A-Level Biology Practice Test 11 – 60 Questions with Answers (Cambridge 9700)

Q1. Which statement about ribosomes is correct?

• (A) Eukaryotic ribosomes are 70S and are found only in mitochondria
• (B) Prokaryotic ribosomes are 80S and are larger than eukaryotic ribosomes
• (C) Prokaryotic ribosomes are 70S and are smaller than eukaryotic 80S ribosomes
• (D) Ribosomes in the rough endoplasmic reticulum are 70S in all eukaryotes

Q2. Which sequence correctly describes the route of a secreted protein through a cell?

• (A) Rough endoplasmic reticulum, vesicle, Golgi apparatus, vesicle, cell surface membrane
• (B) Golgi apparatus, rough endoplasmic reticulum, vesicle, cell surface membrane
• (C) Smooth endoplasmic reticulum, Golgi apparatus, rough endoplasmic reticulum, cell surface membrane
• (D) Rough endoplasmic reticulum, Golgi apparatus, nucleus, vesicle, cell surface membrane

Q3. In an electron micrograph, a mitochondrion is 40 mm long. Its actual length is 4 micrometres. What is the magnification of the micrograph?

• (A) x10
• (B) x100
• (C) x1000
• (D) x10000

Q4. Which property of water depends directly on hydrogen bonding between its molecules?

• (A) Its high specific heat capacity, which buffers temperature change
• (B) Its low boiling point compared with other liquids
• (C) Its inability to dissolve ionic substances
• (D) Its low surface tension at an air-water interface

Q5. A triglyceride is formed from glycerol and three fatty acids. Which statement about this reaction is correct?

• (A) Three water molecules are released as three ester bonds form
• (B) Three water molecules are used up as three peptide bonds form
• (C) One water molecule is released as one glycosidic bond forms
• (D) No water is involved because the reaction is a hydrolysis

Q6. Which feature gives collagen its high tensile strength?

• (A) A triple helix of polypeptides held together by hydrogen bonds, with glycine at every third position
• (B) A single alpha-helix stabilised by disulfide bridges between every residue
• (C) Branched chains of glucose joined by 1,6 glycosidic bonds
• (D) A globular shape with a hydrophobic core that dissolves in water

Q7. Which statement best describes the induced fit model of enzyme action?

• (A) The enzyme changes shape slightly as the substrate binds, improving the fit and stressing bonds in the substrate
• (B) The active site is rigid and only a substrate of exactly the right shape can enter it
• (C) The substrate changes the shape of the whole enzyme permanently
• (D) The active site and substrate both remain unchanged throughout the reaction

Q8. A competitive inhibitor is added to an enzyme-catalysed reaction. What effect does it have on the kinetic constants?

• (A) Vmax stays the same and Km increases
• (B) Vmax decreases and Km stays the same
• (C) Both Vmax and Km decrease
• (D) Both Vmax and Km increase

Q9. Why does an extreme change in pH reduce the rate of an enzyme-catalysed reaction?

• (A) It changes the charges on amino acid side chains, disrupting bonds that hold the tertiary structure and active site shape
• (B) It breaks the peptide bonds of the substrate
• (C) It increases the kinetic energy of the enzyme until it evaporates
• (D) It converts the enzyme into a competitive inhibitor

Q10. Which statement about the fluid mosaic model is correct?

• (A) Phospholipids form a bilayer in which proteins float, and cholesterol helps regulate fluidity
• (B) The membrane is a rigid double layer of protein with phospholipids embedded in it
• (C) Glycolipids form the main structural layer and phospholipids act only as receptors
• (D) The bilayer is made of cholesterol molecules with proteins on the outside only

Q11. Which process requires ATP directly?

• (A) Facilitated diffusion of glucose down its concentration gradient
• (B) Osmosis of water through aquaporins
• (C) Active transport of ions against their concentration gradient
• (D) Simple diffusion of oxygen across a membrane

Q12. In the sodium-potassium pump, what happens in each cycle?

• (A) Three sodium ions are pumped out and two potassium ions are pumped in, using one ATP
• (B) Two sodium ions are pumped out and three potassium ions are pumped in
• (C) Three potassium ions are pumped out and two sodium ions are pumped in, using one ATP
• (D) Equal numbers of sodium and potassium ions move in the same direction

Q13. During which phase of the cell cycle does DNA replication occur, and what is its immediate result?

