Compare anaerobic respiration in a yeast cell with anaerobic respiration in a muscle cell.

Anaeobic respiration in yeast:
glucose -> carbon dioxide + ethanol

Anaerobic respiration in muscle cells:
glucose -> lactic acid

The lactic acid build up in muscles requires oxygen to be broken down and thus creates an oxygen debt, resulting in the animal breathing faster and more deeply to acquire a higher partial pressure of oxygen in their blood. The respiration in yeast results in ethanol and CO2. CO2 bubbles are what make bread rise when yeast is added while ethanol can be used in alcohol production in a process called fermentation. Both respiratory reactions produce energy through glycolysis which is much less efficient than aerobic respiration which releases energy through further reactions such as the Krebs Cycle and Oxidative phosphorylation.