Bacteria are among the smallest living things known. Some are so tiny that it takes 25,000 of them to make a line 1 inch long. Because individual bacteria are too small to be seen, they are best studied in colonies. There are about two thousand known kinds of bacteria. Some cause disease in people, but others produce good food flavors in cheeses, cream, meats, and other foods.

Bacteria are non-green plant microorganisms that can be found almost everywhere. They 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. Observable changes in the contents, such as the production of bubbles and odors, will indicate the growth of bacteria.

Cultures can be transferred to a nutrient medium in petri dishes or test tubes to observe the growth of colonies. To inoculate a medium, dip a sterile cotton swab or glass rod into a culture and streak it across a medium.

Wash your hands. Use soap.

Culture some bacteria and mold. Measure the sizes of the different colonies on a daily basis for a week, then order the organisms by their growth rate.

Wash your hands again. Use soap.

Pour half a culture of bacteria into each of two beakers. Boil the contents of one beaker for twenty minutes. Seal it immediately with a piece of plastic wrap and a a rubber band.

Seal the unboiled water in the same way.

After two days, open and smell the contents and observe differences. You will realize that high temperatures kill bacteria.

Wash your hands again. Use soap.