CIE IGCSE Biology Quiz: Biological Molecules

What are the three main categories of molecules in living organisms?

• Carbohydrates, Vitamins, Minerals

• Carbohydrates, Proteins, Lipids

• Proteins, Nucleic Acids, Fats

• Sugars, Starches, Oils

Answer explanation

The three main categories of molecules in living organisms are carbohydrates, proteins, and lipids. These macromolecules play essential roles in structure, function, and energy storage, making the correct choice 'Carbohydrates, Proteins, Lipids'.

What is the basic unit of fats (lipids)?

• Amino acids

• Glycerol and fatty acids

• Nucleotides

• Monosaccharides

Answer explanation

The basic unit of fats (lipids) is composed of glycerol and fatty acids. These components combine to form triglycerides, which are the main form of stored fat in the body.

What type of sugar is glucose classified as?

• Monosaccharide

• Polysaccharide

• Oligosaccharide

• Disaccharide

Answer explanation

Glucose is classified as a monosaccharide because it is the simplest form of sugar, consisting of a single sugar unit. Other options like polysaccharides and disaccharides consist of multiple sugar units.

What is formed when two glucose molecules join together?

• Glycogen

• Maltose

• Starch

• Cellulose

Answer explanation

When two glucose molecules join together, they form maltose, a disaccharide. Glycogen, starch, and cellulose are polysaccharides made from multiple glucose units, but maltose specifically results from the dimerization of glucose.

What color change indicates a positive test for glucose using Benedict's solution?

• Violet to blue

• Orange to blue-black

• Blue to orange or brick red

• Blue to green

Answer explanation

A positive test for glucose using Benedict's solution is indicated by a color change from blue to orange or brick red, showing the presence of reducing sugars. Other options do not represent the correct reaction.

What is the positive result for the starch test using iodine?

• Color change from blue to orange

• Color change from orange-brown to blue-black

• Color change from blue to violet

• No color change

Answer explanation

The positive result for the starch test using iodine is indicated by a color change from orange-brown to blue-black, confirming the presence of starch. Other options do not represent the correct reaction.

What is the structure of a triglyceride?

• Three glycerol and one fatty acid

• Two glycerol and three fatty acids

• One glycerol and three fatty acids

• One glycerol and two fatty acids

Answer explanation

A triglyceride is composed of one glycerol molecule and three fatty acid chains. This structure allows for efficient energy storage in the body, making the correct answer 'One glycerol and three fatty acids'.

How many different amino acids are there?

• 10

• 50

• 20

• 30

Answer explanation

There are 20 different amino acids that are commonly found in proteins. These amino acids are the building blocks of proteins and play crucial roles in various biological processes.

What color change indicates a positive test for protein using Biuret solution?

• Yellow to red

• Blue to green

• Orange to blue-black

• Blue to violet/purple

Answer explanation

A positive test for protein using Biuret solution is indicated by a color change from blue to violet/purple. This occurs due to the formation of a complex between the copper ions in the Biuret reagent and the peptide bonds in proteins.

What is the positive result for the lipid test?

• Formation of a cloudy emulsion

• Color change from blue to violet

• Color change from orange to blue-black

• No change

Answer explanation

The positive result for a lipid test is indicated by the formation of a cloudy emulsion, which shows the presence of lipids. Other options like color changes are associated with different tests, not lipid testing.