Warburg effect is decrease in the rate of photosynthesis at

Options

A. Low carbon dioxide concentration
B. High oxygen content
C. High carbon dioxide concentration
D. Both A and B.

Answer

### Step-by-Step Solution:

1. **Understanding the Warburg Effect**: The Warburg effect refers to a phenomenon where the rate of photosynthesis decreases under certain conditions, particularly when there is an increase in oxygen concentration.

2. **Identifying the Role of Rubisco**: The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (commonly known as Rubisco) plays a crucial role in the process of photosynthesis. It is responsible for fixing carbon dioxide during the Calvin cycle.

3. **Impact of Oxygen Concentration**: When the concentration of oxygen is high, Rubisco can mistakenly bind to oxygen instead of carbon dioxide. This leads to a process called photorespiration, which is less efficient and results in a decrease in the overall rate of photosynthesis.

4. **Photorespiration**: Photorespiration is considered a wasteful process because it consumes energy and does not produce glucose. Instead, it leads to the production of glycolate, which further reduces the efficiency of photosynthesis in C3 plants.

5. **Conclusion**: Based on the understanding of the Warburg effect and its relation to oxygen concentration, we can conclude that the decrease in the rate of photosynthesis occurs primarily at high oxygen content.

### Final Answer:
The Warburg effect is a decrease in the rate of photosynthesis at **high oxygen content**.

---