Question

Exchange of gases between alveoli and blood in pulmonary capillaries is known as
a. External respiration
b. Internal respiration
c. Cellular respiration
d. None of the above

Answer 1

Hint: Respiration is a biological process that is concerned with exchange of gases between the body of organisms and the environment. The oxygen inhaled helps in breaking down complex organic compounds and thus, producing energy in the body.

Complete Answer
Respiration, being a complex process, completes in three different stages: external respiration, internal respiration and cellular respiration. Let's study each of these to find the correct answer.
External respiration: It is the first stage of respiration. It involves exchange of gases between respiratory organs of the organism (such as lungs, nostrils) and the environment. After that, the oxygen rich air supplies oxygen to blood flowing in pulmonary capillaries and takes back Carbon dioxide. This is the simplest stage of respiration which is also termed as breathing.
Internal respiration: It is the second stage of respiration that involves exchange of gases (that is Carbon dioxide and Oxygen) between oxygenated blood and body tissues. Therefore, option B is an incorrect answer.
Cellular respiration: It is the third stage of respiration that involves usage of oxygen for energy production at cellular level. The oxygen inhaled helps in breakdown of organic compounds (glucose) which in turn supplies energy for carrying out metabolic processes in the body. This is the final stage of the respiration process that involves a set of chemical
reactions besides gaseous exchange.

Thus, from the above discussed concepts about respiration, we can say that option A) External respiration is the correct answer.

Note:
The inhaled air travels through nostrils to the lungs where it travels through narrow pipes called bronchioles. The ends of these bronchioles are fitted with a small air sac called alveoli (the ultimate gas exchanging unit of lungs).