Culture some protozoa, bacteria, mold, yeast, and algae. As each culture develops, you will see that the increases in populations involve new organisms that are like the parent.

I have always thought that "culture" has to do with art, classical music, and ballet. I guess there are more kinds of culture that I don't yet understand.

Microorganisms are too small for the growth of an individual organism to be measured in the classroom; however, growth of populations can be measured.

There appear to be several different kinds of microorganisms:

Protozoan (also spelled proto-zoon) (pronounced "Pro-toe-ZOE- onn"): The encyclopedia says "any of the single-celled, usually microscopic organisms of the phylum or subkingdom Protozoa, which include the most primitive forms of animal life."

a. Protozoa: Obtain some pond water and develop a culture. Collect jars of pond water, including some mud from the bottom. Let the water settle. After two days, stir the
water without disturbing the mud, fill a medicine dropper with the water, and place a few drops in a watch glass or test tube. Use a hand lens to observe the contents.
Count the number of protozoa in a drop of pond water and compare them with a later sample. Keep count of each type of organism that you see. A few drops of gelatin or
methyl cellulose added to the water will slow the animals down for better viewing.

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Bacteria refers to "microscopic, unicellular organisms having three typical forms: rod-shaped (bacillus), round (coccus), and spiral (spirillum). The cytoplasm of most bacteria is surrounded by a cell wall; the nucleus contains DNA but lacks the nuclear membrane found in higher plants and animals."

b. Bacteria: Inoculate the culture medium in a petri dish. (Say "PEA-tree." This is a shallow dish with a loose- fitting cover, used especially to culture micro- organisms.) Cover and seal the dish. To make a gelatin medium, dissolve one beef bouillon cube in 1 cup of boiling water. Add a spoonful of sugar. Prepare unflavored gelatin according to directions on the package (use Knox gelatin or a bacteriological gelatin from a scientific supply house), but substitute the beef broth for the boiling water. Cool the solution, and pour it into sterilized petri dishes or test tubes. Cover and let the containers cool.

Bacteria can be cultured in the classroom by placing plant material (such as dry grass, beans, peas) or various meats in a small amount of water in an open jar and covering the jar for several days.

To inoculate a medium, dip a sterile cotton swab or glass rod into a culture and streak it across a medium.

(Caution: Under most conditions bacteria are harmless; however, disease-producing strains can appear in a culture, so be careful not to spill a culture and always
wash hands and materials thoroughly [use soap] after working with one.)

A sterilized cotton swab or glass rod can be used to streak a culture across a glass slide. When the slide has dried, cover the streak with red ink and let it stand
for several minutes. Gently rinse off the red ink with running water. Examine the slide under the microscope. (The red ink will help you see the culture more clearly.)
Measure changes in the size and shape of the growths inside.

Students can also try to grow bacteria in a petri dish without a culture medium.

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Mold is the "multicellular organism of the division fungi, typified by plant bodies composed of a network of cottony filaments. The colors of molds are due to spores borne on the filaments. Most molds are saprophytes. Some species (e.g., Penicillium) are used in making cheese and antibiotics."

c. Molds: Aspergillis elegans is a relatively slow growing mold that grows on bread. It leaves a ring of spores with each day's growth, making it easy to measure on a
daily basis. To grow mold on bread, place a moist blotter or paper towel on the bottom of a jar. Set a piece of white bread on the blotter, and leave the jar open for thirty minutes. Put a lid on the jar, label it, and store it in a dark place. Cut paper strips each day to represent the distance each mold grows.

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Yeast is the "name for certain microscopic, unicellular fungi, and for commercial products consisting of masses of yeast cells. Yeasts consist of oval or round cells that
reproduce mainly by budding (a small outgrowth on the cell's surface increases in size until a wall forms to separate the new individual, or bud) but also by means of spores. They are used in alcoholic fermentation and to leaven bread. Certain other fungi are also sometimes called yeasts."

d. Yeasts. Culture some yeast. Yeast plants can be grown by mixing baker's yeast with warm water and a little molasses. Allow the mixture to stand for one hour.
Place a drop of it on a glass slide, and observe it under a microscope or on a microprojector.

Estimate the number of plants in one-fourth of a viewed area, then multiply the number by four to obtain an estimate of how many there are. Recount later, after the yeast has risen.

This brilliant writer is also a brilliant bread-maker. Once, following instructions, I prepared a mixture of 1/2 cup rye flour, 1 tablespoon sugar, 1 cup water, and 1 package dry yeast. I put it into a one-quart bowl and put a plastic lid over the bowl, which sealed it quite nicely. Big mistake. Pursuant to the instructions, I then put the bowl in a warm place (on top of my freezer) for the yeast to develop and rise. It developed, and then it exploded! What's more, it smelled horrible! When the instructions said "cover the bowl," it meant that I should cover the bowl with a clean, damp, warm cloth, rather than a plastic seal.

My grandmother used to make root beer, and store it in the basement in bottles. Frequently, a bottle of root beer would explode. That had something to do with yeast, also. Your brilliant science teacher can probably explain the more volatile sides of yeast.

How many students know what "sourdough" really is? In some parts of the world, there are wonderful, wild yeasts in the air. It seems to appear mainly in damp climate areas. Bread can be made to rise without adding commercial yeast, because Mother Nature provides it abundantly. It is called "sour" because sugar is not required to develop the yeast. Some parts of Alaska have great wild yeast, and San Francisco, California has it also. It is wonderful to have if you live in an isolated area, and don't have the ability to obtain and/or store commercial yeast. At some gourmet shops, one can purchase a sourdough "starter." When you want to make bread, take out one cup of the starter to raise your bread. Add 1/2 cup water and 1/2 cup flour to the starter crock, mix well, and close the crock. In a few days, your starter will be ready to be used again. (Actually, instructions are in the package.) If you treat it well, your starter will last the rest of your life, and you can leave it to your grandchildren!

Try to grow yeast without a culture medium.

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Algae are "primitive plants that contain chlorophyll and carry on photosynthesis, but lack true roots, stems, and leaves. They are the chief aquatic plant life both in the
sea and fresh water; nearly all seaweeds are marine algae. Algae occur as microscopic single cells (e.g. diatoms) and more complex forms of many cells grouped in spherical colonies (e.g., Volvox), in ribbonlike filaments (e.g., Spirogyra), and in giant forms (e.g., the marine kelps)..."

e. Algae: You can see the increase in green algae in an aquarium kept in strong, but not direct, sunlight.