• (A) S phase of interphase, when each chromosome consists of two identical sister chromatids
• (B) Prophase, when chromosomes condense
• (C) G1 phase, when the cell grows and organelles are made
• (D) Cytokinesis, when the cytoplasm divides

Q14. Which event occurs during anaphase of mitosis?

• (A) Sister chromatids are pulled apart to opposite poles as centromeres divide
• (B) Chromosomes line up on the equator of the spindle
• (C) Nuclear envelopes reform around two sets of chromosomes
• (D) Homologous chromosomes pair up and exchange segments

Q15. Why is mitosis important in the growth of a multicellular organism?

• (A) It produces genetically varied gametes for sexual reproduction
• (B) It halves the chromosome number in body cells
• (C) It produces genetically identical cells, preserving the chromosome number as tissues grow
• (D) It replaces damaged cells with cells containing new combinations of alleles

Q16. The Meselson and Stahl experiment supported semi-conservative replication. What result was observed after one generation in nitrogen-14?

• (A) All DNA was heavy, containing only nitrogen-15
• (B) Half the DNA was heavy and half was light, with no intermediate band
• (C) All DNA was of intermediate density, with one old and one new strand
• (D) All DNA was light, containing only nitrogen-14

Q17. During transcription, which statement is correct?

• (A) DNA polymerase copies both strands of DNA into mRNA
• (B) Ribosomes join amino acids directly to the DNA template
• (C) RNA polymerase binds to a promoter and copies the template strand into pre-mRNA
• (D) The coding strand is copied and introns are translated

Q18. Which feature of the genetic code is shown when two different codons specify the same amino acid?

• (A) The code is universal
• (B) The code is non-overlapping
• (C) The code is degenerate
• (D) The code is punctuated by start codons only

Q19. Which statement best explains the cohesion-tension theory of water movement in xylem?

• (A) Root pressure pushes water up, and adhesion alone holds the column together
• (B) Active transport in leaves pumps water down the xylem by osmosis
• (C) Transpiration from leaves creates tension that pulls a continuous column of water up, held together by cohesion between water molecules
• (D) Capillary action in root hairs is the only force moving water to the leaves

Q20. Which structural feature allows a xylem vessel to withstand the tension of transpiration pull without collapsing?

• (A) A living cytoplasm that actively pumps water upward
• (B) Sieve plates that distribute pressure evenly
• (C) Thick lignified walls surrounding a hollow, dead lumen
• (D) Chloroplasts that supply ATP for water uptake

Q21. In translocation, how is sucrose loaded into sieve tubes at a source?

• (A) Sucrose diffuses passively from mesophyll cells into the xylem
• (B) Sieve tubes actively pump water into the phloem by osmosis alone
• (C) Companion cells use ATP to pump hydrogen ions out, and sucrose enters with hydrogen ions by cotransport before moving into sieve tubes
• (D) Sucrose is carried upward in the transpiration stream

Q22. Which statement about the mammalian double circulation is correct?

• (A) Blood passes through the heart once per complete circuit
• (B) Oxygenated and deoxygenated blood mix freely in the left ventricle
• (C) The pulmonary circulation carries blood to the lungs and the systemic circulation carries blood to the rest of the body
• (D) The right ventricle pumps blood to the whole body at high pressure

Q23. The Bohr shift describes how haemoglobin affinity for oxygen changes in respiring tissues. What causes it?

• (A) A rise in pH from carbon dioxide removal, which increases affinity
• (B) A rise in temperature that increases the oxygen content of blood
• (C) A fall in pH as carbon dioxide forms carbonic acid, which reduces affinity and releases oxygen
• (D) A fall in carbon dioxide concentration that makes haemoglobin bind oxygen more tightly

Q24. At the venule end of a capillary, why does most tissue fluid re-enter the capillary rather than remain in the tissues?

• (A) Lymph vessels actively pump fluid back into the blood
• (B) Hydrostatic pressure rises sharply at the venule end
• (C) The inward pull of plasma proteins exceeds the lower hydrostatic pressure, drawing water back by osmosis
• (D) Capillary walls become impermeable to water at the venule end

Q25. Which adaptation of alveoli most directly increases the rate of gas exchange by diffusion?

