Arrange the given steps of respiration mechanism in the order they occur in
(I) Diffusion of gases across the alveolar membrane
(II) Diffusion of `O_(2)` and `CO_(2)` between blood and tissue
(III) Breathing or pulmonary ventilation
(IV) Utilisation of `O_(2)` by the cells
(V) Transport of gases by the blood

Options

A. I-II-III-IV-V
B. III-I-II-V-IV
C. III-I-V-II-IV
D. III-II-IV-I-V

Answer

To arrange the steps of the respiration mechanism in the correct order, we will analyze each step and understand the sequence in which they occur during the process of respiration.

### Step-by-Step Solution:

1. **Breathing or Pulmonary Ventilation (Step III)**: The first step in the respiration process is breathing, also known as pulmonary ventilation. This involves inhaling air from the atmosphere into the lungs, where oxygen is present. This step is crucial as it initiates the process of gas exchange.

2. **Diffusion of Gases Across the Alveolar Membrane (Step I)**: Once the air is in the lungs, the next step is the diffusion of gases across the alveolar membrane. The alveoli are tiny air sacs in the lungs where oxygen from the inhaled air diffuses into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled.

3. **Transport of Gases by the Blood (Step V)**: After the diffusion of gases, the oxygen that has entered the blood is then transported throughout the body via the circulatory system. Hemoglobin in red blood cells binds to oxygen and carries it to various tissues.

4. **Diffusion of O2 and CO2 Between Blood and Tissue (Step II)**: Once the oxygen-rich blood reaches the tissues, the next step is the diffusion of oxygen from the blood into the tissues, while carbon dioxide produced by cellular metabolism diffuses from the tissues into the blood.

5. **Utilization of O2 by the Cells (Step IV)**: Finally, the last step is the utilization of oxygen by the cells for cellular respiration, where glucose is broken down to produce energy.

### Correct Order:
The correct sequence of the steps in the respiration mechanism is:
- (III) Breathing or pulmonary ventilation
- (I) Diffusion of gases across the alveolar membrane
- (V) Transport of gases by the blood
- (II) Diffusion of O2 and CO2 between blood and tissue
- (IV) Utilization of O2 by the cells

### Final Answer:
The correct order is: III, I, V, II, IV.

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