The Question is from neet-botany photosynthesis-in-higher-plants photorespiration-and-c4-cycle, and it was created by the author Mr. NARESH KUMAR K

Question

A researcher is studying a C4 plant under controlled conditions.  They suddenly increase the oxygen concentration in the environment while maintaining constant light and CO2 levels. Which of the following is the MOST likely immediate consequence?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: C4 Photosynthesis and Photorespiration
	**Related Topics**: Carbon Fixation, Rubisco, Oxygenase Activity, CO2 Concentration Mechanism
	**Prerequisites**: Understanding of C4 and C3 photosynthetic pathways.
## SOLUTION PATHWAY
**Given Information**:
	- C4 plant
	- Increased oxygen concentration
	- Constant light and CO2 levels
**Method & Steps**:
	1. **C4 Pathway Overview**: C4 plants minimize photorespiration by concentrating CO2 around Rubisco in bundle sheath cells.  This spatial separation reduces Rubisco's exposure to oxygen.
		Reasoning:  PEP carboxylase, the initial CO2-fixing enzyme in C4 plants, has a high affinity for CO2 and does not react with oxygen.
	2. **Effect of Increased Oxygen**: Even with the CO2 concentrating mechanism, a sudden increase in oxygen can slightly increase the oxygenase activity of Rubisco in the bundle sheath cells.
		Working: While the C4 pathway minimizes photorespiration, it doesn't eliminate it entirely. A higher oxygen concentration increases the probability of oxygen competing with CO2 at the Rubisco active site.
		Key Point: The impact is less significant in C4 plants compared to C3 plants because of the CO2 concentrating mechanism.
	3. **Consequence**: A slight increase in photorespiration occurs due to the increased oxygenase activity of Rubisco.
		Result: Increased oxygen leads to slightly more photorespiration.
		Verification: This aligns with the known behavior of C4 plants under elevated oxygen conditions.
## OPTION ANALYSIS
[A] :x: A significant decrease in the rate of photosynthesis: Incorrect. While photorespiration consumes energy and reduces photosynthetic efficiency, the increase in photorespiration would be slight in a C4 plant, not enough to cause a significant decrease in overall photosynthesis under these conditions.
[B] ✓: A slight increase in photorespiration: Correct. The increased oxygen concentration will slightly increase the oxygenase activity of Rubisco, leading to a slight increase in photorespiration.
[C] :x: A significant increase in the rate of photosynthesis: Incorrect. Increased oxygen would not significantly enhance photosynthesis in a C4 plant.  It might even slightly reduce the overall efficiency due to the increased photorespiration.
[D] :x: No change in the rate of photosynthesis or photorespiration: Incorrect. The change in oxygen concentration will affect the balance between carboxylation and oxygenation reactions of Rubisco, leading to a slight increase in photorespiration.
## LEARNING AIDS
	**Common Mistakes**:
		1. Assuming C4 plants completely avoid photorespiration: They minimize it, but it can still occur.
		2. Overestimating the impact of oxygen on C4 photosynthesis: The CO2 concentrating mechanism reduces the impact compared to C3 plants.
	**Quick Tips**:
		1. Remember that Rubisco has both carboxylase and oxygenase activity.
		2. C4 plants have evolved mechanisms to minimize, but not entirely eliminate, photorespiration.

Mr. NARESH KUMAR K · Answer

A significant decrease in the rate of photosynthesis

Mr. NARESH KUMAR K · Answer

The correct Option is "A slight increase in photorespiration"

Mr. NARESH KUMAR K · Answer

A significant increase in the rate of photosynthesis

Mr. NARESH KUMAR K · Answer

No change in the rate of photosynthesis or photorespiration

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