We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP). ATP, a high energy molecule, is expended by working cells.
An Apple a Day. The calories in a McIntosh apple depend on its size. According to the U.S. Department of Agriculture, a medium-sized apple with its skin has about 95 calories. Eating an unpeeled apple is moderately higher in calories than a peeled apple, but don't rush to peel your apple.
Calories and Carbs. An average medium-sized gala apple weighs 140 grams and contains 80 calories. It also has 22 grams of carbohydrates with 5 grams of fiber and 17 grams of sugar.