Alveolus contains a single layer of `"_____________"` cells.

Answer

To answer the question, "Alveolus contains a single layer of '_____________' cells," we can follow these steps:

### Step-by-Step Solution:

1. **Understand what an alveolus is**: An alveolus is a small, balloon-like structure in the lungs where gas exchange occurs. It is crucial for the respiratory process.

2. **Identify the structure of the alveolus**: Alveoli are characterized by their thin walls, which facilitate the exchange of gases (oxygen and carbon dioxide) between the air in the alveoli and the blood in the surrounding capillaries.

3. **Determine the type of cells present**: The walls of the alveoli are made up of a single layer of cells. This single layer is important because it allows for efficient gas exchange.

4. **Specify the type of cells**: The cells that make up this single layer are called "simple squamous epithelial cells." These cells are flat and thin, which is ideal for the diffusion of gases.

5. **Complete the answer**: Therefore, the complete answer to the question is: "Alveolus contains a single layer of 'simple squamous' cells."

### Final Answer:
Alveolus contains a single layer of "simple squamous" cells.

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