ANAEROBIC RESPIRATION

The respiration which takes place in the absence of oxygen is called anaerobic respiration. Ex; yeast and some kinds of bacteria. 
The end products of anaerobic respiration are : lactic acid and carbondioxide (with very little amount of heat ) in bacteria and 
Ethyl alcohol and carbondioxide (with little amount of heat) in yeast. 
When we make dough by adding yeast for making buns, pizza bases, bread etc we observe a peculiar smell of ethyl alcohol. Here yeast undergoes anaerobic respiration reacting with sugar in white flour and releasing carbondioxide gas which gets trapped in the dough due to which holes are formed in the dough. 
DEMOSTRATING ANAEROBIC RESPIRATION IN THE LABORATORY
we can demonstrate anaerobic respiration in the laboratory by a simple experiment. Let's see the complete activity. 
LAB ACTIVITY 
AIM: To  demonstrate anaerobic respiration in yeast 
APPARATUS (MATERIALS)REQUIRED:  A thermometer, bent tube, small test tube and a beaker , glucose solution, yeast powder, diazene green solution, liquid paraffin 
PROCEDURE: 
1. Make gucose solution by adding some sugar in a glass of water. 
2. Boil the glucose solution to remove the dissolved oxygen from it. Immediately cool it and add yeast powder. 
3. Add few drops of diazene green solution or Janus  green B solution. This dye changes the solution to pink in colour in the absence of oxygen. 
4. Now pour 1cm layer of liquid paraffin to stop the flow of oxygen into the solution. 
5. Cover the mouth of the test tube with a two holed rubber stopper. 
6. Through one hole pass thermometer to check the heat evolved and through another hole insert a bent tube whose other end should be in a beaker filled with lime water. 
7. Keep this set up for 7 to 8 hoursand observe. 
OBSERVATION: 
 We observe that the lime water changes to milky white in colour , a peculiar smell from the test tube and there is a rise in thermometer reading after 7 to 8 hours. 
RESULT : Based on the given observation we can say that yeast has undergone anaerobic respiration producing carbondioxide which changes lime water to milky white precipitate and heat is evolved during this process. And peculiar smell from the test tube  because of the ethyl alcohol formed during the respiration. 
 
This process of anaerobic respiration by yeast is also called as fermentation which is commercially used in making if alcoholic beverages like beer, champagne, etc 



 FERMENTATION:
 The process in which yeast converts the natural sugars present in cereals to ethyl alcohol and carbondioxide us called as fermentation. 


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