You will need access to water for this activity.

In addition to the supplies listed above, you will need a well-ventilated area to store your mold terrariums. The space you have available may limit how many terrariums you make.

Each mold terrarium will be sealed in a Ziploc bag that is then sealed with duct tape. Students will observe mold through the clear plastic, but will not open the bags. When your observation period is over, you will throw the entire experiment away. Do not open the bag. Opening the bag would release mold spores, which can exacerbate asthma and cause respiratory illness.

We suggest students work in groups of four. Homeschool students can work on their own.

Plan Your Time

You may want to divide this activity into two sessions.

Part 1 (students brainstorm ideas for their mold terrarium) takes 10 to 15 minutes.

Part 2 (students set up their mold terrariums) takes 15 to 20 minutes. Part 2 begins at Step 7.

Decide What Variables Students Will Test

In this activity, each group of students decides on ONE condition to change — that is, one way that their terrarium will be different from the basic terrarium, which contains only damp food kept at room temperature. They may choose a condition that they think will encourage mold growth (e.g. heat) or one that they think will inhibit it (e.g. preservatives such as salt, sugar, or hot pepper). So you may want to think ahead regarding what materials or conditions (hot vs cold) you can accommodate in your classroom.

If you divide the lesson as discussed in “Plan Your Time,” you have the option of bringing in additional materials for Part 2 when students set up their terrariums and test different variables.

Students may suggest adding garden soil or compost to the food to encourage mold growth. Don’t do it! Some soil bacteria (known as anaerobic bacteria) make nasty smells when they break down foods. These anaerobic bacteria thrive in a sealed plastic bag with water and fruit. A mold terrarium with soil will grow mold — but it will also stink!

Prepare Food Items Before Class

Before class, cut up the food that you will be using in your experiment. In our lesson, we include a half slice of bread, a piece of cheese, a slice of apple, a slice of orange, and a slice of banana. You can use whatever food items are easily available, but include the same items for each terrarium and try to make them the same size to ensure a fair test. For each team, prepare a paper plate with a piece of each kind of food that you’ll be testing. Here’s an example of what our plates looked like:

Make a Basic Mold Terrarium to Use as a Control

You will need to make a basic terrarium that contains damp food at room temperature. This basic mold terrarium will serve as the control so students can compare their experimental results to it. To see how to set this up for yourself, follow our step-by-step instructions (Steps 7 through 12) here. [Note: If you plan to teach the lesson in two parts, wait to prepare your terrarium right before you teach Part 2.]

Get Duct Tape and Water Ready

Each group will need a cup filled with water so that they can moisten each of their food items, and will also need a strip of duct tape longer than the width of the Ziploc bag so they can double seal the bag. You may want to prepare these supplies prior to class to make distribution easier.

Separate Supplies for Easy Distribution

In Part 1, students will only need their Mold Terrarium printout and a writing utensil.

In Part 2, each group will need the following supplies:

You may want to separate these supplies to make classroom distribution easier.

Observe Mold Terrariums for Two Weeks

The second page of the student handout lets students record observations of their terrarium over time. This lets them see which food molds the fastest in their terrarium. By filling in circles to record how much of a given food is covered with mold, they create a bar graph of the mold growth.

We recommend creating a bulletin board where all teams can record and compare results for their terrarium. By comparing results, students can look for patterns and observe which conditions are most conducive to mold growth. They can then answer questions like:

• Does the same food mold the fastest in all conditions?
  
• If you had to take food on a long trip and you had no refrigeration, which of these foods would be the best one to take? How would you store it to keep it fresh as long as you could?