Cell are the smallest and most fundamental structural and functional units of life. Organisms may consist of a single cell ( bacteria, for instance ) or plants and animal that contain huge numbers of cells.Large and complex organic compounds, called macromolecules, make up the basic molecular unit found in cells. Three of these molecules are polymers,formed when a number of simple organic molecules (monomers) are linked together by chemical bonds. The three major types of organic polymers are complex carbohydrates such as cellulose and starch that consist of two or more monomers of simple sugars such as glucose linked together; proteins formed by linking to gather monomers of amino acids; and nucleic acids (such as DNA) formed by linking monomers called nucleotides.