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Biology Lab
Chapter 18
Name ________________________________
Period _________
Bacteria in Our Environment
/20
Bacteria are found virtually everywhere on Earth where water is a liquid. Most bacteria grow best where it is
dark, moist, and warm, and food is present. However, bacteria can remain inactive, or dormant, for a long time if
conditions for their growth and survival are not favorable. When conditions improve, the bacteria again become active.
Many bacteria can be easily grown in a Petri dish containing nutrient agar. The nutrient agar provides food and
moisture necessary for their growth. When cultured at 25o to 40o C (75o to 105o F), bacteria quickly reproduce to form
colonies of different colors and shapes.
Objective: To observe the growth of bacteria taken from different areas.
Problem:
A. Which locations in our school contain the greatest variety of bacteria?
B. Do all bacteria grow at the same rate?
1
2
3
4
Hypothesis:
A. Name 5 locations where you expect a variety of bacteria to live?
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B. Do all bacteria grow at the same rate? _________________
Materials: Sterile Petri dish with nutrient agar, 3 sterile cotton swabs, marking pen, tape
Procedure:
A. Turn the Petri dish upside down. With a marking pen, divide the bottom of the dish into four quadrants. Number
each quadrant as shown.
B. On the side of the dish print your Period Number and the last names of your group members.
C. Record the location of sampling areas in the data table below. Quadrant 1 will be the control. Do not touch
quadrant 1 (control) during sampling.
D. For each sampling location, rub surface sampling area with cotton swab. Carefully lift lid of the Petri dish. Gently
rub agar surface of selected quadrant. Do not penetrate surface of agar. Use a clean swab for each quadrant.
E. Keep your Petri dish sterile. Keep lid closed when not sampling. Do not touch agar surface except when sampling
and only then with sterile cotton swab. Do not touch cotton swabs except on sampling surface. Do not touch inside
surface of Petri dish lid.
F. When sampling is complete, throw away cotton swabs and tape the Petri dish lid closed. DO NOT OPEN PETRI DISH
AGAIN. The Petri dish may contain pathogenic bacteria which can cause serious illness.
G. Turn the dish upside down and return it to the teacher so that it can be incubated for 2 to 6 days at 27o C.
H. After incubation, observe the bacteria colonies growing in the Petri dish and complete the data table below. DO NOT
open the Petri dish. When your observations are completed return the Petri dish to the teacher to be disposed.
Results:
A. In the space to the right, draw what
you see in Petri dish after the bacteria
have grown for several days. Use
color pencils to show color of bacteria
colonies.
1
2
3
4
B. Complete Data Table below.
Quadrant
Sample Location
1
- CONTROL -
Total Number
Number of
of Colonies
Different Species
Remarks
2
3
4
C. What was the purpose of the quadrant 1? ____________________________________________________________
D. If bacteria grow in quadrant 1, what does that tell you?__________________________________________________
E. How does one species of bacteria colony differ from another? _____________________________________________
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F. Name four things bacteria need in their environment in order to grow. 1) ___________________________________
2)_____________________________ 3)_____________________________ 4)_____________________________
G. Why did you observe bacterial growth on the nutrient agar, but not on the surfaces you sampled? _______________
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H. Compare your results with other members of your class. Which locations produced the greatest variety and amount
of bacterial growth?_______________________________________________________________________________
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Conclusion: Write a 4+ sentence conclusion that includes a statement of purpose, summary of results, interpretation
and analysis, and a closing statement.
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