AQA AS BIOLOGY - BIOCHEMICAL TESTS - Short Notes

The 5 tests needed for the AQA Biology Unit 1 Spec.

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BIOCHEMICAL TESTS

Proteins - add biurettes reagent to the sample. If protein is present, clear colour change from blue to purple.

Reducing Sugarsadd Benedict’s reagent to the sample. Heat in bunsen or water bath. If reducing sugars are present, clear colour change from blue -> orange red precipitate.

Lipidsdissolve sample in ethanol. Slowly pour the solution into the water. If lipids are present a white emulation forms on the surface.

Starchadd iodine solution to the sample. If starch is present clear colour change from orange red to blue black.

Non reducing sugarsdo the reducing sugars test. Add Benedict's to the sample & heat. You get a negative result. Take a fresh sample and add heat with dilute acid. Bring to the boil. This hydrolyses it! Then, neutralise it with an alkali and test with pH paper. Add Benedict's and heat again. If non reducing sugars are present, clear colour change from blue to an orange red precipitate. 

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Comments

alex

really good thanks... it good to just summarise these points :D good luck for tommorow x

Naheema

thank you

TomBroadley

john simons wrote:

i think that is a little unfair

N.G

Love these , thank you! :)

Rabqa

A little more detail would be needed for AS. For example the description of the biuret test is GCSE level. For AS the description for a biuret test would need to go something like this- 1.Add soduim hydroxide to sample and shake in test tube, 2. add copper(||) sulphate 3. if peptide bonds (e.g. protein) are present then a purple layer will form in the test tube. If there's no peptide bonds then the solution will remain blue. Extra information you may wish to add to your answer is also that the sodium hydroxide is added to make the test solution akaline.

Rabqa

For the aqa AS level spec the change colour for presence of a reducing sugar is brick red. Orange would not be accepted so please do not write this. However thanks to the writer for sharing what they know. It may be that the spec has changed and this info is just outdated.

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