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.
This Is What 100 Calories of Fruit Really Looks Like. What the portion sizes of 17 popular fruits should actually be. Even healthy calories add up. Because you probably don't whip out a food scale every time you eat an apple, keep these serving sizes in mind to keep your portions in check. Listed from largest to smallest serving by weight per 100-calorie portion, here's what 100 calories of your 17 favorite fruits look like: 1. Watermelon: