Why do living organisms contain more hydrogen atoms than any other atoms, yet 65% of a typical organism's mass is oxygen?

Hydrogen ${H}_{1}^{1}$ Has only one proton and no neutrons and so has an atomic number of 1 and a mass of 1
Oxygen ${O}_{8}^{16}$ Has 8 protons and also 8 neutrons and so has an atomic number of 8 and a mass of 16.