Step 1: Plan ahead.
In this activity, your group will make mold terrariums and observe mold growth for about two weeks. In addition to the supplies listed below, 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 ziplock bag that is then sealed with packing tape. Your students will observe the 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.
Step 2: Get supplies.
For each mold terrarium, you will need the following supplies:
- a sturdy paper or plastic plate that you can throw away when the experiment is done
- a ziplock baggie that is large enough to hold the plate
- half a slice of bread (Ask at a bakery or grocery store for day-old or expired bread.)
- pieces of fruit (oranges and strawberries both mold well)
- a strip of packing tape or duct tape for sealing the baggie
- a label large enough for the team name, date, and starting conditions
- a cup of water for moistening food
You will need to make a basic terrarium that contains damp food at room temperature. To observe the effect of different starting conditions, students will make mold terrariums in which one condition is different from the basic terrarium.
In this activity, students form teams and each team decides on ONE condition to change — that is, one way that their terrarium will be different from the basic terrarium. They may choose a condition that they think will encourage mold growth or one that they think will inhibit it.
For students who want to inhibit mold growth, we suggest you bring in some kitchen chemicals that can act as preservatives available -- such as salt, sugar, and hot pepper.
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!
If you think your students will come up with ideas that you can’t accommodate with materials on hand, consider splitting the activity into two days. On the first day, complete steps 1 to 6 of the activity, where students brainstorm ideas for their terrarium. Then you can bring in additional materials for the second day (steps 7 to 17), when students set up their terrariums.
Step 3: Print handouts.
Each student will need a copy of the Mold Terrarium handout. — print it here
Step 4: Prep before class
Before class, cut up the food that you will be using in your experiment. For each team, prepare a paper plate with a piece of each kind of food that you’ll be testing.
Step 5: Follow up after class
The second page of the student handout lets students record observations of their terrarium over time. This lets them see which food molds 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 that you create a bulletin board where you can post results from all the terrariums in the class. By comparing results, students can see which conditions are most conducive to mold growth and answer questions like these:
- Does the same food mold 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?
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