Section 2: Examining Bacteria in Yogurt

Name: _______________________________________________ Date: _________________ Period: ____
CHARACTERISTICS OF BACTERIA LAB
Section 1: Examining Bacteria slides
Pick a prepared bacteria slide from one of the 3 trays. Observe it under a microscope, and draw what you see
under the highest magnification. Write a short description on the bacteria you observe.
Once you are done, return the slide to the tray you originally removed it from, and pick another slide from a
different tray. Repeat the procedure for all 3 slides.
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Magnification: _____________ Magnification: _____________ Magnification: _______________
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Description: ________________ Description: ________________ Description: ________________
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Section 2: 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 to examine the bacteria found within.
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.
Materials:
Procedure:
• toothpick
• dab of yogurt
• microscope slide
• drop of water
1. Dab a drop of water onto a blank microscope slide
• coverslip
• microscope
2. Using a toothpick, place a small dab of yogurt in the water drop on the microscope slide.
Caution: Do not eat in the laboratory.
3. Mix the yogurt in the drop of water and carefully add a coverslip.
4. Examine the slide with a compound microscope.
5. Record your observations by drawing and labeling a picture of what you see in the microscope, include
the lens you used (magnification). Draw it under low and high magnification.
Draw and label:
Magnification: _______________ Magnification: _________________

Analyze and Conclude:
Use complete sentences!
1. Recall the terms bacillus, coccus, and spirilla. Which type or types of bacteria did you observe in your
slides?
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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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Section 3: Bacterial Replication
Watch the video “Bacterial Replication.” Next, answer the following questions using complete sentences:
(Use your notes, if needed. Answers may not be in the video.)
1. Name the process by which bacteria replicate: ________________________________________________
2. What type of reproduction is it? ____________________________________________________________
3. What is the disadvantage of this type of reproduction? __________________________________________
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4. If bacteria can replicate so quickly (20 minutes per replication cycle for E. coli), then why are we not ‘up to
our knees’ in bacteria? _____________________________________________________________________
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5. Name and describe two uses for bacteria that take advantage of their fast replication rate:
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6. Name another way for bacteria to transfer their genes? What structure of the bacterial cell is necessary for
this? ____________________________________________________________________________________
7. Name the small circular DNA that usually contains very few genes, and is usually transferred in the process
you named in #6: _________________________________________________________________________
8. Describe the process you named in #6 with as much detail as possible: ______________________________
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9. Bacteria are so diverse, that if we were to go outside, pick two random bacteria from the soil, and compare
their DNA, chance are that the differences would be greater than the differences between the DNA of a
human and a fruit fly. How is that possible? (Hint: How old are bacteria?) ___________________________
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