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Class 10
Chapter 6 Class 10 - Life Processes

Give an experiment to prove that carbon dioxide is released during respiration.



Respiration is a biochemical process in which the food is oxidised in order to release energy.

To prove that CO 2 is released during respiration, 

  • We take germinating seeds which are actively respiring to produce CO 2 a
  • And we use Potassium Hydroxide (KOH) to absorb this released CO 2 .
    The overall reaction is as follows:  

Test to confirm presence of CO2 - Teachoo.jpg

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.


  1. Take about 25-30 seeds of gram and germinate these seeds by placing them on moist cotton wool or moist blotting paper for 3-4 days.
  2. Place the germinated seeds into a conical flask and sprinkle a little water in the flask to moist the seeds.
  3. Take freshly prepared 20% KOH solution in a test tube and hang it in a conical flask with help of thread.
  4. Close the mouth of the conical flask by placing a rubber cork containing one hole. .
  5. 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.
  6. Seal all the connections of the experimental set-up with vaseline so as to make it air-tight.
  7. Mark the initial level of water in the U-shaped delivery tube.
  8. Keep the apparatus undisturbed for 1-2 hours and note the change in level of water in the delivery tube.

Observation :

The level of water in the U-shaped delivery tube dipped in water of the beaker rises after sometime.   




  • CO 2 is released by the germinating seeds during respiration in a conical flask. 
  • This CO 2 is absorbed by KOH which is hanging inside the conical flask. 
  • Due to absorption of CO 2 , a vacuum is created which causes an upward movement of water present inside the delivery tube which can be seen by change in level of water in that tube. 



  1. Germinating seeds should be kept moist.
  2. All connections of the set-up should be air-tight.
  3. Freshly prepared KOH solution should be used.
  4. Keep one end of the U-shaped delivery tube in a conical flask and the other end immersed in water of the beaker.
  5. The test tube containing KOH should be hung carefully.

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo