Free Biological Molecules MCQs with Answers

• 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.

• A. form waterproof coatings on leaves, fruits and exoskeletons
• B. store more energy per gram than any other molecule
• C. build the phospholipid bilayer of membranes
• D. act as receptors for hormones

Explanation: Waxes are highly hydrophobic, so the cuticle on leaves and the wax layer on insect exoskeletons prevent water loss and resist wetting.

• A. are attracted to water molecules
• B. carry a strong negative charge
• C. are non polar and are excluded from the surrounding water
• D. are forced inwards by membrane proteins

Explanation: The hydrophobic tails avoid water while the polar phosphate heads face it, so the bilayer assembles itself with tails inside.

• A. Triglyceride
• B. Steroid
• C. Phospholipid
• D. Wax

Explanation: Steroids such as cholesterol and testosterone are built from four fused carbon rings and contain no fatty acid chains.

• A. cytoplasm
• B. ribosome itself
• C. Golgi apparatus
• D. nucleolus

Explanation: The nucleolus transcribes rRNA and assembles it with proteins into ribosomal subunits, which then leave through nuclear pores.

• A. messenger RNA
• B. transfer RNA
• C. ribosomal RNA
• D. DNA

Explanation: Each tRNA carries a three-base anticodon loop that base pairs with the complementary codon on mRNA, ensuring the correct amino acid is…

• A. ribose and uracil
• B. deoxyribose and thymine
• C. ribose and thymine
• D. deoxyribose and uracil

Explanation: RNA has the sugar ribose and uses uracil in place of thymine, pairing uracil with adenine.

• A. Amylose
• B. Palmitic acid
• C. Glycogen
• D. Glycolipid

Explanation: A conjugated molecule combines two different classes of biomolecule, here a carbohydrate with a lipid.

• A. substrate
• B. apoenzyme
• C. prosthetic group
• D. peptide

Explanation: A prosthetic group, such as the haem of haemoglobin, is a non protein part fixed tightly to the protein.

• A. energy storage for the cell
• B. cell recognition and signalling
• C. transport of oxygen
• D. replication of DNA

Explanation: The carbohydrate chains of glycolipids and glycoproteins act as identification markers, which is why blood group antigens sit on the red…