Fission, in biology, is a process of asexual reproduction in which the parent body divides into two approximately equal parts that become independent individuals. Most one-celled plants and animals reproduce by fission. How fission takes place may be seen by studying the reproduction of one of the simplest animal forms, the amoeba.
The amoeba reproduces when the volume of protoplasm has become so great that the membrane surface cannot supply enough food and oxygen and cannot remove wastes efficiently. The body of the amoeba begins to constrict, and the nucleus divides, forming two nuclei that move to opposite ends of the cell. Then the constriction continues and divides the animal into two amoebae. Each one has a nucleus and is capable of living, growing, and re-producing independently.
The paramecium, the euglena, and other protozoa, many bacteria, and many unicellular algae also reproduce by fission. Fission, however, is not limited to unicellular organisms. Multicellular planarians, or flatworms, will constrict and separate into two masses, each of which will then increase until it has grown to adult size.
