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Examining Bacteria in Yogurt

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					Name_____________________________________Date__________________________ Period________ 


                             Examining Bacteria in Yogurt 
Pre‐lab: Some types of bacteria can ferment milk, producing lactic acid in the process. Yogurt is 
a product of fermentation. It is acidic and stays fresh longer than milk, and is also digested 
more easily. In this exercise you will prepare a microscope slide of yogurt. 

Like all organisms, bacteria are given scientific names (usually Latin or Greek roots), in which 
naming rules learned last chapter are seen.  Rod‐shaped bacteria are called bacilli. Spiral‐
shaped bacteria are called spirilla or spirochetes, and spherical bacteria are called cocci. Draw 
the examples below: 

Example:                                                             
 
 
Drawing:                                                             
 
 
 
 
 
 
 
Problem: 

What types of bacteria can you observe in yogurt? 

Materials: 

  • toothpick                         •   microscope slide               •   coverslip 
  • dab of yogurt                     •   drop of water                  •   microscope 
 Procedure: 

1. Using a toothpick, place a dab of yogurt on a microscope slide.  

                              Caution: Do not eat in the laboratory. 

2. Mix the yogurt in a drop of water and carefully add a coverslip.  

3. Examine the slide with a compound microscope. 

4. Record your observations by drawing and labeling a picture of what you see in the 
microscope, include the lens you used (magnification). Do this on the back side. 

 

 
Name_____________________________________Date__________________________ Period________ 


 

                             Examining Bacteria in Yogurt 
Pre‐lab: Some types of bacteria can ferment milk, producing lactic acid in the process. Yogurt is 
a product of fermentation. It is acidic and stays fresh longer than milk, and is also digested 
more easily. In this exercise you will prepare a microscope slide of yogurt. 

Like all organisms, bacteria are given scientific names (usually Latin or Greek roots), in which 
naming rules learned last chapter are seen.  Rod‐shaped bacteria are called bacilli. Spiral‐
shaped bacteria are called spirilla or spirochetes, and spherical bacteria are called cocci. Draw 
the examples below: 

Example:                                                             
 
 
Drawing:                                                             
 
 
 
 
 
 
 
Problem: 

What types of bacteria can you observe in yogurt? 

Materials: 

  • toothpick                         •   microscope slide               •   coverslip 
  • dab of yogurt                     •   drop of water                  •   microscope 
 Procedure: 

1. Using a toothpick, place a dab of yogurt on a microscope slide.  

                              Caution: Do not eat in the laboratory. 

2. Mix the yogurt in a drop of water and carefully add a coverslip.  

3. Examine the slide with a compound microscope. 

4. Record your observations by drawing and labeling a picture of what you see in the 
microscope, include the lens you used (magnification). Do this on the back side. 

 
Name_____________________________________Date__________________________ Period________ 


Draw and label: 

 

 

 

 

 

 

 

 

 

Analyze and Conclude: 

Use complete sentences! 

1. Recall the terms bacillus, coccus, and spirilla from the previous section. Which type or types 
of bacteria did you observe in your slides? 
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________ 
2. Many people do not produce lactase, which is an enzyme that breaks down the milk sugar 
lactose. Thus, lactose‐intolerant people have trouble digesting dairy products. Why might they 
have fewer problems eating yogurt? 
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________ 
Name_____________________________________Date__________________________ Period________ 


Draw and label: 

 

 

 

 

 

 

 

 

 

Analyze and Conclude: 

Use complete sentences! 

1. Recall the terms bacillus, coccus, and spirilla from the previous section. Which type or types 
of bacteria did you observe in your slides? 
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________ 
2. Many people do not produce lactase, which is an enzyme that breaks down the milk sugar 
lactose. Thus, lactose‐intolerant people have trouble digesting dairy products. Why might they 
have fewer problems eating yogurt? 
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________ 

				
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