RQ depends upon

Options

A. temperature
B. `O_(2)` content of substrate
C. types of respiration
D. none of these

Answer

### Step-by-Step Solution:

1. **Understanding RQ (Respiratory Quotient)**:
- RQ is defined as the ratio of the volume of carbon dioxide (CO2) produced to the volume of oxygen (O2) consumed during respiration.
- Mathematically, it can be expressed as:
\[ RQ = \frac{\text{Volume of CO2 evolved}}{\text{Volume of O2 consumed}} \]

2. **Identifying Factors Affecting RQ**:
- RQ can depend on several factors, including:
- The type of respiratory substrate (carbohydrates, fats, proteins).
- The metabolic processes involved (aerobic vs anaerobic respiration).
- Environmental conditions (temperature, oxygen availability).

3. **Evaluating the Given Options**:
- **Option 1: Temperature** - While temperature can influence metabolic rates, it does not directly determine the RQ value itself. Therefore, this option is incorrect.
- **Option 2: Oxygen content of substrate** - This is a crucial factor because the type of substrate used in respiration (like carbohydrates, fats, or proteins) directly affects the RQ. For example, carbohydrates typically have an RQ of 1, while fats have an RQ of less than 1. Thus, this option is correct.
- **Option 3: Type of respiration** - This option is misleading. While the type of respiration (aerobic vs anaerobic) can influence the overall metabolic process, it does not directly define RQ. Hence, this option is incorrect.
- **Option 4: None of these** - Since option 2 is correct, this option is also incorrect.

4. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Option 2: Oxygen content of substrate**.