What is the main site of human respiratory system
where exchange of gases occurs?

Options

A. Alveoli
B. Bronchiole
C. Primary and secondary bronchi
D. Trachea

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the main site in the human respiratory system where gas exchange occurs.

2. **Understand the Respiratory System**: The human respiratory system is composed of various structures including the trachea, bronchi, bronchioles, and alveoli. Each of these structures plays a role in the process of breathing and gas exchange.

3. **Focus on Gas Exchange**: Gas exchange refers to the process where oxygen (O2) is taken into the bloodstream and carbon dioxide (CO2) is expelled from the bloodstream. This process is crucial for maintaining the body's oxygen levels and removing waste gases.

4. **Identify the Key Structure**: The alveoli are small, sac-like structures located at the end of the bronchioles. They are the primary sites for gas exchange in the lungs.

5. **Explain the Function of Alveoli**: When air is inhaled, it enters the alveoli. Here, oxygen from the air passes through the alveolar walls into the surrounding blood capillaries, where it binds to hemoglobin in red blood cells. Simultaneously, carbon dioxide from the blood is released into the alveoli to be exhaled.

6. **Conclusion**: Therefore, the main site of gas exchange in the human respiratory system is the alveoli.

**Final Answer**: The main site of gas exchange in the human respiratory system is the **alveoli**.

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