Biology - Biological Molecules (IGCSE)

A student set up a test-tube containing starch, water and amylase.

How could the student test whether the amylase had digested all the starch?

• Add Biuret solution.

• Add dilute hydrochloric acid.

• Add iodine solution.

• Weigh the test-tubes and contents before and after the experiment.

The diagrams show a leaf cell before and after staining with iodine solution.

Which substance causes the iodine solution to change colour?

• Chlorophyll

• Protein

• Reducing sugar

• Starch

Four foods were tested for each of the following nutrients:

fat (using ethanol);

protein (using the biuret test);

reducing sugar (using Benedict’s solution),

Which food contains protein and fat?

• A

• B

• C

• D

The diagram shows two food tests carried out on solution X.

Which nutrients are present in solution X?

• Protein and starch

• Protein and sugar

• Starch and fat

• Starch and sugar

Which simple molecules are the basic units of protein?

• Amino acids

• Fatty acids

• Sugars

• Vitamins

The diagram represents a protein molecule.

What do the small circles represent?

• Amino acids

• Fatty acids

• Glycerol

• Simple sugars

Small molecules are used as the basic units in the synthesis of large food molecules.

Which statement is correct?

• Amino acids are basic units of carbohydrates.

• Fatty acids are basic units of glycogen.

• Glycerol is a basic unit of oils.

• Simple sugar is a basic unit of protein.

The diagram shows two food molecules before and after they have been digested by enzymes.

What identifies the products of fat digestion?

• P and R

• P and S

• Q and R

• Q and S

Which identifies the chemical elements found in proteins?

• carbon, hydrogen, oxygen and nitrogen

• carbon, hydrogen, and oxygen only, but not nitrogen

• carbon and oxygen only, but not hydrogen and nitrogen

• hydrogen and nitrogen only, but not carbon and oxygen

The table shows the results of some food tests.

Which row shows a food containing both protein and starch?

(i) Benedict’s solution; (ii) biuret test; (iii) ethanol, (iv) iodine solution

• (i) blue;

  (ii) blue;

  (iii) clear;

  (iv) blue-black

• (i) blue;

  (ii) purple;

  (iii) clear;

  (iv) blue-black

• (i) red;

  (ii) blue;

  (iii) cloudy;

  (iv) brown

• (i) red;

  (ii) purple;

  (iii) cloudy;

  (iv) brown