Biology -Mr.Willets Name_________________________________
Bacteria are members of either Kingdom Eubacteria or Kingdom Archaebacteria. In either case, they are prokaryotes and the simplest form of cellular life. They are extremely small and even under high power cannot be clearly seen with our microscopes. When grown under the proper conditions, large number of bacteria cells can form colonies that can be seen with the naked eye. These colonies can be identified as being particular bacteria by the color, texture and shape of the colony. Also, certain bacteria will grow only under specific conditions or only with certain nutrients. These growth conditions can be used to identify the type of bacteria.
Most bacteria are members of Kingdom Eubacteria. It is these bacteria we will see in lab.
To successfully grow bacteria, they must be given food, moisture and a suitable temperature. Most bacteria grow better in the dark.
The food we use is made from a seaweed called Agar. (why is this capitalized and in italics?) The seaweed is dried and powdered. The powder is called agar. When mixed with hot water and cooled, it gels (this tells us that the mixture is a ___________) This provides food and moisture but because the agar is in the gel form, the bacteria cannot move around. As the bacteria divide to form more and more cells, the colony becomes larger and eventually is visible.
Once the agar is mixed, it is sterilized in a machine called an autoclave. It is then poured into Petri dishes where it cools and gels. These are then called agar plates.
Some bacteria require special nutrients added to the agar. For example, the strept throat bacteria require blood added to the agar. We will use a basic agar which means that many of the bacteria that grow in your body will not be able to grow on it.
Each pair of students will get a sterile agar plate. On the top of the plate write your name using a wax pencil. On the bottom of the plate, divide the plate into 3 sections labelled 1,2 &3.
You will now try to find some bacteria to grow on your plate. You will get the bacteria from three different places. Remember, bacteria like dark, moist places where food is available. Some suggestions: your mouth, the sink drain, the rim of a toilet, the water fountain, your eyes, your ears, your nose. Use a clean Q-tip to take material from these places and smear it on the plate. Do this gently so as not to gouge the agar. Record on the on the back of this sheet the location of each of your three sources and which section of the plate you put each on.
Once you have contaminated all three sections, use masking tape to hold the top on and return the plates to me. I will keep them in a warm, dark place until next week when we will see what has grown.
Each group will now get a new agar plate. Label it with your name. Divide it into four sections and label each with a number. In section one, one person will gently rub his/her finger. That person will then wash his/her hands with regular soap and rub the same finger in section 2. In section three, a different person will rub his/her finger. That person will then wash with anti-bacterial soap and rub the same finger in section 4. Secure the top with masking tape and give the plates to me.
DATA SHEET
Draw a circle below to represent your first agar plate. Draw in the various colonies that grew in each section. The sizes should be reasonably accurate but the diagram need only give the general idea of what grew. Mold colonies will appear fuzzy. All others are probably bacterial colonies.
On the left, indicate the source of contamination for each section and the approximate number of mold and bacteria colonies.
Section 1 Source__________________
# of bacteria colonies__________
# of mold colonies____________
Section 2 Source___________________
# of bacteria colonies________
# of mold colonies___________
Section 3 Source__________________
# of bacteria colonies___________
# of mold colonies_____________
Questions-
1) What characteristics of a bacteria colony can be used to identify the type of bacteria?
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2) Why do the bacteria cells stay put and form colonies rather than move around on the agar?
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3) What is the difference between agar and Agar? ________________________________________
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4) What is the function of an autoclave?____________________________
5) Why must the agar be sterilized before using it? ______________________________________
6) Under what conditions do bacteria grow best? ________________________________________
7) How many different types of bacteria colonies did your plate have? Describe 2 different colonies- size, shape, color, texture etc.
8) Compare the bacterial growth on the four sections of the second plate-1) unwashed hands, 2) hands washed with regular soap, 3) unwashed hands 4) hands washed with anti-bacterial soap. What does this say about the effectiveness of washing your hands with the two different kinds of soaps?