A student claims that lipids and carbohydrates both contain carbon, hydrogen and oxygen, so they must have the same properties and functions in the body. Evaluate this claim.

The claim is only partly correct. Both lipids and carbohydrates contain C, H and O, but the ratios differ: lipids have a much higher H:O ratio, giving them a lower polarity and higher hydrophobicity. Lipids are tri‑glycerols made of glycerol and fatty acids, whereas carbohydrates are chains of monosaccharides such as glucose. Because of the high H:O ratio, lipids release more energy per gram when oxidised, making them a more efficient long‑term energy store. Moreover, lipids perform functions that carbohydrates do not, for example forming the phospholipid bilayer of cell membranes and providing insulation and protection as subcutaneous fat. Thus, while the elemental composition is similar, the structural differences give lipids distinct physical properties and biological roles.