Thinking Like a Scientist Activity 5
Science is built up with facts, as a house is with stones. But
a collection of facts is no more a science than a heap of stones is a house.
--Jules-Henri Poincaré
Just the Facts
Objective
Students will investigate the importance of data collection and analysis.
About the Activity
There are three major parts to an experiment. The first part involves
designing and setting up the investigation. The second part includes performing
the investigation, making observations, and collecting data. The third part
involves analysis, which is essential to understanding the implications
of the observations, including whether or not the hypothesis is supported.
The purpose of an experiment is to test a hypothesis, not to substantiate
it. Thus, it is just as valid to prove that a hypothesis is wrong, as it
is to prove the hypothesis is valid.
In this activity, students investigate how food additives affect growth
of microorganisms.
Background Material
Bacteria and other microbes grow rapidly under optimal conditions. These
organisms feed on many of the same substances as humans do, and can bring
about undesirable chemical and physical changes in food. To prevent the
growth of these organisms in food, people use processes such as canning,
heating, irradiating, freezing, and pasteurizing. In addition, preservatives
are often added to the food.
Materials
For each group:
- 2 chicken bouillon cubes
- Hot water
- Measuring cup
- Large beaker or glass jar
- 7 clear baby-food jars or cups with lids
- Salt
- Sugar
- Vinegar
- Teaspoon and tablespoon measures
- Masking tape
- Pen
- Paper
Instructions:
- Have students put a strip of masking tape on each of the seven jars.
On each piece of tape they should write their names, class period, and
jar number.
- Explain to students that they will be testing the effectiveness of
sugar, salt, and vinegar on inhibiting bacterial growth. Have students
dissolve the bouillon cubes in 2 cups of hot water. The resulting solution
should then be divided evenly between the baby-food jars or cups.
- Have students add 1 teaspoon of salt to Jar 1, 1 teaspoon of vinegar
to Jar 2, and 1 teaspoon of sugar to Jar 3. In Jars 4, 5, and 6, students
should place 1 tablespoon of each material. Jar 7 is the control and should
not have any additives. Remind students to label each jar to indicate the
material and amount of material.
- Ask students to place the containers in a warm place overnight. Then
have them carefully cover each container loosly with a lid, or other material.
- Have students develop a code based on the cloudiness of the liquid
for recording observations. (For example, 0 = clear liquid, 1 = slightly
cloudy (can see detail through the liquid), 10 = very cloudy (can't see
anything through the liquid).) Have students check the containers each
day for a week and record their observations in a chart.
- Have students draw conclusions about the effectiveness of each material
as a food preservative and present their findings to the class.
Discussion Questions:
- How can you tell if bacteria are growing in the solution? Record which
containers show bacterial growth and which do not. Of those which show
growth, did all the growth begin at the same time? How can you tell?
- Does the amount of preservative change the results? Do you think the
results would be different if you added more preservative to each container?
Why or why not?
- Why was it important to check the containers over a period of a week,
rather than just one or two days? Do you think the results would be different
if you checked the containers over a longer period of time? Why or why
not?
- What conclusions can you draw from this experiment? Explain your reasons.
- What questions do you have about this experiment? Describe an experiment
you might do next to help answer your questions.
Activity 6: Let's Get Together
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Resource Book Index: On Becoming a Scientist
