Question

The C4 plants usually have the following features -
A. The first stable product in the system is a 4-carbon compound
B. There are two CO2 acceptors, viz., PEP and RUBP
C. Oxygen does not have any inhibitory effect on the process.
D. RUBP carboxylase is present in the mesophyll.
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, B, and C only
• C. B, C, and D only
• D. A, C, and D only

Hint:

Remember that in C4 plants, the enzymes are spatially separated: PEP carboxylase is in the mesophyll cells, whereas RuBisCO is located in the bundle sheath cells. This spatial separation is the key to preventing photorespiration.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
C4 plants are adapted to high-temperature and dry environments.
They utilize a specialized photosynthetic pathway to concentrate carbon dioxide around the enzyme RuBisCO, minimizing photorespiration.
This pathway involves two distinct cell types: mesophyll cells and bundle sheath cells.

Step 2: Detailed Explanation:
Let us analyze each statement individually to determine its correctness:
Statement A: The first stable product of carbon fixation in the C4 pathway is oxaloacetate (OAA), which is a 4-carbon organic acid.
This carboxylation is catalyzed by the enzyme PEP carboxylase.
Thus, Statement A is correct.
Statement B: C4 plants use two different carbon dioxide acceptors.
The primary acceptor in the mesophyll cells is phosphoenolpyruvate (PEP).
The secondary acceptor in the bundle sheath cells is ribulose-1,5-bisphosphate (RuBP).
Thus, Statement B is correct.
Statement C: In C4 plants, oxygen does not inhibit the photosynthetic process.
This is because Kranz anatomy keeps the concentration of carbon dioxide very high around the RuBisCO enzyme in the bundle sheath cells, preventing the oxygenase activity of RuBisCO.
Thus, photorespiration is virtually absent, and Statement C is correct.
Statement D: In C4 plants, RuBP carboxylase (RuBisCO) is present exclusively in the bundle sheath cells, not in the mesophyll cells.
The mesophyll cells only contain PEP carboxylase.
Thus, Statement D is incorrect.

Step 3: Final Answer:
Since statements A, B, and C are correct, and D is incorrect, the correct combination is A, B, and C only.