Biochemical Tests for Molecules - AS OCR Biology Unit 2.1

Biochemical Tests for Molecules - AS OCR Biology Unit 2.1.

Simple procedures for the different tests.

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Biochemical Tests for Molecules ­
Sugars:
To test for sugars you use the Benedict's test.
Reducing Sugars:
1. Add Benedict's reagent (blue) to a sample and heat it to 80o in a water bath.
2. If it is positive it will form a coloured precipitate:
It will go from BLUE to RED.
Non-Reducing Sugars:
If the reducing sugars test is negative:
1. You boil the test solution with hydrochloric acid, and then neutralise it with sodium hydrogencarbonate.
2. Then carry out Benedict's test.
It will go from BLUE to RED.
Starch:
You use the Iodine Test.
1. Add iodine dissolved in potassium iodide solution to test the sample.
If starch is present, the sample changes from BROWNY-ORANGE to a dark BLUE-BLACK.
If there is no starch it stays BROWNY-ORANGE.
Proteins:
You use the Biuret Test.
1. Add a few drops of sodium hydroxide solution to the test solution.
2. Add some copper sulfate solution.
If protein is present a PURPLE layer forms.
If there's no protein, the solution will stay BLUE.
Lipids:
You use the Emulsion Test.
1. Shake the test substnace with ethanol for about a minute.
2. Pour the solution into water.
If lipid is present, the solution will turn MILKY.
The more lipid there is, the more noticeable the milky colour will be.
If there's no lipid, the solution will stay clear.

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