R.Q. Value is an infinity during
Aerobic respiration of carbohydrates as substrate
Aerobic respiration of proteins as substrate
Aerobic respiration of fats as substrate
Anaerobic respiration of carbohydrates as substrate

Options

A. Aerobic respiration of carbohydrates as substrate
B. Aerobic respiration of proteins as substrate
C. Aerobic respiration of fats as substrate
D. Anaerobic respiration of carbohydrates as substrate

Answer

To determine when the R.Q. (Respiratory Quotient) value is infinity, we need to understand the concept of R.Q. and how it is calculated. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand R.Q.
R.Q. or Respiratory Quotient is defined as the ratio of carbon dioxide produced to oxygen consumed during respiration. The formula is:
\[ R.Q. = \frac{\text{CO}_2 \text{ produced}}{\text{O}_2 \text{ consumed}} \]

### Step 2: Identify the Conditions for R.Q.
The value of R.Q. varies depending on the type of substrate being used (carbohydrates, proteins, or fats) and the type of respiration (aerobic or anaerobic):
- **Aerobic respiration of carbohydrates**: R.Q. = 1
- **Aerobic respiration of proteins**: R.Q. = 0.8 to 0.9
- **Aerobic respiration of fats**: R.Q. = 0.7

### Step 3: Analyze Anaerobic Respiration
In anaerobic respiration, oxygen is not present. Therefore, the oxygen consumed is zero. When calculating R.Q. for anaerobic respiration:
- If we take any value (CO₂ produced) and divide it by zero (O₂ consumed), the result is undefined or considered infinity.

### Step 4: Apply This to the Given Options
Among the options provided:
- **Aerobic respiration of carbohydrates**: R.Q. = 1 (not infinity)
- **Aerobic respiration of proteins**: R.Q. = 0.8 to 0.9 (not infinity)
- **Aerobic respiration of fats**: R.Q. = 0.7 (not infinity)
- **Anaerobic respiration of carbohydrates**: Since oxygen is absent, R.Q. = ∞ (infinity)

### Conclusion
The R.Q. value is infinity during anaerobic respiration of carbohydrates as substrate. Therefore, the correct answer is:
**Option D: Anaerobic respiration of carbohydrates as substrate.**

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