MARCH 2024 — BIOLOGY STD 12 Science — Question

Diagrams A and B represent the human respiratory system during the processes of inspiration and expiration.In diagram A, we observe the following changes typical of inspiration:

1. The diaphragm contracts and moves downwards, increasing the volume of the thoracic cavity.
2. The intercostal muscles contract, raising the rib cage and further increasing the thoracic volume.
3. As the volume of the thoracic cavity increases, the pressure inside decreases, leading to the inflow of air into the lungs.

In diagram B, which illustrates expiration, the opposite occurs:

1. The diaphragm relaxes and moves upwards, decreasing the volume of the thoracic cavity.
2. The intercostal muscles relax, causing the rib cage to lower, which further decreases the thoracic volume.
3. As the volume of the thoracic cavity decreases, the pressure inside increases, and air is pushed out of the lungs.

These changes in volume and pressure in the thoracic cavity are critical for the process of breathing, as they enable the flow of air in and out of the lungs.