Why are Organisms Composed of Cells?

All living organisms are composed of structural and functional units called cells. The body of a living organism may be composed of a single cell - as in unicellular organisms or many cells - as in multicellular organisms. The number of cells in the body of multicellular organisms is correlated with the size and complexity of their body.

According to an estimate in the body of human being weighing about 60 kgs, there are about 100 trillion (100 x 10 ¹²) cells!

Living organisms perform a wide variety of functions, which are collectively described as metabolic activities. These metabolic processes can take place only in a delicately balanced environment. Only cells can provide such an environment. Any living cell is capable of maintaining its internal environment, within its boundary by a mechanism called homoeostasis. In a controlled environment of a cell, the various life processes can occur in the desired manner. Hence, the living organisms are composed of cells.

Cell is the Basic Unit of Life

The simplest structural units into which a complex multicellular organism can be divided and still retain the functional characteristic of life, are called cells. One of the unifying generalisations of biology is that certain fundamental activities are common to almost all cells and represent the minimal requirements for maintaining life. Thus, an Amoeba and a human liver cell are remarkably similar in their meanings of exchanging materials with their immediate environment or obtaining energy from organic nutrients or synthesising complex molecules or duplicating themselves. Hence, the cell is the basic unit of life.