Why the usual RQ for humans lies between 0.7 and 1.0 because

Options

A. (a) they respire fat and protein
B. (b) they utilize and respire carbohydrate and fat
C. (c) they respire carbohydrate and proteins
D. (d) they respire proteins and carbohydrate

Answer

**Step-by-Step Solution:**

1. **Understanding RQ**: The respiratory quotient (RQ) is defined as the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration. It is a crucial measure in understanding metabolic processes.

2. **Formula for RQ**: The formula for calculating RQ is:
\[ RQ = \frac{\text{Volume of CO}_2 \text{ evolved}}{\text{Volume of O}_2 \text{ consumed}} \]

3. **Determining RQ Values for Different Substrates**:
- Carbohydrates have an RQ of 1.0.
- Proteins have an RQ of approximately 0.9.
- Fats have an RQ of approximately 0.7.

4. **Balanced Diet in Humans**: Humans typically consume a balanced diet that includes carbohydrates, proteins, and fats. This balance affects the overall RQ value.

5. **Calculating the Usual RQ for Humans**: Since humans utilize a mix of carbohydrates, proteins, and fats for energy, the resulting RQ will fall between the RQ values of these substrates. Therefore, the usual RQ for humans lies between 0.7 (when primarily using fats) and 1.0 (when primarily using carbohydrates).

6. **Evaluating Options**:
- Option A: "They respire fat and protein." (Incorrect, as it would yield an RQ less than 0.7)
- Option B: "They utilize and respire carbohydrates and fat." (Correct, as it includes both high and low RQ substrates)
- Option C: "They respire carbohydrates and proteins." (Incorrect, as it would yield an RQ greater than 0.9)
- Option D: "They respire proteins and carbohydrates." (Similar to option C, hence incorrect)

7. **Conclusion**: The correct answer is Option B, as it accurately reflects the combination of substrates that results in an RQ value between 0.7 and 1.0.

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