Today we are super sleuths conducting an experiment on the things that can be found all around us – namely bacteria!  Each group will be given the opportunity to select and sample a “dirty” location within our school and watch what cool and disgusting things grow over the next few days.  Each group will compare results and will report to the rest of the class what they find living all over our school.  Bacteria are microscopic and we normally cannot see them when they are living individually or in very small groups.  This means that we touch bacteria without knowing it all the time!  In this lab we will try to grow only the bacteria from our sample location so be careful to not open or contaminate your Petri dish during the experiment. 


As a follow-up to the lab you will be required to write a laboratory report in your lab notebook.  You will work in a group of four and will share one Petri dish but each group will be divided into two sets of partners who will work together to track the dirtiest place in our school.  Each pair should select a location that they would like to sample and remember you must have your location approved by your teacher!  One member of your group will come up to the front and obtain your Petri dish, during this time the rest of your group should be starting to write your lab report to reduce your homework.  The written work will be set up according to the guidelines for lab report sheet located in your science binder.


Remember to act safely and conduct your work in an appropriate manner or you will receive a zero for today’s assignment.  Now lets get started and see what tiny microbes we are in contact with everyday!


Laboratory Procedure Day One

1. Once you have a Petri dish turn the dish over and draw a line on the bottom that divides the agar into two equal halves.  Each set of partners should write their initial, the date and their sample location around the outside of their half of the Petri dish.

2.Next obtain a sterile Q-tip and be careful to only touch the Q-tip to your sample location or your results may become contaminated. 

3. Go quickly and carefully to your assigned area and come back.

4. Carefully open your side of the Petri dish (only as much as is necessary) and very lightly wipe the surface of the agar with your Q-tip.  Make sure you do not tear or gouge the surface of the agar.

5. Once all members of your group have plated their sample tape the Petri dish shut.  Make sure you draw the dish in your lab notebook for your lab report.

6. Turn the Petri dish upside down and place it in the incubation location for a few days.

7.  Carefully clean up your workstation and wash your hands before leaving class.



















Petri dish immediately after plating bacteria


Laboratory Procedure Day Two


1.                  Carefully obtain your Petri dish and observe any growth on the plate.

2.                  Allow each group member to accurately draw the size, color, shape and location of bacterial colonies on the plate.  * Remember fuzzy colonies are not bacteria but fungus *

3.                  In your lab notebook record the following from both halves of the plate:

The sample location

The type of colonies

The amount of colonies

The shape of colonies

The location of colonies

4.                  Discuss and record the similarities and differences between both sample locations on your plate.

5.                  Write your results on the board (Classroom Results).  Also record all the information in your notebook so you can make conclusions about the different locations sampled throughout the school.  Use this information to create your analysis and graph.

6.                  Carefully place the Petri dish in the appropriate disposal location, clean up your workstation and wash your hands before leaving the classroom.
















Petri dish after incubation


Lab Report

Remember to include in your lab report the following:




Procedure (an abbreviated version will do)

Results include the following: 1. A written description of your sample location

2. All the observations from your Petri dish

    (As above but listed in table form)

3. Two complete diagrams from the experiment

4. The “Classroom Results” table from the board

5. A graph comparing sample location, number and type of   

    Colonies found.


Include in the discussion a summary of what you did and what you found out.  Also include answers to the following points in a paragraph form:


1.         Explain the science of Microbiology and define the role of a Bacteriologist

2.         A complete count and description of the types of colonies grown on your plate.

3.         Name from the Classroom Results which Petri dishes had the least amount of growth and which had the most.

4.         Explain why the agar had to be sterilized before the experiment and why care had to be taken to not introduce bacteria from the air or other sources into your Petri dish.

5.         Describe what kind of environmental conditions promote or inhibit bacterial growth.

6.             2-3 sentences describing what you have learned and, finally, name the dirtiest place in the school!