Bell Jar Model Labeled – What Each Part Stands For

All 12 parts on the diagram

Show the list

The model 6

Balloons They stand for the lungs and fill with air.
Rubber sheet It stands for the diaphragm, the muscle under the lungs.
Bell jar It stands for the chest wall and its rib cage.
Glass tube It stands for the trachea, or windpipe.
Y-tube branches They stand for the two bronchi, one to each lung.
Stopper It plugs the neck; the glass tube passes through it.

The chest 6

Lungs The two organs that fill with air; the model’s balloons.
Diaphragm A dome of muscle under the lungs; the model’s rubber sheet.
Chest wall (rib cage) It surrounds the chest cavity; the model’s bell jar.
Trachea (windpipe) The model’s glass tube stands for this windpipe.
Bronchi The trachea divides into two bronchi, one for each lung.
Thoracic cavity (chest cavity) The space inside the chest; the space inside the jar.

How this list was compiled: Every name and pairing was read on 2026-10-03 and kept only where two independent sources give it. The model and what each part stands for: (1) Richard W. Sharpe, A Laboratory Manual for the Solution of Problems in Biology (1911, public domain), Mechanics of Respiration, The Diaphragm, https://archive.org/details/laboratorymanual00shar ; (2) New York State Education Department, Science Syllabus for Middle and Junior High Schools, Living Systems, Block B (1977), activity B-79, https://archive.org/details/micro_IA41155102_0449 ; (3) An Improved Model for Demonstrating the Mechanism of Breathing, in Biology Labs That Work, volume II (2000), https://archive.org/details/micro_IA41153645_0740 ; (4) Getting Enough Oxygen, Annotated Teacher's Edition (1976), https://archive.org/details/gettingenoughoxyunse ; (5) Learning about Body Systems (1984), A Model of the Respiratory System, https://archive.org/details/micro_IA41152901_0894 ; (6) My Own Science Problems (1935), To Show How We Breathe, https://archive.org/details/myownscienceprob00huntrich . The chest: (7) Wikipedia, text only: Breathing, Thoracic diaphragm, Thoracic cavity, Bronchus and Pleura, https://en.wikipedia.org/wiki/Breathing ; (8) US National Cancer Institute, SEER Training Modules, Mechanics of Ventilation and Bronchi, Bronchial Tree, and Lungs, https://training.seer.cancer.gov/anatomy/respiratory/mechanics.html . The drawing is our own. Licence: own work

The drawing: Drawn for this site on 2026-10-03 from plain geometry. Own original drawing; nothing traced or copied. Licence: own work

How it works

The first view is the bell jar model labeled part by part. The second is the chest, drawn the same way around, so each part of the model sits where its body part sits.

Read the full guide

Pull the sheet down

The rubber sheet stands for the diaphragm and the balloons for the lungs. Pulling the sheet down makes the space inside the jar larger, so the air pressure in it drops. Air from outside moves down the tube and the balloons fill. In the chest the diaphragm contracts, the chest cavity gets larger and air flows into the lungs.

Let the sheet go

The space gets smaller again and air is pushed out of the balloons. In the chest the diaphragm relaxes back into its dome and air leaves the lungs.

The two views share one layout: find a part in the model, then look in the same place on the chest.

Questions and answers

What does each part of the bell jar model represent?

The balloons represent the lungs, the glass tube the trachea, its two branches the bronchi, the rubber sheet the diaphragm and the bell jar the chest wall with its rib cage. The space inside the jar stands for the chest cavity.

What does the rubber sheet represent in the bell jar model?

The diaphragm, the dome of muscle under the lungs. Pulling the sheet down copies the diaphragm contracting as a breath is taken in.

Why do the balloons inflate when the rubber sheet is pulled down?

Pulling the sheet down makes the space inside the jar larger, so the air pressure in the jar drops. Air from outside then moves down the tube into the balloons.

What are the limitations of the bell jar model?

It shows the work of the diaphragm only. In the body the muscles between the ribs also lift the rib cage on a breath in. The jar is full of air, while the thin space around each lung holds fluid.