The organelle involved in the oxygen-requiring process by which energy macromolecules are stored as ATP is the mitochondrion.

Here's why:

* Cellular Respiration: Mitochondria are the powerhouses of the cell. They are the site of cellular respiration, the process that breaks down glucose (a sugar) in the presence of oxygen to produce ATP.

* ATP Production: ATP is the primary energy currency of the cell. Mitochondria use the energy released from glucose breakdown to create ATP through a series of chemical reactions.

* Oxygen Requirement: This process requires oxygen as the final electron acceptor in the electron transport chain, a key step in cellular respiration.

Let me know if you'd like more details about cellular respiration or the role of mitochondria!