Biological Molecules: Practicals

Question 1

Give the test for a reducing sugar and the results for a positive and negative test:

Answer 1

1) Prepare a sample and mix with Benedict’s reagent
2) Heat the mixture in a water bath for 5 minutes
3) A positive result will show a colour change from blue to a green precipitate to a brick-red precipitate (depending on the concentration). A negative result will stay blue.

Question 2

Give the test for a non-reducing sugar and the results for a positive and negative test:

Answer 2

1) Test for reducing sugars first
2) If the sample stays blue, prepare a new sample and add dilute hydrochloric acid, bicarbonate soda and benedict’s reagent
3) Heat in a water bath for 5 minutes.
4) A positive result will produce a brick-red precipitate. A negative result will stay blue.

Question 3

What test tests for lipids?

Answer 3

Emulsion

Question 4

Give the emulsion test method and results for lipids:

Answer 4

• Add food sample to a test tube.
• Add in ethanol to the food sample.
• Add this mixture into water in another test tube.

Positive result = milky-white colour
Negative result = clear colour