A-Level Biology Practice Test 9 – 60 Questions with Answers (Cambridge 9700)
Use this test to practise the most demanding A-Level ideas, including gene regulation, ultrafiltration, chemiosmosis and Hardy-Weinberg calculations. Each explanation states the principle behind the correct answer.
Cell structure
Q1. Which evidence supports the endosymbiotic theory for mitochondria?
- (A) Mitochondria are found only in animal cells
- (B) Mitochondria have a single membrane
- (C) Mitochondria have their own circular DNA and 70S ribosomes
- (D) Mitochondria cannot divide independently
Show Answer
Answer: C – Circular DNA and bacterial-type ribosomes suggest descent from engulfed prokaryotes.
Q2. Which organelle detoxifies hydrogen peroxide?
- (A) Peroxisome, using catalase
- (B) Ribosome
- (C) Nucleolus
- (D) Vacuole in animal cells only
Show Answer
Answer: A – Catalase in peroxisomes breaks hydrogen peroxide into water and oxygen.
Q3. A cell is observed to have no membrane-bound organelles, a cell wall of peptidoglycan, and a single circular chromosome. Which additional feature would confirm that it is prokaryotic rather than a small eukaryotic cell?
- (A) A nucleus enclosed by a double membrane
- (B) Mitochondria for aerobic respiration
- (C) Chloroplasts for photosynthesis
- (D) Small 70S ribosomes free in the cytoplasm
Show Answer
Answer: D – Prokaryotes have 70S ribosomes, while eukaryotes have larger 80S ribosomes in their cytoplasm.
Biological molecules
Q4. Which bond stabilises the tertiary structure of a protein through interactions between R groups?
- (A) Glycosidic bond
- (B) Disulfide bridge, ionic bond or hydrophobic interaction
- (C) Peptide bond only
- (D) Ester bond
Show Answer
Answer: B – Tertiary folding is held by bonds between side chains, including disulfide bridges.
Q5. Why does water have a high specific heat capacity?
- (A) Water molecules are very small
- (B) Water is non-polar
- (C) Hydrogen bonds absorb much energy before temperature rises
- (D) Water cannot form hydrogen bonds
Show Answer
Answer: C – Energy is used to break hydrogen bonds, buffering temperature change in cells and aquatic habitats.
Q6. Which statement about saturated and unsaturated fatty acids is correct?
- (A) Unsaturated fatty acids have double bonds that kink the chain and lower melting point
- (B) Saturated fatty acids have many double bonds
- (C) Unsaturated fatty acids pack more tightly
- (D) Both types are identical in structure
Show Answer
Answer: A – Kinks prevent close packing, so unsaturated fats remain liquid at lower temperatures.
Enzymes
Q7. At low substrate concentration, what is the order of reaction with respect to substrate for most enzymes?
- (A) Zero order, because active sites are saturated
- (B) Second order always
- (C) Negative order
- (D) First order, because rate is proportional to substrate concentration
Show Answer
Answer: D – When few sites are occupied, more substrate gives proportionally more enzyme-substrate complexes.
Q8. Why does a small decrease in temperature slow an enzyme reaction without denaturing the enzyme?
- (A) Bonds in the active site break permanently
- (B) Molecules move more slowly, so collisions are less frequent and less energetic
- (C) The substrate is destroyed
- (D) The enzyme concentration falls
Show Answer
Answer: B – Lower kinetic energy reduces successful collisions, but the enzyme structure remains intact.
Q9. Which enzyme is used in biological washing powder, and why?
- (A) Amylase only, to remove proteins
- (B) Catalase, to bleach fabric
- (C) Lipase or protease, to break down stains at lower temperatures
- (D) DNA polymerase, to copy stains
Show Answer
Answer: C – Proteases digest protein stains and lipases digest fats, allowing effective washing in cooler water.
Cell membranes and transport
Q10. Which factor increases the rate of facilitated diffusion?
- (A) A larger concentration gradient and more channel proteins
- (B) A smaller concentration gradient
- (C) Fewer carrier proteins
- (D) A thicker membrane only
Show Answer
Answer: A – Diffusion rate depends on gradient steepness, surface area and number of transport proteins.
Q11. What happens to a plant cell in a concentrated salt solution?
- (A) It becomes turgid
- (B) It bursts
- (C) It takes up salt by osmosis
- (D) It becomes plasmolysed as water leaves by osmosis
Show Answer
Answer: D – Water leaves the vacuole, the protoplast shrinks and pulls away from the wall.
