Microbes Petri Dish Experiment (Lab Report)

Topics: Agar plate, Agar, Microbiological culture Pages: 7 (1795 words) Published: September 28, 2010
Lab Report - Microbes

Aim: To investigate four areas of the school and to find out which of the four have the most microbes.

Areas to Sample:

1. Girl’s locker room (Senior school)
2. Girl’s locker room (Elementary school)
3. Boy’s locker room (Senior school)
4. Boy’s locker room (Elementary school)


We predict that the boy’s locker room in the senior school will have the most microbes. First of all, there are more people using our locker rooms in the Senior School than the elementary ones. The classes in the Elementary school are generally much smaller.

Also, pupils from the senior school are going through puberty and tend to sweat a lot more than little kids, especially the boys. Sweat glands also work more rapidly with boys going through puberty, as their hormone levels are beginning to increase.

During P.E classes, girls also are more reserved and are not as intense about sports during the day as the boys are. This is more of a social aspect than a scientific one, but is relatively true. On top of that, girls and boys generally have different standards when it comes to hygiene. Judging from personal experience, I would assume that girls tend to care more about their hygiene and aesthetics than boys do.

Lastly, the Senior School gym has been there for quite a long time. The elementary school is still relatively new, especially compared to the senior one. Therefore, I also would assume that the senior school gym would have more microbes than the elementary.

Independent variables: The independent variable for this experiment will be the location/area in which we will take samples from (Senior School, Elementary School girls and boys locker rooms). Independent variables generally answer the question “What do we change?” In this case, we get to alter the areas in which we will be sampling from.

Dependent variables: Our dependent variable will be the number of microbes growing in an area. Dependent variables tend to answer the question “What will we observe or measure?” In this case, we will indeed be observing the microbes growing on the Petri dish after put in an incubator for 72 hours.

Controlled variables: Controlled variables are there for us to keep constant. The temperature, time, medium, the way the sample is collected and the incubation will be our controlled variables. It is important that they remain the same throughout our whole experiment. Also, we will be having an open controlled as well as a closed Petri dish. We will be testing the agar dishes, to see if they really are as sterile as we think. If the open controlled will have bacteria growing on it after being incubated, that is as expected. However, the closed control should be spotless in order for our other results to be completely accurate. Apparatus:

▪ 3 Petri dishes with lids
▪ Agar jelly
▪ 4 cotton buds
▪ Incubator set at 25 degrees Celsius
▪ Tape
▪ Screw top vials
▪ Bunsen burner
▪ Soap
▪ Ethanol
▪ Four different locations

Risk assessment:
We must make sure to follow certain rules for this investigation. It is important to wash hands before eating and before class/at the beginning of class. Also, once the dish has been incubated, we should not open the lid. The incubator, for this experiment, must be kept below human pathogenic growing levels, which is 37 degrees Celsius. Sterile gloves should also be worn to collect samples for accurate results. Petri dishes should definitely be safely and properly disposed of when the experiment has ended.

Method (sterile technique included):
Before anything is done, it is important that hands are disinfected. Wash them with warm water and soap. It is important to wash them with warm water, as cold water does not clear away most of the bacteria. Afterwards, put on some sterile gloves to make sure sampling is done accurately. Following, make sure that there are two Petri dishes, one open controlled...
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