There is a world of tiny living things
called microbes, which live all around us. They are almost everywhere and on
almost everything you can think of. They're in the air, the water, the soil,
your food, your clothes, on your hands, even on your desk and pencil! Microbes
are small, too small for us to see with our eyes. People who study microbes
use microscopes to see them.
Certain microbes cause disease, but they
make up a very small part of the whole microbe population. Most are harmless,
in fact, about one in every thirty thousand are likely to cause disease. Two
of our most common drugs, penicillin and streptomycin are from the activity of
certain microbes. The word microbe comes from two Greek words Mikros
meaning small and Bios meaning life.
This lab will focus on molds, which belong
to the Fungi Kingdom. Molds can grow in both hot and cold places but they grow
best in warm places. The colder it is the slower they grow. This is why foods
get moldy more in the summer than in the winter. Molds also like damp places
such as a damp towel left at the bottom of the clothes hamper. Molds also grow
well on damp wood or soggy paper. Ask students why we put food into a
refrigerator. To keep the food from spoiling we must put it where molds don't
like to grow, in the coldness of a refrigerator. To keep foods fresh for a
longer period of time we put them in the freezer, where molds do not like to
- PRIOR TO LAB: Place
a piece of bread into the bottom of a shallow dish. Moisten the bread with a
little water using a dropper. Don't soak it! Allow it to stand open to the air
for 45 minutes. Cover it and leave in a warm, dark place. About 1 week prior
to lab, start a few molds, then 2 days after start another group, and then a
third group 3 days before the lab begins. You should have bread that is 1 week
old, and 5 and 3 days old for students to observe. Include a fresh piece of
that same brand of bread. Also include any other food item that might be
- Set your molds out for students to
observe. Make sure you label how old the molds are. Students should observe
different stages of mold growth. Thin, transparent threads growing all over
the slice of bread are a mold garden. The cluster will look like a tangled
spider web. If you single out one of the threads and observe it with a
microscope you will see many branches of threads. At the ends of some of these
branches are little round balls. These balls are hollow round cases and each
one is filled with tiny seeds called spores. The spores are the mold's seeds.
In a 2-3 day old mold you will begin to see the spores on the garden. The
spores are the black substances sitting on top of the threads. Each black ball
or spore contains more than 20,000 smaller spores of their own. The threads
and their cases have no color but the spores within the cases are all colored.
So mold plants have no color, their spores make them appear to have different
colors. The 3-4 day old mold should have produced hundreds of millions of new
spores. Later they may fall on moist food left out somewhere, sprout threads
of their own, and give rise to new spores.
- ADDITIONAL EXPERIMENTS WITH MOLDS
Have children save a piece of something
from lunch and set these foods out on a clean sheet of paper. Let them stand
for 45 minutes in the open and then cover each of the foods with a dish. In a
period of a day or two observe what happens. Molds grow best in foods that
have a large amount of sugar or acid such as fruit, fruit juices, jellies, and
Select a certain food and put it in
different areas to grow. Again allow it to stand in the open uncovered for 45
minutes and then cover. Areas selected should include light, dark, moist, dry,
cold or hot conditions. Observe and see what happens. What do you think?
A piece of Roquefort or Blue cheese has
green spots all over. These spots are mold spores called penicillium molds.
Touch a toothpick to the green blue cheese mold and transfer it to a piece of
bread and an orange slice. Don't forget to moisten the bread a little. Cover
both soon after transferring mold. Which grew mold and why?