Atoms differ from one another by having different numbers of protons, neutrons and electrons.
Groups of atoms bonded together are called molecules. A cell is bounded by a membrane that separates the inside of the cell from the outer environment. During this stage, they appear under a microscope as long tangled threads. A commercial cytology laboratory examines the structure of chromosomes for genetic disorders. The precise arrangement of these four subunits is used to store all information necessary for life processes.