CO2 Released During Respiration MCQs Quiz | Class 10

Understanding CO2 Release During Respiration

Respiration is a vital metabolic process common to all living organisms, through which organic substances are broken down to release energy. A key byproduct of this process, especially aerobic respiration, is carbon dioxide (CO2).

The Demonstration Experiment

To experimentally demonstrate the release of CO2 during respiration, a common setup involves using germinating seeds. Germinating seeds are preferred because they are metabolically very active and respire at a high rate.

Materials Required:

• Two conical flasks (A and B)
• Germinating gram or pea seeds (for flask A)
• Boiled or dead seeds (for flask B – control)
• Small test tubes with freshly prepared lime water (calcium hydroxide solution, Ca(OH)2)
• U-tube or delivery tube
• Cork stoppers
• Petroleum jelly or wax for sealing

Procedure:

1. Take two conical flasks, A and B.
2. In flask A, place a handful of germinating seeds. Suspend a small test tube containing fresh lime water inside the flask without touching the seeds. Seal the flask with a cork stopper.
3. In flask B (control), place an equal quantity of boiled or dead seeds (which are no longer respiring). Similarly, suspend a test tube with fresh lime water and seal the flask.
4. Ensure both flasks are airtight using petroleum jelly or wax if necessary.
5. Leave both setups undisturbed in normal conditions for a few hours or overnight.

Observation

After a few hours, the following observations will be made:

• Flask A (Germinating seeds): The lime water in the small test tube inside flask A will turn milky or cloudy.
• Flask B (Boiled/Dead seeds – Control): The lime water in the small test tube inside flask B will remain clear or show very negligible change.
• A slight increase in temperature might also be observed in flask A compared to flask B, indicating energy release.

The turning of lime water milky is a standard chemical test for the presence of carbon dioxide. Calcium hydroxide (lime water) reacts with carbon dioxide to form insoluble calcium carbonate, which appears as a white precipitate, making the solution milky:

Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)

Conclusion

Based on the observations, we can conclude that:

• Living organisms (represented by germinating seeds) release carbon dioxide during the process of respiration.
• The control setup (boiled seeds) confirms that this CO2 release is a characteristic of living, respiring organisms and not due to any atmospheric CO2 or other factors.

Quick Revision Points:

• Respiration is the process of energy release from food.
• Aerobic respiration produces carbon dioxide and water.
• Lime water (Ca(OH)2) is used to detect CO2.
• CO2 turns lime water milky due to the formation of calcium carbonate (CaCO3).
• Germinating seeds respire actively, making them ideal for this experiment.
• Boiled/dead seeds act as a control as they do not respire.
• The experiment confirms CO2 as a byproduct of respiration in living organisms.

Extra Practice Questions:

1. What would happen if potassium hydroxide (KOH) solution was placed instead of lime water in the respiration experiment?
2. Why is it important for the flasks to be airtight in this experiment?
3. Name the type of respiration that produces CO2 and requires oxygen.
4. If an animal is used instead of seeds to demonstrate CO2 release, what precautions should be taken?
5. What other gas is utilized by organisms during aerobic respiration, and how could its consumption be demonstrated?