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.
There are 53 calories in 1 extra small [4 oz with refuse, 2.5 dia] (3.6 oz) of Apples with Skin, raw. You'd need to walk 14 minutes to burn 53 calories. Visit CalorieKing to see calorie count and nutrient data for all portion sizes.