A-Level Biology Practice Test 16 – 60 Questions with Answers (Cambridge 9700)

Q1. Which feature of a prokaryotic cell distinguishes it most clearly from a eukaryotic cell?

• (A) Absence of membrane-bound organelles and a true nucleus
• (B) Presence of a cell wall made of cellulose
• (C) Presence of mitochondria for aerobic respiration
• (D) Presence of a large permanent vacuole

Q2. The rough endoplasmic reticulum is closely associated with protein synthesis because it is studded with which structures?

• (A) Lysosomes
• (B) Ribosomes
• (C) Peroxisomes
• (D) Centrioles

Q3. Which organelle modifies, packages and secretes proteins, forming vesicles that carry them to the cell surface?

• (A) Nucleolus
• (B) Smooth endoplasmic reticulum
• (C) Golgi apparatus
• (D) Chloroplast

Q4. Which bond is formed when two monosaccharides join in a condensation reaction?

• (A) Peptide bond
• (B) Glycosidic bond
• (C) Hydrogen bond
• (D) Ester bond

Q5. Why is glycogen a more suitable storage polysaccharide in animals than glucose alone?

• (A) It is soluble and raises the water potential of liver cells
• (B) It is transported freely in the blood plasma
• (C) It is insoluble and therefore has little osmotic effect, yet is rapidly hydrolysed when glucose is needed
• (D) It cannot be broken down by enzymes in animal cells

Q6. A triglyceride is formed from glycerol and three fatty acids. Which type of bond links each fatty acid to the glycerol?

• (A) Glycosidic bond
• (B) Peptide bond
• (C) Hydrogen bond
• (D) Ester bond

Q7. Which statement best explains why a competitive inhibitor reduces the rate of an enzyme-catalysed reaction at low substrate concentration?

• (A) It denatures the enzyme by breaking its tertiary structure
• (B) It binds to an allosteric site and changes the shape of the active site
• (C) It occupies the active site, so fewer substrate molecules can bind
• (D) It increases the activation energy of the reaction permanently

Q8. A non-competitive inhibitor differs from a competitive inhibitor in that it does what?

• (A) Binds only when substrate concentration is very high
• (B) Binds reversibly to the active site of the enzyme
• (C) Raises the maximum rate of reaction if more substrate is added
• (D) Binds to a site other than the active site and alters the active site shape

Q9. Immobilised enzymes are widely used in industry because they offer which advantage over free enzymes?

• (A) They can be recovered and reused, and they do not contaminate the product
• (B) They always work faster than the same enzyme in solution
• (C) They are unaffected by temperature or pH changes
• (D) They no longer require a specific substrate to function

Q10. In the fluid mosaic model, which component is mainly responsible for the fluidity of the membrane?

• (A) Glycoproteins anchored to the cytoskeleton
• (B) Cholesterol molecules packed between phospholipids only at low temperature
• (C) Channel proteins spanning the whole bilayer
• (D) Phospholipid molecules moving laterally within each layer

Q11. Facilitated diffusion differs from simple diffusion in that it requires what?

• (A) A transport protein in the membrane
• (B) ATP hydrolysed directly by the transported molecule
• (C) Movement against a concentration gradient
• (D) Endocytosis of the surrounding fluid

Q12. Which process moves sodium ions out of a cell against their concentration gradient using energy from ATP?

• (A) Osmosis through aquaporins
• (B) Active transport by a sodium-potassium pump
• (C) Facilitated diffusion through a channel
• (D) Simple diffusion across the lipid bilayer

Q13. During which stage of the cell cycle does DNA replication occur?

• (A) S phase of interphase
• (B) Prophase of mitosis
• (C) Cytokinesis
• (D) Metaphase of mitosis

Q14. What is the key event of anaphase in mitosis?

