Experiments on Respiration

To Demonstrate that Oxygen is Used up During Respiration

To Demonstrate Aerobic Respiration

The apparatus shown is called the respiroscope that is used to demonstrate respiration.

Few germinating seeds are taken in the bulb of the respirometer. The tube is inserted into a beaker containing mercury. A pellet of KOH is introduced into the set-up.

Another experiment is set up without any seeds but with the KOH pellet. This acts as the control.

After a day, the mercury level is found to be raised in the tube.

Why does the level of the mercury go up?

The oxygen in the apparatus is used up in respiration. This lowers the air pressure inside the bulb raising the level of mercury.

Why is the KOH pellet introduced?

KOH absorbs carbon dioxide. It is to rule out that carbon dioxide may be absorbed by the seeds.

To Demonstrate that Carbon Dioxide is Released during Respiration

To Demonstrate Evolution of Carbon Dioxide During Respiration

The experiment is set up as shown. Bottle C is covered with a black cloth to prevent photosynthesis.

On opening the stop cork near the aspirator, the lime water in D turns milky after sometime. However, the lime water in B does not turn milky.

Why does the lime water in D turn milky?

The lime water in D turns milky because the air given out from the seeds contains carbon dioxide.

Why does the lime water in B remain clear?

This is because the soda lime in A absorbs the carbon dioxide and it is this air that is entering the flask B.

To Demonstrate that Water is Lost During Expiration

Breathe gently on to a cold surface. Minute droplets of water can be observed. This shows that expired air has more water vapour than the inspired air. Thus, water is lost during respiration.

To Demonstrate that Heat is Liberated During Respiration

Flask A that contains germinating seeds will show rise in temperature after sometime whereas flask B will not. Why?

Experiment to Demonstrate that Heat is Liberated During Respiration

The seeds in B have been boiled. This destroys the enzymes and kills the seeds. Thus, respiration cannot take place. In A, the temperature rises because heat is liberated during respiration.

To Demonstrate Anaerobic Respiration in Plants

Kuhne's Tube(Glucose Solution + Yeast)

The above apparatus is called the Kuhne's fermentation vessel. It is filled with 10% glucose solution along with yeast. The vertical tube is filled completely and the bulb is half-filled. After sometime, the level in the bulb goes up and the level in the tube comes down. Why?

This is because, a gas is liberated. This displaces the liquid and being lighter, it occupies the top of the tube.

How is the gas proved to be carbon dioxide?

A KOH pellet is introduced into the solution. It rises up through the solution to the top of the tube and absorbs the gas. This proves that it is carbon dioxide.