Cell biology is the study of cell structure and function, based on the concept that the cell is the basic unit of life. Understanding cells permits a detailed understanding of the tissues and organisms that cells make up.
A cell is the smallest organism capable of carrying out the functions that define a living thing. These functions are metabolism, waste excretion, growth and development, response to stimuli, reproduction and trait heredity, and evolution in response to the environment.
Cell biology is based on modern cell theory, which states that all known living things are made of cells, all cells come from pre-existing cells through division, all cells are basically the same in chemical composition and all energy flow of life occurs within cells.