In muscles during exercise, when oxygen is inadequate for cellular respiration pyruvic acid is reduced to

Options

A. Acetyl coenzyme A
B. Ethyl alcohol
C. Lactic acid
D. Acetic acid

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: During exercise, muscle cells require energy. This energy is primarily produced through cellular respiration. However, when oxygen levels are low, the process of aerobic respiration cannot proceed efficiently.

2. **Glycolysis**: The first step in cellular respiration is glycolysis, where glucose is broken down into pyruvic acid. This process occurs in the cytoplasm and does not require oxygen.

3. **Oxygen Deficiency**: When oxygen is inadequate, the pyruvic acid produced from glycolysis cannot enter the mitochondria for aerobic respiration. Instead, it undergoes a different pathway.

4. **Fermentation Process**: In the absence of oxygen, pyruvic acid is converted into lactic acid through a process known as lactic acid fermentation. This process allows for the regeneration of NAD+, which is essential for glycolysis to continue.

5. **Role of Enzymes**: The enzyme responsible for this conversion is lactate dehydrogenase. It catalyzes the reduction of pyruvic acid to lactic acid.

6. **Energy Yield**: During this conversion, a small amount of energy, specifically 2 ATP molecules, is produced. However, this is significantly less than what is produced during aerobic respiration.

7. **Final Answer**: Therefore, in muscles during exercise, when oxygen is inadequate for cellular respiration, pyruvic acid is reduced to **lactic acid**.

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