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.
How Many Calories In An Apple. Calories in an Apple (raw with skin) The Calories in an Apple range from approximately 53 calories for an extra small apple (2-12 inch diameter) up to about 116 calories (for a large apple of approximately 3-1/4 inch diameter). The vast majority of the calories in an apple come from carbohydrates.