Anaerobic Glycolysis - Lactic Acid System

The net gain of ATP once the lactic acid system is completed is 2. This system is an anaerobic pathway that occurs when there is a lack of oxygen available for energy production. During this process, glucose is broken down into pyruvate, which is then converted into lactic acid. In this process, a total of 4 ATP molecules are produced, but 2 ATP molecules are used in the initial steps, resulting in a net gain of 2 ATP molecules.

Glucose-6-phosphate is converted into pyruvic acid through a series of reactions known as glycolysis. This process occurs in the cytoplasm of cells and is an important step in cellular respiration. Pyruvic acid can then be further metabolized in the presence of oxygen to produce more energy through the citric acid cycle and oxidative phosphorylation. Lactic acid is produced during anaerobic respiration, while citric acid is a product of the citric acid cycle. Therefore, the correct answer is pyruvic acid.