Glycogen is degraded to lactic acid by enzymes in muscles and liver when the animal is

Options

A. Exhausted
B. Starved
C. Killed
D. Defaecated.

Answer

### Step-by-Step Solution:

1. **Understanding Glycogen Storage**:
- Glycogen is a polysaccharide that serves as a form of energy storage in animals. It is primarily stored in the liver and muscles. The liver contains about 10% glycogen by mass, while muscles contain about 1%.

2. **Energy Utilization**:
- During physical activities, the body utilizes glucose as the main source of energy. When the glucose levels drop due to extensive use, the body needs to find an alternative source of energy.

3. **Glycogen Degradation**:
- When glucose is depleted, the body begins to break down glycogen into glucose through a process called glycogenolysis. This glucose can then be used for energy.

4. **Formation of Lactic Acid**:
- If the energy demand exceeds the oxygen supply (like during intense exercise), the glucose is further metabolized anaerobically (without oxygen) to produce lactic acid. This process occurs in the muscles and liver.

5. **Condition of the Animal**:
- The question asks under what condition glycogen is degraded to lactic acid. This typically occurs when the animal is exhausted, as it indicates that the energy reserves (glucose and glycogen) have been significantly depleted.

6. **Conclusion**:
- Therefore, the correct answer to the question is that glycogen is degraded to lactic acid by enzymes in muscles and liver when the animal is **exhausted**.