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

### Step-by-Step Solution:

1. **Understanding Alveoli**: Begin by recognizing that alveoli are tiny air sacs located in the lungs. They play a crucial role in the respiratory system as they are the primary sites for gas exchange between the air and the bloodstream.

2. **Function of Alveoli**: Alveoli facilitate the exchange of oxygen and carbon dioxide. This exchange occurs due to differences in the partial pressures of these gases in the alveoli and the blood.

3. **Importance of Surface Area**: The number of alveoli is significant because a higher number increases the surface area available for gas exchange, enhancing the efficiency of respiration.

4. **Estimating the Number of Alveoli**: Research and studies have estimated that the number of alveoli in human lungs ranges from approximately 274 million to 790 million.

5. **Selecting the Correct Answer**: Given the options provided (100 million, 300 million, 125 million, or 300 billion), the most accurate estimate based on the range mentioned 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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