R.Q. can vary due to

Options

A. Temperature
B. Respiratory substrate
C. Light and oxygen
D. Respiratory product.

Answer

### Step-by-Step Solution:

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

2. **Factors Affecting RQ**:
- RQ can vary based on the type of respiratory substrate being utilized. Different substrates yield different amounts of CO2 and O2 during respiration.

3. **Analyzing Different Substrates**:
- **Carbohydrates**: When carbohydrates are used as the substrate, the RQ is typically 1. This means that the amount of CO2 produced is equal to the amount of O2 consumed.
- **Fats**: The RQ for fats is around 0.7, indicating that less CO2 is produced compared to the amount of O2 consumed.
- **Proteins**: The RQ for proteins is approximately 0.9.
- **Organic Acids**: Some organic acids can have an RQ greater than 1; for example, malic acid has an RQ of 1.33.

4. **Conclusion**:
- The variation in RQ is primarily due to the type of respiratory substrate being metabolized. Therefore, the correct answer to the question is that RQ can vary due to the type of respiratory substrate.

### Final Answer:
RQ can vary due to the type of respiratory substrate being utilized.

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