Lipids store roughly twice as much energy per gram as carbohydrates. Which property of lipid molecules best explains this?
ALong hydrocarbon chains contain many C–H bonds that can be oxidized to release energy
BThey are insoluble in water, so they take up less space when stored
CThey form longer polymer chains than carbohydrates
DThey contain more nitrogen atoms than carbohydrates
Explanation
Lipid fatty-acid tails are long chains of carbon–hydrogen bonds. Oxidizing each C–H bond releases energy, so the more C–H bonds per gram, the more energy is stored. Carbohydrates have fewer C–H bonds per carbon because oxygen atoms are already attached. Distractors: water insolubility relates to *where* lipids are stored, not how much energy they hold. Lipids aren't true polymers. Lipids contain almost no nitrogen — that's a feature of proteins and nucleic acids.