AP Biology Practice Test 15 – 60 Questions with Answers (College Board)

Q1. A water strider can walk on the surface of a pond. Which property of water makes this possible?

• (A) Low specific heat of water
• (B) The high density of ice
• (C) The nonpolar nature of water
• (D) Surface tension from hydrogen bonding between water molecules

Q2. Blood pH is maintained near 7.4 by the bicarbonate buffer system. If blood becomes too acidic, what does the buffer do?

• (A) Hydrogen ions are converted to oxygen
• (B) Bicarbonate ions combine with excess H⁺ to form carbonic acid
• (C) The buffer releases more H⁺ into the blood
• (D) The buffer stops all metabolic reactions

Q3. Which functional group is characteristic of carboxylic acids and amino acids?

• (A) The carboxyl group (-COOH)
• (B) The amino group only
• (C) The phosphate group
• (D) The methyl group

Q4. Starch is made of glucose units joined by alpha 1-4 linkages with alpha 1-6 branches. Which molecule has this structure?

• (A) Amylopectin, the branched component of starch
• (B) Cellulose
• (C) Chitin
• (D) Glycogen is the only branched polymer

Q5. A triglyceride is formed from glycerol and three fatty acids. What type of bond joins them?

• (A) A peptide bond
• (B) An ester bond, formed by dehydration synthesis
• (C) A glycosidic bond
• (D) A phosphodiester bond

Q6. The primary structure of a protein is its sequence of amino acids. What type of bond holds this sequence together?

• (A) Hydrogen bonds between bases
• (B) Peptide bonds
• (C) Disulfide bonds only
• (D) Ionic bonds between side chains

Q7. A nucleotide in RNA contains ribose, phosphate and uracil. How does this differ from a nucleotide in DNA?

• (A) DNA nucleotides contain no phosphate
• (B) RNA nucleotides contain no sugar
• (C) There is no difference between them
• (D) DNA nucleotides contain deoxyribose and thymine instead of ribose and uracil

Q8. Which statement about hydrogen bonds in water is correct?

• (A) They are weak attractions between the hydrogen of one water molecule and the oxygen of another
• (B) They are strong covalent bonds within a water molecule
• (C) They form only between water and nonpolar molecules
• (D) They are permanent bonds that never break

Q9. Which organelle contains hydrolytic enzymes that digest worn-out organelles?

• (A) The vacuole in animal cells
• (B) The chloroplast
• (C) The lysosome
• (D) The nucleolus

Q10. A cell has a nucleus, mitochondria and a Golgi apparatus but no chloroplasts. What can be concluded?

• (A) It is a prokaryotic cell
• (B) It is a eukaryotic cell, most likely an animal or fungal cell, not a photosynthetic plant cell
• (C) It must be a plant root cell with chloroplasts
• (D) It cannot carry out respiration

Q11. A red blood cell is placed in a hypertonic solution. What happens to it?

• (A) It swells and bursts
• (B) It shrinks as water leaves by osmosis
• (C) It stays the same size
• (D) It takes in salt by diffusion

Q12. Which transport protein uses ATP to pump sodium out of the cell and potassium into the cell?

• (A) An aquaporin
• (B) A glucose channel
• (C) The sodium-potassium pump
• (D) A facilitated diffusion carrier for oxygen

Q13. A cell membrane is treated with a drug that removes cholesterol. What is the expected effect at high temperature?

• (A) The membrane becomes rigid and impermeable
• (B) Transport proteins stop working immediately
• (C) The membrane dissolves completely
• (D) The membrane becomes more fluid and less stable

Q14. Which structure is shared by chloroplasts and mitochondria?

• (A) A nucleus
• (B) A double membrane and their own DNA
• (C) Thylakoids in both
• (D) A cell wall

Q15. A protein is synthesised on a free ribosome in the cytoplasm. Where is it most likely to function?

• (A) Outside the cell after secretion
• (B) In the cytoplasm or nucleus, not in the secretory pathway
• (C) In the lumen of the endoplasmic reticulum
• (D) In the Golgi apparatus

Q16. A cell is exposed to a toxin that blocks the formation of vesicles from the Golgi apparatus. Which process is most affected?

• (A) DNA replication
• (B) Glycolysis in the cytoplasm
• (C) Active transport of ions
• (D) Secretion of proteins and delivery of membrane lipids

Q17. Which molecule is oxidised and which is reduced in the overall equation for cellular respiration?

• (A) Glucose is oxidised and oxygen is reduced
• (B) Oxygen is oxidised and glucose is reduced
• (C) Water is oxidised and carbon dioxide is reduced
• (D) ATP is oxidised and ADP is reduced

Q18. An inhibitor blocks ATP synthase in mitochondria. What happens to the proton gradient?

• (A) It disappears immediately
• (B) It builds up because protons cannot flow back into the matrix
• (C) It reverses direction
• (D) It is used to make glucose

Q19. In the Calvin cycle, what is the role of Rubisco?

