Summary Biochemical tests for A level Biology

Test Testing for Method Result

Benedicts Reducing sugars Add an excess of Colour change from
benedicts reagent blue to brick red
(to make sure all the precipitate
sugar reacts) The closer to brick
Heat in a water bath red, the higher
until it boils concentration of
reducing sugar is
present


Benedicts Non-reducing After initial negative Coloured precipitate
sugars benedicts result will form as for the
Heat sample with reducing sugars test
dilute hydrochloric
acid (to break them
down in to
monosaccharides)
Heat in a water bath
until it boils
Neutralise with
sodium
hydrocarbonate
Carry out same test
as reducing sugars



Iodine Starch Add iodine dissolved Colour change from
in potassium iodide orange to blue-black
solution

Emulsion Lipids Shake the test Lipid will show up as
substance with a milky emulsion
ethanol for a minute
so that it dissolves
Pour the solution in
to water

Biuret Protein Add a few drops of If protein is present,
sodium hydroxide solution will turn
solution from blue to purple
Add some copper (ii)
sulphate solution