• (A) Their thick muscular walls that contract during breathing
• (B) Their connection to the trachea by cartilage rings
• (C) Their production of mucus that traps dust particles
• (D) Their large total surface area combined with walls one cell thick

Q26. Why is countercurrent flow in fish gills more efficient than parallel flow?

• (A) It allows blood and water to reach the same oxygen concentration at the start of the lamella
• (B) It pumps oxygen actively into the blood against its gradient
• (C) It stops water from flowing over the gills altogether
• (D) It maintains a concentration gradient along the whole length of the lamella, so oxygen diffuses in continuously

Q27. In insects, how does oxygen reach respiring muscle cells?

• (A) It is carried in the blood to the cells by haemoglobin
• (B) It is pumped through the gut by peristalsis
• (C) It dissolves in tissue fluid after crossing a lung surface
• (D) It diffuses through spiracles and tracheae directly to tracheoles close to the cells

Q28. HIV is classified as a retrovirus. What does this mean for its replication?

• (A) It carries DNA that is copied directly by host ribosomes
• (B) It forms spores that survive in the environment for years
• (C) It reproduces by binary fission outside host cells
• (D) It carries RNA that is converted to DNA by reverse transcriptase and inserted into the host genome

Q29. How does the cholera toxin cause the main symptom of cholera?

• (A) It destroys red blood cells, causing anaemia
• (B) It prevents absorption of glucose in the small intestine only
• (C) It blocks nerve impulses to the gut wall, preventing peristalsis
• (D) It causes chloride ions and water to be secreted into the gut lumen, producing severe watery diarrhoea

Q30. A patient with tuberculosis is advised to complete a six-month course of antibiotics even after symptoms improve. Why is completing the course important?

• (A) It kills a virus spread through contaminated water
• (B) It prevents spread by mosquitoes
• (C) It kills a fungus that grows only on the skin
• (D) It kills slow-growing Mycobacterium tuberculosis, including persistent bacteria, so resistant survivors are less likely to remain

Q31. Which sequence correctly describes phagocytosis of a bacterium?

• (A) Antibodies are produced, then the bacterium is engulfed by a lymphocyte
• (B) Memory cells divide and release histamine to kill the bacterium
• (C) The bacterium is coated with complement, then destroyed by plasma cells
• (D) The phagocyte recognises the bacterium, engulfs it into a phagosome, lysosomes fuse with it, and enzymes digest it

Q32. Which statement distinguishes the cell-mediated response from the humoral response?

• (A) The humoral response uses T killer cells to destroy infected body cells, while the cell-mediated response uses antibodies
• (B) The humoral response acts only against fungi, while the cell-mediated response acts only against bacteria
• (C) Both responses are carried out only by phagocytes
• (D) The cell-mediated response involves T lymphocytes destroying infected cells, while the humoral response involves B lymphocytes producing antibodies

Q33. Why is the secondary immune response faster and stronger than the primary response?

• (A) The pathogen is weaker on second exposure
• (B) The skin becomes impermeable after the first infection
• (C) Phagocytes permanently retain antibodies from the first infection
• (D) Memory B and T cells from the first exposure divide rapidly and produce a larger, faster antibody response

Q34. Which statement about ATP is correct?

• (A) ATP is a long-term energy store made only in photosynthesis
• (B) ATP stores energy in its ribose sugar, which is broken down in respiration
• (C) ATP is synthesised by breaking down ADP with energy from light only
• (D) Hydrolysis of ATP to ADP and inorganic phosphate releases energy that can drive endergonic reactions

Q35. In the link reaction, pyruvate is converted to acetyl coenzyme A. What else happens?

• (A) Carbon dioxide is released and NAD is reduced to NADH
• (B) Oxygen is used up and water is formed
• (C) Glucose is regenerated and ATP is hydrolysed
• (D) Acetyl coenzyme A is oxidised directly to carbon dioxide and water

Q36. Which statement best describes chemiosmosis in oxidative phosphorylation?

