Aerobic respiration takes place in two major steps;
- Glycolysis
- Kreb’s cycle
Glycolysis
It is the first step involving a series of reactions. It is the breakdown of glucose molecule into two pyruvic acid molecules (pyruvate) with production of two ATP molecules. Glycolysis occurs in the cytoplasm of the cells and does not require oxygen.
The fate of pyruvic acid depends on the availability of Oxygen. In the presence of oxygen, pyruvic acid enters the mitochondria. In absence of oxygen pyruvic acid is then partially broken down to lactic acid in animals or to ethyl alcohol (ethanol) and carbon (IV) oxide in plants.
Alcohol production occurs in plant tissues and during fermentation by yeasts and many bacteria. The alcohol accumulates in these organisms provided oxygen is excluded.