Q12. A nerve cell maintains a low internal sodium concentration despite sodium leaking inward. Which feature of the sodium-potassium pump makes this possible?
- (A) It moves sodium and potassium both into the cell
- (B) It uses ATP to pump sodium out against its concentration gradient, faster than it leaks in
- (C) It allows sodium to diffuse passively down its gradient only
- (D) It requires no energy input
Show Answer
Answer: B – Active transport by the pump maintains the gradient that passive leakage would otherwise dissipate, at the cost of ATP.
The mitotic cell cycle
Q13. Which checkpoint ensures chromosomes are correctly attached to the spindle before separation?
- (A) The G1 checkpoint
- (B) The G2 checkpoint
- (C) The metaphase or spindle checkpoint
- (D) The cytokinesis checkpoint only
Show Answer
Answer: C – The spindle checkpoint delays anaphase until every kinetochore is attached.
Q14. What is the function of telomeres?
- (A) To protect chromosome ends from shortening during replication
- (B) To code for spindle proteins
- (C) To attach chromosomes to the equator
- (D) To trigger cytokinesis
Show Answer
Answer: A – Repeated non-coding sequences buffer loss of DNA at chromosome ends.
Q15. During which phase do sister chromatids become visible as separate structures under a microscope?
- (A) Telophase only
- (B) Interphase only
- (C) Cytokinesis only
- (D) Prophase, as chromosomes condense
Show Answer
Answer: D – Condensed chromosomes in prophase show two chromatids joined at the centromere.
Nucleic acids and protein synthesis
Q16. Which molecule binds to the lac repressor protein and prevents it from blocking transcription of the lac operon?
- (A) RNA polymerase
- (B) Allolactose, a form of lactose
- (C) The operator DNA sequence
- (D) A ribosome subunit
Show Answer
Answer: B – Allolactose binds the repressor and changes its shape, so it can no longer bind the operator and transcription proceeds.
Q17. How is gene expression controlled in eukaryotes at the transcriptional level?
- (A) By ribosomes blocking DNA only
- (B) By changing the genetic code itself
- (C) By transcription factors binding to promoter and enhancer regions
- (D) By deleting all introns permanently
Show Answer
Answer: C – Regulatory proteins determine whether RNA polymerase can initiate transcription.
Q18. Which type of RNA carries amino acids, and which carries the code from DNA?
- (A) tRNA carries amino acids; mRNA carries the code
- (B) mRNA carries amino acids; tRNA carries the code
- (C) rRNA carries amino acids; mRNA carries the code
- (D) tRNA carries the code; rRNA carries amino acids
Show Answer
Answer: A – Transfer RNA delivers amino acids, while messenger RNA is the template for translation.
Q19. A point mutation creates a premature stop codon. What is the likely effect on the protein?
- (A) No effect at all
- (B) A longer protein with extra amino acids
- (C) The gene is duplicated
- (D) A shortened, usually non-functional protein
Show Answer
Answer: D – Translation stops early, so the polypeptide lacks its later amino acids and normal folding.
Transport in plants
Q20. Which evidence supports the mass flow hypothesis for phloem transport?
- (A) Phloem sap moves only by diffusion
- (B) Phloem sap moves faster than diffusion and from source to sink
- (C) Sucrose moves only in xylem
- (D) Companion cells have no mitochondria
Show Answer
Answer: B – Measured flow rates are far too fast for diffusion and follow source-to-sink pressure gradients.
Q21. What is the Casparian strip, and what does it force water to do?
- (A) A band in the epidermis forcing water into xylem directly
- (B) A layer in the phloem blocking sucrose
- (C) A waterproof band in the endodermis forcing water through cell membranes into the symplast
- (D) A waxy layer on leaves only
Show Answer
Answer: C – The strip blocks the apoplast route, so solutes must cross a selectively permeable membrane.
Q22. Which adaptation of root hairs increases water uptake?
- (A) A large surface area and thin walls
- (B) A thick cuticle
- (C) A small surface area
- (D) Lignified walls
Show Answer
Answer: A – Extensions of epidermal cells give a huge area for osmosis close to soil water.
Q23. Why does transpiration increase on a sunny day?
