How did Lavoisier’s oxygen theory explain combustion and respiration?

Antoine Lavoisier’s oxygen theory fundamentally transformed chemistry by replacing the phlogiston theory, which incorrectly posited that combustion involved the release of a hypothetical fire principle.12

Combustion

Lavoisier demonstrated that combustion is not a process of losing phlogiston, but rather a chemical combination between a substance and oxygen from the atmosphere. By observing that metals gained weight when converted into calxes (oxides), he proved that the substance was absorbing oxygen rather than emitting a weightless principle. This established that oxygen is the active agent required for burning.3124

Respiration

Lavoisier extended his theory to respiration, identifying it as a process analogous to combustion. He concluded that living organisms consume oxygen from the air to sustain life, effectively treating respiration as a slow oxidation process within the body. This shift in understanding allowed scientists to quantify the chemical changes occurring in both inanimate burning and biological life, ultimately discrediting the notion that air merely served to carry away phlogiston.1342