IGCSE Biology – Biological Molecules & Related Tests

29 question-and-answer flashcards covering carbohydrates, lipids, proteins, food tests, DNA structure and the biological importance of water.

Which three major categories include most molecules in living organisms?

Carbohydrates, proteins and lipids.

What elements are found in all carbohydrates?

Carbon, hydrogen and oxygen.

Glucose is an example of what type of sugar?

A monosaccharide (simple sugar).

What disaccharide is produced when two glucose molecules join together?

Maltose.

Name three polysaccharides made from many glucose units.

Starch, glycogen and cellulose.

What are the basic units of lipids (triglycerides)?

One glycerol molecule and three fatty acids.

At room temperature, what is the physical difference between fats and oils?

Fats are solids; oils are liquids.

Which elements make up proteins?

Carbon, hydrogen, oxygen and nitrogen (some also contain sulfur).

Proteins are long chains of which monomers?

Amino acids.

Approximately how many different amino acids exist?

About 20.

What part of an amino acid varies to create different amino acids?

The ‘R’ group (side chain).

Why do proteins have unique 3-D shapes?

Different sequences of amino acids cause polypeptide chains to fold in specific ways.

What is the region on an enzyme where the substrate binds called?

The active site.

Why must an antibody’s shape match an antigen?

To allow the antibody to attach to the antigen and signal it for destruction.

Describe the positive result of Benedict’s test for glucose.

Colour change from blue to orange/brick-red after heating.

Describe the positive result of the Biuret test for protein.

Colour change from blue to violet/purple.

What colour change indicates starch in the iodine test?

Orange-brown to blue-black.

How is the ethanol test for lipids carried out, and what indicates a positive result?

Mix food with ethanol, then add cold water; a cloudy emulsion forms if lipids are present.

What happens to DCPIP solution if vitamin C is present?

The blue colour of DCPIP disappears (becomes colourless).

What does DNA stand for?

Deoxyribonucleic acid.

What overall shape describes a DNA molecule?

A double helix made of two strands.

What are the three components of a DNA nucleotide?

A phosphate group, deoxyribose sugar and a nitrogenous base.

List the four DNA bases and their complementary pairing rules.

Adenine pairs with Thymine (A-T); Cytosine pairs with Guanine (C-G).

Which parts of nucleotides form the ‘backbone’ of the DNA strand?

The phosphate and deoxyribose sugar sections.

Why is water described as an important solvent for organisms?

Many substances dissolve in it, enabling transport, removal of wastes, and metabolic reactions.

Give two examples of transport in organisms that rely on water as a solvent.

Xylem/phloem transport in plants and movement of dissolved food molecules in blood.

How does water aid in excretion of urea and excess salts?

These substances dissolve in water, making them easy to remove in urine.