[IGCSE] Biology Secondary 3 Unit 3 to Unit 4 Revision

Which elements make up carbohydrates?

• Carbon, Hydrogen, Nitrogen

• Carbon, Hydrogen, Oxygen

• Carbon, Nitrogen, Oxygen

• Carbon, Hydrogen, Sulfur

Answer explanation

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. The correct choice is 'Carbon, Hydrogen, Oxygen', as these elements are essential for forming sugars and starches, which are types of carbohydrates.

Which of the following elements is found in proteins but not in carbohydrates?

• Nitrogen

• Oxygen

• Hydrogen

• Carbon

Answer explanation

Proteins contain nitrogen, which is essential for amino acids, while carbohydrates are primarily made of carbon, hydrogen, and oxygen. Therefore, nitrogen is the element found in proteins but not in carbohydrates.

Which macromolecule contains the element phosphorus as part of its structure?

• Carbohydrates

• Proteins

• Nucleic acids

• Fats

Answer explanation

Nucleic acids, such as DNA and RNA, contain phosphorus in their backbone structure, specifically in the phosphate groups. In contrast, carbohydrates, proteins, and fats do not include phosphorus in their composition.

Which element is common to carbohydrates, fats, and proteins?

• Nitrogen

• Sulfur

• Carbon

• Phosphorus

Answer explanation

Carbon is a fundamental element found in all organic molecules, including carbohydrates, fats, and proteins. It forms the backbone of these macromolecules, making it the common element among them.

The elements Carbon, Hydrogen, and Oxygen are found in which of the following?

• Only carbohydrates

• Only proteins

• Only fats

• Carbohydrates, fats, and proteins

Answer explanation

Carbon, Hydrogen, and Oxygen are fundamental elements found in carbohydrates, fats, and proteins. Therefore, the correct answer is 'Carbohydrates, fats, and proteins' as all three types of biomolecules contain these elements.

Which small molecules make up starch?

• Amino acids

• Glucose

• Fatty acids

• Glycerol

Answer explanation

Starch is a polysaccharide made up of glucose molecules linked together. Therefore, the correct answer is glucose, as it is the fundamental building block of starch.

Which large molecule is made from glucose units?

• Protein

• Glycogen

• Lipid

• Fatty acid

Answer explanation

Glycogen is a large molecule made up of glucose units linked together. It serves as a storage form of glucose in animals, while proteins and lipids are made from different building blocks, making glycogen the correct answer.

Proteins are made up of smaller units called:

• Fatty acids

• Glycerol

• Amino acids

• Glucose

Answer explanation

Proteins are polymers made from amino acids, which are the building blocks of proteins. Fatty acids, glycerol, and glucose are components of lipids and carbohydrates, not proteins.

What is glycogen?

• A fat molecule made from fatty acids

• A polysaccharide made from glucose

• A protein made from amino acids

• A sugar made from starch

Answer explanation

Glycogen is a polysaccharide made from glucose, serving as a form of energy storage in animals. It is not a fat, protein, or sugar derived from starch, making the correct choice the second option.

Which of the following is NOT a polysaccharide?

• Glycogen

• Starch

• Cellulose

• Amino acids

Answer explanation

Amino acids are the building blocks of proteins, not polysaccharides. Glycogen, starch, and cellulose are all polysaccharides made of sugar units, while amino acids are individual molecules.