Biological Molecule Tests

Question 1

Test for Carbohydrates

Answer 1

1. Add sample to a test tube
2. Add 2cm3 of iodine
3. If starch is present, the solution will go orange to blue-black

Question 2

Test for Proteins

Answer 2

1. Add sample to a test tube
2. Add 2cm3 of biuret reagent
3. If protein is present, the solution will go blue to purple

Question 3

Test for Lipids

Answer 3

1. Add sample to test tube
2. Add 2cm3 of cold water
3. Add 2cm3 of ethanol
4. Shake and a white emulsion should form

Question 4

Test for Reducing Sugar (glucose)

Answer 4

1. Add Benedict’s reagent to the sample you are testing
2. Heat in a waterbath for 5 minutes
3. If a reducing sugar is present, a colour change from blue to yellow/green/red should be observerd

Question 5

Test for Non-Reducing Sugar (Sucrose)

Answer 5

1. Mix non-reducing sugar with HCl and boil it
2. Coll the solution and then add NaOH to make the solution alkaline
3. Add benedicts and reheat
4. A coluor change from blue to yellow/green/red should be observered

Question 6

Why can’t a non-reducing sugar be tested normally?

Answer 6

Non-reducing sugfars cannot reduce Cu2+ due to the chemical group needed to reduce it being in a glycosidic bond and so needs to be hydrolysed