How many FADH2 molecules are produced in the Krebs cycle?

A - 1

B - 2

C - 3

D - 4

Answer: B - 2

Explanation:

In aerobic respiration, the cell harvests energy from glucose molecules in a sequence of four major pathways: glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain. In the process of aerobic respiration, glucose is completely used. The 6-carbon glucose molecule is first cleaved into a pair of 3-carbon pyruvate molecules during glycolysis. One of the carbons of each pyruvate is then lost as CO2 in the conversion of pyruvate to acetyl-CoA; two other carbons are lost as CO2 during the oxidations of the Krebs cycle. All that is left to designate the passing of the glucose molecule into 6 CO2 molecules is its energy, some of which is preserved in 4 ATP molecules and in the reduced state of 12 electron carriers. 10 of these carriers are NADH molecules; the other 2 are FADH2.