Chapter 13. Chemicals of life No molecule in a living organism is a permanent resident. Within 7 years, most of the molecules in a human body have been replaced by new one Individual? Decided completely by the genetic code? No! An individual's identity is continually re-established each and every momentChapter 13 .Chemicals of life No molecule in a living organism is a permanent resident. Within 7 years, most of the molecules in a human body have been replaced by new one! Individual? Decided completely by the genetic code? No! An individual’s identity is continually re-established each and every moment