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

Question

How does an increase in atmospheric CO2 concentration initially affect the rate of photosynthesis, assuming other factors are optimal?

D VINOD · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Photosynthesis and its dependence on carbon dioxide.
 **Related Topics**:  Carbon fixation, the Calvin cycle, limiting factors in photosynthesis.
 **Prerequisites**: Basic understanding of the process of photosynthesis.
## SOLUTION PATHWAY
**Given Information**:
  Increased atmospheric CO2 concentration.
  Other factors (light intensity, temperature, water availability) are optimal.
**Method & Steps**:
 1. Understanding the role of CO2 in photosynthesis:
  Reasoning: Photosynthesis uses CO2 as a substrate in the Calvin cycle (light-independent reactions) to produce glucose.  The enzyme RuBisCO catalyzes the first step of this cycle, the carboxylation of RuBP with CO2.
  Formula/Rule:  $CO_2 + RuBP ightarrow 2(3PGA)$
 2. Analyzing the effect of increased CO2:
  Working:  If CO2 concentration increases and other factors are optimal, the rate of carboxylation by RuBisCO will increase, leading to a higher rate of 3-PGA production and subsequently, a higher rate of glucose synthesis.
  Key Point: This effect is only true up to a certain point; after a saturation point, increasing CO2 will not further enhance photosynthesis.
 3. Final Conclusion:
  Result: An increase in atmospheric CO2 concentration initially increases the rate of photosynthesis.
  Verification:  This aligns with the understanding of CO2 as a reactant in photosynthesis.  Experiments have demonstrated increased photosynthetic rates with elevated CO2 levels, at least initially.
 ## OPTION ANALYSIS
A ✓: Increases the rate: Correct. As explained above, increased CO2 directly increases the substrate for the rate-limiting step in the Calvin cycle.
B :x: Decreases the rate: Incorrect.  Higher CO2 concentration, under optimal conditions, will not decrease the rate of photosynthesis.
C :x: Has no effect: Incorrect. CO2 is a crucial reactant in photosynthesis; its concentration directly impacts the rate.
D :x: Causes photorespiration: Incorrect. While high CO2 can reduce photorespiration (a competing process), the initial effect is an increase in the rate of photosynthesis. Photorespiration is more related to the balance between CO2 and O2.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the effect of CO2 on photosynthesis with its long-term environmental consequences (climate change):  The question focuses solely on the initial, direct effect.
  How to avoid: Carefully read and answer only what the question asks.
  2.Ignoring other limiting factors: The question specifies that other factors are optimal.  If light or other factors were limiting, the effect would be different.
  How to avoid: Pay close attention to the conditions stated in the problem.
 **Quick Tips**:
  1.Remember CO2 is a reactant in photosynthesis.
  2.Visualize the Calvin cycle and the role of RuBisCO.

D VINOD · Answer

The correct Option is "Increases the rate"

D VINOD · Answer

Decreases the rate

D VINOD · Answer

Has no effect

D VINOD · Answer

Causes photorespiration

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