Which of the following is not a respiratory exchange surface?

Options

A. Air sacs of birds
B. Skin of amphibians
C. Gills of larval amphibians
D. Alveoli of mammals

Explanation

To determine which of the following is not a respiratory exchange surface, we need to analyze the options provided and understand the function of each structure in the context of gas exchange.

### Step-by-Step Solution:

1. **Understand Respiratory Exchange Surfaces**:
- Respiratory exchange surfaces are specialized structures in organisms where the exchange of gases (oxygen and carbon dioxide) occurs. Common examples include alveoli in mammals, gills in fish, and the skin in amphibians.

2. **Identify Common Respiratory Structures**:
- **Alveoli**: These are tiny air sacs in the lungs of mammals where gas exchange occurs.
- **Gills**: Found in fish and some amphibians, gills extract oxygen from water.
- **Skin**: In amphibians, moist skin can serve as a respiratory surface for gas exchange (cutaneous respiration).

3. **Consider the Options**:
- If the options include structures like alveoli, gills, and skin, these are all recognized respiratory surfaces.
- However, if one of the options is "air sacs of birds," we need to evaluate their role.

4. **Evaluate Air Sacs of Birds**:
- Air sacs in birds are part of their respiratory system but do not directly participate in gas exchange. Instead, they function to increase lung capacity and ensure a continuous flow of air through the lungs, which is essential for efficient respiration during flight.

5. **Conclusion**:
- Based on the analysis, the air sacs of birds do not serve as a respiratory exchange surface. Therefore, the correct answer to the question is the air sacs of birds.

### Final Answer:
The air sacs of birds are not a respiratory exchange surface.

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