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

Question

A plant is exposed to an environment with high CO2 and low O2 concentrations.  Which process would be MOST directly and significantly inhibited under these conditions?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Photorespiration and its dependence on oxygen.
 **Related Topics**: Photosynthesis (Calvin cycle, C4 cycle), cellular respiration, gas exchange in plants.
 **Prerequisites**: Understanding of the basic processes of photosynthesis and photorespiration.
## SOLUTION PATHWAY
**Given Information**:
  High CO2 concentration
  Low O2 concentration
**Method & Steps**:
 1. Analyze the effect of high CO2 on the given options.
  Reasoning: High CO2 would favor the Calvin cycle (carbon fixation) and C4 cycle (CO2 concentrating mechanism).  It would not directly inhibit these processes.
 2. Analyze the effect of low O2 on the given options.
  Reasoning: Low O2 would directly impact processes that require oxygen.  The electron transport chain uses oxygen as the final electron acceptor. Photorespiration is a process where rubisco, an enzyme in the Calvin cycle, binds to oxygen instead of CO2, leading to a wasteful cycle. 
  Key Point: Photorespiration is an oxygen-dependent process that competes with the Calvin cycle.
 3. Compare the impact of the environmental conditions on each option.
  Result: Photorespiration is the process most directly and significantly inhibited by low oxygen concentration.
  Verification: High CO2 favors photosynthesis, making photorespiration even less likely.
 ## OPTION ANALYSIS
A :x: The Calvin cycle uses CO2 and is actually favored by high CO2 concentrations. 
B ✓: Photorespiration is directly inhibited by low O2.  It's an oxygenase activity of Rubisco, competing with carboxylase activity.
C :x: The electron transport chain is affected by low O2, but indirectly.  The primary impact is on cellular respiration, not directly on photosynthesis.
D :x: The C4 cycle is a CO2-concentrating mechanism that minimizes photorespiration.  It is actually enhanced by high CO2.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing photorespiration with photosynthesis: Photorespiration is a wasteful process that competes with the Calvin cycle.
   How to avoid: Remember that photorespiration occurs when Rubisco binds to oxygen instead of CO2 under conditions of high O2 and low CO2.
  2. Focusing only on CO2:  While high CO2 favors photosynthesis, the low O2 concentration is the key factor for inhibiting photorespiration.
   How to avoid:  Consider the impact of both high CO2 and low O2 on each process.
 **Quick Tips**:
  1.Remember that Rubisco has dual functionality: It can fix CO2 (carboxylase) or O2 (oxygenase). Low O2 reduces oxygenase activity.
  2.Photorespiration is a rescue mechanism which is wasteful and reduces the efficiency of photosynthesis.

K SURESH KUMAR · Answer

Calvin cycle

K SURESH KUMAR · Answer

The correct Option is "Photorespiration"

K SURESH KUMAR · Answer

Electron transport chain

K SURESH KUMAR · Answer

C4 cycle

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