OBJECTIVE:
  • Observing fungi.
  • Exploring the ecosystem of rot.
VOCABULARY:
  • rot
  • spore
  • hyphae

MATERIALS:

BACKGROUND:

How many times have you looked for an orange to eat and found that the last one left had grown soft, blue-green fuzz? Have you ever left a wet towel at the bottom of your clothes hamper and at the time of washing you found that it had green "freckles" all over it? Or how many times have you found bread that has gone stale and has grown black "whiskers?" The green fuzz on the orange, the green freckles on the towel and the black whiskers on the bread are all known as molds. Molds are really tiny fungi belonging to one of the 5 kingdoms. "Molds" are a term that is not really a natural grouping, but until scientists figure out exactly where they belong, we will consider them fungi. Molds are so tiny that we cannot see them unless there are many of them bunched together. To see just one mold you need a microscope. There are many kinds of molds. One of the most common molds is the one which turns oranges into green fuzzy balls. It is called penicillium. This is where the drug penicillin comes from.

Plants use sunlight to make food in their leaves. The green coloring matter acts as a kind of food factory. Molds have no food factories, so they take the food they need from their host. All molds are food robbers.

Foods will eventually rot if not kept cool or not eaten within a certain time unless frozen. The more time food stays around the more of a chance spores from a mold have of landing on it and growing. A spore is the reproductive part of the fungi.

Wherever there is food, air, and moisture, some mold spores will find their way there to settle and begin to grow. If a spore doesn't find the food, air or moisture it needs to grow it does not die. It just waits. It can remain alive for years in its case, waiting for the right conditions to burst open and grow.

Organisms found in the Fungi Kingdom are heterotrophic. Fungi obtain food by decomposing anything that is organic in nature. Fungi live everywhere. They grow best in warm, moist places. They are not green and do not possess chlorophyll. Fungi can grow on vegetables, bread, meat, fur, wood, leather, or anything that is in a warm and moist area.

Fungi that obtains nutrients from non-living organic matter are called saprobes. Other fungi obtain nutrients directly from a living host, these are parasites. In either case, the fungi secretes enzymes that allow digestion to take place outside of the fungal body. Nutrients are then absorbed across the cell membranes. Together with bacteria, fungi are the decomposers of the earth. Fungi include yeast, bread mold, and mushrooms.

Fungus itself is made up of a fungal body or what is called mycelium. The mycelium is a mesh of filaments that branch out in any direction living over or within the organic matter. Each filament is a hypha. Hypha are transparent thin walled tubes.


PROCEDURE:

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 molding.

You will need to divide the bread and set up the microscopes so they can take turns looking at the various stages of mold.   Be sure to review with them how to use the microscopes, they focus by moving up and down.  Once the microscopes are in focus they shouldn’t touch them. 

1.     Go over the Mold Powerpoint.  The first slides review the different kingdoms and their characteristics.  You may want to review some of the lower grade material if your students have not developed a feeling for the diversity of life. In this unit, students will look at organisms that they see, but rarely think about as being living. Mold is a super decomposer so it is important for students to understand what is happening when they see something moldy.

2.    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.

3.  Students should use the rot guide to try to identify the type of mold they see. They should fill in the worksheet using the Rot Guide and then drawing what they see in the microscope.

4.  At the end, review with students how the mold is different from three day old to a week old—how does mold change over time?

NOTE:  Some students are very sensitive to mold.  You can buy some of the one-use face masks to have on hand for the more sensitive students.

 
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