NCERT Solutions for Class 7th Science Chapter 9 .2.1 Respiration in humans — In-text Question
Book page 1319 Updated on2026-09-19
Q1.
What do the balloons in the model mentioned in Fig. 9.9 represent? What does the rubber sheet represent?
Fig. 9.9, page 130 — model made in Activity 9.2 to show the mechanism of breathing.
Answer
In this model, the balloons represent the lungs and the rubber sheet represents the diaphragm.
Part of the model
Part of the body it represents
Two balloons
The two lungs
Thin rubber sheet at the base
The diaphragm
Y-shaped hollow tube
The windpipe and its two branches
Wide plastic bottle
The chest cavity, enclosed by the rib cage
Why it happens: pulling the sheet down copies the diaphragm moving downwards during inhalation, which increases the space inside the chest so that air enters the lungs. Releasing it copies the diaphragm moving upwards during exhalation, which reduces the space and pushes air out.
Tip: the model has one limitation — the bottle is rigid, so it cannot show the ribs moving up and outwards. In the real chest, the ribs move as well as the diaphragm.