What are alveoli?

Explanation

### Step-by-Step Solution

1. **Definition of Alveoli**: Alveoli are tiny, balloon-like structures found in the lungs of mammals, including humans.

2. **Location**: They are located at the end of the bronchial tubes in the respiratory system. This is where the air enters after passing through the trachea and bronchi.

3. **Function**: The primary function of alveoli is to facilitate the exchange of gases. During respiration, oxygen from the air inside the alveoli diffuses into the blood, while carbon dioxide from the blood diffuses into the alveoli to be exhaled.

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