• (A) It splits water to release oxygen
• (B) It produces ATP by chemiosmosis
• (C) It transports electrons to NADP⁺
• (D) It catalyses the fixation of CO₂ onto RuBP

Q20. A plant is kept in darkness for 24 hours. Which process continues and which stops?

• (A) Photosynthesis continues; respiration stops
• (B) Both processes stop completely
• (C) Cellular respiration continues; photosynthesis stops
• (D) Both processes continue at the same rate

Q21. During glycolysis, NAD⁺ is reduced to NADH. What is the fate of this NADH in aerobic respiration?

• (A) It is converted to glucose
• (B) It is excreted from the cell
• (C) It is oxidised by the electron transport chain, donating electrons for ATP synthesis
• (D) It is used to fix carbon dioxide

Q22. A student measures oxygen consumption in germinating seeds at different temperatures. Oxygen consumption rises with temperature up to 40 degrees C, then falls. What best explains the fall?

• (A) Respiratory enzymes are denatured at high temperature
• (B) Seeds stop respiring because they run out of oxygen
• (C) Photosynthesis overtakes respiration
• (D) The seeds germinate faster at high temperature

Q23. Which of the following yields the most ATP per glucose molecule?

• (A) Aerobic respiration
• (B) Fermentation
• (C) Glycolysis alone
• (D) Anaerobic respiration in yeast

Q24. A hormone binds to a receptor on the surface of a target cell, but a neighbouring cell with no receptor does not respond. What does this demonstrate?

• (A) Cellular response depends on the presence of specific receptors
• (B) Hormones act on all cells equally
• (C) Receptors are not needed for signalling
• (D) The hormone enters every cell

Q25. In a pathway, a ligand activates a receptor, which activates a kinase, which activates another kinase. What is this sequence called?

• (A) A phosphorylation cascade
• (B) A feedback loop
• (C) A metabolic pathway
• (D) A transport chain

Q26. A cell in a developing embryo receives a signal that triggers apoptosis. What is the biological significance?

• (A) It removes cells in a controlled way to shape tissues, such as separating fingers
• (B) It kills the whole embryo
• (C) It causes uncontrolled growth
• (D) It prevents all cell division

Q27. Which phase of the cell cycle is the longest in most actively dividing cells?

• (A) M phase
• (B) Interphase, especially G₁
• (C) Cytokinesis
• (D) Anaphase

Q28. A cell has completed DNA replication but has not yet divided. How many chromosomes and chromatids does a human cell have at this stage?

• (A) 46 chromosomes and 92 chromatids
• (B) 92 chromosomes and 46 chromatids
• (C) 23 chromosomes and 46 chromatids
• (D) 46 chromosomes and 46 chromatids

Q29. Cancer cells often have mutations in genes that control the cell cycle. Which type of gene, when mutated, can act as an accelerator of division?

• (A) A tumour suppressor gene
• (B) A gene for ribosomal RNA
• (C) A proto-oncogene
• (D) A gene for a structural protein

Q30. A researcher adds a growth factor to cultured cells and observes increased division. What is the growth factor acting as?

• (A) An enzyme that digests the cell wall
• (B) A nutrient that provides ATP directly
• (C) A toxin that kills the cells
• (D) A signal that activates a cell division pathway

Q31. A trait is controlled by a single gene with two alleles, T (tall) and t (short). A cross Tt x tt produces 100 offspring. How many are expected to be tall?

• (A) 50
• (B) 25
• (C) 75
• (D) 100

Q32. In a family, a mother has blood type A and a father has blood type B. Their child has blood type O. What are the parents’ genotypes?

• (A) Both are homozygous
• (B) Mother is I^AI^A and father is I^BI^B
• (C) Both are heterozygous: I^Ai and I^Bi
• (D) Mother is ii and father is I^AI^B

Q33. A gene is located on the X chromosome. A father passes his X chromosome to which of his children?

• (A) Only his sons
• (B) All of his children
• (C) None of his children
• (D) Only his daughters

Q34. Which process during meiosis I is the main source of new combinations of maternal and paternal chromosomes?

• (A) Independent assortment of homologous pairs
• (B) Crossing over between sister chromatids only
• (C) DNA replication
• (D) Cytokinesis

Q35. A dihybrid test cross gives offspring in the ratio 1:1:1:1. What does this tell us about the two genes?

• (A) They are tightly linked
• (B) They assort independently (or are far apart on the same chromosome)
• (C) They are on the same chromosome with no crossing over
• (D) They are sex-linked

Q36. A couple are both carriers for cystic fibrosis, an autosomal recessive disorder. What is the probability that their child will be affected?

• (A) 1/2
• (B) 3/4
• (C) 1/4
• (D) 1/8

Q37. A chromosome segment is duplicated. What type of mutation is this?

• (A) A point mutation
• (B) A frameshift mutation
• (C) A chromosomal duplication
• (D) A deletion

Q38. During translation, the ribosome moves along the mRNA in which direction?

• (A) 3′ to 5′
• (B) From the 3′ end to the 5′ end only in eukaryotes
• (C) In both directions simultaneously
• (D) 5′ to 3′

Q39. A gene has the template strand 3′-AAA-5′. What is the codon in the mRNA?

