A-Level Biology Practice Test 7 – 60 Questions with Answers (Cambridge 9700)

Q1. A student wants to view the internal structure of a mitochondrion, including its cristae. Why is a transmission electron microscope more suitable than a light microscope for this task?

• (A) Electrons are larger than photons
• (B) Electron microscopes use living specimens only
• (C) Electron microscopes magnify colour better
• (D) Electrons have a shorter wavelength than visible light, giving higher resolution

Q2. In cell fractionation, which organelle pellets first at the lowest centrifugation speed?

• (A) Ribosomes
• (B) Lysosomes
• (C) Nuclei
• (D) Mitochondria

Q3. Which cytoskeletal component is involved in the movement of chromosomes during mitosis?

• (A) Intermediate filaments of the nuclear lamina only
• (B) Microtubules of the spindle
• (C) Cellulose microfibrils
• (D) Plasmodesmata

Q4. A student calculates magnification as image size divided by actual size. The image is 40 mm and the actual size is 0.02 mm. What is the magnification?

• (A) 2000
• (B) 200
• (C) 800
• (D) 20000

Q5. Which property of water is most important for its role as a solvent in cells?

• (A) Its low specific heat capacity
• (B) Its low density as ice
• (C) Its inability to dissolve ions
• (D) Its polarity, allowing hydrogen bonds with solutes

Q6. Which level of protein structure is formed by hydrogen bonding between amino acids in the chain?

• (A) Primary structure
• (B) Quaternary structure only
• (C) Secondary structure
• (D) Primary and quaternary together

Q7. A triglyceride is formed from glycerol and three fatty acids. How many water molecules are released?

• (A) One
• (B) Three
• (C) Two
• (D) Four

Q8. A food sample gives a purple colour in the biuret test and remains blue after heating with Benedict’s reagent. What does this combination indicate?

• (A) The sample contains protein but no reducing sugar
• (B) The sample contains reducing sugar but no protein
• (C) The sample contains starch but no protein
• (D) The sample contains lipid but no protein

Q9. A competitive inhibitor is added to an enzyme reaction. What happens if substrate concentration is greatly increased?

• (A) Inhibition cannot be overcome
• (B) Vmax falls permanently
• (C) The enzyme is denatured
• (D) The effect of the inhibitor is reduced because substrate outcompetes it

Q10. Which factor would denature an enzyme rather than simply slow it?

• (A) A small fall in substrate concentration
• (B) A small fall in temperature
• (C) Extreme pH that disrupts bonds holding the tertiary structure
• (D) A competitive inhibitor binding briefly

Q11. In an immobilised enzyme reactor, what is a major advantage over using free enzyme?

• (A) The enzyme is used once and discarded easily
• (B) The enzyme can be reused and the product is not contaminated with enzyme
• (C) The enzyme works only at one temperature
• (D) The substrate cannot reach the enzyme

Q12. Which molecules can pass directly through the phospholipid bilayer by simple diffusion?

• (A) Small non-polar molecules such as oxygen
• (B) Large polar proteins
• (C) Ions such as sodium
• (D) Glucose without a carrier

Q13. Co-transport of glucose in the ileum depends on which gradient?

• (A) A glucose gradient created by diffusion alone
• (B) A water potential gradient in the blood
• (C) A potassium gradient in the lumen
• (D) A sodium ion gradient created by active transport

Q14. A white blood cell engulfs a bacterium by extending its membrane around it until the bacterium is enclosed in a vesicle. Which process is this an example of?

• (A) Exocytosis, the release of substances by vesicle fusion
• (B) Diffusion of water across a membrane
• (C) Phagocytosis, a form of endocytosis
• (D) Active pumping of single ions

Q15. Bone marrow stem cells are used to treat a patient whose blood cells are failing. Which property of stem cells makes this treatment possible?

• (A) They are already specialised blood cells that cannot divide further
• (B) They are unspecialised and can divide by mitosis to produce specialised blood cells
• (C) They have no DNA of their own
• (D) They can divide only once in a lifetime

Q16. Why is uncontrolled mitosis dangerous?

• (A) It can form a tumour of genetically identical cells
• (B) It always produces haploid cells
• (C) It prevents DNA replication
• (D) It stops all cell division elsewhere

Q17. During metaphase, where are chromosomes positioned?

• (A) Randomly throughout the cytoplasm
• (B) At opposite poles
• (C) Inside the reforming nucleus only
• (D) On the equator, attached to spindle fibres

Q18. Which enzyme unwinds DNA and which joins Okazaki fragments during replication?

• (A) DNA polymerase unwinds; helicase joins
• (B) Ligase unwinds; polymerase joins
• (C) Helicase unwinds; DNA ligase joins
• (D) RNA polymerase unwinds; ligase copies

Q19. A tRNA molecule with anticodon UAC arrives at a ribosome during translation. Which statement correctly describes the mRNA codon it pairs with?

