Question

In humans, respiration occurs in the following steps. Arrange these steps in the correct order.
A. Diffusion of $O_2$ and $CO_2$ between blood and tissues
B. Diffusion of $O_2$ and $CO_2$ across alveolar membrane
C. Pulmonary ventilation by which atmospheric air is drawn in and $CO_2$ rich alveolar air is released out
D. Cellular respiration
E. Transport of gases by the blood
Choose the correct answer from the options given below:

• A. A, B, C, D, E
• B. E, A, C, D, B
• C. C, B, E, A, D
• D. C, A, B, E, D

Hint:

Logic Tip: Follow the path of an oxygen molecule: It goes into the lungs (C), crosses into the blood (B), rides the blood stream (E), crosses into the muscle (A), and is finally "burned" for energy (D).

Answer 1

The Correct Option is C

Concept:
Respiration in humans is a multi-step process that involves the physical movement of air, the exchange of gases across membranes, the transport of those gases throughout the body, and their final utilization within the cells to produce energy.
Step 1:
The process begins with the physical act of getting air into the lungs. This is Pulmonary ventilation (breathing in oxygen-rich air and breathing out carbon dioxide-rich air). First step: C
Step 2:
Once the air is in the alveoli (air sacs) of the lungs, gases must exchange with the bloodstream. This is the diffusion of $O_2$ and $CO_2$ across the alveolar membrane. Second step: B
Step 3:
After oxygen enters the blood, it must be carried to the rest of the body. This is the transport of gases by the blood. Third step: E
Step 4:
When the oxygenated blood reaches the target cells, gas exchange occurs again, this time between the capillaries and the body cells. This is the diffusion of $O_2$ and $CO_2$ between blood and tissues. Fourth step: A
Step 5:
Finally, the cells use the oxygen to break down glucose and release energy, producing carbon dioxide as a byproduct. This metabolic process is cellular respiration. Fifth step: D
Step 6:
Combining the steps yields the sequence: C $\rightarrow$ B $\rightarrow$ E $\rightarrow$ A $\rightarrow$ D.