Among the millions of species on this planet, the cell is the common denominator. Cells are the most basic living unit. In many species, such as bacteria and amoeba, the entire organism consists of a single isolated cell. But for plants and animals, including us, the organism exists as a compilation of many cells working together. In fact, every adult human is a compilation of some 60 to 100 trillion cells.
As a rule of nature life begets other life and thus all cells must come from existing cells. This is to say that in order to create a new cell, an existing cell has to divide into two cells. It also suggests that all life-forms on Earth may be derived from the same cell or type of cell. The process of cell division is tightly regulated and, as we will discuss in later chapters, when this regulation is lost and cells divide out of control, cancer can arise.
When you and I were conceived, an egg (ovum) from our mother was penetrated by our father’s sperm. This resulted in the formation of the first cell of a new life. Therefore, everyone you know was only a single cell at first. That cell had to then develop and divide in two cells, which themselves divided to create four cells, and so on.
Our body is composed of 60 to 100 trillion cells, each of which contributes to overall health and well-being.
The term cell implies the concept of separation. Each cell has the ability to function on its own. In living things composed of numerous cells, such as humans, individual cells are also sensitive and responsive to what is going on in the organism as a whole. Therefore, these cells survive as independent living units and also cooperatively participate in the vitality of the organism to which they belong.
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