Question

Which of the following statement is wrong about C\(_4\) plants

• A. Kranz anatomy is present
• B. Initial CO\(_2\) acceptor is Phosphoenol-pyruvate (PEP)
• C. First stable product is 3-phosphoglycerate
• D. Calvin cycle operates along with the Hatch and Slack cycle.

Hint:

The names C3 and C4 come directly from the number of carbons in the first stable product of CO2 fixation. For C3 plants, it's a 3-carbon compound (3-PGA). For C4 plants, it's a 4-carbon compound (oxaloacetate).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
C\(_4\) photosynthesis (or the Hatch-Slack pathway) is an adaptation found in plants in hot, dry climates. It acts as a CO\(_2\)-concentrating mechanism to reduce photorespiration. The question asks to identify an incorrect statement about this pathway.
Step 2: Detailed Explanation:
Let's analyze each statement:


(A) Kranz anatomy is present: This is correct. C\(_4\) plants have a specialized leaf structure called Kranz ("wreath" in German) anatomy, with photosynthetic bundle sheath cells surrounding the vascular bundles, which are in turn surrounded by mesophyll cells.

(B) Initial CO\(_2\) acceptor is Phosphoenol-pyruvate (PEP): This is correct. In the mesophyll cells, CO\(_2\) is first fixed by the enzyme PEP carboxylase, which uses the 3-carbon molecule PEP as the substrate.

(C) First stable product is 3-phosphoglycerate: This is wrong. The product of the initial CO\(_2\) fixation by PEP carboxylase is oxaloacetate, a 4-carbon acid (hence the name C\(_4\) plants). 3-phosphoglycerate (a 3-carbon compound) is the first stable product of the Calvin cycle (C\(_3\) pathway).

(D) Calvin cycle operates along with the Hatch and Slack cycle: This is correct. The C\(_4\) cycle's purpose is to capture CO\(_2\) in mesophyll cells and transport it as a 4-carbon acid to the bundle sheath cells. There, the CO\(_2\) is released and re-fixed by RuBisCO in the Calvin cycle.

Step 3: Final Answer:
The statement that the first stable product is 3-phosphoglycerate is wrong; that is true for C\(_3\) plants, not C\(_4\) plants.