Final answer:
Aerobic respiration is carried out by an organism when it needs to generate energy and has oxygen available.
Step-by-step explanation:
Aerobic respiration is carried out by an organism when it needs to generate energy and has oxygen available. Oxygen is required for cellular respiration, which is the process that breaks down glucose and produces ATP, the energy currency of the cell. With oxygen, organisms can break down glucose all the way to carbon dioxide, releasing much more energy compared to anaerobic respiration. Therefore, when an organism has access to oxygen and needs to generate a significant amount of energy, it performs aerobic respiration.