Breathing invovles two stages (a)___ during which atmospheric air is drawn in and (b)_____ by which the alveolar air is released out.

Answer

To answer the question regarding the two stages of breathing, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Breathing**: Breathing is a biological process that involves the exchange of gases, primarily oxygen (O2) and carbon dioxide (CO2). It consists of two main stages.

2. **First Stage - Inhalation**: The first stage of breathing is known as **inhalation** or **inspiration**. During this phase, atmospheric air, which contains oxygen, is drawn into the lungs. This process occurs when the diaphragm contracts and the chest cavity expands, creating a negative pressure that pulls air into the respiratory system.

3. **Second Stage - Exhalation**: The second stage of breathing is known as **exhalation** or **expiration**. In this phase, the air that is rich in carbon dioxide (which has been exchanged in the alveoli) is released from the lungs back into the atmosphere. This occurs when the diaphragm relaxes and the chest cavity decreases in volume, pushing the air out.

4. **Conclusion**: Therefore, the two stages of breathing can be summarized as:
- (a) **Inhalation** (or **inspiration**) during which atmospheric air is drawn in.
- (b) **Exhalation** (or **expiration**) by which the alveolar air is released out.

### Final Answer:
Breathing involves two stages: (a) **Inhalation** during which atmospheric air is drawn in and (b) **Exhalation** by which the alveolar air is released out.

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