Experimentally Show That Carbon Dioxide is Given out During Respiration

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Aim of Experiment

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Aim of the experiment is to show that carbon dioxide is given out during respiration using germinating seeds.

Theory

Aerobic respiration is a catabolic process in the living cell which involves the oxidation of complex organic food substances resulting in the release of energy in the form of ATP and carbon dioxide is given out with each intake of oxygen.

In this experiment, gram or pea seeds are used because they show active respiration and release a good amount of carbon dioxide. The released carbon dioxide is absorbed by the freshly prepared potassium hydroxide (KOH) solution taken in the test tube.

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Materials and Apparatus Required

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Materials Required

Soaked and germinating gram or pea seeds, moist cotton wool or blotting paper, 20% of freshly prepared potassium hydroxide (KOH) solution, water, vaseline, and thread.

Apparatus Required

A conical flask (100 mL), beaker (200 mL), U-shaped glass tube, rubber cork with one hole, and a test tube (small).

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Procedure of Experiment

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1. Collect and prepare about 30-40 seeds of gram or pea. Then germinate the collected seeds for 4-5 days by wrapping them in moist cotton wool or blotting paper at a cool, dark place.
2. After 4-5 days, the germinating seeds will start sprouting. Take these seeds and keep them in a conical flask and moisten them by spraying some water.
3. Next, take 20% of the freshly prepared potassium hydroxide (KOH) solution in a test tube and suspend it in the conical flask using a thread.
4. Close the mouth of the conical flask using a rubber cork and adjust the thread accordingly so that the test tube is placed properly in it.
5. Now, take the U-shaped glass tube which is bent twice at right angles and insert one end of it through the hole in the rubber cork placed on the mouth of the conical flask and fix it. Take the other end of it and insert it in a 200 mL beaker containing water. Take the initial reading of the water level in the glass tube due to capillary action.
6. Seal every opening of the apparatus using vaseline to make them air-tight.
7. Keep the experimental setup in bright sunlight for one or two hours without any interruptions. Observe the change and note the final reading of the water level in the glass tube.

Fig. Respiration Experiment Using Germinating Seeds

Observation

After one or two hours, it is observed that there is a rise in the water level at the end of the U-shaped glass tube kept inside the beaker.

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Result of Experiment

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The production and release of carbon dioxide during respiration in germinating seeds is indicated by the rise of water level in the U-shaped glass tube. The germinating gram or pea seeds kept in the conical flask undergo active respiration and give out carbon dioxide.

Carbon dioxide is then absorbed by the potassium hydroxide (KOH) solution creating a partial vacuum at the end of the U-shaped glass tube fixed on the conical flask. This leads to air movement from the U-shaped glass tube to the conical flask which leads to the rise in water level on the glass tube from the other end fixed in the beaker.

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Precautions

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1. Before beginning the experiment, make sure that the germinating seeds in the conical flask are moistened.
2. The potassium hydroxide (KOH) solution used must be freshly prepared. It should be handled with care since the KOH solution is highly corrosive.
3. All the openings and connections of the apparatuses must be sealed with vaseline and the whole experimental setup must be airtight.
4. While suspending the test tube containing potassium hydroxide (KOH) solution using a thread inside the conical flask, extra care should be taken.
5. The U-shaped glass tube should have one of its ends fixed on the conical flask through a rubber cork while the other end must be submerged inside the beaker containing water.

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Things to Remember

• Before beginning the experiment, make sure that the germinating seeds in the conical flask are moistened.
• Germinating gram or pea seeds are selected for this experiment as they undergo active respiration and give out carbon dioxide into the air.
• The potassium hydroxide (KOH) solution used must be freshly prepared. It should be handled with care since the KOH solution is highly corrosive.
• All the openings and connections of the apparatuses must be sealed with vaseline and the whole experimental setup must be airtight.
• After completing the experimental setup, keep it in bright sunlight for one or two hours without any interruptions. After one or two hours, it is observed that there is a rise in the water level at the end of the U-shaped glass tube kept inside the beaker.
• The production and release of carbon dioxide during respiration in germinating seeds is indicated by the rise of water level in the U-shaped glass tube.