Biological Molecule Tests

Question 1

Test for Sugars?

Answer 1

Benedict’s test reagent

Reducing sugars- add reagent to sample, then heat in water bath. If positive, coloured precipitate will form

Non-reducing sugars- If reducing sugar test is negative, then get new sample, add HCL (dilute) and carefully heat, then neutralise with NaHCO3. Then repeat Benedict’s test. If positive, there will be a coloured precipitate.

Question 2

Test for Glucose?

Answer 2

Glucose can be tested using test strips coated with reagent. Dip strips in test solution and if strips changes colour, glucose is present. This colour can be compared to chart for the concentration of glucose.

Question 3

Test for starch?

Answer 3

Add iodine (dissolved in potassium iodide solution) to the test sample. If present, changes from browny orange to dark blue black

Question 4

Test for proteins?

Answer 4

Biuret Test
Test solution must be alkaline, so add a few drops of NaOH
Then add some copper sulfate solution, if protein is present, then solution turns purple

Question 5

Test for Lipids?

Answer 5

Emulsion test
Shake test substance with ethanol for about a minute, then pour solution into water
If lipid is present, solution turns milky