Question

Arrange the following steps of photosynthesis in C$_4$ plant in a correct sequence: A. Conversion of Oxaloacetate to Malate B. Malate releases CO$_2$ C. Adding of CO$_2$ to phosphoenolpyruvate to form Oxaloacetate D. CO$_2$ reassimilated into organic material by Rubisco in the Calvin cycle E. Export of malate to bundle sheath cells through plasmodesmata

• A. A, E, B, C, D
• B. B, C, A, D, E
• C. C, A, E, B, D
• D. E, A, D, B, C

Hint:

C$_4$ pathway: PEP + CO$_2$ $\rightarrow$ OAA $\rightarrow$ Malate $\rightarrow$ bundle sheath $\rightarrow$ CO$_2$ release $\rightarrow$ Calvin cycle.

Answer 1

The Correct Option is C

Step 1: Concept
The C$_4$ photosynthetic pathway (Hatch--Slack cycle).

Step 2: Meaning
C$_4$ plants separate initial CO$_2$ fixation (mesophyll cells) from the Calvin cycle (bundle sheath cells) to minimise photorespiration.

Step 3: Analysis
C: CO$_2$ + PEP $\xrightarrow{\text{PEP carboxylase}}$ Oxaloacetate (OAA) in mesophyll.
A: OAA $\rightarrow$ Malate (by NADP-malate dehydrogenase).
E: Malate exported to bundle sheath cells via plasmodesmata.
B: Malate decarboxylated, releasing CO$_2$ and pyruvate.
D: CO$_2$ fixed by Rubisco in the Calvin cycle.

Step 4: Conclusion
Correct sequence: C $\rightarrow$ A $\rightarrow$ E $\rightarrow$ B $\rightarrow$ D. Final Answer: (C)