Yeast plants are a common form of microscopic fungi that cannot make their own food, thus do not contain chlorophyll. More than fifty-five thousand kinds are known.

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 under a microscope or on a microprojector. You can easily see the yeast plants. Estimate the number you see.

[One way to estimate is to divide the visual area into fourths, count the number in one fourth of the area, then multiply the number by four.]

Now let the mixture stand overnight. Look at it the next day and determine the number. These tiny yeast plants are in the air almost everywhere.

Make some bread dough with yeast (There is a wonderful recipe in the project entitled "Let's Make Bread".) Divide the dough into three parts, and place each part into a bowl; cover the dough with a clean, damp dish towel. Put the first in a fridge, the second in a warm place, away from drafts, and the third in a hot place.

Examine the dough each hour and describe the effects of the different temperatures.

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Place a piece of baker's yeast into a small bottle and add a little molasses and warm water. Shake the mixture. Observe a drop of the mixture under a microscope. You will see a small bulge grow out of a larger cell, remain attached for a short period of time, then eventually separate from it as an independent plant. This kind of reproduction is called "budding."