Mark the true statement among the following with reference to normal breathing.

Options

A. Inspiration is a passive process where as expiration is active
B. Inspiration is an active process where as expiration is passive.
C. Both inspiration and expiration are active processes
D. Both inspiration and expiration are passive processes

Answer

To determine the true statement regarding normal breathing, let's analyze the options provided:

1. **Inspiration is a passive process, whereas expiration is active.**
2. **Inspiration is an active process, whereas expiration is passive.**
3. **Both inspiration and expiration are active processes.**
4. **Both inspiration and expiration are passive processes.**

### Step 1: Understand the Process of Inspiration
- **Inspiration** is the process of taking air into the lungs. It involves the contraction of the diaphragm and intercostal muscles, which increases the volume of the thoracic cavity and decreases the pressure inside the lungs, allowing air to flow in. This process requires energy and is therefore considered **active**.

### Step 2: Understand the Process of Expiration
- **Expiration** is the process of expelling air from the lungs. During normal, quiet breathing, expiration is primarily a passive process. It occurs when the diaphragm and intercostal muscles relax, causing the thoracic cavity to decrease in volume and air to be pushed out of the lungs due to increased pressure. However, during forced expiration (like during exercise), it can become an active process, but in the context of normal breathing, it is **passive**.

### Step 3: Analyze the Options
- **Option 1** states that inspiration is passive and expiration is active. This is incorrect because inspiration is active.
- **Option 2** states that inspiration is active and expiration is passive. This is correct based on our understanding of the processes.
- **Option 3** states that both processes are active. This is incorrect as we established that expiration is passive during normal breathing.
- **Option 4** states that both processes are passive. This is also incorrect as inspiration is active.

### Conclusion
The true statement regarding normal breathing is: **Inspiration is an active process, whereas expiration is passive.**