Cells People like to say, as if it were obvious, that life is hard to define. This is simply not so.
Life has properties that clearly distinguish it from everything else.
Every living thing is cellular. In other words, it is either a single-celled creature or a creature composed of biological cells. Every cell is bounded by its own outer membrane and contains a full set of instructions necessary for its operation and reproduction. DNA is a long complex molecule that contains the cell's instructions. Either individually or in sexual pairs, they have both the encoded instructions and the machinery necessary for self-reproduction .