• (A) Chromosomes condense and the nuclear envelope breaks down
• (B) Sister chromatids separate and move to opposite poles
• (C) Chromosomes align along the equator of the cell
• (D) The nuclear envelope reforms around each set of chromosomes

Q15. Uncontrolled mitosis is dangerous because it can lead to which outcome?

• (A) Loss of all cell differentiation in every tissue
• (B) Failure of meiosis in reproductive organs only
• (C) Formation of a tumour of genetically identical cells
• (D) Immediate death of the affected cell by apoptosis

Q16. Which feature of DNA structure allows it to be copied accurately during semi-conservative replication?

• (A) The sugar-phosphate backbone is identical in both strands
• (B) Complementary base pairing between the two strands
• (C) The presence of uracil in place of thymine
• (D) The double helix is held together only by covalent bonds

Q17. In protein synthesis, the role of tRNA is best described as what?

• (A) Carrying the genetic code from the nucleus to the cytoplasm
• (B) Forming the structural framework of the ribosome
• (C) Carrying a specific amino acid to the ribosome according to its anticodon
• (D) Splicing introns out of pre-mRNA in the nucleus

Q18. A mutation that changes a single base in a codon but leaves the amino acid unchanged is best described as which type?

• (A) A frameshift mutation
• (B) A nonsense mutation
• (C) A deletion mutation
• (D) A silent mutation

Q19. Which tissue transports assimilates such as sucrose from sources to sinks, and which feature supports that role?

• (A) Xylem, with lignified walls that withstand tension
• (B) Cambium, with rapidly dividing meristematic cells
• (C) Phloem, with sieve tube elements lacking nuclei but supported by companion cells
• (D) Epidermis, with a waxy cuticle that limits water loss

Q20. Transpiration pull depends mainly on which property of water?

• (A) Water is a good solvent for mineral ions
• (B) Water has a low specific heat capacity
• (C) Water molecules are small enough to pass through cell walls
• (D) Cohesion between water molecules and adhesion to xylem walls

Q21. At a sink in mass flow, sucrose is actively unloaded from phloem sieve tubes. What happens to water in the sieve tubes as a result, and why?

• (A) Water potential in the sieve tubes rises as sucrose is removed, so water leaves by osmosis and hydrostatic pressure falls
• (B) Water evaporates from leaf stomata, pulling sap upward
• (C) Root pressure pushes sap from the roots into the leaves
• (D) Gravity acting on sap in vertical sieve tubes drives the flow

Q22. Why is the left ventricle wall much thicker than the right ventricle wall?

• (A) It must prevent backflow into the left atrium
• (B) It contracts less frequently than the right ventricle
• (C) It receives blood directly from the pulmonary vein
• (D) It must generate enough pressure to pump blood around the whole body

Q23. Which sequence correctly describes the mammalian double circulation, starting at the right ventricle?

• (A) Pulmonary artery, lungs, pulmonary vein, left atrium, left ventricle, body, vena cava, right atrium
• (B) Aorta, body, pulmonary vein, left atrium, lungs, right atrium, vena cava
• (C) Pulmonary vein, lungs, aorta, body, vena cava, left atrium, right ventricle
• (D) Vena cava, right atrium, aorta, body, pulmonary artery, lungs, left ventricle

Q24. Tissue fluid formation at the arteriole end of a capillary is driven mainly by which pressure difference?

• (A) Lower solute potential in the tissue fluid than in the blood
• (B) Higher hydrostatic pressure in the capillary than the opposing solute potential gradient
• (C) Active transport of plasma proteins out of the capillary
• (D) Lower hydrostatic pressure in the capillary than in the surrounding tissue

Q25. Haemoglobin unloads oxygen more readily in actively respiring tissue because of which combined effect?

• (A) Higher carbon dioxide concentration and lower pH shifting the dissociation curve to the right
• (B) Higher oxygen concentration and higher pH shifting the curve to the left
• (C) Lower temperature and lower carbon dioxide concentration in the tissue
• (D) Direct binding of carbon dioxide to the haem group of haemoglobin

Q26. Which feature of mammalian alveoli most increases the rate of gas exchange?

