Biological molecules

Question 1

What chemical elements are present in carbohydrates?

Answer 1

Carbon, Oxygen and Hydrogen

Question 2

What chemical elements are present in proteins?

Answer 2

Carbon, Oxygen, Nitrogen, Hydrogen and Sulfur

Question 3

What chemical elements are present in lipids?

Answer 3

Carbon, Hydrogen and Oxygen

Question 4

Describe the structure of carbohydrates, proteins and lipids.

Answer 4

Large molecules made up of smaller basic units.
Starch and glycogen from monosaccharides.
Protein from amino acids.
Lipids from fatty acids and glycerol.

Question 5

How do plants store carbohydrates?

Answer 5

Plants store carbohydrates in long polysaccharides chains called starch.

Question 6

How do humans store carbohydrates?

Answer 6

In the liver and muscles.

Question 7

How do animals store carbohydrates?

Answer 7

Animals store carbohydrates as the molecule glycogen.

Question 8

Practical to test for glucose.

Answer 8

Add Benedict’s solution to the sample solution in a test tube
Heat in a boiling water bath for 5 minutes
A positive test will show a colour change from blue to orange / brick red.

Question 9

Practical to test for starch.

Answer 9

Add food sample to a test tube.
Add a few drops of iodine.
A sample containing starch will turn blue/black.

Question 10

Practical to test for starch.

Answer 10

Add drops of Biuret solution to the food sample
A positive test will show a colour change from blue to violet / purple.

Question 11

Practical to test for fats ( lipids).

Answer 11

Mix the food sample with 4cm3 of ethanol and shake
Allow time for the sample to dissolve in the ethanol
Strain the ethanol solution into another test tube
Add the ethanol solution to an equal volume of cold distilled water (4cm3)
A positive test will show a cloudy emulsion forming.