The Question is from neet-botany photosynthesis-in-higher-plants , and it was created by the author NISHANTH

Question

In C4 plants, the initial fixation of $\rm{CO_2}$ by PEP carboxylase occurs in the:

NISHANTH · Accepted Answer

## CORE INFORMATION
✓ **Answer**: Option A
## CONCEPT FRAMEWORK
 **Primary Concept**: C4 photosynthesis
 **Related Topics**: Photosynthesis, carbon fixation, plant anatomy, enzyme function
 **Prerequisites**: Understanding of the different stages of photosynthesis and the roles of various cell types in leaves.
## SOLUTION PATHWAY
**Given Information**:
  The question asks about the location of initial CO2 fixation in C4 plants by PEP carboxylase.
  The options are Mesophyll cells, Bundle sheath cells, Epidermal cells, and Stomatal guard cells.
**Method & Steps**:
 1. Understand C4 photosynthesis:
  Reasoning: C4 plants have a specialized mechanism to overcome photorespiration, a process that reduces the efficiency of photosynthesis in hot, dry conditions. This mechanism involves two cell types: mesophyll cells and bundle sheath cells.
  Formula/Rule: No specific formula is needed.
 2. Identify the role of PEP carboxylase:
  Working: PEP carboxylase is the enzyme responsible for the initial fixation of CO2 in C4 plants. This enzyme has a high affinity for CO2 and is found in the mesophyll cells.
  Key Point: The initial CO2 fixation by PEP carboxylase is the first step in the C4 pathway, which concentrates CO2 in the bundle sheath cells to minimize photorespiration.
 3. Determine the location:
  Result: The initial fixation of CO2 by PEP carboxylase occurs in the mesophyll cells of C4 plants.
  Verification: This is consistent with the understanding of C4 photosynthesis and the roles of mesophyll and bundle sheath cells.
 ## OPTION ANALYSIS
[A] ✓: Mesophyll cells are the correct answer because PEP carboxylase, responsible for the initial CO2 fixation in C4 plants, is located in these cells.
[B] :x: Bundle sheath cells are involved in the later stages of C4 photosynthesis, where CO2 is released from a four-carbon compound and used in the Calvin cycle.
[C] :x: Epidermal cells are the outer layer of cells and are not directly involved in photosynthesis.
[D] :x: Stomatal guard cells regulate gas exchange, but they do not directly participate in the initial CO2 fixation.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of mesophyll and bundle sheath cells: Remember that initial CO2 fixation happens in mesophyll cells, while the Calvin cycle primarily occurs in bundle sheath cells in C4 plants.
  2.Associating RuBisCO with initial CO2 fixation in C4 plants: RuBisCO is involved in the Calvin cycle, which occurs after the initial CO2 fixation by PEP carboxylase.
 **Quick Tips**:
  1.Remember the acronym PEP for the enzyme involved in the initial CO2 fixation in C4 plants.
  2.Visualize the anatomy of a C4 leaf to understand the spatial separation of the initial CO2 fixation and the Calvin cycle.

NISHANTH · Answer

The correct Option is "Mesophyll cells"

NISHANTH · Answer

Bundle sheath cells

NISHANTH · Answer

Epidermal cells

NISHANTH · Answer

Stomatal guard cells

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