- (A) Stomata close in light
- (B) Roots stop taking up water
- (C) The cuticle thickens in sunlight
- (D) Stomata open for photosynthesis and leaf temperature rises, increasing evaporation
Show Answer
Answer: D – Open stomata and warmer leaves increase the water vapour gradient to the air.
Transport in mammals
Q24. Which blood vessel has valves, thin walls and a wide lumen?
- (A) Artery
- (B) Vein
- (C) Capillary
- (D) Arteriole
Show Answer
Answer: B – Veins carry blood at low pressure, so valves prevent backflow.
Q25. How does the structure of red blood cells suit oxygen transport?
- (A) They have a nucleus and large volume
- (B) They have mitochondria for respiration
- (C) They are biconcave, lack a nucleus and contain haemoglobin
- (D) They are large and spherical
Show Answer
Answer: C – Biconcave shape gives a large surface area, and absence of a nucleus leaves room for haemoglobin.
Q26. At the venule end of a capillary, why does tissue fluid re-enter the blood?
- (A) Water potential of blood is lower due to plasma proteins, so water moves in by osmosis
- (B) Hydrostatic pressure exceeds solute potential
- (C) Active transport pumps fluid back
- (D) Lymph vessels push fluid in
Show Answer
Answer: A – Falling hydrostatic pressure leaves the osmotic effect of plasma proteins dominant.
Q27. Which factor shifts the oxygen dissociation curve to the right?
- (A) Lower carbon dioxide concentration
- (B) Lower temperature only
- (C) Higher pH only
- (D) Higher temperature and lower pH
Show Answer
Answer: D – Active tissues are warm and acidic, favouring oxygen release where it is needed.
Gas exchange
Q28. Why do mammals have a diaphragm and intercostal muscles?
- (A) To filter inhaled air
- (B) To change thoracic volume and ventilate the lungs
- (C) To produce surfactant
- (D) To carry blood to alveoli
Show Answer
Answer: B – Muscle contraction increases volume and lowers pressure, drawing air in.
Q29. In insects, how is gas exchange increased during flight?
- (A) Spiracles close permanently
- (B) Tracheae fill with blood
- (C) Air sacs act as bellows, ventilating the tracheal system
- (D) The exoskeleton becomes permeable
Show Answer
Answer: C – Abdominal pumping moves air through air sacs to meet high respiratory demand.
Q30. Which feature of the fish gill system prevents blood and water mixing while allowing exchange?
- (A) Lamellae are separated by a thin epithelium and capillary walls
- (B) Blood flows directly into water
- (C) Gills have no blood supply
- (D) Water is pumped into the blood
Show Answer
Answer: A – Gases diffuse across the thin barrier without fluids mixing.
Infectious diseases
Q31. A farmer stops giving antibiotics to healthy animals as a routine growth promoter. How could this practice help slow antibiotic resistance in bacteria affecting humans?
- (A) Antibiotics create mutations in bacteria
- (B) Resistance only occurs in viruses
- (C) All bacteria become resistant after one dose
- (D) It reduces selection pressure favouring pre-existing resistant bacteria, so they multiply less readily
Show Answer
Answer: D – Selection, not creation by the drug, explains the spread of resistance alleles, so lower antibiotic use slows that selection.
Q32. Why can malaria be hard to eliminate even with bed nets?
- (A) Bed nets increase mosquito numbers
- (B) Mosquitoes develop insecticide resistance and Plasmodium develops drug resistance
- (C) Malaria is spread by water alone
- (D) Humans cannot develop immunity
Show Answer
Answer: B – Resistance in both vector and parasite undermines control measures.
Q33. Which pathogen type causes athlete’s foot?
- (A) A bacterium
- (B) A virus
- (C) A fungus
- (D) A protoctist
Show Answer
Answer: C – Dermatophyte fungi infect skin, especially in warm, moist conditions.
Immunity
Q34. Which immune cells kill virus-infected cells directly?
- (A) Cytotoxic T cells
- (B) B lymphocytes
- (C) Plasma cells
- (D) Red blood cells
Show Answer
Answer: A – Cytotoxic T cells recognise foreign antigen on infected cells and destroy them.
Q35. What is herd immunity?
- (A) Immunity gained only by animals
- (B) Immunity that lasts for one day only
- (C) Passive immunity from mother to child only
- (D) Protection of unvaccinated individuals when most of a population is immune
Show Answer
Answer: D – High vaccination coverage breaks chains of transmission.