• (A) 5′-AAA-3′
• (B) 5′-UUU-3′
• (C) 5′-TTT-3′
• (D) 3′-UUU-5′

Q40. Which enzyme is responsible for synthesising RNA from a DNA template?

• (A) RNA polymerase
• (B) DNA polymerase
• (C) Reverse transcriptase
• (D) DNA ligase

Q41. A cell is exposed to a signal that activates a transcription factor. What is the most direct result?

• (A) Decreased DNA replication
• (B) Increased protein degradation
• (C) Blocked translation of all mRNAs
• (D) Increased transcription of target genes

Q42. A mutation in an intron affects splicing, causing an exon to be skipped. What is the likely effect on the protein?

• (A) A shorter protein missing the amino acids coded by the skipped exon
• (B) No effect, because introns are never transcribed
• (C) A longer protein with extra amino acids
• (D) A protein with a single amino-acid change

Q43. A scientist uses a DNA probe to detect a specific gene on a Southern blot. What does the probe bind to?

• (A) Any protein in the sample
• (B) The RNA polymerase
• (C) A complementary DNA sequence
• (D) The gel matrix

Q44. In bacteria, the lac operon is an example of what type of gene regulation?

• (A) Regulation by alternative splicing only
• (B) Regulation by RNA interference only
• (C) Negative regulation by a repressor, with positive regulation by CAP
• (D) No regulation at all

Q45. A population of birds has a range of beak sizes. During a drought, only large, hard seeds are available, and birds with large beaks survive better. This is an example of

• (A) stabilising selection
• (B) disruptive selection
• (C) sexual selection
• (D) directional selection

Q46. A small population of animals is isolated on an island. Over generations, allele frequencies change randomly. This is an example of

• (A) natural selection
• (B) gene flow
• (C) genetic drift
• (D) mutation

Q47. Which of the following would violate Hardy-Weinberg equilibrium?

• (A) Random mating in a large population
• (B) No selection acting on the gene
• (C) Non-random mating, such as inbreeding
• (D) No migration

Q48. Two populations of the same species are separated by a mountain range. Over time, they become unable to interbreed. This is an example of

• (A) sympatric speciation
• (B) allopatric speciation
• (C) artificial selection
• (D) convergent evolution

Q49. A fossil is found in a rock layer dated to 300 million years ago. What can be inferred about the organism?

• (A) It is the direct ancestor of all modern species
• (B) It lived around 300 million years ago, assuming the dating is correct
• (C) It lived only 300 years ago
• (D) It evolved from modern species

Q50. Which structure is homologous to the human arm?

• (A) The wing of an insect
• (B) The wing of a bat
• (C) The fin of a shark
• (D) The leg of a spider

Q51. A phylogenetic tree shows a node where two lineages diverge. What does the node represent?

• (A) A species that is extinct
• (B) A mutation event
• (C) A common ancestor of the two lineages
• (D) A geographic barrier

Q52. Which evidence best supports the theory of evolution by natural selection?

• (A) A single fossil
• (B) The fact that all organisms look similar
• (C) The absence of variation in populations
• (D) The fossil record, comparative anatomy, molecular data and observed selection all converge on the same conclusion

Q53. A plant species is adapted to dry conditions with thick, waxy leaves. What is the main advantage of this adaptation?

• (A) Increased photosynthesis in the dark
• (B) Faster growth in wet soil
• (C) Attraction of more pollinators
• (D) Reduced water loss through the leaves

Q54. In a food chain, energy flows from producers to consumers. What happens to most of the energy at each step?

• (A) It is stored as biomass in the consumer
• (B) It is recycled back to producers
• (C) It is converted to light
• (D) It is lost as heat through respiration and in waste

Q55. A population of rabbits is introduced to an island with no predators. What is the most likely initial growth pattern?

• (A) Logistic growth at carrying capacity
• (B) Immediate extinction
• (C) Exponential growth
• (D) No growth

Q56. Which interaction benefits one species and harms the other?

• (A) Mutualism
• (B) Commensalism
• (C) Parasitism
• (D) Competition between unrelated species

Q57. A community has high species richness and evenness. What does this indicate about its biodiversity?

• (A) It has low biodiversity
• (B) It has only one species
• (C) It is dominated by a single species
• (D) It has high biodiversity

Q58. Nitrogen-fixing bacteria in root nodules convert nitrogen gas into ammonia. What is this process called?

• (A) Denitrification
• (B) Nitrogen fixation
• (C) Nitrification
• (D) Assimilation

Q59. A river is dammed, blocking fish migration. What is the most likely ecological consequence?

• (A) Fish populations increase immediately
• (B) The river ecosystem becomes more diverse
• (C) No effect on the fish
• (D) Fish populations decline because they cannot reach breeding grounds

Q60. Which of the following is a density-dependent factor that limits population growth?

• (A) Disease spreading more easily in crowded populations
• (B) A drought affecting all individuals equally
• (C) A volcanic eruption
• (D) A sudden frost