• (A) Electrons pass directly from NADH to ATP synthase, forming ATP
• (B) Hydrogen ions are pumped into the mitochondrial matrix, then diffuse out through ATP synthase
• (C) Hydrogen ions accumulate in the intermembrane space, and their flow back through ATP synthase drives ATP synthesis
• (D) Oxygen accepts electrons in the matrix and pumps protons across the outer membrane

Q37. A yeast culture respires anaerobically. Which products and net ATP yield per glucose molecule are expected?

• (A) Lactic acid only, with a net yield of 2 ATP
• (B) Ethanol and water, with a net yield of 36 ATP
• (C) Carbon dioxide and water, with a net yield of 38 ATP
• (D) Ethanol and carbon dioxide, with a net yield of 2 ATP

Q38. What is produced directly by photolysis of water in the light-dependent stage?

• (A) Glucose, oxygen and ATP
• (B) Glycerate 3-phosphate and RuBP
• (C) Carbon dioxide, reduced NADP and ADP
• (D) Oxygen, protons and electrons

Q39. In the Calvin cycle, carbon dioxide combines with RuBP. What happens next in the cycle?

• (A) The six-carbon product splits into two molecules of glycerate 3-phosphate, which are reduced to triose phosphate using ATP and reduced NADP
• (B) The product is oxidised directly to glucose without any ATP input
• (C) RuBP is converted to oxygen and water
• (D) Glycerate 3-phosphate is used to make chlorophyll

Q40. At low light intensity, increasing the carbon dioxide concentration has little effect on the rate of photosynthesis. Why?

• (A) Carbon dioxide is toxic at low light intensity
• (B) Chlorophyll is destroyed when carbon dioxide rises
• (C) The stomata close completely in dim light, preventing all gas exchange
• (D) Light intensity is the limiting factor, so the light-dependent stage cannot supply enough ATP and reduced NADP

Q41. Why do leaves appear green?

• (A) Chlorophyll absorbs green light most strongly and reflects red light
• (B) The leaf epidermis filters out red and blue light
• (C) Carotenoids reflect all wavelengths except green
• (D) Chlorophyll absorbs mainly red and blue light and reflects green light

Q42. Which statement describes negative feedback in the control of water potential of the blood?

• (A) A rise in water potential stimulates ADH release, which increases water reabsorption until water potential falls
• (B) A fall in water potential is detected by osmoreceptors, ADH release increases, water reabsorption rises, and water potential returns towards normal
• (C) ADH release always increases, regardless of blood water potential
• (D) A fall in water potential inhibits ADH, causing more water to be lost in urine

Q43. During ultrafiltration in the glomerulus, which substances are prevented from entering the Bowman’s capsule?

• (A) Glucose, amino acids and salts
• (B) Urea and water
• (C) Blood cells and most plasma proteins
• (D) Small ions and vitamins

Q44. After a meal, blood glucose concentration rises. Which hormonal sequence restores it?

• (A) Glucagon stimulates glycogenolysis in the liver, raising blood glucose further
• (B) Insulin stimulates uptake of glucose by cells and conversion of glucose to glycogen in the liver and muscles
• (C) Adrenaline inhibits insulin release and blocks glucose uptake
• (D) Insulin stimulates breakdown of glycogen to glucose in the liver

Q45. On a cold day, a mammal’s skin feels pale and its core temperature stays stable. Which mechanism best explains the pale skin?

• (A) Vasodilation of arterioles supplying skin capillaries
• (B) Vasoconstriction of arterioles supplying skin capillaries, reducing warm blood flow near the surface
• (C) Sweating to increase evaporative heat loss
• (D) Relaxation of erector pili muscles so hairs lie flat

Q46. What maintains the resting potential of a neurone at about -70 mV?

• (A) Sodium ions diffuse freely into the axon while potassium ions are pumped out
• (B) The sodium-potassium pump exports sodium and imports potassium, and potassium leaks out through channels, leaving the inside negative
• (C) Chloride ions are actively pumped into the axon by ATP synthase
• (D) The myelin sheath blocks all ion movement across the membrane

Q47. Which sequence describes transmission across a cholinergic synapse?