• (A) A very large total surface area and a thin diffusion barrier
• (B) A thick layer of mucus trapping inhaled particles
• (C) Cartilage rings keeping the airways permanently open
• (D) Ciliated cells moving mucus toward the pharynx

Q27. In fish, countercurrent flow across the gills is advantageous because it does what?

• (A) Prevents water from entering the mouth
• (B) Maintains a concentration gradient along the whole length of the lamella
• (C) Allows blood to flow in the same direction as water for faster exchange
• (D) Increases the oxygen content of water before it reaches the gills

Q28. During inspiration in mammals, which sequence of events occurs?

• (A) Diaphragm relaxes, intercostal muscles relax, thorax volume falls, pressure rises
• (B) Diaphragm contracts, internal intercostal muscles contract, ribs move down and in
• (C) Diaphragm contracts and flattens, external intercostal muscles contract, thorax volume rises, pressure falls
• (D) Diaphragm flattens, thorax volume falls, air is forced out of the lungs

Q29. Insects use a tracheal system for gas exchange. Which feature of tracheoles makes them effective for direct delivery to tissues?

• (A) They are lined with cartilage that holds them open
• (B) They contain blood that carries oxygen to muscles
• (C) They open and close using a diaphragm muscle
• (D) Their walls are very thin and they penetrate deep into tissues

Q30. Which statement about the transmission of cholera is correct?

• (A) It is spread mainly by airborne droplets from coughing
• (B) It is spread through water or food contaminated with faeces containing Vibrio cholerae
• (C) It is spread only by direct skin contact with an infected person
• (D) It is spread by the bite of an infected mosquito

Q31. The human immunodeficiency virus (HIV) causes AIDS by progressively destroying which cells of the immune system?

• (A) B lymphocytes that produce antibodies
• (B) Neutrophils that carry out phagocytosis
• (C) Helper T lymphocytes (CD4 cells) that coordinate the immune response
• (D) Platelets involved in blood clotting

Q32. Why does antibiotic resistance spread rapidly in a bacterial population exposed to an antibiotic?

• (A) Antibiotics cause new mutations in every bacterium they contact
• (B) Bacteria learn to recognise and avoid the antibiotic molecule
• (C) Antibiotics weaken the immune system so bacteria multiply unchecked
• (D) Resistant mutants survive and reproduce, passing resistance genes to offspring and sometimes to other bacteria

Q33. Which measure is most effective for controlling malaria in a region where the mosquito vector is present?

• (A) Quarantining all infected people in hospitals
• (B) Reducing mosquito breeding sites, using insecticide-treated nets, and treating cases promptly
• (C) Vaccinating the whole population against the Plasmodium parasite with a single lifelong dose
• (D) Adding antibiotics to the local drinking water supply

Q34. In the primary immune response, which sequence occurs after a pathogen enters the body?

• (A) Memory cells are activated immediately and produce large amounts of antibody within hours
• (B) Antibodies are produced before any phagocyte encounters the pathogen
• (C) Phagocytes engulf the pathogen, present antigens, and specific B and T lymphocytes are activated and divide
• (D) Plasma cells form first and only later stimulate phagocytosis

Q35. What distinguishes the secondary immune response from the primary response?

• (A) It involves only the non-specific defences of the skin and mucus
• (B) It produces no memory cells at all
• (C) It relies entirely on antibiotics rather than antibodies
• (D) It is faster and stronger because memory cells are already present

Q36. A vaccine gives long-lasting protection because it does what?

• (A) Introduces memory cells and triggers the formation of memory cells without causing the full disease
• (B) Kills all pathogens already present in the body permanently
• (C) Replaces the need for phagocytes in future infections
• (D) Provides ready-made antibodies that remain in the blood for life

Q37. In aerobic respiration, most ATP is produced during which stage and by what mechanism?

