What are the three main functions of lipids?

 Energy storage  Heat insulation  Buoyancy

 We refer to triglyceride lipids in solid form as fats.  In liquid form, triglycerides are called oils.  Everyone is aware of the role fat plays in energy storage.  If you eat more food than you burn, your body will store much of the excess as fat in adipose cells.  People either gain or lose weight depending on how much lipid is being stored at any given time in a fairly fixed number of adipose cells.

 Lipids are very efficient molecules for storing energy.  As seen earlier, carbohydrates are also used for storing energy in living organisms.  Glycogen is a carbohydrate used by animals to store energy and starch is used by plants.

 Lipids are important for thermal insulation.  A good reminder of this is to study the amount of blubber (fat) that cold-climate animals form in order to stay warm; 30% or more of the body mass of some seals may be due to the blubber layer beneath their skin.

 As you know a special category of lipid called phospholipid makes up the bilayer of all cell membranes.  These phospholipid molecules have a polar head turned towards water and a non-polar tail which turns away from water.

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