Cells Are Little Life Units

Cells Are Little Life Units
What Are Cells?
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.