Respiration is the production of energy through the breakdown of complex organic structures. Anaerobic respiration is respiration without oxygen. The products of anaerobic respiration are alcohol and carbon dioxide.
To identify the products of anaerobic respiration.
Plastic bottle with lid, plastic syringe, delivery tube*, cotton wool, test tube*, beaker*, yeast, glucose*, water, and lime water*.
1. Make a hole on one side of plastic water bottle and connect the delivery tube, making sure there is an airtight seal.
2. Boil some water to remove dissolved oxygen and let it cool.
3. Prepare a water bath by mixing hot and cold water. The ideal temper-ature is the same as human body temperature - the water should feel warm but not hot.
1. In the plastic bottle mix 1/4 spoon of glucose, 1/2 spoon of yeast, and approximately 30 mL of cool boiled water. Mix thoroughly.
2. Add about 2 mL of lime water in the test tube, insert the free end of the delivery tube into the test tube, making sure that it is immersed in the lime water. Cover the test tube with cotton wool.
3. Dip the bottle containing the mixture of yeast and sugar in a warm water bath, make sure that the opening of the delivery tube remains submerged in the lime water.
4. Check periodically for bubbles passing through the lime water and note any changes that occur in the limewater.
5. After a change in the lime water has been noted, smell the yeast solu-tion.
The lime water will turn milky showing the presence of carbon dioxide gas. The students should detect a slight smell of alcohol from the mixture of glucose and yeast showing that anaerobic respiration produces alcohol.
1. Unused lime water should be stored in a well labeled reagent bottle for further use.
2. Collect all the used materials, cleaning and storing items that will be used later. No special waste disposal is required.
This principle is applied in the manufacture of alcoholic beverages, both in industry and by local brewers. If you find that the gas is taking a long time to form, you can gently squeeze the bottle containing the yeast solution. This will force any gas formed through the delivery tube and will speed up the change in lime water. If this is done, be sure not to release the bottle before removing the cap when the straw is still submerged in limewater - otherwise air pressure will force the limewater back into the yeast solution, ending the experiment. The smell of alcohol may be faint and hard to detect; if this is the case leave the solution for 3-4 days and smell again.