It is important to determine or know whether an organism is aerobic or anaerobic because from there you would be able to know the perfect conditions for the organism to grow and reproduce. If you are culturing the organism you would need if it needs oxygen and how much of oxygen is needed. Anaerobic organisms does not need the presence of oxygen in order to grow. You can determine an organism that is anaerobic by trying to put them in conditions that dos not have oxygen. After a few hours or days, when you observe that more organisms are present, then most likely it is an anaerobic organism.