• (A) Glycolysis, by substrate-level phosphorylation in the cytoplasm
• (B) Link reaction, by direct transfer of phosphate to ADP
• (C) Krebs cycle, by photophosphorylation in the mitochondria
• (D) Oxidative phosphorylation, by chemiosmosis as protons flow through ATP synthase

Q38. Anaerobic respiration in mammalian muscle produces lactate. Why is lactate formation necessary?

• (A) It regenerates NAD from reduced NAD, allowing glycolysis to continue
• (B) It produces more ATP than aerobic respiration per glucose molecule
• (C) It removes all carbon dioxide from the muscle cell
• (D) It directly supplies oxygen to the mitochondria

Q39. Which molecule is the final electron acceptor in the electron transport chain of aerobic respiration?

• (A) Carbon dioxide
• (B) Oxygen
• (C) NAD
• (D) Glucose

Q40. In the light-dependent stage, photolysis of water provides which products for the rest of photosynthesis?

• (A) Electrons, protons and oxygen
• (B) Glucose and carbon dioxide
• (C) ATP and glycerate 3-phosphate only
• (D) NADP and ADP only

Q41. Cyclic photophosphorylation differs from non-cyclic photophosphorylation in that it produces what?

• (A) Oxygen and reduced NADP in equal amounts
• (B) ATP only, with no reduced NADP and no oxygen released
• (C) Glucose directly from carbon dioxide
• (D) Reduced NADP only, with no ATP formed

Q42. In the Calvin cycle, what is the role of reduced NADP and ATP from the light-dependent stage?

• (A) They split water to release oxygen
• (B) They fix carbon dioxide directly to ribulose bisphosphate
• (C) They reduce glycerate 3-phosphate to triose phosphate
• (D) They regenerate chlorophyll in the photosystems

Q43. Which sequence correctly describes negative feedback control of blood glucose after a meal?

• (A) Blood glucose falls, glucagon is released, liver glycogen is broken down
• (B) Blood glucose rises, insulin is released, liver and muscle cells take up glucose and store glycogen
• (C) Blood glucose rises, glucagon is released, glucose is converted to glycogen in the liver
• (D) Blood glucose falls, insulin is released, fat stores are mobilised

Q44. In the kidney, ultrafiltration occurs in the glomerulus because of which combination of factors?

• (A) Active transport of plasma proteins through the basement membrane
• (B) Low blood pressure and a wide efferent arteriole
• (C) High hydrostatic pressure from a narrow efferent arteriole and a large filtration surface
• (D) Reabsorption of water in the collecting duct

Q45. Antidiuretic hormone (ADH) increases water reabsorption in the kidney by acting on which structures?

• (A) Glomerular capillaries, increasing the filtration rate
• (B) Proximal convoluted tubule cells, increasing glucose reabsorption
• (C) Loop of Henle, preventing all sodium reabsorption
• (D) Collecting duct walls, inserting aquaporins that make them more permeable to water

Q46. At a cholinergic synapse, an action potential arrives at the presynaptic neurone. Why is calcium influx into the synaptic knob essential for transmission?

• (A) Acetylcholinesterase is released from the postsynaptic membrane
• (B) The presynaptic membrane becomes impermeable to calcium ions
• (C) Calcium ions trigger synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine
• (D) Vesicles in the postsynaptic cell release more acetylcholine

Q47. Which statement about the refractory period of a neurone is correct?

• (A) It allows action potentials to travel in both directions along the axon
• (B) It is the time when the resting potential is maintained by the sodium-potassium pump alone
• (C) It increases the speed of impulse transmission in myelinated neurones
• (D) It prevents a new action potential being generated immediately, ensuring impulses travel one way

Q48. In the eye, accommodation for a near object involves which changes?

