The number of alveoli in the human lungs has been estimated to be approximately

Options

A. 100 million
B. 300 million
C. 125 million
D. 300 billion

Answer

To answer the question regarding the estimated number of alveoli in the human lungs, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Lungs**:
- The lungs are the primary respiratory organs in humans, located in the thoracic cavity. They consist of various structures including bronchi, bronchioles, and alveoli.

2. **Identify the Function of Alveoli**:
- Alveoli are small, bag-like structures at the end of the bronchioles. They are crucial for gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled.

3. **Estimate the Number of Alveoli**:
- It has been estimated that there are approximately 300 million alveoli in a single pair of human lungs. This high number significantly increases the surface area available for gas exchange.

4. **Evaluate the Given Options**:
- The question provides four options regarding the number of alveoli:
- a) 100 million
- b) 300 million
- c) 125 million
- d) 300 billion
- Based on the information gathered, the correct answer is 300 million.

5. **Conclusion**:
- Therefore, the estimated number of alveoli in human lungs is approximately 300 million.

### Final Answer:
The number of alveoli in the human lungs has been estimated to be approximately **300 million**.

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