| Energy content | Lipids contain more energy per gram than carbohydrates, so lipids stores are lighter than carbohydrates storing an equivalent amount of energy. |
| Density | Lipids are less dense than water; so fat stores help large aquatic animals to float. |
| Solubility | Lipids are non-polar, insoluble molecules so they do not affect the movement of water in and out of cells by osmosis |
| Insulation | Lipids are also important in providing heat insulation. Fat stored under the skin reduces heat loss and is vital for animals such as seals, polar bears and whales, which live in cold conditions. |
Fats and oils, or triglyceride lipids, are compounds of glycerol and fatty acids, formed by linking 3 or more fatty acids and one glycerol in a condensation reaction. Glycerol has just one structural form but fatty acids have a wide variety of structures, which give the lipids that contain them their different physical and chemical properties.
They are fats if they are solid at room temperature or oils if they are liquid at room temperature. Animals store energy as fat whereas plants store oils, for example, olive oil.
Other types of lipids include steroids, that act as hormones, waxes, that serve as hydrophobic barriers on the upper surface of leaves, and fatty acids that serve as structural components of cell membranes.
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