The living world is a hierarchical organization of structures extending from molecules to biosphere. System properties emerge out of interaction between components at the lower level while additional properties emerge at each successive level. The lowest level is the ordering of atoms into molecules and the interactions of molecules in a cell.

The essential elements of life are about twenty five and just four elements namely carbon, oxygen, hydrogen and nitrogen constitute ninety six percent of living matter with water as the solvent of life. Iron, Phosphorous, sulfur, calcium, sodium, potassium, iodine and a few others constitute the remaining four percent.

Biochemistry is the chemistry of life as it deals with study of life molecules that make up cells (proteins, carbohydrates and lipids), those that play key roles in chemical reactions vital to life (e.g., nucleic acids, vitamins, and hormones) and with many other complex and interrelated chemical changes and processes that occur in organisms.