Q.67 Which of the following combinations of statements are true about C4 cycle?
(A). Malic acid formed in the chloroplast of mesophyll cells
(B). Malic acid is transported to the chloroplast of bundle sheath cell
(C). Pyruvic acid produced in mesophyll cells move to the chloroplast of bundle sheath cells
(D). Malic acid is transported to the chloroplast of mesophyll cells
1. (A), and (B) only.
2. (A), and (C) only.
3. (C) and (D) only
4. (B), (C) and (D) only
itle: C4 Cycle Statements: Correct Malic Acid Transport Explained (MCQ Solved)**
In the C4 cycle, malic acid forms in mesophyll cell chloroplasts and moves to bundle sheath cell chloroplasts—making statements (A) and (B) true.
Correct Answer: 1. (A), and (B) only
C4 Pathway (NADP-ME type): CO₂ + PEP → oxaloacetate (cytosol, mesophyll) → malic acid (mesophyll chloroplast via NADP-MDH) → transported via plasmodesmata to bundle sheath chloroplasts → decarboxylated to pyruvate + CO₂ (Rubisco fixes CO₂). Pyruvate returns to mesophyll chloroplasts (not bundle sheath).
C4 Cycle Flowchart
Mesophyll Chloroplast: PEP + CO₂ → OAA → **Malic Acid** (A ✓)
↓ Transport (B ✓)
Bundle Sheath Chloroplast: **Malic Acid** → Pyruvate + CO₂
Pyruvate → Mesophyll Chloroplast (C ✗, D ✗)
Statement Analysis
| Statement | True/False | Explanation |
|---|---|---|
| (A) Malic acid formed in chloroplast of mesophyll cells | True | NADP-MDH reduces OAA to malate in M chloroplasts. |
| (B) Malic acid transported to chloroplast of bundle sheath cell | True | Primary C4 acid shuttle to BS chloroplasts. |
| (C) Pyruvate from mesophyll moves to bundle sheath | False | Pyruvate generated in BS, returns to mesophyll chloroplasts. |
| (D) Malic acid to mesophyll chloroplasts | False | Wrong direction; malate moves M→BS. |
Options Breakdown
| Choice | Statements | Correct? |
|---|---|---|
| 1. (A), (B) | Mesophyll malate → BS transport | Yes: Core C4 mechanism. |
| 2. (A), (C) | Malate formation + wrong pyruvate path | No |
| 3. (C), (D) | Both pyruvate/malate directions wrong | No |
| 4. (B), (C), (D) | Includes false pyruvate/malate paths | No |
