Final answer:
One gram of protein and one gram of carbohydrate each contain 4 calories, one gram of fat contains 9 calories, and ethanol contains approximately 7 calories per gram.
Step-by-step explanation:
The amount of calories in a gram of protein, carbohydrate, fat, and ethanol differs by the nutrient. One gram of protein has 4 calories, one gram of carbohydrate also has 4 calories, one gram of fat has 9 calories, and ethanol, although not typically listed on a food label, contains approximately 7 calories per gram. These values are averages derived from bomb calorimetry tests and are used in the Atwater system to calculate the energy content of foods.