Lipids

This lesson covers the structure, properties and biological functions of lipids — specifically triglycerides and phospholipids — as required by the Edexcel A-Level Biology B specification (9BI0), Topic 1: Biological Molecules. You need to understand the formation of ester bonds, the difference between saturated and unsaturated fatty acids, and the relationship between the structure and function of these molecules.

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What Are Lipids?

Lipids are a diverse group of biological molecules that are insoluble in water but soluble in organic solvents such as ethanol and acetone. They contain the elements carbon (C), hydrogen (H) and oxygen (O), but they have a much higher proportion of hydrogen relative to oxygen compared with carbohydrates.

Lipids are not true polymers — they are not built from repeating monomer subunits in the same way as polysaccharides or proteins. However, triglycerides are formed from glycerol and fatty acids by condensation reactions.

The main types of lipid you need to know are:

1. Triglycerides (fats and oils) — used for energy storage and insulation.
2. Phospholipids — the major structural component of cell membranes.

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Fatty Acids