SBI 3U – Diversity of Living Things
Humberside C. I.
Bacterial Growth Lab
Purpose: To observe the growth of bacteria from various sources.
Materials:
pressure cooker
hot plate
flasks
aluminum foil
incubator
sterile Petri dishes
marker
cotton swabs
nutrient agar
Method:
Note: Steps #1 – 3 have been completed before the lab period.
1. Powdered agar was weighed, added to distilled water and boiled to dissolve the agar.
2. The liquid agar was poured into flasks, covered with aluminum foil and heated in a pressure cooker at 15 pounds of
pressure for 15 minutes.
3. The sterilized agar was then poured into sterilized Petri dishes and allowed to cool.
4. Obtain a Petri dish. Do NOT OPEN lid. Using a marker, divide the bottom of the Petri dish into
four quadrants. One of the quadrants will be left blank while the other three will represent a
different source of bacteria. Possible sources may be doorknobs, drinking fountain, fingers, toilet
seat, air, soil particles, desk surface, floor, etc.
5. Use a cotton swab to obtain bacteria. Wipe the swab in one direction and in only one of the quadrants. Each member
of your group will do at least one quadrant.
Use sterile technique throughout this exercise.
 Hold the Petri plate cover in your hand while inoculating the plate
 Do no puncture the surface of the agar while streaking it
 Replace the lid as soon as possible to prevent contamination
 Immediately dispose of the cotton swab in the waste basket
6. Tape the lid and bottom of the Petri dish together. With a permanent marker, label your name, your teacher’s name
and Biology period on the bottom of the Petri dish.
Never label the lid.
7. Incubate the plate, agar side up for 48 hours.
Observations
1. Create and complete a table with the following
headings: quadrant number, Source of Bacteria
and Description of Growth. (e.g. colour, shape,
elevation, border, presence of isolated colonies
and distribution). (7 marks)
Discussions Questions:
1. Having the water warm, but not necessarily boiling may have dissolved the agar. Other than
the speed of dissolving, what advantage does boiling the agar have for this lab? (1 mark)
2. In the pressure cooker, we covered the flasks loosely with aluminum rather than sealing them
with rubber stoppers. Why? (1 mark)
3. a) Though you may not have witnessed it first hand, what is the predominant process involved
in the formation of the bacterial colony? (1 mark)
b) If you were to isolate some bacterial cells from a single colony and compare their
characteristics (i.e. shape, size, DNA content), what are you likely to find? (1 mark)
4. Why have these bacteria grown so abundantly on the agar, while a similar culture is not
present at the source (in other words, where you obtained the bacteria)? (2 marks)
5. What was the purpose of leaving one of the quadrants blank? (1 mark)
6. a) Rank order the quadrants (i.e. source of bacteria) from most amount of growth to least
amount of growth. (1 mark)
b) What part of your results surprised you the most? Explain. (1 mark)
Bacterial Growth Lab Expectations
Lab Due Date: ________________________________________ at the start of class.
(if you are late to class, so is your lab report)
You must include the following items in your TYPED lab report INDIVIDUALLY:
i) Observations (8 COM marks) – Chart must be complete and descriptive.
ii) Photograph of Bacterial Growth (1 COM mark)
iii) Discussions (4 INQUIRY marks) – Answers must be in complete sentences.
LAB QUIZ: Thursday, October 10, 2013
Contents of the Quiz
 Purpose of the procedure of the lab
 How bacteria reproduce?
 Possible sources of error
 A completed observation table is required (see above) + photo of Petri dish
 Differences between bacterial growth vs. fungal growth
 Discussion questions
Marketplace – Superbugs in the Supermarket
1) Why was the ‘special clinic’ started?
2) What bacteria can now be found on supermarket chicken?
3) Farmers give antibiotics like the ones humans use. What do they put the antibiotics in and under what
circumstances are they given?
4) Why is overuse of antibiotics dangerous?
5) Why does it matter if we run out of antibiotics?
6) How many of the bugs found in the chicken from the supermarket are resistant to antibiotics?
7) ___________________________ is one of the most important antibiotics we have. It’s given to pregnant women
and children, almost half
Discussions
7. Having the water warm, but not necessarily boiling may have dissolved the agar. Other than
the speed of dissolving, what advantage does boiling the agar have for this lab? (1 mark)
8. In the pressure cooker, we covered the flasks loosely with aluminum rather than sealing them
with rubber stoppers. Why? (1 mark)
9. a) Though you may not have witnessed it first hand, what is the predominant process involved
in the formation of the bacterial colony? (1 mark)
b) If you were to isolate some bacterial cells from a single colony and compare their
characteristics (i.e. shape, size, DNA content), what are you likely to find? (1 mark)
10. Why have these bacteria grown so abundantly on the agar, while a similar culture is not
present at the source (in other words, where you obtained the bacteria)? (2 marks)
11. What was the purpose of leaving one of the quadrants blank? (1 mark)
12. a) Rank order the quadrants (i.e. source of bacteria) from most amount of growth to least
amount of growth. (1 mark)
b) What part of your results surprised you the most? Explain. (1 mark)
Bacterial Growth Lab Expectations
Lab Due Date: ________________________________________ at the start of class.
(if you are late to class, so is your lab report)
You must include the following items in your TYPED lab report INDIVIDUALLY:
i) Observations (8 COM marks) – Chart must be complete and descriptive.
ii) Photograph of Bacterial Growth (1 COM mark)
iii) Discussions (9 INQUIRY marks) – Answers must be in complete sentences.