Final answer:
Lactic acid fermentation occurs in animal cells under conditions of low oxygen, such as during heavy exercise when muscles become fatigued. Pyruvic acid is converted to lactic acid with the concomitant regeneration of NAD+ which is essential for glycolysis to continue, allowing energy production to be maintained.
Step-by-step explanation:
The type of fermentation that readily occurs in animal cells is lactic acid fermentation. This process is employed by animal cells, particularly in mammalian red blood cells and skeletal muscle cells when conditions of insufficient oxygen arise, such as during intense physical activity leading to muscle fatigue. In lactic acid fermentation, pyruvic acid from glycolysis is reduced to lactic acid by the enzyme lactate dehydrogenase, with NADH being oxidized to NAD+ in the process. This allows glycolysis to continue by replenishing the NAD+ needed for the breakdown of glucose. Accumulated lactic acid is then transported from the muscles to the liver by the blood circulation for further metabolism.
Facultatively anaerobic prokaryotes can switch between aerobic respiration and fermentation based on oxygen availability. On the other hand, obligate anaerobes, such as Clostridia, cannot tolerate oxygen and die upon its exposure. It's important to note that unlike other types of fermentation which produce gas, lactic acid fermentation does not.