• (A) A sequence of three bases on tRNA
• (B) AUG on mRNA, a sequence of three bases coding for one amino acid, methionine
• (C) A gene that codes for a ribosome
• (D) A stop signal in DNA only

Q20. A mutation changes one base in a codon, but the amino acid stays the same. What is the most likely explanation?

• (A) The code is degenerate
• (B) The mutation occurred in an intron
• (C) The gene was deleted
• (D) Transcription stopped

Q21. Which cells load sucrose into phloem at a source?

• (A) Guard cells
• (B) Xylem parenchyma only
• (C) Epidermal cells
• (D) Companion cells, using ATP

Q22. How can a potometer be used to compare transpiration rates?

• (A) By counting stomata directly
• (B) By measuring root pressure only
• (C) By measuring bubble movement as water is taken up to replace water lost
• (D) By weighing dry mass after a week

Q23. Why do xylem vessels have lignified walls?

• (A) To allow active transport of sucrose
• (B) To withstand tension and prevent collapse, and to waterproof the vessel
• (C) To photosynthesise
• (D) To store starch

Q24. What is the Bohr effect?

• (A) Oxygen is released more readily where carbon dioxide concentration is high
• (B) Oxygen binds more tightly where carbon dioxide is high
• (C) Haemoglobin carries more oxygen at low pH in the lungs
• (D) Carbon dioxide is carried only as carbamino compounds

Q25. Which sequence correctly describes the cardiac cycle after atrial systole?

• (A) Ventricular diastole, then atrial systole again immediately
• (B) Atrial diastole with closed semilunar valves only
• (C) Ventricular systole with open atrioventricular valves
• (D) Ventricular systole, then ventricular diastole

Q26. How is most carbon dioxide transported in blood?

• (A) Dissolved directly in plasma only
• (B) Bound to haemoglobin as oxyhaemoglobin
• (C) As hydrogencarbonate ions in plasma
• (D) As carbonic acid in red cells only

Q27. Which feature is an adaptation of insect tracheoles for gas exchange?

• (A) They have thick, impermeable walls
• (B) They have thin walls and are in close contact with muscle cells
• (C) They carry blood to tissues
• (D) They open only during flight

Q28. In the mammalian lung, what maintains a steep diffusion gradient for oxygen?

• (A) Ventilation replacing air and blood flow removing oxygenated blood
• (B) Slow blood flow and thick alveolar walls
• (C) Mucus trapping oxygen
• (D) Surfactant blocking diffusion

Q29. Why do large, active mammals need a specialised gas exchange surface?

• (A) Their surface area to volume ratio is too large
• (B) They cannot diffuse gases at all
• (C) Their skin is too thin
• (D) Diffusion across the body surface alone would be too slow for their metabolic demand

Q30. Which statement about the life cycle of Plasmodium is correct?

• (A) It reproduces only in the mosquito gut
• (B) It is a bacterium spread by water
• (C) It infects liver cells and then red blood cells in humans
• (D) It infects only mosquitoes

Q31. Why is it difficult to develop a vaccine against HIV?

• (A) HIV is a bacterium with a thick wall
• (B) HIV has a very high mutation rate and attacks immune cells
• (C) HIV cannot be grown in a laboratory
• (D) HIV does not trigger any immune response

Q32. Which control measure most directly reduces cholera transmission in a community?

• (A) Providing clean drinking water and sanitation
• (B) Vaccinating against the toxin only
• (C) Using insecticide-treated nets
• (D) Quarantining all healthy people

Q33. What is the difference between active and passive immunity?

• (A) Active immunity is always short-lived
• (B) Passive immunity creates memory cells
• (C) Active immunity requires antibiotics
• (D) Active immunity involves making your own antibodies; passive immunity involves receiving ready-made antibodies

Q34. Which antibody function helps phagocytes recognise a pathogen?

• (A) Neutralisation only
• (B) Agglutination of red cells only
• (C) Opsonisation, marking the pathogen for phagocytosis
• (D) Direct lysis by antibodies alone

Q35. Why does a second exposure to the same antigen produce more antibodies faster?

• (A) Phagocytes are larger
• (B) Memory B cells divide rapidly into plasma cells
• (C) Antigens are smaller the second time
• (D) T cells block antibody production

Q36. Where in the cell does glycolysis occur?

• (A) In the cytoplasm
• (B) In the mitochondrial matrix
• (C) On the inner mitochondrial membrane
• (D) In the chloroplast stroma

Q37. In anaerobic respiration in yeast, what are the products?

• (A) Lactate and ATP only
• (B) Water and carbon dioxide only
• (C) Pyruvate and oxygen
• (D) Ethanol, carbon dioxide and ATP

Q38. A muscle cell during intense exercise produces lactate. Why does NAD need to be regenerated from reduced NAD in this process?

• (A) It acts as the final electron acceptor forming water
• (B) It phosphorylates ADP directly
• (C) Reduced NAD must be oxidised so that glycolysis can continue producing ATP
• (D) It splits water in the chloroplast

Q39. Which stage of photosynthesis involves photolysis of water?

