Section 3: Resources
Reinforcement Activity
Collecting Evidence for Non-Obvious Decomposers: Growing Microbes on Bread
A Caution about Mold
Because some children may be allergic to molds, it is important to use re-sealable plastic bags to hold the moldy bread, and to remind students to keep the bags sealed at all times. While keeping the moldy bread in plastic bags is generally a safe practice for this experiment, you may suggest that children with allergies wear dust masks to minimize exposure to any possible airborne allergens from the specimens. If you have any students with severe mold allergies, you may need to substitute a different activity.
This activity helps students understand that microbes are so tiny that you can't see them, but you can witness their effects. It is a particularly useful support activity for students who are unconvinced that microbes exist.
Have students take a piece of bread and rub it somewhere in their school. (The cafeteria floor, the banister in the stairwell, and the jungle gym on the playground are good choices). The bread you use should not contain preservatives in order to see results in a short period of time (bread from a bakery is likely to contain little or no preservatives). After rubbing the bread somewhere, students should seal the bread in a plastic re-sealable bag and then wash their hands. Direct them to put a piece of masking tape on the outside of the bag and write their name on it, as well as the date and the place where they got their sample. The bags should be pinned up (on the very top edge of the bag so as not to puncture the sealed part) in a place that does not receive direct sunlight. A hallway is an excellent choice as long as the bags are pinned up high enough so that students unfamiliar with the project will not open them. Tell the students not to open them.
After a few weeks, ask students to observe their bread samples (through the bag, they should not open it) carefully with hand lenses and describe what they see. Ask how their observations of the bread are similar to their observations of the logs. How are the processes similar? Explain that they are observing decomposition that is being caused by tiny organisms, some of which are not visible with a bare eye, and that these things are called "microbes." Students may be familiar with bacteria or germs. Explain that bacteria and fungus are two types of microbes. Mold is a type of fungus that they may have seen on their bread samples, or on old fruit or old leftovers. Remind students that some types of bacteria and fungi are harmless, like the kinds of fungi that we eat. Other types are dangerous and may cause people to become sick. For that reason we will not touch the fungi and bacteria on the bread and will keep the bags sealed. The mold they are looking at is feeding, and the fuzz they see are called "hyphae." These hyphae are actually threads or roots that are attached to the bread and are the way that molds absorb their food. These strands digest the food.
Where did the microbes come from and why didn't you see them there? Students should realize that their microbes came from the places where they rubbed the bread. They weren't seen there because microbes are hard to see unless there are many of them growing together, as is the case with the bread. This requires the right conditions. Microbe decomposers are everywhere, but they need the right conditions to grow. Ask students what they think those conditions are. They need food to live and grow, like any other organism. Other conditions, such as dampness, dark, and warmth encourage microbes to grow.
