Petri Dish Experiment

The sample essay on Petri Dish Experiment deals with a framework of research-based facts, approaches, and arguments concerning this theme. To see the essay’s introduction, body paragraphs and conclusion, read on.

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, loud 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. Variables: 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.

Get quality help now

Proficient in: Experiment

4.9 (247)

“ Rhizman is absolutely amazing at what he does . I highly recommend him if you need an assignment done ”

+84 relevant experts are online
Hire writer

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.

Petri Dish Experiments

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 and closed controlled.

One should be kept open the entire time, while the other should be kept closed. This is to test the sterility of the Petri dishes. Afterwards, take four cotton buds and screw top vials. For good results, you should wet the cotton buds with distilled water and then swab the areas you wanted to sample. After that is done, head back to the science lab, making sure that you have Petri dishes with agar jelly, tape, a Bunsen burner and ethanol. (All of this should’ve been done with sterile gloves on). For the best effect, operate the Bunsen burner with the safety flame.

This should ensure that the atmosphere is relatively bacteria free. After, clean the table using ethanol (also to sterilize the area) and place the Petri dish (which you will swab with your samples) on top of the table. When that is done, swish the cotton buds lightly inside the Petri dish (one in each separate quarter) where the agar jelly should already be. Make sure you do not dig the cotton bud in, as we do not want the microbes to be growing in the middle of the jelly. We want to be able to observe the microbes from above.

Finally, after all four quarters of the Petri dish are finished with swabbing, tape the open controlled, closed controlled and the experiment dish closed. To save place, tape those three altogether and place them in an incubator (25 degrees Celsius). This must stay constant, as e WOUld not like the incubator to reach human pathogenic temperature (37 degrees Celsius). After 72 hours have passed, take the Petri dish out, but do not open it. Observe and record the results. Below is a diagram of how everything was set up. Processed Data Discussion/Evaluation Overall, the experiment went quite smoothly.

Of course, there could’ve been improvements. The results should’ve definitely been more accurate, especially for the counting of the colonies that we did, and the percentage cover. We had a lot of microbes growing in our Petri dish and it was very difficult to count the exact amount of colonies. These were just estimated approximately. Perhaps we could’ve had more people verify our counting skills, for example, get someone else to count the colonies after we did for comparison and accuracy. Also, for these four locker rooms, we swabbed different places/areas each time. Since locker rooms are quite large, this is rather imprecise.

We should’ve stuck to swishing only the floors with the cotton buds or the walls instead of taking a variety. Our results showed that the place with the most microbes out of the four areas was the elementary boy’s locker room. In that quarter of the Petri dish, there ere a total of 78 colonies. Actually, I think there definitely were more. However, it was just too difficult to count, as most of them were clustered together, relatively small and the color was hard to see. Also, compared to the rest of the results, the elementary school boy’s locker room had a significantly higher percentage coverage and colony number.

The next place with the most microbes was the elementary girls. They had a total of 47 colonies and a percentage cover of 43%. The difference between this quarter of the Petri dish and the elementary boys was that this one had larger colonies which were easier to count. They also weren’t so clustered and were scattered all over their quarter. Perhaps this is to do with how we swished the cotton buds on top of the agar jelly. The last two with the least microbes were the girls and boys senior locker rooms.

The boys had about 34 colonies covering 30% of their quarter. This area looked quite similar to the elementary boy’s quarter. The colonies were both extremely small, very hard to count and clustered altogether. The only difference between them is that the senior boys generally had less in numbers. The senior girls had 19 colonies covering 20%. This was one of the most interesting quarters. The colonies itself were relatively small, however, they were clustered very tightly together to form almost a large group and was most definitely scattered around the quarter.

The larger groups were definitely not in each other’s vicinities. This again, perhaps, has something to do with the way my partner and I worked with the Petri dish. We took turns swabbing the dishes, so perhaps that affected our results in some way. For example, maybe I put more pressure on the agar jelly than my partner did, or vice versa. Conclusion Unfortunately, for this experiment, most of my hypothesis was incorrect. However, now that I’ve done the experiment, I can see why. The elementary boys locker room proved to be the one with the most microbes.

I can deduce that this is because elementary school children tend to go outside a lot more and run around, getting themselves dirty in the process. One would hardly find any middle and high-school pupils running around and getting dirty. After all, small children even like to run around in the rain and cold, where certain microbes love to thrive in. My partner and I did guess right about the girl’s locker room having fewer microbes than the boys though. The elementary girls had less than the elementary boys and the senior girls had less than the senior boys. However, am not yet ready to accept these results.

Cite this page

Petri Dish Experiment. (2019, Dec 06). Retrieved from

Let’s chat?  We're online 24/7