Final answer:
The electron transport chain for cellular respiration is located in the mitochondria. In the absence of oxygen, pyruvate molecules formed in glycolysis are converted to lactic acid through lactic acid fermentation. These processes play crucial roles in ATP production and energy metabolism within cells.
Step-by-step explanation:
The electron transport chain for cellular respiration is located in the inner membrane of the mitochondria. When oxygen is present, pyruvate molecules formed in glycolysis enter the mitochondria and are transformed into acetyl-CoA, which then enters the Krebs cycle. However, in the absence of oxygen, pyruvate is converted to lactic acid in a process known as anaerobic glycolysis or fermentation. During glycolysis, glucose is broken down into two molecules of pyruvate, which are then oxidized and converted into Acetyl CoA. These steps occur in the cytoplasm of the cell. Acetyl CoA enters the mitochondria, where it goes through the Krebs cycle. Then, in the electron transport chain, the electrons obtained from Acetyl CoA oxidation move along a series of electron carriers, creating an electrochemical gradient that is used to produce ATP, the energy currency of the cell. In summary, the correct answer to the student's question is a. Electron transport chain is in the mitochondria; Pyruvate is converted to lactic acid in the absence of oxygen.