Final answer:
The untrue statement about fatty acids is that cholesterol is a fatty acid; cholesterol is actually a sterol, another type of lipid. Fatty acids are amphiphilic, can be saturated or unsaturated, and triacylglycerols store significantly more energy than sugars by weight.
Step-by-step explanation:
The student asked which statement about fatty acids is untrue. Among the given options, the incorrect statement is that cholesterol is a fatty acid. In fact, cholesterol is a type of lipid, specifically a sterol, not a fatty acid. Fatty acids are long-chain hydrocarbons ending with a carboxylic acid group, and they are amphiphilic because they contain both a hydrophilic (water-attracting) carboxyl head and a hydrophobic (water-repellent) hydrocarbon tail. They can be saturated or unsaturated, with unsaturated fatty acids containing one or more double bonds. Triacylglycerols, also known as triglycerides, are esters formed from three fatty acid molecules and one glycerol molecule. Compared to sugars, triacylglycerols store significantly more energy by weight, which can be up to 2 times more, though the actual value can vary.