edexcel unit 1 biology

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Unit One – Lifestyle, Health and Risk

Biological Molecules

A macromolecule is a giant molecule made from many repeating units. In Biology, polymers are long chains of biological molecules made up of units that can be pulled apart to form more simple substances e.g. starch can be broken down into glucose monomers. A polymer is formed when monomers link together. In order to do this a simple reaction occurs to bond the monomers together. This is called a condensation reaction and is where a molecule of water is removed. Not all polymers link this way, but starch and proteins do.


Carbohydrates are a very large group of biological molecules, with diverse functions. They are compounds containing carbon, hydrogen and oxygen. They are the most abundant organic compounds found in nature being produced by green plants and photosynthetic bacteria:

                Solar energy

6CO2  +  6H2O      C6H12O6  +  6O2

The small, simple ones are metabolic i.e. part of the cell’s reactions e.g. glucose, fructose, maltose. The larger ones are used for storage (of glucose) e.g. starch in plants and glycogen in animals. They are also structural e.g. cellulose in plant cell walls.


These are the simplest of the sugars, containing only one unit or monomer. They are sweet, soluble crystalline molecules of low molecular mass. Each contains an aldehyde (- CHO) or a ketone (- C=O) group. Monosaccharides have at least 3 carbon atoms in the molecule and the name ends in –ose. e.g:        

Triose = 3-C sugar                        glyceraldehyde

        Pentose = 5-C sugar                ribose (in RNA)

        Hexose = 6-C sugar                glucose, fructose

How to build a glucose molecule:

The formula is C6H12O6 . Each carbon atom is bonded to another carbon, a hydrogen and a hydroxyl group (-OH) (except carbon 1, which has no –OH as it forms part of the aldehyde group). This can be written as a straight chain:

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The straight chain structure is in equilibrium with a 6-membered ring structure in solution:


The ring structure occurs because the straight chain can turn back on itself and the reactive (aldehyde) group on carbon 1 can react with a hydroxyl (-OH) group on carbon 5. The reason why glucose is soluble is because the –OH group can hydrogen bond with water molecules.

The ring structure can be of two types at carbon 1, α glucose is the standard glucose; β glucose is not common in ...

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