Kim Hampton, age 15, of Williamsport, Pennsylvania, for her question:
Are bacteria plants or viruses?
The status of bacteria has been shifted from the animal to the plant kingdom and finally to a sort of no man's land in the middle. When first identified under primitive microscopes, they were called animalcules because they were assumed to be tiny animals. This was more than 300 years ago. Later researchers thought that bacteria were more like plants. Until very recently, many scientists classified them as microscopic cousins of the fungi plants.
Modern science techniques have made it possible for researchers to delve deeply into the secrets of bacteria. These single celled organisms teem everywhere in our environment and recent evidence has shed some surprising new light on their mode of life. Many of their basic chemical processes are similar to those in both plant and animal cells. But the cell structures themselves are so different that they cannot be compared with either. Most scientists now regard them as very primate animal¬plant cells. But they have no kinship with the viruses.
The key word for a typical plant or animal cell is organization. The cytoplasm within the cell wall contains heat compartments where various cellular activities are performed with amazing efficiency. The nucleus contains the DNA, the miraculous blueprint chemical that directs the entire life activity of the cell. Ribosome bodies in the cytoplasm carry out the DNA instructions. The chemical energy for the operations is provided by football shaped bodies called mitochondria. Everything is a microscopic model of compartmentalized efficiency.
A bacterium cell has little or none of this compartmental organization. It has no nucleus. Its DNA is free in the cell cytoplasm and there are no special compartments for producing the cell's energy. Apparently energy functions are scattered around the membrane, the wall of the bacterium cell. Compared with the well organized plant or animal cell, the bacterium appears to be a model of haphazard inefficiency. Nevertheless, it carries on the chemical processes of life sometimes even more successfully than plant or animal cells.
On the other hand, a virus cannot be compared to a cell of any sort. It has no living protoplasm and none of the mechanisms for cellular activities, either in or out of compartments. It appears to be merely a wad of genetic material encased in a tough, protein shell. Since a virus has no way to support itself, it must invade another living cell. Every virus is a parasite of either plant or animal life.
Thousands of bacteria have been identified and their sizes range from midgets to whoppers. A row of about 60 average sized ones equals the thickness of a hair on your head. The viruses are infinitely smaller. If bacteria were whales, the average virus would be smaller than a fly. And virus parasites infect bacteria, just as they do plants, animals and people.