Answer:
Plants create oxygen as a byproduct of the photosynthesis process. While the majority of this oxygen is released into the atmosphere, a small portion is not. Instead, the plant uses this oxygen for metabolic functions.
The oxygen that is not released into the environment is predominantly used by the mitochondria of plants during cellular respiration. Mitochondria are the cell's powerhouses, producing ATP (adenosine triphosphate), the cell's primary energy currency. To make ATP, mitochondria require oxygen, which is required in the oxidative phosphorylation process. This process includes the transport of electrons from NADH and FADH2 to oxygen molecules, which produces ATP.
Thus, the plant uses the oxygen that is not released into the environment to generate energy for its metabolic processes. It is an essential component of the plant's energy cycle and is required for the plant to grow, develop, and perform its biological tasks.