Chap 3) Biolgical Molecules

Question 1

Describe how to test for Starch

Answer 1

-1 drop of of iodine into food sample
-starch present, iodine turns blue-black
-starch absent, iodine remains brown

Question 2

Describe how to test for reducing sugars

Answer 2

Benedict’s test:
-reducing sugars will produce a red precipitate when boiled with Benedict’s solution.

-add 2cm3 if liquid food sample + 2cm3 Benedict’s solution into a test tube
-shake the test tube
-boil the solution for 2-3min
-record colour observed
Blue-green-orange-red
->increasing amt of reducing sugars->

Question 3

Describe how to test for fats.

Answer 3

Ethanol emulsion test:
-add 2cm3 liquid food sample (or decant of solid) + 2cm3 ethanol into a test tube
-shake the test tube
-fats present, white emulsion forms
-fats absent, no reaction

Question 4

Describe how to test for proteins

Answer 4

Biuret test:
-add 2cm3 liquid food sample + 2cm3 biuret solution into a test tube
-shake the test tube
-let solution rest for 5min
-proteins present, violet
-proteins absent, solution remains blue

Question 5

What is glycogen synthesised from?

Answer 5

Glucose;
-Glycogen is a branched molecule, made of many glucose molecules joined together.

Question 6

What are protein/polypeptides synthesised from?

Answer 6

Amino acids

Question 7

What are fats synthesised from?

Answer 7

Fatty acids & glycerol