In the experimental set up to show that “CO₂ is given out during respiration”, name the substance taken in the small test tube kept in the conical flask. State its function and the consequence of its use.

For the experiment to prove that CO₂ is given out during respiration, moist gram seeds are taken. These are actively respiring and releasing CO₂. The CO₂ released is absorbed by KOH and forms K₂CO₃.

The experiment:

•A few gram seeds were taken and germinated by making them moist.

•The germinated seeds were kept in a conical flask and water was sprinkled on top of them to make them moist.

•20% KOH (freshly prepared) was taken in a test tube and hung in the conical flask with the help of a thread.

•The mouth of the conical flask was closed with the help of a rubber cork containing a hole.

•Through the hole of rubber cork, insert one end of the U-shaped glass delivery tube in the conical flask and place the other end into a beaker filled with water.

•The initial level of water was marked in the U-shaped delivery tube.

•The set up was left undisturbed for 1-2 hours.

•It was observed that the level of water in the U-shaped delivery tube dipped in the beaker water rises.

The substance taken in the small tube is: KOH i.e. Potassium hydroxide.

Function: The KOH absorbs the carbon dioxide released by the germinating seeds and a partial vacuum is created because of the loss of CO₂ in the flask.

Consequence: Germinated gram seeds in a conical flask release CO₂ during respiration. The CO₂ released is absorbed by KOH present in the hanging test tube in conical flask. This creates a vacuum in conical flask which causes upward movement of water in the delivery tube leading to change in level of water in the delivery tube.