Human Lung Model in Bell Jar

Quick Answer: The human lung model in a bell jar is a breathing demonstration in which a bell-shaped jar stands for the chest, two balloons on a branched tube stand for the lungs, and a rubber sheet across the open base acts as the diaphragm. Pulling the sheet down inflates the balloons.

Setting Up and Running the Bell Jar Model

A bell jar lung model only works if the jar is airtight. The branched tube passes through a stopper in the neck of the jar, the balloons are fitted over its two lower ends, and a rubber sheet is stretched over the wide base and fastened so that no air can creep past its edge. Before a lesson, a quick test is to pull the sheet down and watch: if the balloons stay limp, air is entering around the stopper or the sheet rather than through the tube.

In class, pull the sheet down slowly by its knob or tab and pause, so students see the balloons fill as the space in the jar increases; then let it return and watch them empty. Asking the class to predict what will happen before each step, and then to explain it in terms of volume and pressure, turns a quick demonstration into a reasoning exercise.

The model also allows a memorable extension on what happens when the chest wall is breached. If the neck stopper is loosened slightly so that air can leak into the jar, pulling the sheet no longer inflates the balloons, because air enters the jar directly instead of the balloons. This mirrors a pneumothorax, in which air in the pleural space lets a lung collapse. The same design is sold as the respiratory system jar model in the STEM range, and the jar material and size of this listing should be confirmed.

Specifications

Where the Bell Jar Model Fits

• Demonstrating inhalation and exhalation in middle and secondary school biology
• Predict, observe and explain activities on volume and pressure
• Modelling a pneumothorax by letting air leak into the jar
• Revising the parts of the respiratory system and what each part of the model stands for

Care & Handling

• Store the bell jar lung model with the rubber sheet relaxed, not pulled down, so it keeps its elasticity.
• Replace balloons as soon as they become sticky or show cracks; perished rubber leaks and bursts.
• Wash the jar with warm soapy water only, and dry it before refitting the sheet, as trapped moisture spoils the seal.
• Carry the jar with both hands under the base; with its stopper and tube fitted it is top-heavy.

Why Choose LabEquip

Schools choose a bell jar model because it gives a clear, reusable breathing demonstration for the whole class. It is listed within LabEquip’s biology lab products; use the LabEquip contact page to confirm the jar size and what is supplied.

Frequently Asked Questions

How do I check the bell jar model for leaks?

Pull the rubber sheet down and hold it. If the balloons stay limp or slowly shrink, air is getting in around the stopper or the edge of the sheet. Re-seat the stopper, tighten the sheet’s fastening and try again.

How can the model show a collapsed lung?

Loosen the stopper slightly so air can enter the jar directly. Pulling the sheet then fails to inflate the balloons, just as a lung collapses when air enters the pleural space in a pneumothorax.

Does the rubber sheet move like a real diaphragm?

Not exactly. The sheet is pulled downward, whereas the real diaphragm is a dome-shaped muscle that flattens as it contracts. The direction of change in chest volume is the same, which is the point the model makes.

What does the space inside the jar represent?

It stands for the pleural space and chest cavity around the lungs. Changing the volume of that space changes the pressure acting on the balloons, which is how the real lungs are made to fill and empty.

What should students record during the demonstration?

A simple table works well: the movement of the sheet, the change in jar volume, the change in pressure and whether the balloons inflate or deflate. Students then match each row to inhalation or exhalation.

Is the bell jar model the same as other breathing models?

It uses the same principle as most breathing demonstrations, but its jar, branched tube, balloons and rubber sheet are a specific design. Other demonstration models may use a plunger or a closed plastic chamber instead.

Last Updated: September 2026