With regard to the respiratory system and the process of respiration in man, answer the following questions:

(a) Name the two muscles that help in breathing.

(b) Briefly describe how the above mentioned muscles help in the inspiration of air.

(c) Give the overall chemical equation to represent the process of respiration in humans.

(d) What is meant by:

1. Residual air
2. Dead air space

(a) The two muscles that help in breathing are — intercostal muscles and abdominal muscles.

(b) When the intercostal muscles stretch between the ribs, they move outwards and inwards causing them to enlarge the chest cavity.

(c) The overall chemical equation for the process of respiration in humans is as given below:

$C$6H{12}O6 + 6O2 \overset{\text{enzymes}}{\longrightarrow} 6CO2 + 6H2O + \underset{\text{chemical energy}}{38 ATP} + \underset{\text{heat energy}}{420 kcal}

(d) The meanings of Residual air and Dead air space are as follows:

1. Residual Air — Even after forcibly breathing out, some air always remains in the lungs. This air is referred to as residual air. The volume of this air is 1500mL.
2. Dead air space — Some tidal air is remaining in the respiratory passages such as bronchi and trachea. Here no gas diffusion takes place. This volume is referred to as dead air space and its volume is 150mL.