When `O_2` is not available to a muscle, NAOH formed in glycolysis does not pass electrons to the ETC. Instead it passes them to

Options

A. Acetyl Co A
B. pyruvic acid
C. fructose
D. ADP

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: When oxygen (O2) is not available in muscle cells, they undergo anaerobic respiration instead of aerobic respiration. This occurs during intense exercise when the demand for energy exceeds the oxygen supply.

**Hint**: Recall the difference between aerobic and anaerobic respiration.

2. **Role of Glycolysis**: Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing a small amount of ATP and NADH in the process. In the absence of oxygen, the NADH produced during glycolysis cannot transfer its electrons to the electron transport chain (ETC).

**Hint**: Remember what glycolysis produces and its end products.

3. **Fate of NADH**: In anaerobic conditions, the NADH formed during glycolysis needs to be oxidized back to NAD+ to allow glycolysis to continue. Since there is no oxygen to accept the electrons, NADH transfers its electrons to the pyruvate produced from glycolysis.

**Hint**: Think about how cells regenerate NAD+ during anaerobic respiration.

4. **Conversion of Pyruvate**: The pyruvate then undergoes fermentation. In muscle cells, this typically leads to the conversion of pyruvate into lactic acid (or lactate), which allows for the regeneration of NAD+.

**Hint**: Consider what happens to pyruvate in anaerobic conditions.

5. **Identifying the Correct Answer**: Given the options provided, the correct answer is that NADH formed in glycolysis passes its electrons to pyruvic acid (pyruvate).

**Hint**: Review the options carefully and match them with the process described.

**Final Answer**: NADH formed in glycolysis passes its electrons to pyruvic acid (pyruvate).

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