In germinating seed, R.Q. falls when there is shift from

Options

A. Carbohydrate to fat as substrate
B. Fat to carbohydrate
C. Aerobic to anaerobic respiration
D. Protein to carbohydrate.

Answer

To solve the question regarding the respiratory quotient (R.Q.) in germinating seeds, we need to understand the concept of R.Q. and how it changes with different substrates used in respiration.

### Step-by-Step Solution:

1. **Understanding R.Q.**:
- The respiratory quotient (R.Q.) is defined as the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration.
- R.Q. = (Volume of CO2 evolved) / (Volume of O2 consumed)

2. **Identifying Substrates**:
- Different substrates yield different R.Q. values:
- Carbohydrates (e.g., glucose): R.Q. = 1
- Fats: R.Q. = 0.7
- Proteins: R.Q. = 0.9
- Organic acids: R.Q. > 1 (e.g., malic acid = 1.33)

3. **Analyzing the Shift in Substrates**:
- In germinating seeds, the initial substrate used for respiration is typically carbohydrates (like starch).
- As the seed continues to germinate and utilize its energy reserves, it may shift from using carbohydrates to fats as the primary source of energy.

4. **Determining the Change in R.Q.**:
- When the substrate shifts from carbohydrates (R.Q. = 1) to fats (R.Q. = 0.7), the R.Q. value decreases.
- This indicates a fall in the R.Q. when the seed transitions from carbohydrate metabolism to fat metabolism.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the R.Q. falls when there is a shift from carbohydrates to fats.

### Final Answer:
The R.Q. falls when there is a shift from carbohydrates to fats.

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