AP BIOLOGY

Detailed explanation-1: -Humans obtain energy from three classes of fuel molecules: carbohydrates, lipids, and proteins. The potential chemical energy of these molecules is transformed into other forms, such as thermal, kinetic, and other chemical forms.

Detailed explanation-2: -Carbohydrates are the main energy source of the human diet. The metabolic disposal of dietary carbohydrates is direct oxidation in various tissues, glycogen synthesis (in liver and muscles), and hepatic de novo lipogenesis.

Detailed explanation-3: -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-4: -The stomach and small intestines absorb the glucose and then release it into the bloodstream. Once in the bloodstream, glucose can be used immediately for energy or stored in our bodies, to be used later. However, our bodies need insulin in order to use or store glucose for energy.