Smallest Unit of Life: Cell Biology

Abstract

The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, are multicellular.

The human body is built from an estimated 100 trillion or 10¹⁴ cells. Such complex living systems have developed several levels of organization depending on each other, for example, organs, tissues, cells, and subcellular structures (Fig. 2.1). For the understanding of these biological systems, small units must be investigated at a time. The logical starting point for the examinations is the cell, since at the cellular level, all life is remarkably similar.