• (A) Ciliary muscles contract, suspensory ligaments slacken, lens becomes more convex
• (B) Ciliary muscles relax, suspensory ligaments tighten, lens becomes flatter
• (C) Radial muscles of the iris contract and the pupil dilates
• (D) Suspensory ligaments contract and pull the lens into a flat shape

Q49. In a dihybrid cross between two heterozygotes (AaBb x AaBb), what phenotypic ratio is expected if the genes assort independently?

• (A) 3:1
• (B) 1:2:1
• (C) 1:1:1:1
• (D) 9:3:3:1

Q50. A woman who is a carrier for haemophilia (X-linked recessive) has children with an unaffected man. What is the probability that a son will have haemophilia?

• (A) 1 in 2 (50 percent)
• (B) 1 in 4 (25 percent)
• (C) 0 percent, because the father is unaffected
• (D) 100 percent, because the mother is a carrier

Q51. Codominance is best illustrated by which example?

• (A) A pink flower produced by crossing red and white parents
• (B) AB blood group, where both A and B antigens are expressed on red blood cells
• (C) A recessive allele masked in the heterozygous phenotype
• (D) Continuous variation in human height

Q52. Which statement best describes natural selection?

• (A) Individuals with alleles that increase survival and reproduction become more common in the population over generations
• (B) Individuals change their genes during their lifetime to suit the environment
• (C) All individuals in a population acquire identical advantageous mutations
• (D) The environment directly creates the mutations that a species needs

Q53. Directional selection differs from stabilising selection in that it does what?

• (A) Favours the average phenotype and reduces variation
• (B) Favours one extreme phenotype, shifting the population mean over time
• (C) Favours both extremes at the expense of the average
• (D) Acts only on discontinuous variation

Q54. The Hardy-Weinberg principle can be used to estimate allele frequencies in a population provided which condition holds?

• (A) Mutation and migration are frequent
• (B) The population is very small and isolated
• (C) Mating is random and there is no selection, mutation, migration or genetic drift
• (D) Only dominant alleles are present in the population

Q55. Which hierarchy correctly lists taxonomic groups from largest to smallest?

• (A) Species, genus, family, order, class, phylum, kingdom, domain
• (B) Domain, kingdom, phylum, class, order, family, genus, species
• (C) Kingdom, domain, class, phylum, family, order, genus, species
• (D) Domain, phylum, kingdom, order, class, genus, family, species

Q56. The Simpson index of diversity takes account of which two factors?

• (A) The total area of the habitat and the age of the community
• (B) The number of trophic levels and the biomass of producers
• (C) Species richness and the evenness of abundance across species
• (D) Genetic variation within a single species only

Q57. Why is in situ conservation generally preferred to ex situ conservation for maintaining a species?

• (A) It is always cheaper and requires no management
• (B) It removes all predators and competitors from the habitat
• (C) It allows unlimited captive breeding without genetic problems
• (D) It preserves the species in its natural habitat, maintaining ecological interactions and natural selection

Q58. In recombinant DNA technology, what is the role of a restriction enzyme?

• (A) It joins DNA fragments together with phosphodiester bonds
• (B) It copies a target DNA sequence many times in a thermal cycler
• (C) It cuts DNA at specific recognition sequences, producing fragments that can be joined into a vector
• (D) It translates mRNA into a protein product

Q59. In the polymerase chain reaction (PCR), what is the purpose of the high-temperature step in each cycle?

• (A) To activate DNA ligase
• (B) To allow primers to anneal to the template strands
• (C) To synthesise new DNA strands from primers
• (D) To denature double-stranded DNA into separate template strands

Q60. Genetically modified bacteria can produce human insulin because of which fact?

• (A) The genetic code is universal, so bacterial ribosomes can translate human insulin mRNA correctly
• (B) Bacteria naturally contain the human insulin gene in their plasmids
• (C) Human insulin is identical in structure to bacterial enzymes
• (D) Bacteria can absorb insulin directly from their growth medium