Question

(a) Describe the mechanism of breathing in human beings. (b) (i) Under normal conditions, what is the rate of breathing per minute? (ii) Why does the rate of breathing increase by 20 to 25 times during vigorous exercise?

Answer 1

(a) Mechanics of Breathing. The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. This action is also known as external respiration. When we inhale the intercostal muscles (between the ribs) and diaphragm contract to expand the chest cavity.
(b) (i) The normal respiration rate for an adult at rest is 12 to 20 breaths per minute.
(ii) Because muscles consume more energy when we exercise and we breath faster so that our heart can work faster to deliver the oxygen.