Patrick Grupinski, age 14, of Gadsden, Ala., for his question:
WHAT EXACTLY IS AN AMOEBA?
An amoeba is a tiny, one celled animal that usually can be seen only under a microscope. Some amoebas live in water and moist soil while others live in the bodies of animals and humans.
Amoebas eat other one celled animals and tiny plant life such as bacteria. They engulf their food by slowly wrapping themselves around a food particle. In this way, the food gets inside the cell.
You would have to put 100 amoebas next to each other to form a line one inch long. Only one cell makes up the amoeba's whole body. The cell is a shapeless mass of protoplasm, the living, jellylike material found in the cells of all living things.
A thin, elastic membrane surrounds the amoeba's protoplasm and holds it together. Water and gases pass in and out of the amoeba through the membrane.
The amoeba has no feet. To move about, it must change its body shape. The protoplasm pushes out on one side of the elastic membrane to form a fingerlike pseudopod, or "false foot." All the protoplasm seems to flow into the pseudopod.
For every "step," another pseudopod must form.
Cells that move in this way are called "amoeboid cells." The white blood cells of man are amoeboid cells.
The section of the amoeba's cell that contains the food is called a food vacuole. It floats in the protoplasm until the food is digested. All undigested food is forced out of the cell.
Amoebas in fresh water must control water taken into their bodies or they will burst. They have a contractile vacuole to collect the extra water that builds up in the cell. When the vacuole is filled, it empties through the cell membrane.
Amoebas reproduce by fission, or splitting apart, when they reach a certain size.
When an amoeba reproduces by fission, the nucleus, which is a mass of special protoplasm, divides first. Then the remainder of the body divides.
Most amoebas are harmless to man. But one type causes a serious ailment when it gets into the large intestine of humans. The ailment is called amoebic dysentery.
Amoebic dysentery results in severe inflammation of the colon. The disease is spread by taking the tiny amoebas into the mouth through food and objects. Fresh vegetables and fruits which have been handled by infected people have been known to carry the amoebas.
Fortunately, amoebic dysentery isn't a common disease. It is usually successfully prevented by cleanliness and sanitation. It is most common in warm and tropical countries.