Bioenergetics

Bioenergetics is the study of how organisms capture, convert, and utilize energy to sustain life. It integrates biochemistry, physiology, and cell biology to explain how energy from nutrients is transformed into a usable form—primarily adenosine triphosphate (ATP)—and how ATP is then allocated to cellular processes. Energy flow is governed by the laws of thermodynamics and redox chemistry, with organisms acting as open systems exchanging energy with their environment.

In cellular respiration, heterotrophs extract energy from carbohydrates, fats, and proteins via glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation. NADH and FADH2 donate electrons to an electron transport chain; the resulting proton motive force powers ATP synthase to produce ATP. In photosynthetic organisms, light reactions generate ATP and NADPH, which drive carbon fixation in the Calvin cycle; chloroplasts are the primary organelles. Both mitochondria and chloroplasts illustrate energy transduction via chemiosmotic coupling.

Bioenergetics also covers energy budgeting, energy demand in organisms, and regulation of metabolism via hormonal and allosteric controls. Practical applications include understanding metabolic disorders, exercise physiology, nutrition, aging, plant biology, and biotechnological energy systems. The field has shaped concepts such as the chemiosmotic theory of Mitchell and the central role of ATP as the cellular energy currency.