If the formation of a standard amount of ATP under certain conditions requires 12 kcal of energy…?

If the formation of a standard amount of ATP under certain conditions requires 12 kcal of energy and the complete oxidation of glucose yields 686 kcal of energy, how efficient is glycolysis at extracting energy from glucose?

if you divide 686 by 12, then that would be the amount of ATP molecules created in a 100% efficient process. Since glycolysis is less than 100% efficient, it will not produce that much. This is a little bit of an odd question, since they give you the amount of energy possibly extracted from glucose by all of cellular respiration, not just glycolysis, and yet they ask for the efficiency of glycolysis. Cellular respiration is approximately 40% efficient so (686/12)0.4= 22.8 ATPs produced from cellular respiration and the electron transport chain as a whole. Glycolysis itself produces a net of 2 ATP and 2 NADH along with the 2 pyruvate molecules. Each NADH translates into about 3 ATPs after being put through the electron transport chain so that’s about 8 ATP per turn of glycolysis, which is about a third of what is produced in all of respiration. You can use that number to come up with the same sort of answer if you wish, but i think it’s just a poorly worded question and they just wanted the answer for all of respiration. Hope this helps!

Metabolism of Carbohydrates: Oxidation Rates of CHOs and Uptake Processes