The respiratory quotient varies due to

Options

A. Respiratory substrate
B. Light and `O_2`
C. Respiratory product
D. Temperature

Answer

To solve the question regarding the variation of the respiratory quotient (RQ), we can break it down into several steps:

### Step-by-Step Solution:

1. **Understanding Respiratory Quotient (RQ)**:
- The respiratory quotient is defined as the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration.
- Mathematically, it is expressed as:
\[ RQ = \frac{\text{Volume of CO}_2 \text{ produced}}{\text{Volume of O}_2 \text{ consumed}} \]

2. **RQ Values for Different Substrates**:
- The RQ varies depending on the type of substrate being metabolized:
- **Carbohydrates**: When carbohydrates are oxidized, the RQ is approximately 1. This is because the amount of CO₂ produced is equal to the amount of O₂ consumed.
- **Fats**: The RQ for fats is around 0.7. This indicates that more oxygen is consumed relative to the carbon dioxide produced.
- **Proteins**: The RQ for proteins is approximately 0.9, which is also less than 1.
- **Organic Acids**: Certain organic acids can have an RQ greater than 1 (e.g., malic acid, aspartic acid), indicating that more CO₂ is produced than O₂ consumed.

3. **Factors Influencing RQ**:
- The primary factor that influences the respiratory quotient is the type of substrate being utilized for respiration. Different substrates yield different amounts of CO₂ and O₂ during metabolic processes.
- Other factors such as temperature, light, and respiratory products do not significantly affect the RQ.

4. **Conclusion**:
- Therefore, the respiratory quotient varies due to the type of respiratory substrate being utilized in the metabolic reactions.

### Final Answer:
The respiratory quotient varies due to the type of respiratory substrate (Option 1).

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