Q36. Why are monoclonal antibodies useful in diagnosis?
- (A) They bind to many different antigens randomly
- (B) They bind specifically to one antigen, allowing precise detection
- (C) They kill all pathogens on contact
- (D) They replace vaccination entirely
Show Answer
Answer: B – Specificity allows a test to detect a single target molecule in a sample.
Energy and respiration
Q37. How many ATP molecules are produced in total by substrate-level phosphorylation in aerobic respiration of one glucose?
- (A) Two
- (B) Ten
- (C) Four
- (D) Thirty-two
Show Answer
Answer: C – Glycolysis yields two net ATP and the Krebs cycle yields two more by substrate-level phosphorylation; the rest comes from oxidative phosphorylation.
Q38. What is the final electron acceptor in aerobic respiration?
- (A) Oxygen
- (B) NAD
- (C) Pyruvate
- (D) Carbon dioxide
Show Answer
Answer: A – Oxygen accepts electrons and hydrogen at the end of the chain, forming water.
Q39. A respirometer shows oxygen uptake of 60 cubic millimetres in 10 minutes. What is the rate per minute?
- (A) 0.6 cubic millimetres per minute
- (B) 60 cubic millimetres per minute
- (C) 600 cubic millimetres per minute
- (D) 6 cubic millimetres per minute
Show Answer
Answer: D – Dividing total uptake by time gives 6 cubic millimetres per minute.
Photosynthesis
Q40. Which reaction in the light-dependent stage produces ATP by chemiosmosis?
- (A) Photolysis alone
- (B) Proton accumulation in the thylakoid lumen driving ATP synthase
- (C) Carbon fixation
- (D) Reduction of glycerate 3-phosphate
Show Answer
Answer: B – Protons pumped into the lumen flow back through ATP synthase in the thylakoid membrane.
Q41. Why do plants appear green in white light?
- (A) Chlorophyll absorbs green light most strongly
- (B) Leaves contain no other pigments
- (C) Chlorophyll reflects and transmits green light while absorbing blue and red
- (D) Green light is used fastest in photosynthesis
Show Answer
Answer: C – The action spectrum peaks in blue and red, with a dip in green.
Q42. If carbon dioxide concentration is limiting, which stage is directly affected first?
- (A) Carbon fixation by Rubisco in the Calvin cycle
- (B) Photolysis of water
- (C) Electron transport in photosystem II
- (D) Chlorophyll excitation only
Show Answer
Answer: A – Less carbon dioxide means less substrate for Rubisco, slowing the Calvin cycle.
Homeostasis
Q43. Where are osmoreceptors located?
- (A) In the kidney cortex
- (B) In the adrenal cortex
- (C) In the collecting duct
- (D) In the hypothalamus of the brain
Show Answer
Answer: D – Hypothalamic osmoreceptors detect changes in blood water potential and trigger ADH release.
Q44. Which cells in the pancreas secrete insulin?
- (A) Alpha cells of the islets of Langerhans
- (B) Beta cells of the islets of Langerhans
- (C) Acinar cells
- (D) Hepatocytes
Show Answer
Answer: B – Beta cells release insulin in response to rising blood glucose.
Q45. What is the role of the liver in glucose homeostasis?
- (A) It produces insulin
- (B) It excretes excess glucose in bile
- (C) It stores glucose as glycogen and releases glucose by glycogenolysis and gluconeogenesis
- (D) It converts glucose to ADH
Show Answer
Answer: C – The liver acts as a glucose buffer under hormonal control.
Control and coordination
Q46. What is temporal summation at a synapse?
- (A) Repeated impulses from one presynaptic neurone building up transmitter release
- (B) Several presynaptic neurones firing together
- (C) Inhibitory signals cancelling all excitation
- (D) Action potentials travelling in both directions
Show Answer
Answer: A – Rapid repeated firing sums generator potentials to reach threshold.
Q47. Which reflex arc component carries impulses to the effector?
- (A) Sensory neurone
- (B) Relay neurone
- (C) Receptor
- (D) Motor neurone
Show Answer
Answer: D – Motor neurones carry impulses from the central nervous system to muscles or glands.
Q48. In the eye, which structure changes shape to focus on near objects?
- (A) Cornea only
- (B) Lens, made more convex by ciliary muscles
- (C) Retina
- (D) Iris alone
Show Answer
Answer: B – Ciliary muscles contract, suspensory ligaments slacken, and the elastic lens becomes rounder.
