Summer time and the livin' is easy (for bacteria and molds, at least)

This lesson is a very effective one for the students to learn about the scientific method. It is also a great way to learn about food spoilage. Before allowing the students to begin their independent experiments, discuss what it means for foods to spoil. Ask them if they have ever seen something spoil (or smelled something spoil). Make a list of what they have noticed. Then ask them how long does it take for something to spoil. Ask them how does one prevent something from spoiling. Make a list of these ideas also. Some possible answers would be to cover the food, refrigerate it, etc. However, what would the students do if they didn't have a refrigerator? What if they were going on a picnic but didn't have a cooler? Furthermore, what did people do a long time ago before refrigerators were invented?

A major way that people prevent food spoilage is through spices. For example, check out the list of ingredients on the jar of pickles. It includes vinegar, salt, sugar~ and spices. Do these ingredients help preserve the pickles? The experiment in this lesson will help the students answer this question. (First make sure the students understand that a pickle is simply a spiced cucumber.)

preserve/spoil

hypothesis

control

(The details will vary since each experiment will be designed by a single student or small group of students.)

1. Decide which ingredients you think are important in preserving cucumbers to make pickles. This is your HYPOTHESIS.
2. Using the above materials, design an experiment to test that hypothesis. Since pickles are packed in water, think about putting a slice of cucumber in a cup and adding water. How much water will you add? What else will you put in and how much? How many cups do you need to set up? What will be your CONTROL? How will you keep track of which cups are yours and what's in them?
3. You cannot eat anything in the lab, nor can you feed it to anyone or anything. So, you need to think about how you will determine if your cucumbers spoil. What will you look for? You will need to record your observations at the beginning of the experiment and over the next few days. Keep track of each cup, as well as the times and dates you make each observation. What did you discover? Do the cups all look the same? Why or why not?

Ask the students to write up the experiment they designed in scientific format including a hypothesis, materials, procedure, observations, conclusions.

What might be causing the cucumbers to spoil? You could put a drop of the liquid from one of the cucumber cups on a microscope slide, put a coverslip on it, and look at it under the microscope. Can you see any microorganisms, any bacteria or fungi?

Have the students think about where these microorganisms come from. Can they design an experiment to test whether or not the microorganisms come from the air?

This lesson should lead to a discussion of the role of microorganisms in food spoilage. As the microorganisms use the cucumber as a food source, they decompose it. The cell walls break down and the cucumber becomes mushy. As the microorganisms multiply, they scatter the light shining through the cup and the water becomes cloudy.

Moreover, these ideas above could lead to a discussion of microorganisms in general. Some microorganisms cause diseases. That is why it is bad to eat food that has been left out for too long. It can make us feel sick. However, other bacteria are essential to maintaining health. For example, there is a certain type found in our guts which works to maintain the proper type of environment. It is the same bacteria which makes yogurt taste sour while at the same time making yogurt so nutritious.

In addition, this lesson could serve as a starting point to learning about spices A great web site about can be found at http://www.mccormick.com

This site contains a history of spices throughout the world along with many wonderful recipes. The students could research this site (or other resources also) to discover which spices are important in the part of the world that their ancestors came from. Or the students could pick a particular region of the world that they are interested in and research the spices from that area. Perhaps the class could pick one recipe collectively that they could make together to demonstrate the use of spices (not just in food preservation but also in taste). This would be a great exposure to how one little teaspoon of spice can drastically change the taste of a recipe. Yummy! !

SCIENCE CONTENT STANDARD #1: NATURE OF SCIENCE

This experiment satisf~es Benchmark 1 for grades 5-8 which states that students should be able to "design, modify, and conduct and investigation through testing. revising, and occasionally discarding ideas all of which lead to a better understanding of how things work." The lesson satisfies Benchmark 3: "collect. and summarize data from an experiment and interpret the results in terms of the data."

SCIENCE CONTENT STANDARD #3: LIVING ENVIRONMENT

Benchmark 1 asks students to understand how "organisms with similar needs may compete with one another for resources and how some survive and others do not". In this lesson, bacteria is an example of an organism that is competing for resources. It lives off food that we leave out, or it lives off of the materials found within our bodies.

SCIENCE CONTENT STANDARD #4: HUMAN ORGANISM

This lesson could serve as introduction to the activity of microorganisms; therefore, it would help to satisfy Benchmark 6: "determine how viruses, bacteria, fungi, and other organisms may interfere with the functioning of body systems".

SCIENCE CONTENT STANDARD #7: HISTORICAL PERSPECTIVES

Since the introduction to this lesson asks students to think about how people preserved foods before they had refrigerators, it would satisfy Benchmark 3 for grades K-4 which states that students should be able to "compare life today to life in earlier times and the role science and technology have played in the changes that have occurred". Furthermore, if the lesson leads to a discussion of the role of microorganisms in disease, then it would also satisfy Benchmark 4 for grades 5-8 which says that students should "know that through the work of many scientists, which began in the 19th century and continued through the 20th century, people began to understand that some diseases were caused by microorganisms, bacteria, fungi, and viruses".

First, this lesson is a great way to expose students to the method of designing an experiment in order to answer a question. But besides that, it could serve as an introduction to the topic of microorganisms. Finally, this lesson could be integrated with a social studies lesson -- during a unit on exploration (since many spices were discoered as different areas of the world were explored) or during a unit on immigration (since the . reason that the United States uses such a variety of spices is that immigrants from many different countries each brought their traditional favorites).