Cell biology is a branch of biology which deals with the study of cells.
Cells are building blocks of living organisms and fundamental unit.
Organisms are made up of different types of cells, and cells give structure to the organism. So they are known as a structural unit, cells play biological mechanisms for organisms, so they are known as biological units, and cells play different functions to carry out a life of organisms, so they are known as a functional unit.
Cell theory states that cells are building blocks of organisms, and every cell come from the pre-existing cell.