Given below is a list of different steps (i-vi) involved in respiration.
(i) Utilisation of `O_(2)` by the cells for catabolic reactions.
(ii) Transport of gases by the blood.
(iii) Pulmonary ventilation by which atmospheric air is drawn in and `CO_(2)` is released out.
(iv) Release of resultant `CO_(2)`.
(v) Diffusion of `O_(2)` and `CO_(2)` between blood and tissues.
(vi) Diffusion of gases (`O_(2)` and `CO_(2)`) across alveolar tissues.
Select an option which has correct sequence of all the steps.

Options

A. `(iii), (vi), (ii), (v), (i), (iv)`
B. `(iii), (vi), (i), (v), (ii), (iv)`
C. `(iv), (ii), (v), (iii), (i), (vi)`
D. `(iv), (vi), (ii), (v), (i), (iii)`

Answer

To solve the question regarding the correct sequence of steps involved in respiration, we will analyze each step and determine the logical order in which they occur.

### Step-by-Step Solution:

1. **Step 3: Pulmonary Ventilation**
The first step in respiration is pulmonary ventilation, which involves the inhalation of atmospheric air rich in oxygen and the exhalation of carbon dioxide. This is the initial phase where air enters the lungs.

2. **Step 6: Diffusion of Gases Across Alveolar Tissues**
After pulmonary ventilation, the next step is the diffusion of gases across the alveolar membranes. Here, oxygen from the inhaled air diffuses into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled.

3. **Step 2: Transport of Gases by the Blood**
Once the oxygen has diffused into the blood, it is then transported by the blood to various tissues throughout the body. This is the third step in the sequence.

4. **Step 5: Diffusion of O2 and CO2 Between Blood and Tissues**
After the oxygen reaches the tissues, the next step is the diffusion of oxygen from the blood into the tissues, and the diffusion of carbon dioxide from the tissues back into the blood.

5. **Step 1: Utilization of O2 by the Cells for Catabolic Reactions**
The oxygen that has diffused into the tissues is utilized by the cells for catabolic reactions, which produce energy.

6. **Step 4: Release of Resultant CO2**
Finally, as a result of cellular respiration, carbon dioxide is produced and released from the cells into the blood, completing the cycle of respiration.

### Correct Sequence:
The correct sequence of steps in respiration is:
**3, 6, 2, 5, 1, 4**