======Aerobic vs. Anaerobic Yeast Respiration======


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**Alternative titles:** Balloon Inflation Yeast Experiment
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====Summary====                   
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====Procedure====  
  -Prepare two clean bottles and label them “aerobic” and “anaerobic.”  
  -Add warm water (not hot) and sugar to each bottle, stirring until dissolved.  
  -Add an equal amount of yeast to each bottle and swirl gently.  
  -Stretch a balloon over the mouth of each bottle to seal it.  
  -For aerobic conditions, leave the setup as is so oxygen can dissolve into the solution.  
  -For anaerobic conditions, limit oxygen by wrapping the bottle in plastic or using a balloon that fits tightly and prevents outside air from entering.  
  -Leave the bottles in a warm place and observe over time.  
  -Record the rate and size of balloon inflation for each condition.



====Links==== 
Yeast Aerobic and Anaerobic Respiration - Animated Science: 
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The Yeast Respiration Experiment with S4's Biologist Ali - S4 Project: 
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====Variations====
  *Test different sugars (glucose, sucrose, honey) to compare respiration rates.  
  *Vary the temperature of the water to see the effect on yeast activity. 
  *Try one setup with no sugar as a control.



====Safety Precautions====
  *Do not drink or taste the yeast mixtures.  
  *Use bottles that can withstand slight pressure but avoid sealing too tightly to prevent bursting.  
  *Handle warm water carefully to avoid burns.  
  *Dispose of yeast mixtures in the sink with plenty of water; do not store sealed bottles for long periods.




====Questions to Consider====
  *Why does the balloon inflate during yeast respiration? (CO2 gas is produced and collects in the balloon.)  
  *Why does the aerobic bottle inflate more quickly? (Oxygen allows yeast to fully respire sugar, releasing more energy and carbon dioxide.)  
  *What additional product is made in anaerobic respiration? (Ethanol, along with CO2.)  
  *Why is warm water used instead of hot water? (Hot water can kill yeast, while warm water activates it.)  
  *What does this experiment reveal about yeast’s role in bread-making or brewing? (CO2 makes bread rise, while ethanol is central to brewing alcohol.)