Compared with carbohydrates, lipids yield more energy per gram because they
- A. contain more oxygen atoms per carbon
- B. are more highly reduced, with more carbon-hydrogen bonds per gram
- C. are soluble in water
- D. are broken down without any oxygen
Explanation
Energy is released when carbon-hydrogen bonds are oxidised, and a fatty acid chain is almost entirely carbon and hydrogen with very little oxygen already attached. Carbohydrates are partly oxidised to begin with, so less energy remains to be released, which is why fat yields about 9 kcal per gram against roughly 4 for carbohydrate. Lipids are insoluble in water and their breakdown is fully aerobic.
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