A gram of fat oxidized by respiration produces approximately twice as much ATP as a gram of carbohydrate. Which of the following best explains this observation?

• A. Fats are produced when cells take in more food than they need.
• B. Fats are less soluble in water than sugars.
• C. Fats do not form true macromolecules as sugars do.
• D. Fats are closely related to lipid molecules, which are the basic building blocks of cellular membranes.
• E. Fats are better electron donors to oxygen than are sugars.

Answer: (E)

Verified step by step guidance

1. Understand that ATP production during cellular respiration is linked to the oxidation of molecules, where electrons are transferred to oxygen.
2. Recognize that fats and carbohydrates are both sources of energy, but they differ in their chemical structure and energy content.
3. Fats have long hydrocarbon chains, which contain many hydrogen atoms. These hydrogen atoms are excellent sources of electrons for the electron transport chain.
4. Carbohydrates, on the other hand, have a higher proportion of oxygen atoms and fewer hydrogen atoms compared to fats, making them less efficient electron donors.
5. Conclude that because fats have more hydrogen atoms, they can donate more electrons to oxygen during cellular respiration, resulting in the production of more ATP compared to carbohydrates.