Warbung effect refers to

Options

A. decreased photosynthetic rate at very high `O_(2)` concentration
B. increased photosynthetic rate at very high `O_(2)` concentration
C. decreased photosynthetic rate at very low `O_(2)` concentration
D. increased photosynthetic rate at very low `O_(2)` concentration

Explanation

### Step-by-Step Solution

1. **Understanding the Wurmburg Effect**: The Wurmburg effect is a phenomenon observed in plant physiology, particularly related to the process of photosynthesis.

2. **Identifying the Conditions**: The effect specifically refers to the impact of oxygen concentration on the rate of photosynthesis.

3. **Analyzing High Oxygen Concentration**: At very high concentrations of oxygen, the rate of photosynthesis in plants decreases. This is the core of the Wurmburg effect.

4. **Role of Oxygen**: Oxygen acts as an inhibitor in the photosynthetic process. It inhibits the enzyme RuBisCO, which is crucial for the fixation of carbon dioxide during photosynthesis.

5. **Understanding Photorespiration**: In addition to inhibiting photosynthesis, high levels of oxygen stimulate another process known as photorespiration. This process competes with photosynthesis for resources, leading to a decrease in the overall rate of photosynthesis.

6. **Conclusion**: Therefore, the Wurmburg effect can be concluded as the decreased photosynthetic rate at a very high oxygen concentration.

### Final Answer
The Wurmburg effect refers to the decreased photosynthetic rate at a very high oxygen concentration.

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