The Question is from neet-botany , and it was created by the author Mr. NARESH KUMAR K

Question

A plant exhibiting Kranz anatomy experiences a sudden drop in atmospheric CO2 levels. Which of the following is the MOST LIKELY immediate consequence on its photosynthetic efficiency?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: C4 photosynthesis and its response to CO2 levels
 **Related Topics**: Kranz anatomy, PEP carboxylase, RuBisCO, photorespiration, Calvin cycle
 **Prerequisites**: Understanding of C4 photosynthetic pathway, the roles of mesophyll and bundle sheath cells, and the effect of CO2 concentration on enzyme activity.
## SOLUTION PATHWAY
**Given Information**:
	* Plant with Kranz anatomy (indicating C4 photosynthesis)
	* Sudden drop in atmospheric CO2 levels
**Method & Steps**:
 1. Identify the initial step of CO2 fixation in C4 plants.
  Reasoning: In C4 plants, initial CO2 fixation occurs in mesophyll cells via PEP carboxylase, which has a higher affinity for CO2 than RuBisCO.
  Formula/Rule: None directly applicable, but understanding of the C4 pathway is crucial.
 2. Analyze the impact of reduced CO2 on PEP carboxylase activity.
  Working: A decrease in atmospheric CO2 will directly reduce the substrate availability for PEP carboxylase in the mesophyll cells. This will lead to a lower rate of initial CO2 fixation.
  Key Point: PEP carboxylase is the primary enzyme responsible for initial CO2 fixation in C4 plants. Its activity is directly proportional to CO2 concentration.
 3. Evaluate the consequences on photosynthetic efficiency.
  Result: Reduced initial CO2 fixation by PEP carboxylase will directly impact the overall photosynthetic efficiency, as less CO2 will be available for the Calvin cycle in the bundle sheath cells.
  Verification: This aligns with the understanding of C4 photosynthesis, where efficient CO2 concentration is crucial for optimal function.
 ## OPTION ANALYSIS
A] ✓: Reduced initial fixation of CO2 by PEP carboxylase in mesophyll cells. This is the direct and immediate consequence of reduced atmospheric CO2. 
B] :x: Increased oxygenation of RuBisCO in bundle sheath cells. While reduced CO2 might indirectly increase oxygenation, the immediate effect is on PEP carboxylase in mesophyll cells.
C] :x: Immediate cessation of the Calvin cycle in bundle sheath cells. The Calvin cycle won't immediately cease; it will be slowed down due to reduced CO2 supply.
D] :x: Enhanced activity of photorespiration in mesophyll cells.  Photorespiration is less of a concern in C4 plants due to the spatial separation of CO2 fixation and the Calvin cycle.  The immediate effect is on the initial CO2 fixation.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of PEP carboxylase and RuBisCO: Remember PEP carboxylase fixes CO2 initially in mesophyll cells, while RuBisCO fixes CO2 in the Calvin cycle within bundle sheath cells in C4 plants.
  2.Ignoring the spatial separation in C4 photosynthesis: The Kranz anatomy is key; understanding the distinct roles of mesophyll and bundle sheath cells is crucial.
 **Quick Tips**:
  1.Focus on the immediate effect: The question asks for the MOST LIKELY immediate consequence.
  2.Remember the high CO2 affinity of PEP carboxylase: This enzyme is designed to work efficiently even at lower CO2 levels compared to RuBisCO, but a drastic drop will still affect it.

Mr. NARESH KUMAR K · Answer

The correct Option is "Reduced initial fixation of CO2 by PEP carboxylase in mesophyll cells."

Mr. NARESH KUMAR K · Answer

Increased oxygenation of RuBisCO in bundle sheath cells.

Mr. NARESH KUMAR K · Answer

Immediate cessation of the Calvin cycle in bundle sheath cells.

Mr. NARESH KUMAR K · Answer

Enhanced activity of photorespiration in mesophyll cells.

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