Liberation of Carbon Dioxide During Fermentation

Introduction to Experiment

Living organisms derive their energy from food through a biological process known as cellular respiration. Most organisms are classified as aerobic, meaning they rely on oxygen to fully metabolise glucose into carbon dioxide and water, simultaneously generating energy. 

However, certain organisms, such as yeast and specific bacteria, can undergo respiration in the absence of oxygen, a process known as anaerobic respiration.

In this anaerobic respiration, glucose is transformed into ethanol and carbon dioxide, with energy being released as a result. This particular mode of respiration observed in certain microorganisms under anaerobic conditions is referred to as fermentation.

Experiment Procedure

• The procedure to conduct this experiment is as follows:
• Fill a test tube to the brim with fruit juice or a sugar solution.
• In another test tube, dissolve baker’s yeast granules in water. Use a dropper to add approximately twenty drops (equivalent to 2 mL) of this yeast suspension to the test tube filled with fruit juice. 
• Take note of the smell of the resulting liquid mixture.
• Seal the filled test tube with a cork. 
• Ensure an airtight seal by applying a thin layer of petroleum jelly around the cork.
• Insert a delivery tube through the single-hole cork in the fully-filled test tube.
• Securely attach the test tube to a laboratory stand.
• Submerge the other end of the delivery tube in a beaker containing freshly prepared lime water.
• Leave the setup undisturbed in bright sunlight for approximately sixty minutes.
• Observe if you notice any gas bubbles passing through the lime water. Also, check if the lime water turns milky. Record your observations.
• Finally, note any changes in the smell of the fruit juice mixture in the test tube at the end of the experiment.

Conclusion

Yeast actively participates in the utilisation of sugar present in the fruit juice. Within the yeast cell’s cytoplasm, enzymes facilitate the ethanol and carbon dioxide production from the glucose, accompanied by the release of energy. Since this metabolic activity occurs in the absence of oxygen, it is termed anaerobic respiration, and the overall process is known as fermentation.

The fermented juice exhibits a noticeable sweet and alcoholic aroma due to the formation of ethanol during fermentation. Meanwhile, carbon dioxide generated during this process enters the delivery tube. In the delivery tube, the gaseous carbon dioxide bubbles interact with the lime water, calcium hydroxide in aqueous form (Ca(OH)2), converting lime water into calcium carbonate and water. This chemical reaction causes the lime water to become milky in appearance.

Alternate Method

In this experiment, a phenol red indicator solution is used. One test tube containing phenol red can be used instead of the test tube with lime water. After a brief period, it is observed that the phenol red solution changes to a pale yellow colour. This observation strongly supports the fact that carbon dioxide is generated during fermentation.

As a result, we can confidently conclude that fermentation results in the release of carbon dioxide.

FAQs about Liberation of Carbon Dioxide During Fermentation