The Question is from neet-botany plant-physiology transpiration-and-photosynthesis-compromise, and it was created by the author B VENKAT

Question

A C4 plant exhibiting high stomatal conductance in response to elevated atmospheric CO2 experiences a sudden drop in CO2 levels. Which of the following is the MOST likely immediate consequence regarding the transpiration and photosynthesis compromise?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: C4 photosynthesis and stomatal conductance
 **Related Topics**: Transpiration, CO2 concentration, photosynthesis rate
 **Prerequisites**: Understanding of C4 photosynthetic pathway, stomatal function, and the relationship between CO2, transpiration, and photosynthesis.
## SOLUTION PATHWAY
**Given Information**:
  * C4 plant with high stomatal conductance (meaning stomata are open wide)
  * Initially, elevated atmospheric CO2 levels
  * Sudden drop in CO2 levels
**Method & Steps**:
 1. **Effect of high CO2 on C4 plants:** Under elevated CO2, C4 plants maintain high stomatal conductance to maximize CO2 uptake for photosynthesis.  However, this also leads to increased transpiration (water loss).
  Reasoning:  The enzyme PEP carboxylase in C4 plants is not as sensitive to CO2 concentration as RuBisCO in C3 plants.  High CO2 initially doesn't cause stomata to close in C4 plants.
  Formula/Rule:  No specific formula, but understanding the relationship between stomatal conductance, CO2 uptake, and transpiration is key.
 2. **Sudden drop in CO2:** When CO2 levels suddenly drop, the photosynthetic rate in the C4 plant will immediately decrease because there is less substrate for the initial carboxylation step (PEP carboxylase).
  Working: Less CO2 means less carbon fixation, hence reduced sugar production.
  Key Point: The response is immediate because the CO2 is directly involved in the initial step of C4 photosynthesis.
 3. **Transpiration remains high:** However, the stomata will not immediately close in response to the drop in CO2.  The stomata's response to CO2 levels is not instantaneous.
  Result: Increased transpiration and decreased photosynthetic rate.
  Verification: This aligns with the understanding of C4 photosynthesis and stomatal regulation.  A sudden drop in CO2 will immediately affect photosynthesis, but stomatal closure takes time.
 ## OPTION ANALYSIS
A ✓: Increased transpiration and decreased photosynthetic rate: This is correct because the stomata remain open (high transpiration), but the reduced CO2 limits photosynthesis.
B :x: Decreased transpiration and increased photosynthetic rate: This is incorrect because a drop in CO2 would decrease, not increase, the photosynthetic rate. Stomatal closure (decreased transpiration) is not immediate.
C :x: Decreased transpiration and decreased photosynthetic rate: This is incorrect because stomatal closure is not an immediate response to the decreased CO2.
D :x: No significant change in either transpiration or photosynthetic rate: This is incorrect because both transpiration and photosynthesis will be affected by the sudden drop in CO2.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming immediate stomatal closure: Stomatal response to CO2 change isn't instantaneous.
   How to avoid: Understand the time lag between CO2 change and stomatal response.
  2.Confusing C3 and C4 photosynthetic pathways: C4 plants have a different response to CO2 than C3 plants.
   How to avoid:  Clearly understand the mechanisms of both pathways.
 **Quick Tips**:
  1.Remember that C4 plants typically have higher stomatal conductance than C3 plants, even under high CO2.
  2.Focus on the immediate consequences – the stomata don't close instantly.

B VENKAT · Answer

The correct Option is "Increased transpiration and decreased photosynthetic rate"

B VENKAT · Answer

Decreased transpiration and increased photosynthetic rate

B VENKAT · Answer

Decreased transpiration and decreased photosynthetic rate

B VENKAT · Answer

No significant change in either transpiration or photosynthetic rate

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