Answer: The correct answer for the fill in the blank is energy and matter within living organisms.
Biochemistry is the branch of science, which deals with the study of chemicals and various chemical processes occurring inside the living organisms.
Energy and matter is present in the living forms. For instance, food is broken down and energy is produced in this metabolic reaction. The energy is utilized by the living organism in performing various activities. As this metabolic reaction occurs inside the body of an organism. Thus, it is the part of biochemistry.
Thus, biochemistry is the study of energy and matter within living organisms.