Sam Sandimarino, age 12, of Youngstown, Ohio, for his question:
Are bacteria classed as plants or animals?
None of the scientists believe that bacteria should be classified in the animal kingdom, and some suspect that the tiny organisms are not plants either. Hence, some classify them as plants and some place them in an in between kingdom of their own. But let's not blame the experts for this confusion. After all, the average bacterium measures only a couple of microns or so and there are 25,400 microns to the inch.
Bacteria come in hundreds of different varieties and together they outnumber all other living things in the world. They thrive everywhere from the deep ocean to miles up in the atmosphere. There are about 100 bacteria in the average cubic foot of ordinary air. Where ever we go, we cannot escape them and neither can anything else on the earth.
The trouble in studying and classifying the bacteria is their infinitesimal size. Usually they are measured by the micron. Most of the bacteria types range between half a micron and ten microns. Their various shapes may be squiggles or rods, round balls or sausages. Their life styles may be friendly or harmful to man, though most types neither help nor harm us.
Not so long ago, almost all scientists classified bacteria as mini fungi of the plant kingdom. Some still do. Others classify them in a group called Protista, in between the plant and animal kingdoms. This is because bacteria have certain plant features and certain animal features. These single celled organisms dwell in a realm of their own, though biologists suspect that some may have descended from plants and some from animals.
In any case, a bacterium is a single living cell. The busy cytoplasm of the living cell is encased in a thin membrane and usually protected by a sturdy cell wall. The outer shell may or may not have a slimy cover to protect the cell from corrosive chem¬icals.
A few bacteria have hairy tails called flagella, which they wave to swim through the water. Hence, they cannot be plants, which can neither swim nor walk. Most bac¬teria multiply by dividing into a pair of duplicates. So do certain simplified animals, though this method of reproduction is not typical of the animal kingdom.
Bacteria have another feature which is unknown in either the plant or animal kingdoms. All living cells are governed by the biochemical DNA, which is present in the cell nucleus. In plants and animals, the nucleus is contained in a special mem¬brane. A bacterium has but one long DNA molecule and the nucleus has no membrane.
Maybe the majority of scientists now classify the bacteria in the Protista group, between plants and animals. The various types are grouped according to their shapes. A sphere type is a coccus bacterium. A squiggly rod may be a spirillum or a spirochete. A straight rod or long, sausage shaped bacterium is rated as a bacillus. Some of the cocci and bacilli cause diseases, but the spirilla types tend to be harmless to humans.