Question

The phenomenon of normal breathing in a human being comprises of
A. An active inspiratory and a passive expiratory phase.
B. A passive inspiratory and an inactive expiratory phase.
C. Both active inspiratory and expiratory phases.
D. Both passive inspiratory and expiratory phases.

Answer 1

Hint: Breathing is defined as the process of intake of fresh air from the environment and expulsion of foul air from the body. It is carried out by different respiratory organs. Breathing involves oxidation of complex substances into simpler ones.

Complete answer: When we breathe, we take in oxygen inward from the air and give out carbon dioxide which is utilized by plants. The process by which oxygen is taken in is known as inhalation, while the process of giving out carbon dioxide is known as exhalation. The breathing rate can be explained as the number of breaths per minute. It is inversely proportional to the size of the body of an organism. For example, the breathing rate that of an adult is 15-16 times in comparison to that of a new-born baby, which is 40-50 times. The breathing mechanism is composed of two processes; inspiration and expiration.
a) Inspiration: It involves the contraction of the diaphragm and external intercostal muscles. Intercostal muscles are muscles present in the intermediate and between the ribs. They are of two types; internal and external intercostal muscles. The internal intercostal muscles make the middle layer of intercostal muscles, while the external intercostal muscles develop on the interior surface of the ribs. It is usually an active process that completes in two seconds. When the radial muscle of the diaphragm contracts, the diaphragm becomes flattened. As a result, the intrapulmonary volume increases and the intrapulmonary pressure decreases. At the time when external intercostal muscles contract, the ribs and sternum move upward and outward respectively. It results in an increase in intrapulmonary volume and increases the intrapulmonary pressure. Due to this, the environmental air enters into the lungs through the respiratory tract.
b) Expiration: It is defined as the process of giving out of air. It constitutes the relaxation of the diaphragm and external intercostal muscles. It is a passive process processed in five seconds. When the radial muscles of the diaphragm relax, it becomes dome-shaped. As a result, the intrapulmonary volume decreases and intrapulmonary pressure increases. At the time, when external intercostal muscles relax, the ribs and sternum move downward and inward respectively. It also results in a decrease of the intrapulmonary volume and increases the intrapulmonary pressure. So, air expels out of the lungs through the respiratory tract.
Hence, the correct answer is option A.

Note: At the time of forceful expiration, abdominal muscles and internal intercostal muscle contracts, which decreases the intrapulmonary volume and the intrapulmonary pressure increases. Due to this, air expels out of the lungs. Breathing is a physical process, while respiration is a biochemical process that involves the oxidation of the food.