Lipids in cells have three main functions: energy storage, signal transduction and forming the matrix of biological membranes.
Lipid membrane have asymmetric distribution of lipids between two leaflets. Cell membrane composed of polar lipids that self assemble to form bilayer. Thus, cell membrane forms asymmetric structure which means two sides of membrane are functionally and structurally different.
The structure and composition of lipid bilayers varies from one organism to organism. This is because all cell membranes have same structure, but varies from one organism to another. In some organisms, the composition of lipid membranes changes when exposed to different temperatures.
For example, animals in cold climates have more unsaturated fatty acids because Unsaturated fats have kinks in the hydrocarbon tails thus they cannot pack closely together. This makes them liquid at room temperature. Therefore, it prevents fats to solidify. Saturated fats become solid at room temperature. Thus, they replace saturated with unsaturated fatty acids.