Learning
Objectives
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WHAT IS
BIOLOGICAL
MOLECULES?
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Carbohydrate
Carbohydrate
Simple
Carbohydrate
Complex
Carbohydrate
Protein
Lipids
Summary
DNA
Vitamin
Molecule
Testing
FAT
• Shake two drops of cooking oil with about 5 cm3 ethanol in a dry test-tube
until the fat dissolves.
• Pour this solution into a test-tube containing a few cm3 water. A milky white
emulsion will form. This shows that the solution contained some fat or oil.
SUGAR
Heat a little glucose solution with an equal volume of Benedict’s solution in a
test-tube. The heating is done by placing the test-tube in a beaker of boiling
water or warming it gently over a blue Bunsen flame. However, if this second
technique is used, the test-tube should be moved constantly in and out of the
Bunsen flame to prevent the liquid boiling and shooting out of the tube. The
solution will change from clear blue to cloudy green, then yellow and finally to a
red precipitate (deposit) of copper(I) oxide.
PROTEIN
To a 1% solution of albumen (the protein of egg-white) add 5 cm3 dilute sodium
hydroxide (CARE: this solution is caustic), followed by 5 cm3 1% copper sulfate
solution. A purple colour indicates protein. If the copper sulfate is run into the
food solution without mixing, a violet halo appears where the two
liquids come into contact.
STARCH
• Shake a little starch powder in a test-tube with some
warm water to make a suspension.
• Add 3 or 4 drops of iodine solution. A dark blue
colour should be produced.
Molecule
Testing
FAT
REDUCING SUGAR
STARCH
PROTEIN
Molecule
Testing
VITAMIN C
• Draw up 2 cm3 fresh lemon juice into a plastic syringe.
• Add this juice drop by drop to 2 cm3 of a 0.1% solution of DCPIP (a blue dye) in a test-tube.
The DCPIP will become colourless quite suddenly as the juice is added. The amount of juice
added from the syringe should be noted down.
• Repeat the experiment but with orange juice in the syringe. If it takes more orange juice
than lemon juice to decolourise the DCPIP, the orange juice must contain less vitamin C.
Question