AIM
To show that carbon dioxide is given out during respiration.
MATERIALS REQUIRED
Conical flask, U-shaped delivery tube (tube bent twice at right angles), cotton wool or moist blotting paper, water, thread, beaker, test tube, rubber cork with one hole, 20% freshly prepared KOH solution, Vaseline, soaked gram seeds.
THEORY
1. Respiration is a catabolic process during which food (glucose) is oxidized to liberate energy.
2. In the experiment, moist gram seeds are taken as they are actively respiring and releasing carbon dioxide.
3. The carbon oxide released is absorbed by KOH and forms K2CO3.
4. The reaction is given below:
PROCEDURE
1. Take about 20-30 gram of gram seed and germinate these seeds by placing them on moist cotton cloth or moist blotting paper for at least 3-4 days.
2. Place the germinated seeds into a conical flask and add some water in the flask to moist the seeds.
3. Prepare a 20% KOH solution in a test tube and hang it in the conical flask with the help of thread, as shown in the figure:
4. The mouth of the conical flask should be blocked by placing a rubber cork on the mouth of the conical flask.
5. Through the hole in the 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.
6. vaseline must be applied to all the connections of the set-up to make the connection air-tight.
7. Also, mark the initial level of water in the U-shaped delivery tube.
8. Keep the apparatus undisturbed for 2-3 hours and then note the change in the level of water in the delivery tube.
OBSERVATIONS
After some time, the water level in U-shaped delivery tube dipped in water of the beaker rises.
RESULT
1. The CO2 is released by the germinated gram seeds during respiration.
2. The CO2 released is absorbed by KOH present in the hanging test tube in a conical flask.
3. The absorption of CO2 creates a vacuum in the conical flask which causes an upward movement of water in the delivery tube leading to a change in the level of water in the delivery tube.
PRECAUTIONS
1. Seeds should be kept under a moist condition to undergo germination.
2. The test tube containing KOH must be hung carefully inside the flask.
3. Freshly prepared KOH solution should be used.