1. The chemistry of living organisms and of the chemical, molecular, and physical changes occurring therein; such as, biological chemistry and physiological chemistry.
2. The science dealing with the substances present in living organisms and with their relation to each other and to the life of the organism; biological or physiological chemistry.
3. The branch of biochemistry that deals with the relation of chemicals found in the soil to living organisms; the biological application of geochemistry.

Biochemistry includes the chemical reactions of living cells. It is based on the idea that all of life can be understood as chemistry. Situated between biology and chemistry, the field of biochemistry relates to all branches of chemistry and biology, ranging from genetics to physical chemistry, from medicine to agriculture, from nutrition to biotechnology.