Question

Which of the following is true for $CO_2$ concentration?
A. More in alveolar air than in expired air
B. More in expired air than in alveolar air
C. More in inspired air than in alveolar air
D. More in inspired air than in expired air

Answer 1

The respiration in humans, like other organisms, involves the intake or inspiration of oxygen and the expulsion of carbon dioxide. These processes are dependent on the partial pressures of these gases.

Complete answer:
Since the process of respiration is dependent mainly on the partial pressure of oxygen as well as carbon dioxide, the movement of the air occurs from a region of higher concentration to that of lower concentration. Since carbon dioxide is expired, the partial pressure of carbon dioxide within the lungs should be greater than that of the expired air. Therefore during expiration, the carbon dioxide concentration in the alveolar air is greater than that in the expired air.
Considering the other given options:
The concentration of carbon dioxide cannot be more in expired air than in alveolar air since it is not possible for expiration to occur. Thus it, not the appropriate answer.
The concentration of carbon dioxide cannot be more in inspired air than in alveolar air, since for inspiration to occur, the concentration or the partial pressure of oxygen should be higher in the inspired air. Thus the option is not the appropriate answer.
The concentration of carbon dioxide cannot be more in inspired air than in expired air. For normal expiration to occur. Therefore it is not the correct option.
Thus from the above-given options, the most appropriate answer is A. The concentration of carbon dioxide is more in alveolar air than in expired air.

Note: Multiple factors affect the rate and process of respiration. They can be broadly categorized as external and internal factors. The external factors are temperature, oxygen concentration, and carbon dioxide concentration. The internal factors are the acidity of the cytoplasm and the functioning of respiratory enzymes.