The last substrate which would be used in respiration is

Options

A. Carbohydrate
B. Protein
C. Fat
D. Organic acid

Answer

To determine the last substrate used in respiration, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Respiration**:
- Respiration can be categorized into two types: aerobic respiration and anaerobic respiration. In aerobic respiration, glucose is the primary substrate.

2. **Identify the Primary Substrates**:
- In aerobic respiration, the main substrate is glucose (C6H12O6). It is oxidized to release energy, carbon dioxide, and water.

3. **Recognize the Role of Carbohydrates and Fats**:
- During respiration, carbohydrates and fats are typically used as substrates. Carbohydrates are the first choice, followed by fats if carbohydrates are scarce.

4. **Understand Protoplasmic Respiration**:
- When carbohydrates and fats are not available, the body resorts to protoplasmic respiration. In this case, proteins become the substrate for respiration.

5. **Determine the Last Substrate**:
- The last substrate used in respiration is protein. This occurs when there is a shortage of carbohydrates and fats.

6. **Conclusion**:
- Therefore, the last substrate that would be used in respiration is **protein**.

### Final Answer:
The last substrate which would be used in respiration is **protein**.

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