How does oxygen affect the energy output of respiration? 
· More energy is released from glucose.
· Glucose is completely broken down into carbon dioxide and water.
· This process occurs in the mitochondria

How much energy is released during aerobic respiration?
· All steps including glycolysis release 36 ATP

Which is more efficient aerobic or anaerobic respiration?  Explain how this affects muscle fatigue.
· Aerobic respiration is nearly 20 times more efficient than anaerobic respiration. 
· All of a glucose molecule is broken down during aerobic respiration while only a small part is during anaerobic.
· When there is not enough oxygen muscles cell will burn glucose anaerobically which produces lactic acid.  Lactic acid causes muscles to get tired and sore.

What is oxygen debt? How is it paid back?
· Oxygen debt is the amount of oxygen needed to get rid of built up lactic acid
· While resting, extra oxygen is used to break down excess lactic acid. 
· Heavy breathing and heart rate contribute to this.