Glucose is a six carbon molecule which is oxidized in different ways in the human body depending upon the presence or absence of oxygen.

First, the glucose molecule is broken down into Pyruvate in the cytoplasm.

In case of aerobic respiration (When oxygen is present) pyruvate is oxidized into carbon dioxide and water. This takes place in mitochondria.

In case of anaerobic respiration (absence of oxygen) pyruvate gets broken down into ethanol, carbon dioxide and energy. This takes place in yeast.

The different pathways can be depicted as in the diagram below.