What in combination with oxygen is used by the cells to release energy from glucose?
This is a very general question, but I'll give it an attempt. Glucose is oxidized via glycolysis to produce reduced coenzymes (2 NADH) and ATP. The product of glycolysis (pyruvate) then enters the citric acid cycle and is further oxidized to produce more reduced coenzymes (3 NADH and 1FADH2) and GTP (a high energy phosphate equivalent to ATP). The reduced coenzymes (NADH, FADH2) enter the electron transport chain and then are oxidized to release electrons. The electrons traverse the electron transport chain via several electron transport molecules and ultimately reduce oxygen to form metabolic water.