Comparing Bacteria Cultures in
Lavelle Prep Charter School
Name:
Class:
Introduction:
The purpose of this experiment is to find out which of the two locations in Lavelle Prep Charter
School contained the greatest amount of bacteria.
We will be looking at our collected bacteria in a petri dish filled with agar. Agar is a jelly-like
substance used to culture bacteria. It is made from a type of red algae, which provides an ideal growing
surface for bacteria.
Bacteria generally grow in colonies. A bacterial colony is a visible cluster of bacteria growing on
the surface.
1. The two locations that were compared in this experiment were
and
.
2. The hypothesis was that
would have more bacteria than
because
.
Materials and Methods:
Materials


1 Petri dish with agar
2 Cotton Q-tips
Methods
1. Design a controlled experiment to compare the presence of bacteria from two locations in
Lavelle Prep.
2. Have test design approved by teacher.
3. Answer pre-lab questions.
4. Using teacher approved design; prepare to swab two different locations in the school.
5. Each group uses one Petri dish.
6. Turn the dish upside down and use a permanent marker to divide the Petri dish into thirds.
(Write on the side of the Petri dish containing the agar.)
7. Place group member initials, date and sample location along the bottom perimeter of the dish,
NOT in the middle.
8. After Petri dish is prepared, get two Q-tips. Be very careful not to touch the end that will collect
the sample or contamination might occur.
9. Go to the 1st location in design (
). Swab the location by rotating Q-tip
while rubbing over the area.
10. Carefully open Petri dish (Pac Man style as demonstrated in class) and lightly rub the Q-tip
across the agar on the designated 1/3 of the Petri dish.
11. Go to the 2nd location in design (
). Swab the location by rotating Q-tip
while rubbing over the area.
12. Carefully open Petri dish (Pac Man style as demonstrated in class) and lightly rub the Q-tip
across the agar on the designated 1/3 of the Petri dish.
13. Leave the last 1/3 of the untouched to serve as the control.
14. Tape the dish shut.
15. Turn Petri dish upside down and place in the warm plant light box.
16. Examine the dish over the next 6 days to count the number of colonies. Record the number of
colonies in Table 1.
17. Each day, draw your Petri dish (Figures 1-3).
Data:
Day
Sample Location
Location 1 _____________________________________
1
Location 2 _____________________________________
Control
Location 1 _____________________________________
2
Location 2 _____________________________________
Control
Location 1 _____________________________________
6
Location 2 _____________________________________
Control
Number of
Colonies
Petri Dish Day 1:
Describe what each sample location looks like:
Location 1:
Location 2:
Control:
Petri Dish Day 2:
Describe what each sample location looks like:
Location 1:
Location 2:
Control:
Petri Dish Day 6:
Describe what each sample location looks like:
Location 1:
Location 2:
Control:
Analysis:
 Present your results and explain what happened. Be sure to use specific examples from
your data.

EXAMPLE: More bacteria colonies were noticed on the section of medium from the swabs
taken from the girl’s bathroom sink drain when compared to the boy’s bathroom. This difference
could be attributed to…
 Look for relationships in the data/observations. Identifies trends along with similarities or
differences.

EXAMPLE: There were fewer colonies of bacteria growing from the swab of the keyboard in
Mrs. Carr’s room when compared to the keyboard in Mrs. Miller’s room. However, the colonies
from Mrs. Carr’s room were much larger. This difference in size could be because…

EXAMPLE: The control had some contamination. This could be explained by…

EXAMPLE: Fungus eventually took over the whole plate. This could be because…
Conclusion:
The results of this lab (did / did not) support the initial hypothesis that more bacteria would be
found________________________________________________________ than __________
__________________________________________. These results most likely occurred because _________
______________________________.
Some things that were learned from this experiment were
This experiment could be extended in the future by