2 class periods of 45 minutes each
Students plan and conduct an experiment on the topic of food spoilage.
No classroom materials are needed.
Student will be responsible to collect their own materials for their experiments.
A teacher may want to provide some materials to assist student efforts.
Students have had many experiences in science and have participated in and designed simple investigations. This lesson directs students in identifying the steps of experimentation. While microorganisms are the topic and the subject of the experimentation, the emphasis and learning should center on scientific steps and processes of scientific experiments.
Designing and conducting an experiment involves an integration or combining of science process skills.
Research Questions and Hypotheses
Questions rise out of experiences and observations. Hypotheses or statements of potential explanation to the research question suggest the type of strategies that might be used to answer the question.
An experiment planned to test a hypothesis includes two identical set ups. Both are the same with the exception of one variable condition in the set up. The factor that differs is called a variable. The variable is related to the hypothesis and is the condition being tested.
At all stages of the experiment, data must be collected and recorded using systematic procedures. Remember to record facts and observations. Though ideas and inferences can be helpful in interpreting the data, they should not be confused with observations. The Newbery Award winning book, The Hero and the Crown (1985) by Robin McKinley gives a wonderful account of the scientific steps of experimenting. The heroine, Aerin, finds an idea of kenet, an ointment that protects one against dragonfire. She experiments and shares the steps, frustration, and long-awaited success. These ideas can be found in The Hero and the Crown, page 31, paragraphs 2 and 3; page 56, paragraph 2-5. Read these passages to your class as you prepare for this lesson.
Analyze Data and Draw Inferences
A conclusion is a statement of what was learned when all the data from an experiment have been collected and analyzed.
Experimenting provides important information whether or not it supports the initial hypothesis. Students have a misconception that an experiment is wrong if they cannot support their hypothesis. It is vital to ensure that importance is placed on scientific openness and willingness to analyze procedures and seek alternate explanations and not getting the “right” or “wrong” answer.
In this activity, students will design and conduct experiments related to food spoilage. The variables will be those things which affect food spoilage. The following is an example of an experimental design. It should not be given to students to conduct but should serve as a model for designing their own experiments.
What causes milk to spoil?
Warmth will cause milk to spoil.
1. Fill two glasses with 50 ml of milk and cover.
2. Label the two glasses A and B.
3. Place glass A in the refrigerator.
4. Place glass B in the kitchen window sill.
5. Leave glasses alone for 7 days.
Collect and Record Data:
Observe the glasses of milk each day before going to school and record observations.
(Remember to only record the facts - what is observable.)
Analyze Data and Draw Inferences:
The milk in the refrigerator was not spoiled.
The milk on the window sill was spoiled.
Refrigeration slows down the spoiling process in milk.
Although this experiment helped us recognize a variable that might assist the spoiling process, (heat) it does not tell us why the milk spoiled. To identify bacteria as the change agent and to link these results to the fact that chemical changes occur more quickly at room temperatures would take additional investigations.
Class Period #1:
Class Period #2:
Use the Experiment Rubric to assess individual experiments.