AP BIOLOGY

Detailed explanation-1: -The calories in food come from carbohydrates, proteins, and fats: A gram of carbohydrate has 4 calories. A gram of protein has 4 calories. A gram of fat has 9 calories-more than twice as much as the other two.

Detailed explanation-2: -Macromolecules : Example Question #4 Explanation: There are four classes of biological molecules: fats, carbohydrates, proteins, and nucleic acids. Of these, fats produce the most energy per gram at a whopping nine calories per gram.

Detailed explanation-3: -Answer and Explanation: The correct answer: The macromolecule which acts as the primary energy source for an organism is D) carbohydrate. The primary source of energy in most of the organisms is carbohydrate as it is the most abundant in most of the organism.

Detailed explanation-4: -Fats are the slowest source of energy but the most energy-efficient form of food. Each gram of fat supplies the body with about 9 calories, more than twice that supplied by proteins or carbohydrates.