Which of the following accurately describes a reason why fats store more energy than carbohydrates?

• A. Fats contain more oxygen atoms than carbohydrates, increasing their energy content.
• B. Fats are more soluble in water, which enhances their energy storage capacity.
• C. Fats are composed of amino acids, which provide more energy than sugars.
• D. Fats have a higher proportion of reduced carbon atoms, allowing for more energy release upon oxidation.

Answer: (D)

Verified step by step guidance

1. Understand the energy storage difference between fats and carbohydrates: Fats store more energy per gram than carbohydrates because of their chemical structure and the degree of reduction of their carbon atoms.
2. Analyze the chemical composition of fats: Fats are primarily composed of long hydrocarbon chains (fatty acids) attached to a glycerol backbone. These hydrocarbon chains contain a high proportion of reduced carbon atoms, which are less oxidized compared to the carbon atoms in carbohydrates.
3. Compare the oxidation states of carbon atoms: Reduced carbon atoms in fats can undergo more oxidation during metabolic processes, such as β-oxidation and the citric acid cycle, releasing more energy in the form of ATP. Carbohydrates, on the other hand, have more oxidized carbon atoms (e.g., in glucose), which limits their energy yield.
4. Clarify why oxygen content is not the determining factor: Fats contain fewer oxygen atoms compared to carbohydrates, which is why they are less oxidized initially. This lower oxygen content contributes to their higher energy storage capacity, contrary to the incorrect statement that fats contain more oxygen atoms.
5. Conclude with the correct reasoning: The correct answer is that fats have a higher proportion of reduced carbon atoms, allowing for more energy release upon oxidation. This is the key biochemical principle explaining why fats store more energy than carbohydrates.