ABSTRACT
Heredity is the passing of traits from parents to offspring. Heredity begins with a single cell, the smallest unit of life. Heredity is like that, except the messages are the genes that are passed from parents to offspring. All cells come from other cells through cellular reproduction. A body that is made of only one cell is called unicellular. Once a cell is differentiated, it loses its ability to change into another kind of cell because unneeded genes are permanently 'switched off'. Tube-like structures crisscross the cytoplasm to form a cytoskeleton, or cell skeleton. Plant and animal cells reproduce asexually using a process called mitosis. In the right environment, a bacterium might divide every twenty minutes or so, which is how diseases spread. In animal cells, this division occurs when the cell membrane, which surrounds the cell and protects it from the outside world, pinches off in the middle like a long balloon twisted into two sections.
