Free Classification of Biological Molecules MCQs with Answers

• A. Carbohydrates
• B. Proteins
• C. Lipids
• D. Nucleic acids

Explanation: Proteins account for roughly half the dry mass because they serve as enzymes, transporters, receptors, antibodies and structural fibres…

• A. Starch
• B. Glycogen
• C. Glucose
• D. Cellulose

Explanation: Glucose is a monosaccharide, a single small unit and therefore a micromolecule, while the other three are polysaccharides built from…

• A. carbon, hydrogen, oxygen and nitrogen
• B. carbon, hydrogen, oxygen and sulphur
• C. sodium, potassium, calcium and chlorine
• D. carbon, nitrogen, phosphorus and sulphur

Explanation: Carbon, hydrogen, oxygen and nitrogen are the backbone of carbohydrates, lipids, proteins and nucleic acids, with phosphorus and sulphur…

• A. an amino acid
• B. a monosaccharide
• C. a nucleotide
• D. a fatty acid

Explanation: Each nucleotide consists of a pentose sugar, a phosphate group and a nitrogenous base, and successive nucleotides are linked by…

• A. condensation
• B. hydrolysis
• C. oxidation
• D. photolysis

Explanation: In condensation, an OH from one molecule and an H from the other leave as water while a covalent bond forms, which is how disaccharides…

• A. Phosphorus
• B. Nitrogen
• C. Magnesium
• D. Calcium

Explanation: Every amino acid carries an amino group, so nitrogen is a constant feature of proteins, and sulphur also appears in some.

• A. Proteins
• B. Nucleic acids
• C. Lipids
• D. Carbohydrates

Explanation: Lipids are small molecules, a triglyceride being glycerol plus three fatty acids, and they do not form long repeating chains.

• A. peptide bond
• B. ester bond
• C. phosphodiester bond
• D. glycosidic bond

Explanation: A glycosidic bond forms by condensation between the hydroxyl groups of two sugars.

• A. makes water an excellent solvent for ions
• B. allows cell temperature to fluctuate rapidly with the surroundings
• C. keeps the temperature of cells and of water bodies relatively stable
• D. speeds up every enzyme controlled reaction

Explanation: A large amount of heat is needed to raise the temperature of water because much of the energy first breaks hydrogen bonds between…

• A. lakes freeze from the surface down, insulating the water below
• B. ice sinks to the bottom of lakes in winter
• C. water boils at a higher temperature than expected
• D. evaporation from the skin removes very little heat

Explanation: Water colder than 4 degrees becomes less dense and stays at the surface, so ice forms on top and acts as an insulating lid while liquid…

• A. the hydrolysis of glycogen
• B. the conversion of pyruvate to lactate
• C. alcoholic fermentation
• D. the aerobic oxidation of glucose

Explanation: At the end of the electron transport chain, oxygen accepts electrons and hydrogen ions and is reduced to water, so aerobic respiration…

• A. Its molecules are held together by ionic bonds
• B. It has an unusually high boiling point for such a small molecule because of hydrogen bonding
• C. Its solid form is denser than its liquid form
• D. It ionises completely into hydrogen and hydroxide ions

Explanation: Hydrogen bonding between polar water molecules means far more energy is needed to separate them than its tiny molecular mass would…

• A. glucose and fructose
• B. two glucose units
• C. glucose and galactose
• D. fructose and galactose

Explanation: Maltose is two glucose units joined by a glycosidic bond, typically produced when starch is broken down.

• A. Cellulose
• B. Glycogen
• C. Pectin
• D. Chitin

Explanation: Chitin is a tough nitrogen-containing polysaccharide that builds arthropod exoskeletons and fungal walls.

• A. green, then yellow, then brick red
• B. purple within a few seconds
• C. blue black
• D. completely colourless

Explanation: The free aldehyde or ketone group of a reducing sugar reduces copper ions in Benedict's solution, precipitating red copper oxide, with…

• A. highly branched through 1,6 glycosidic bonds
• B. a structural polymer of beta glucose
• C. largely unbranched and coils into a helix
• D. resistant to digestion by human amylase

Explanation: Amylose is an unbranched chain of alpha glucose that coils into a compact helix, while amylopectin carries frequent branches that give…

• A. secondary structure
• B. tertiary structure
• C. quaternary structure
• D. primary structure

Explanation: Primary structure is simply the amino acid order, dictated by the gene.

• A. Haemoglobin
• B. Insulin
• C. Collagen
• D. Amylase

Explanation: Collagen forms long rope-like triple helices that give strength to skin, tendons and bone, the hallmark of fibrous proteins.

• A. the structure of its amino group
• B. the nature of its R group
• C. the structure of its carboxyl group
• D. the number of peptide bonds it can form

Explanation: Every amino acid shares the same amino group, carboxyl group and central carbon, so only the variable R group distinguishes one from…

• A. a protein's function depends on its precise amino acid sequence
• B. haemoglobin is a fibrous structural protein
• C. every mutation is lethal
• D. haemoglobin normally cannot bind oxygen

Explanation: One change in the primary structure alters haemoglobin's shape so that it polymerises in low oxygen, distorting the red cell.