• (A) The Calvin cycle
• (B) The light-dependent reactions on thylakoid membranes
• (C) Starch synthesis in the stroma
• (D) Carbon fixation in the dark

Q40. How many carbon dioxide molecules must enter the Calvin cycle to produce one molecule of glucose?

• (A) Six
• (B) One
• (C) Three
• (D) Twelve

Q41. A plant is kept at low temperature. Why does photosynthesis slow even in bright light?

• (A) Light-dependent reactions stop completely
• (B) Chlorophyll is destroyed by cold
• (C) Stomata open wider
• (D) Enzymes of the Calvin cycle work more slowly

Q42. Which part of the nephron is the main site of selective reabsorption?

• (A) Glomerulus
• (B) Collecting duct only
• (C) Proximal convoluted tubule
• (D) Loop of Henle only

Q43. When blood water potential falls, what sequence restores it?

• (A) Osmoreceptors detect the fall, ADH release falls, less water is reabsorbed
• (B) Osmoreceptors detect the fall, ADH release rises, more water is reabsorbed
• (C) ADH is released by the kidney directly
• (D) Insulin release rises and water is excreted

Q44. Which response helps a mammal conserve heat in cold conditions?

• (A) Vasoconstriction and shivering
• (B) Vasodilation in the skin
• (C) Sweating
• (D) Lowering metabolic rate to zero

Q45. What is the resting potential of a neurone, and how is it maintained?

• (A) Positive inside, maintained by sodium-potassium pumps
• (B) Zero, maintained by diffusion alone
• (C) Negative outside, maintained by myelin
• (D) Negative inside, maintained by sodium-potassium pumps

Q46. Why is transmission at a synapse one-way only?

• (A) Vesicles exist on both sides
• (B) Ions cannot cross the synaptic cleft
• (C) Neurotransmitter is released only from the presynaptic membrane and receptors are only postsynaptic
• (D) Myelin blocks reverse flow

Q47. Which hormone is released in a fight-or-flight response, and what is one effect?

• (A) Insulin, lowering blood glucose
• (B) Adrenaline, increasing heart rate and blood glucose
• (C) ADH, increasing water reabsorption
• (D) Thyroxine, slowing metabolism

Q48. A woman is heterozygous for a recessive X-linked condition. What proportion of her sons will be affected?

• (A) One half
• (B) None
• (C) One quarter
• (D) All

Q49. In a test cross, an organism with the dominant phenotype is crossed with a homozygous recessive organism. What does a 1:1 offspring ratio indicate?

• (A) The parent is homozygous dominant
• (B) The gene is sex-linked
• (C) The gene shows codominance
• (D) The parent is heterozygous

Q50. Which inheritance pattern explains AB blood group in a child of parents with groups A and B?

• (A) Complete dominance
• (B) Recessive inheritance
• (C) Codominance
• (D) Sex linkage

Q51. Which statement best defines natural selection?

• (A) Organisms choose to mutate to suit the environment
• (B) Individuals with advantageous alleles survive and reproduce more successfully
• (C) All individuals in a population survive equally
• (D) Humans select the best individuals to breed

Q52. Stabilising selection is most likely when the environment is stable. What happens to the population?

• (A) Intermediate phenotypes are favoured and variation decreases
• (B) Extreme phenotypes increase
• (C) The mean phenotype shifts in one direction
• (D) The population splits into two species immediately

Q53. Which factor increases genetic variation in a population?

• (A) Inbreeding only
• (B) Stabilising selection alone
• (C) A population bottleneck alone
• (D) Mutation and meiosis, including crossing over

Q54. Which kingdom includes organisms with chitin cell walls that absorb nutrients?

• (A) Plantae
• (B) Animalia
• (C) Fungi
• (D) Protoctista

Q55. Why is genetic diversity important for conservation?

• (A) It guarantees larger body size
• (B) It increases the chance that some individuals survive environmental change
• (C) It prevents all mutations
• (D) It makes species easier to classify by appearance

Q56. Why are endemic species often prioritised in conservation assessments even when their total population seems stable?

• (A) Their entire range is small, so a single local disturbance can threaten all individuals
• (B) They are found on every continent
• (C) They migrate annually to new habitats
• (D) They were introduced by humans and spread rapidly

Q57. What is the first step in a PCR cycle?

• (A) Annealing of primers at a low temperature
• (B) Extension by Taq polymerase
• (C) Gel electrophoresis
• (D) Denaturation of DNA at about 95 degrees Celsius

Q58. Which enzyme seals a gene into a plasmid during genetic engineering?

• (A) Restriction endonuclease
• (B) Reverse transcriptase
• (C) DNA ligase
• (D) DNA polymerase only

Q59. Why is a marker gene included in a plasmid vector?

• (A) To make the plasmid larger
• (B) To identify cells that have taken up the plasmid
• (C) To prevent bacterial growth
• (D) To cut the plasmid open

Q60. Which application uses DNA profiling?

• (A) Identifying individuals from variable DNA regions
• (B) Producing insulin in bacteria only
• (C) Fixing nitrogen in plants
• (D) Cloning whole animals only