches to CAM under stress.