Using Yeast To Blow Up A Balloon

Use yeast to inflate a balloon 

Here is a fun and easy experiment to do with the kids.

Materials 
six packages of active dry yeast
2 cups (480 ml) of very cold water
2 cups(473 ml)of very hot water,but not boiling 
2 cups (480 ml) of warm water
6 table spoons (90 ml) of sugar 
six small plastic soda bottles
six latex balloons 
tape
marker
tape measure

Step 1 : Assemble the bottles
Empty and rinse the soda bottles.Add one packet of yeast to each bottle add 1 cup of cold (240 ml) water to each of two bottles.Add 1 cup of hot  water (240 ml)  to each of the next two  bottles.Add 1 cup (240 ml) of warm water to each of the final two bottles. Label the bottles cold,hot ,or warm. Add 1 tablespoon of sugar to one of each of the cold,hot and warm bottles and label the bottles with sugar Do NOT  add sugar to the other bottles. Swirl each soda bottle around to mix the ingredients.Attach a balloon over the mouth of each bottle.You can add some tape around the mouths of the bottles to secure the balloons in place. 

Step 2 : Watch the Balloons
Observe the bottles.What happens to the balloons after five minutes ? After fifteen minutes ? After thirty minutes? Use the tape measure to determine the girth of the balloons (measure them at their widest point)as they inflate (or not) over time does the balloon s on the bottles without sugar inflate? And how do those balloons compare to the other ones with sugar 

Here is What Happening
In this experiment ,covering the bottle with a balloon cuts of the oxygen supply to the yeast.For a while the yeast cells use aerobic respiration for energy.When the trapped oxygen runs out ,though,they switch to anaerobic respiration.  
Carbon dioxide is also made during this process although it doesn't give the organism any energy and that is what inflates the balloons. Since carbon dioxide is also by-product of aerobic respiration,the balloons will begin to inflate even before  the oxygen runs out. As carbon dioxide continues to be produced,the balloons continue to inflate,which proves the yeast cells can respirate anaerobically.
Neither form of respiration will take place with out a food source-in this case, the  sugar.That's why the balloons over the bottles with yeast but no sugar do not inflate-their yeast cells are not respirating.
By testing different water temperatures,you can examine how other external factors affect the way cells function.You probably noticed the balloons over the bottles of hot and cold water did not inflate as much  as the one over the bottle of warm water.What does this tell you about the temperature that's  best for cells to grow?  

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