Final answer:
Lactic acid fermentation converts pyruvic acid to lactic acid and NAD+, and is used by muscle cells during high-intensity activity and by certain bacteria in yogurt production.
Step-by-step explanation:
In lactic acid fermentation, pyruvic acid is converted to two things: lactic acid and NAD+. The process begins with pyruvate, the end product of glycolysis, which accepts electrons from NADH. This reduction results in the formation of lactic acid. Concurrently, NAD+ is regenerated from NADH, allowing glycolysis to continue and produce additional ATP (energy currency of the cell). This type of fermentation is crucial for producing energy in muscle cells during intense activity when there is a lack of oxygen, and it is also utilized by certain bacteria, such as those involved in yogurt production.
During the conversion of pyruvic acid to lactic acid, there is no carbon dioxide produced, which contrasts with alcoholic fermentation. This pathway is key in situations where oxygen is scarce and cells must rely on anaerobic processes to meet their energy demands. For human muscle cells, this can occur during strenuous exercises, like sprinting, which rely on lactic acid fermentation for a rapid energy supply.