the main portion of all cells is fiied with a fluid material. just like a human body , the interior of the cell contains food , waste material or even extra water. on the inside of all cells is a protective covering called a membrane. It is just like the shell of an oyster. sometimes cells divide in half, forming a new cell. in other words. one cell splits in half and an exact duplicate forms. now there are two cells. when we are growing as a baby, cell division is responsible for muchof our growth.