Where Can We Find Bacteria?

Objectives: to take bacterial swabs from various places in the school to inoculate a Petri dish with a bacterial culture to count bacterial colonies to find out where bacteria hang out to determine what kind of environmental conditions influence bacterial growth

Safety:  Handle all glassware safely Do not smell the bacteria Tie back loose hair/clothing

Materials: (per group of 3-4 students) 1 Petri dish with agar 2 cotton Q-tips Masking Tape Permanent marker An incubator or really warm place

Procedure:1. You will share one Petri dish with your group.2. Place your initials, date and sample location along the bottom perimeter of the dish, NOT in the middle. 3. When you and your partner are ready, come up and get your sterile Q-tip.  Be very careful not to touch

the side that will collect your sample, your hands can contaminate the Q-tip and alter your results. 4. Go to your areas you are going to swab and come back quickly!   5. One section of the Petri dish will be left as the control (no swab or sample). Your teacher will give your

group one area to swab. Your group must decide on two other sample places to swab (check with your teacher for permission first).

6. We will examine the dishes in a few days and you will draw your finding in Figure 1.

Hypothesis:1. Where do you think you will find the highest amount of bacteria? 2. What do you think the Petri dish will look like in 2-3 days?

Observations/Data: Observe your Petri dish. White or cloudy areas of the agar indicate bacterial growth.

Figure 1:       Draw you Petri Dish after 2-3 days

Table 1:        Number of Colonies on Petri dish

 

Sample Location Number of ColoniesApproximate Size of

Blooms

         

Analysis:   1. How many clusters of bacteria appear to be growing in each Petri dish? 2. Which Petri dish had the most growth? The Least? 3. Why was the agar sterilized before this investigation? 4. What kind of environmental conditions seem to influence where bacteria are found? 5. How can you control the amount of bacteria that you will encounter?

 Conclusion:In your conclusion be sure to include the answers to the following questions:

1. How does your data relate to your hypothesis (support or reject)? Does this surprise you? Why or why not?

2. Name two sources of error that could have occurred during this experiment. Include the cause and effect of each error.

 Lab Write-Up:

Include the following when completed with lab:

Hypotheses #1 and #2; explained fully; complete sentences. (10 points) Figure 1 – Drawing of your Petri dish after 2-3 days – details/labeling included. (5 points) Table 1 – Copy and complete Table 1. (5 points) Analysis Questions AND Answers #1-5; complete sentences. (10 points) Conclusion Questions AND Answers #1-2; complete sentences. (10 points) Neatness (2 points) Correct Format – Hypotheses, Data, Analysis, and Conclusion. (8 points)

Total Grade – 50 Points