Sometimes when we do heavy exercise, anaerobic respiration takes place in our muscle cells. What is produced during this process?

Options

A. alcohol and lactic acid
B. alcohol and `CO_(2)`
C. lactic acid and `CO_(2)`
D. lactic acid only

Explanation

To answer the question about what is produced during anaerobic respiration in muscle cells when we do heavy exercise, follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Respiration**:
- There are two main types of respiration: aerobic and anaerobic.
- Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen.

2. **Identify the Process During Heavy Exercise**:
- During heavy exercise, our muscle cells undergo anaerobic respiration due to a lack of sufficient oxygen.

3. **Know the Breakdown of Glucose**:
- In anaerobic respiration, glucose does not break down completely.
- Instead of producing carbon dioxide (CO2) and water (H2O) like in aerobic respiration, anaerobic respiration results in an incomplete breakdown of glucose.

4. **Determine the Products of Anaerobic Respiration in Muscles**:
- The primary product of anaerobic respiration in muscle cells is lactic acid.
- Along with lactic acid, energy is also produced, but the question specifically asks about the products.

5. **Evaluate the Options Given**:
- Option A: Alcohol and lactic acid - Incorrect, as alcohol is not produced in muscle cells.
- Option B: Alcohol and CO2 - Incorrect, as this occurs in yeast, not in muscle cells.
- Option C: Lactic acid and CO2 - Incorrect, as CO2 is not produced in muscle cells during anaerobic respiration.
- Option D: Lactic acid only - Correct, as lactic acid is the main product produced in muscle cells during anaerobic respiration.

6. **Conclusion**:
- The correct answer is **Option D: Lactic acid only**.