Question

Which of the following differentiates the expired air from the inspired air?
A) Less oxygen
B) Presence of bacteria
C) More water vapour
D) All of the above

Answer 1

Hint: The air that moves out of the chest during the process of expiration is called expired air while inspired air is the air that enters the lungs during the process of inspiration, provided the larynx is open. When the air pressure within the alveoli exceeds the atmospheric pressure, the air is blown from the lungs which is called expiration.

Complete answer:
The air inside the lungs is not being completely replaced. There is always the presence of a mixture of air left inside and the air inspired. Exhalation takes longer than inhalation and it facilitates a better exchange of gases.

The difference in expired and inhaled air is as listed below:

Parameters	Expired air	Inspired air
Oxygen	Contains less oxygen compared to inspired air.Has fourteen percent oxygen.	Comprises more oxygen than exhaled air.Has twenty-one percent of oxygen
Water vapour	Contains more water vapour which is four percent.	Has only some water vapour than exhaled air.
Carbon dioxide	Has more carbon dioxide.Has four percent of carbon dioxide.	Has less carbon dioxide
Temperature	It possesses the same temperature as the body which is warmer.	Has a cooler temperature than expired air.
Bacteria	Contains bacteria.	Inspired air also contains bacteria.

It is during the exhalation process that the olfaction contribution to flavour occurs in comparison to that of ordinary smell which occurs during the inhalation phase. Therefore, we can say expired air differs from inspired air in terms of oxygen, the presence of bacteria and also water vapor.

Therefore the correct answer is option ‘D’.

Note: The main reason for exhalation to happen is to get rid of the carbon dioxide in the body, which is the waste product of the process of gas exchange in humans. Air is brought in the body through the process of inhalation during which air is taken in through the lungs. Parts of the nervous system helps in regulating the respiration in humans.