If the formation of 38 molecules of ATP requires 266 kcal of energy and the complete oxidation of glucose yields 686 kcal of energy, how efficient is cellular respiration at extracting energy from glucose?

39%

Explanation:

Total kcal of the energy required for the production of 38 ATP molecules = 266 kcal.

Complete oxidation of glucose by the process of cellular respiration produces total energy = 686 kcal

This means that the proportion of the energy of glucose stored in the form of ATP molecules = 266 / 686 x 100 = 38.775 or 39%

Therefore, only 39% of the total energy of the glucose molecule is stored in the form of ATP by the process of cellular respiration or cellular respiration is only 39% efficient process.