Which metabolic pathway is common to both the aerobic and anaerobic catabolism of sugar?

Options

A. Synthesis of acetyl CoA from pyruvic acid
B. Glycolysis
C. Krebs cycle
D. Electron transport chain

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a metabolic pathway that is common to both aerobic and anaerobic catabolism of sugar.

2. **Defining Aerobic and Anaerobic Respiration**:
- **Aerobic Respiration**: This process occurs in the presence of oxygen. It involves several stages including glycolysis, oxidative decarboxylation, and the TCA cycle (Krebs cycle).
- **Anaerobic Respiration**: This process occurs in the absence of oxygen. It also begins with glycolysis, but instead of proceeding through the TCA cycle, it leads to fermentation.

3. **Identifying the Common Pathway**:
- **Glycolysis**: This is the first step in both aerobic and anaerobic respiration. In glycolysis, glucose is converted into pyruvate, regardless of whether oxygen is present or not.

4. **Explaining the Subsequent Steps**:
- In **aerobic respiration**, after glycolysis, pyruvate is converted into acetyl-CoA through oxidative decarboxylation, followed by the TCA cycle where acetyl-CoA is further processed.
- In **anaerobic respiration**, after glycolysis, pyruvate undergoes fermentation, leading to products like lactate or ethanol, without proceeding to the TCA cycle.

5. **Conclusion**: The only metabolic pathway that is common to both aerobic and anaerobic catabolism of sugar is **glycolysis**.

### Final Answer:
The metabolic pathway that is common to both the aerobic and anaerobic catabolism of sugar is **glycolysis**.

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