(c) : Energy gain in one complete cycle of aerobic respiration is :
In aerobic respiration complete oxidation of one glucose molecule produces 38 ATP molecules. But the number of ATP molecules so produced may vary depending upon the mode of entry of NADH2 in the mitochondria. If the electrons of NADH2 are accepted by malate then each molecule of NADH ‌2 yields 3 ATP molecules and the total would be 38 ATP molecules. But if the electrons of NADH2 are accepted by FAD it yields only 2 ATP molecules making the total of 36 ATP molecules. This type of shuttle occurs in most of the eukaryotic cells.
(38 molecules of ATP are produced during aerobic respiration. Of these 2 ATP are used in link reaction. Hence net gain is of 36 ATP.)