BioEd Online

Teacher Background

The old saying “There’s a fungus among us” contains an element of truth. There are at least 100,000 different fungus species, and members of the fungus kingdom (collectively known as fungi) are found almost everywhere. Fungi, along with some bacteria and other organisms, are the decomposers of our world. They break down the remains of dead plants, animals, and other living things and, in the process, obtain the energy they need to grow and reproduce.

Fungi are essential for the continued recycling of nutrients into the soil and the release of carbon dioxide into the air. However, fungi also can be a nuisance to humans. For example, fungi do not discriminate between fruits in a natural setting (such as those that have fallen on the ground) and fruits in the refrigerator. Many fungi attack living organisms and are sources of disease in both plants and animals. Fungi grow especially well in damp places and can attack cloth, paint, paper, leather, cable insulation, and even photographic film. The various fuzzy-looking fungi that grow on damp surfaces often are called molds.

Fungi spread by producing spores—tiny particles that can remain suspended in the air for long periods of time. The powdery appearance and bright colors of many kinds of molds actually are caused by the spores they have produced. Some fungi, such as yeasts, are one-celled organisms. Most, however, consist of mats of slender tubes or hyphae (singular, hypha). In some fungi, the hyphae are loosely packed and easy to see. In others, the hyphae are packed so densely that the structure appears solid. Mushrooms, the spore-producing parts of some fungi, are good examples of structures composed of these tightly packed filaments.

Inside buildings, fungi can grow in damp places, such as basements, shower curtains, food storage areas, and window air-conditioning units. The spores produced by molds can contribute significantly to indoor air pollution and can trigger allergic reactions in some individuals. Fortunately, indoor air pollution from mold spores can be controlled by keeping humidity levels low (below 30%), improving ventilation, and keeping damp areas clean.

Bread mold (Rhizopus stolonifer) is a common fungus that is easy to grow and observe. In this activity, students also may see greenish colonies of penicillium (the fungus that produces the antibiotic, penicillin) and other related fungi.

Objectives and Standards

Concepts

• Fungi grow from spores.

• Fungi spores are present almost everywhere.

• Molds and other fungi grow in damp places.

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Science, Health, and Math Skills

• Predicting

• Observing

• Recording qualitative data

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

• transparency of “Common Bread Mold” student sheet

• bread mold (Rhizopus stolonifer) (optional, order from a science supply company)

Materials per Group of Students

• piece of old bread (see Setup)

• pipette or dropper

Materials per Student

• clear resealable plastic bag, 4 in. x 6 in. (or small jar or plastic container)

• hand lens (magnifier) or microscope

• disposable plastic gloves (optional)

• copy of the student sheets

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Setup

1. A day or two before you plan to begin this activity, ask each student or group of students to bring a piece of bread to class (bakery-type or “natural” bread without preservatives works best). As an alternative, you many want to consider baking bread or having students bake bread at home with a parent as part of this activity (see PDF for recipes).

2. If you do not wish to grow bread mold in the classroom, pure cultures can be purchased (see PDF).

Procedure and Extensions

Time

One session of 20 minutes to set up cultures; daily 10-minute observations for 3–7 days; concluding session of 30–45 minutes to make final observations

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Part 1. Getting started

1. Hold up a piece of bread and ask the students if they know who or what might use it for food. Prompt them to consider all the possibilities. Follow by asking if they ever have seen a rotten apple or moldy slice of bread, etc. Point out that when something is rotting, other living things are using that object for food. Ask, How do you think these living things spread from place to place? Remind the students of the particles they observed in the “Make a Dust Catcher” activity. Mention that some of the tiniest particles in dust are produced by organisms as a means of spreading to other places. Tell students they will be able to observe some living things that spread in this way.

2. Have Materials Managers pick up materials for all members of their groups. Have each student label a container with a piece of tape on which the student has written his/her name.

3. Direct the students to examine their bread samples with a magnifying glass and draw or describe what they predict will happen to the bread in the first space on the “Bread Mold Observations” sheet. In the second space, have students draw or describe the bread as it appears at the beginning of the investigation.

4. Each student should place the bread in his/her container and add a few drops of water. Store the containers in a dark corner or cupboard.

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Part 2. Observations

1. For the next 3–7 days, have students observe their cultures (with and without a hand lens) at one- or two-day intervals. Do not allow students to open the containers in which molds are growing. Some breads may grow mold in as little as 24 hours; others may require seven days or more.

2. Have students record their observations on their data sheets.

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Part 3. Final observations

1. When all or most cultures have visible molds (some breads treated with preservatives may not grow mold within the time allotted), instruct students to make their final observations.

2. As a class, decide how many different kinds of molds are present on the bread samples. Have students make a list of the characteristics they use to distinguish one mold from another. Prompt them to think about whether some molds seem to grow on certain types of bread. Ask, How did the mold get to the bread? (Spores were present in the air and landed on the bread.)

3. One fungus that will be present is bread mold. It consists of dark gray threads forming a loose, tangled mat that may reach a centimeter in thickness. Find several samples of bread mold from the class’s cultures, and give a container with bread mold to each group.

4. Have students observe the bread mold inside their containers with their magnifying glasses. They will be able to see the individual threads with small dark dots at the ends. The dots are the spore-producing parts of the fungus. (The actual spores are very tiny.) If you have access to microscopes, place a few strands of the bread mold (using forceps or tweezers) under microscopes for students to observe. Students will be able to see the tubular structure of the filaments (hyphae), the round, dark heads that produce spores, and, depending on the magnification, some of the tiny, round spores. Project the “Common Bread Mold” page to help students spot the different parts.

5. Conclude by leading a class discussion of the role of molds in causing indoor air pollution. You may wish to refer to the story Mr. Slaptail’s Secret, in which Rosie, one of the characters, is allergic to mold spores.

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Extensions

• Have students invent names for the different kinds of molds they grew and create a key to identify each one.

• Make one or more kinds of bread with your students. Try using a recipe with baking soda for leavening, and compare the results with a recipe that uses yeast (a fungus). Mention that, in both cases, the bubbles in the dough are caused by carbon dioxide gas being released into the dough.

Handouts and Downloads