Inheritance
Q49. Which statement about codominance and incomplete dominance is correct?
- (A) Both patterns give a 3:1 phenotypic ratio
- (B) Codominance only occurs in blood groups
- (C) In codominance both alleles are fully expressed; in incomplete dominance the heterozygote is intermediate
- (D) Incomplete dominance means one allele is dominant
Show Answer
Answer: C – Codominant alleles both appear in the phenotype, while incomplete dominance blends them.
Q50. A chi-squared test gives a value below the critical value. What conclusion is drawn?
- (A) There is no significant difference; the null hypothesis is accepted
- (B) The observed results differ significantly from expected
- (C) The experiment must be repeated with no controls
- (D) The gene must be sex-linked
Show Answer
Answer: A – A low chi-squared value means observed ratios fit the expected Mendelian ratio.
Q51. Why can a recessive allele remain in a population at low frequency?
- (A) It is expressed in heterozygotes
- (B) It is always lethal
- (C) It mutates back each generation
- (D) It is hidden in heterozygotes and only expressed when homozygous
Show Answer
Answer: D – Carriers pass the allele on without showing the phenotype.
Selection and evolution
Q52. Which statement defines a species under the biological species concept?
- (A) A group that looks identical
- (B) A group that can interbreed to produce fertile offspring
- (C) A group living in the same habitat only
- (D) A group with identical DNA
Show Answer
Answer: B – Reproductive isolation defines species boundaries in this concept.
Q53. Which type of variation is usually continuous?
- (A) Blood group, controlled by one gene
- (B) Ability to roll the tongue only
- (C) Height, controlled by many genes and environment
- (D) Presence of a single mutation only
Show Answer
Answer: C – Polygenic traits show a range of phenotypes in a normal distribution.
Q54. How does gene flow affect allele frequencies?
- (A) It can introduce new alleles or change frequencies through migration
- (B) It always increases variation within a population
- (C) It prevents all mutation
- (D) It only occurs by mutation
Show Answer
Answer: A – Movement of individuals between populations transfers alleles.
Classification, biodiversity and conservation
Q55. Which domain includes bacteria without a membrane-bound nucleus?
- (A) Eukarya
- (B) Archaea only for all prokaryotes
- (C) Plantae
- (D) Bacteria
Show Answer
Answer: D – The domain Bacteria contains true bacteria; Archaea is a separate prokaryotic domain.
Q56. Why are some species classified as endangered?
- (A) They are found in zoos only
- (B) Their population is very small or falling rapidly, with high extinction risk
- (C) They have large populations everywhere
- (D) They are newly discovered
Show Answer
Answer: B – Endangered status reflects population size, decline rate and threats, not zoo presence alone.
Q57. Which human activity most directly causes habitat fragmentation?
- (A) Establishing a nature reserve
- (B) Captive breeding
- (C) Building roads and clearing land for agriculture
- (D) Releasing rehabilitated animals
Show Answer
Answer: C – Roads and fields split continuous habitat into isolated patches.
Genetic technology
Q58. A patient with cystic fibrosis is treated by delivering a working copy of the CFTR gene to lung cells using a modified virus. Which term describes this approach?
- (A) Gene therapy
- (B) Cloning a whole patient
- (C) Screening embryos only
- (D) Producing antibodies in bacteria
Show Answer
Answer: A – Gene therapy delivers a functional allele to a patient’s cells to compensate for a faulty gene.
Q59. Why is reverse transcriptase useful in genetic engineering?
- (A) It cuts DNA at specific sites
- (B) It separates DNA fragments by size
- (C) It synthesises RNA primers
- (D) It copies mRNA into complementary DNA without introns
Show Answer
Answer: D – cDNA made from mRNA contains only coding sequences, useful for expression in bacteria.
Q60. Which ethical concern is raised by genetic screening?
- (A) Screening always cures genetic disease
- (B) Results may affect insurance, employment or family decisions
- (C) Screening changes the genetic code itself
- (D) Screening works only for infectious disease
Show Answer
Answer: B – Knowledge of genetic risk raises privacy and discrimination concerns.
Work through any questions you missed again, then revise those areas before moving on to the next test.
📥 Prefer pen and paper? Take this test offline.
Download Printable PDF – Test 9
Free printable version: all 60 questions + answer key. Explanations stay here on the website.