Where the Bacteria are

Where the Bacteria are.

Organisms called bacteria surround us. They are present on our skin, in the food we eat, and inside of our bodies. Many types of bacteria are important to life processes on Earth. Certain bacteria change nitrogen gas into a form that plants can use. Other bacteria live in the digestive systems of animals, breaking down nutrients into vitamins. Others act as decomposers, breaking down organic material in the soil and making nutrients available for living things. Harmful bacteria, however, can cause diseases like tuberculosis and pneumonia, as well as food poisoning.

The warm, moist conditions of the human body make it an ideal place for bacteria to grow. Bacteria can reproduce quickly, producing toxic waste products that can make you feel sick. One of the easiest and most effective ways to keep harmful bacteria from entering the body is to wash your hands often. Antibacterial soaps and antibacterial gels are designed to kill bacteria found on the body.

In this activity, you will design and conduct an experiment that compares the prevalence of bacteria on different surfaces or in different situations.

OBJECTIVES

Design an experiment that compares the bacterial contamination of different surfaces/products/situations.

Compare bacterial exposure in three test conditions (locations, times, or moisture content for example).

Evaluate the importance of hand washing, the 5 second rule, or routine cleaning procedures in daily life.

MATERIALS: agar plates, sterile swabs, incubator, gloves, (the rest is up to you, list below)

PROCEDURE

PART I—DAY 1: DESIGNING AND CARRYING OUT THE EXPERIMENT

1. With your group, consider the materials available. Discuss the goal of the experiment. a. What is the question your group is trying to answer?

b. Propose an experimental hypothesis:

c. State your specific predictions below:

2. What are the independent and dependent variables in your experiment?

3. Establish an experimental control. To what condition will you compare the results of the experiment (explain your rationale)?

4. List experimental constants. What conditions should be held the same throughout the experiment (specifically explain why)?

5. In the space below write a brief procedure outlining the steps of your experiment.

6. Carry out your experiment.

7. Once you have collected bacteria on the agar, secure the lid of each Petri dish to its bottom half with tape. Label your group’s dishes (on the bottom of the plate) with sharpie. Place all three dishes upside down in the tray provided. Incubate overnight at 37 degrees C.

PART II—DAY 2: ANALYZING EXPERIMENTAL RESULTS

8. Remove the Petri dishes from the incubator. Turn them right side up, and study each plate for the presence of bacterial colonies. Count the number of colonies present on each plate, and record this information in Table 1.

TABLE 1: BACTERIA CULTURES

9. After all observations have been recorded, dispose of agar plates as directed by your teacher. Wash your hands thoroughly with soap and water.

10. Clean up your work area with disinfectant before leaving the lab.

ANALYSIS STATEMENTS

1. Examine your data. Compare the number of bacterial colonies on the control plate and experimental plates.

Which test condition produced the most bacteria?

On which agar plate were the fewest bacteria growing?

2. Between which two agar plates was there the least difference in the amount of bacteria present?

CONCLUSIONS

3. Explain the possible reasons why you observed the most/least bacterial growth in the various experimental trials you conducted (i.e. which was the dirtiest and why).

4. What effect might various other considerations have had on the results (i.e. locations, surfaces, item choices, time of day, etc.)?

5. Explain the significance of your results. How can your results be applied in a practical way (in life, health, activities, etc.)?