How to prove germinating seeds evolve carbon dioxide during their respiration?

In this article are details of the experiment on how to prove germinating seeds evolve carbon dioxide during their respiration. The various precautions to be followed in doing this experiment are explained and exam questions related to the experiment which will be useful for those preparing for final practical or theory exams of various Boards.

Aim of the experiment

Germinating seeds evolve carbon dioxide during their respiration.

Materials required

Germinating gram seeds, freshly prepared Potassium hydroxide (KOH) solution, Petroleum jelly or wax, conical flask (500 ml), beaker (250 ml.), rubber cork with a hole, clean delivery tube bent twice at right angles, a small test tube, a piece of thread, marker and a measuring scale.


Respiration is a process by which food is oxidized by living cells of the organism to release energy for its life processes. Germinating seeds require a lot of energy during the germination process of the embryo. During that time they respire much faster and so they release more carbon dioxide.

Procedure of the experiment

  1. Take a conical flask and keep wet cotton wool at the bottom of the flask.

  2. Take some moist germinating pea seeds and keep them at the bottom of the flask on wet cotton wool.

  3. Close the mouth of the flask with one-holed rubber cork.

  4. Suspend a test tube containing freshly prepared potassium hydroxide solution inside the flask with the help of a thread.

  5. The mouth of the test tube is closed with a one-holed rubber cork.

  6. A double bent glass tube is taken, one end of it is KOH in the conical flask and the other end of it is kept in the conical flask and the other end of it is kept in a beaker containing water.

  7. The apparatus is made an airtight by applying petroleum jelly or wax at the lace of joints in the apparatus.

  8. With the help of a marker note down the level of water initially in the bent glass tube kept in the beaker.

  9. Leave the apparatus undisturbed for one hour under sunlight.

  10. Record the final water level after the end of the experiment.

Germinating seeds evolve carbon dioxide during their respiration
Germinating seeds evolve carbon dioxide during their respiration (Image by the author)

Result of the experiment

We notice there is an increase in the final water level in the glass tube after the experiment. During the experiment, the moist germinating seeds absorbed oxygen present in the conical flask and evolved carbon dioxide during the respiration of seeds. The carbon dioxide is then absorbed by the KOH solution kept inside the flask. Due to this a low pressure or vacuum is created in the flask which allowed a rise in the water level of the bent glass tube. Thus, we can prove carbon dioxide is evolved during the respiration of germinating seeds.


  1. The entire experimental setup should be made airtight.

  2. Seeds used for this experiment must be germinating and moist.

  3. Freshly prepared KOH solution only to be used for this experiment.

  4. Cotton plug should not be used instead of rubber cork.

  5. The end of the delivery tube kept in the conical flask should not touch germinating seeds.

  6. The end of delivery tube kept in the beaker should be dipped inside the beaker

  7. The initial and final readings of the water level in the delivery tube should be noted carefully.

Here is another biological experiment "How to prepare a temporary mount of a leaf peel to show stomata?".

Questions based on the experiment from various Boards

  1. Why wet cotton wool is kept at the bottom of the flask?
    Ans. The germinating seeds when become dry cannot respire and give out carbon dioxide. So to keep the germinating seeds moist wet cotton wool used in the flask.
  2. If a student not able to get the proper result after the experiment, what two reasons you may say?
    Ans. Freshly prepared KOH solution may not be kept in the conical flask/The apparatus may not be made airtight/The germinating seeds may become dry.

  3. Name the type of respiration carried out by germinating seeds in the flask and define it.
    Ans.The germinating seeds carrying out aerobic respiration. Aerobic respiration is the type of respiration in which food molecules are oxidized by using oxygen to release energy to carry life activities.

  4. Give an overall balanced chemical reaction of the above-mentioned process.
    Ans. C6H12O6 + 6O2 --------------> 6CO2 + 12H2O +38 ATP + heat energy

  5. What is the role of KOH solution in the conical flask?
    Ans. KOH solution in the flask will absorb the carbon dioxide evolved by germinating seeds during their respiration by consuming oxygen present in the air of flask. Due to this a low pressure or vacuum is created in the flask which makes the water to rise in the delivery tube from its initial level.

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