naturally occurring elements in living cells:
O, Oxygen, atomic number: 8, atomic mass: 16, % of human body weight: 65.0
C, Carbon, atomic number: 6, atomic mass: 12, % = 18.5
H, Hydrogen, atomic number: 1, atomic mass: 1, % = 9.5
N, Nitrogen, atomic number: 7, atomic mass: 14, % = 3.3
Ca, Calcium, atomic number: 20, % = 1.5