Lab: Sampling Bacteria

Topics: Bacteria, Petri dish, Agar plate Pages: 3 (809 words) Published: September 16, 2014
Lab: Sampling Bacteria
Purpose:
Refer to handout sheet.

Materials:
Refer to handout sheet.

Procedure:
Refer to handout sheet.

Pre-Lab Questions:
1. Why is one dish being reserved for the class as a "control"? Having a controlled variable is important in order to be able to look at what the bacteria would look like if it hadn't been contaminated and just left as agar. Having a sample of agar that wasnt exposed to any bacteria will provide a clear picutre of what grew on the agar upon feeding bacteria to it.

2. Why shoudn't a student swab his or her mouth or cough onto an agar plate to initiate a culture? Even though most bacteria in the human body is harmless, if one was knowingly or unknowingly ill then harmful bacteria could be bread.

3. Why isn't the upper lid of the Petri dish completely removed during the inoculation? During the inoculation the upper lid of only partially removed to prevent bacteria in the air from contaminating the bacteria being bread on the agar.

Observations:
Refer to attatched chart.

Analysis Questions:
1. Compare the samples obtained from different sources. What similarities and differences did you find among the bacterial colonies from different sources? For how wide spread of a sampling of bacteria we obtained, the actual colony observations didn't differ drastically. All samples, including the control, were in and around the same color spectrum in lightish brown coloring. The control, stair railing and neath of the fingernail were all circular in form and the margin for those three was also entire and all elevations were convex. The diameter of the actual colonies was where the most diverse observations occurred. The percentage varied from one to fifty percent and the millimetre size also varied from less than 2mm to about 5mm.

2. Would a very high concentration of bacteria in a particular dish indicate a dangerous area in the lab? If the bacteria gathered and bread was a harmful...
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