The Question is from neet-botany photosynthesis-in-higher-plants photorespiration-and-c4-cycle, and it was created by the author B VENKAT

Question

In C4 plants, the initial carboxylation reaction occurs in:

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: C4 photosynthesis
 **Related Topics**: Photosynthesis, carbon fixation, mesophyll cells, bundle sheath cells
 **Prerequisites**: Understanding of the basic process of photosynthesis and the differences between C3 and C4 plants.
## SOLUTION PATHWAY
**Given Information**:
The question asks about the location of the initial carboxylation reaction in C4 plants.
**Method & Steps**:
1. Understanding C4 photosynthesis:
  Reasoning: C4 plants have evolved a specialized mechanism to overcome photorespiration, a process that reduces the efficiency of photosynthesis in C3 plants. This mechanism involves two distinct carboxylation steps in different cell types.
  Formula/Rule: None directly applicable.
 2. Identifying the initial carboxylation step:
  Working: The initial carboxylation in C4 plants uses the enzyme PEP carboxylase (PEPcase), which has a high affinity for CO2 and does not catalyze the oxygenase reaction (unlike RuBisCO). This reaction takes place in the mesophyll cells.
  Key Point: The product of this initial carboxylation is a four-carbon compound (hence the name C4), which is then transported to the bundle sheath cells.
 3. Finalizing the answer:
  Result: The initial carboxylation reaction in C4 plants occurs in the mesophyll cells.
  Verification: This is consistent with the understanding of C4 photosynthesis and the roles of PEPcase and RuBisCO.
 ## OPTION ANALYSIS
A ✓: Mesophyll cells - Correct. The initial carboxylation using PEP carboxylase happens in the mesophyll cells.
B :x: Bundle sheath cells - Incorrect.  While the Calvin cycle (where RuBisCO is used) occurs in the bundle sheath cells, the initial carboxylation is in the mesophyll cells.
C :x: Both mesophyll and bundle sheath cells - Incorrect. The initial carboxylation is specific to mesophyll cells.
D :x: Neither mesophyll nor bundle sheath cells - Incorrect. The initial carboxylation must occur in one of the leaf cell types.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of mesophyll and bundle sheath cells: Remembering that PEP carboxylase is in mesophyll and RuBisCO is in bundle sheath cells is key.
  2.Thinking the Calvin cycle is the initial carboxylation: The Calvin cycle is a later step in both C3 and C4 photosynthesis.
 **Quick Tips**:
  1.Remember PEPcase (mesophyll) and RuBisCO (bundle sheath) to distinguish the locations.
  2.C4 plants have spatial separation of carboxylation steps to optimize CO2 concentration.

B VENKAT · Answer

The correct Option is "Mesophyll cells"

B VENKAT · Answer

Bundle sheath cells

B VENKAT · Answer

Both mesophyll and bundle sheath cells

B VENKAT · Answer

Neither mesophyll nor bundle sheath cells

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