Biology Tests Unit 1

How to test for certain molecules

Emulsion Test - Lipid

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Biuret test - Proteins

Add an alkaline solution of copper(//) sulfate to the solution.

If colour turns to pink-purple, proteins is present, as peptide bonds are detected.

The test is qualitative and semi-quantitative.

The range of colours will be:

Pink --> Violet --> Blue-violet ---> Purple

--------------Increasing number of peptide bonds------>

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Benedict's Test - Reducing/non-reducing sugars

Reducing sugars:

Mix the solution with a few drops of Benedict's reagent.

If the solution turns from blue to red, a reducing sugar is present.

Non-reducing Sugars:

Do the test for reducing sugars to make sure no reducing sugars are present.

Mix the solution with dilute Hydrochloric acid and heat it.

Perform the Benedict's test again.

If you get a negative result the first time, and a positive result the second time, a non-reducing sugar is present. 

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Iodine test - Starch.

Mix the solution with potassium iodide solution.

If it turns blue-black, Starch is present

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