• (A) Action potential arrives, calcium ions enter, vesicles release acetylcholine, acetylcholine binds receptors on the postsynaptic membrane
• (B) Acetylcholine is released first, then calcium ions enter the presynaptic neurone
• (C) The action potential jumps directly across the synaptic cleft
• (D) Vesicles fuse with the postsynaptic membrane and release sodium ions

Q48. Which sequence correctly lists the components of a simple reflex arc?

• (A) Effector, motor neurone, relay neurone, sensory neurone, receptor
• (B) Receptor, sensory neurone, relay neurone, motor neurone, effector
• (C) Receptor, motor neurone, sensory neurone, relay neurone, effector
• (D) Sensory neurone, receptor, motor neurone, effector, relay neurone

Q49. In a dihybrid cross between two individuals heterozygous for two unlinked genes, what phenotypic ratio is expected in the offspring?

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

Q50. Haemophilia is caused by a recessive allele on the X chromosome. Why are males more likely than females to show the condition?

• (A) Males have two X chromosomes, so they always inherit the allele twice
• (B) Males have only one X chromosome, so a single recessive allele is expressed
• (C) The allele is dominant in males and recessive in females
• (D) Females cannot inherit the allele from their fathers

Q51. A person with blood group AB has both A and B antigens on their red blood cells. What type of inheritance does this illustrate?

• (A) Complete dominance
• (B) Codominance
• (C) Incomplete dominance
• (D) Polygenic inheritance

Q52. Which sequence best summarises natural selection?

• (A) Mutation creates variation, individuals better adapted to the environment survive and reproduce more, and allele frequencies in the population change
• (B) The environment directly changes the genes of individuals during their lifetimes, and these changes are inherited
• (C) All individuals reproduce equally, but the strongest survive longest
• (D) Selection acts on genotypes directly, without any effect on phenotypes

Q53. A bacterial population is exposed to an antibiotic. Resistant bacteria become common. Which explanation is correct?

• (A) The antibiotic caused mutations for resistance in the bacteria it touched
• (B) Resistant variants were already present, and the antibiotic selected for them by killing susceptible bacteria
• (C) All bacteria acquired resistance by learning to avoid the antibiotic
• (D) The antibiotic changed the bacterial species into a new genus

Q54. Which condition is essential for allopatric speciation to occur?

• (A) Two populations must live in the same area and interbreed freely
• (B) A geographical barrier must separate populations so gene flow stops and they diverge
• (C) Individuals must acquire identical mutations at the same time
• (D) The populations must have identical selection pressures

Q55. In the three-domain system, which domains contain prokaryotic organisms?

• (A) Eukarya and Archaea
• (B) Bacteria and Archaea
• (C) Bacteria and Eukarya
• (D) Archaea only

Q56. A community has a high Simpson’s index of diversity, D. What does this indicate?

• (A) One species dominates the community and species richness is low
• (B) The community has many species with fairly even abundances
• (C) The community contains only a few individuals in total
• (D) The community has high genetic diversity within a single species only

Q57. Which of these is an example of in situ conservation?

• (A) Storing seeds of a rare plant in a seed bank away from its habitat
• (B) Protecting a coral reef in a marine reserve where it naturally occurs
• (C) Breeding an endangered animal in a zoo
• (D) Growing a rare plant in a botanical garden

Q58. Which sequence correctly describes one cycle of the polymerase chain reaction?

• (A) Extension, annealing, denaturation
• (B) Denaturation at high temperature, annealing of primers, extension by Taq polymerase
• (C) Annealing, ligation, translation
• (D) Denaturation, transcription, gel electrophoresis

Q59. In gel electrophoresis of DNA fragments, why do smaller fragments travel further than larger ones?

• (A) DNA is positively charged and moves towards the negative electrode
• (B) DNA is negatively charged and moves towards the positive electrode, with smaller fragments passing through the gel pores more easily
• (C) Larger fragments are attracted to the wells and do not move
• (D) The gel actively pumps small fragments forward

Q60. To make recombinant DNA, a gene is inserted into a plasmid. Which enzymes are needed?

• (A) DNA polymerase to cut the plasmid and ligase to copy the gene
• (B) A restriction enzyme to cut both DNA molecules and DNA ligase to join them
• (C) Reverse transcriptase to cut the plasmid and Taq polymerase to seal it
• (D) Helicase to join the fragments and protease to remove introns