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AP Biology Full-length practice exam 1

60 questions

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Full-length practice exam 1

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Question 1

Ecologists studying a forest community notice that one species of tree (species A) grows quickly and shades other species. Over 50 years, species A is replaced by longer-lived tree species that are shade-tolerant. This process is best described as which of the following?

A.Primary succession, because the change begins with pioneer species colonizing bare substrateB.Secondary succession, where one community replaces another following a disturbanceC.Ecological succession toward a climax community, as early-successional species are replaced by late-successional speciesD.Competitive exclusion, where species A eliminates all other tree species from the community

Question 2

Why does the surface area to volume ratio limit cell size?

A.Larger cells have insufficient genetic material.B.As volume grows faster than surface area, exchange with the environment becomes inadequate.C.Gravity collapses larger cells.D.Larger cells run out of DNA.

Question 3

A food chain is: grass → rabbit → fox → eagle. If energy transfer efficiency between each trophic level is approximately 10%, and the grass (producers) fix 10,000 kcal of energy, how much energy is available to eagles?

A.1,000 kcalB.10 kcalC.100 kcalD.0.1 kcal

Question 4

A lipid-soluble steroid hormone passes through the plasma membrane and binds to an intracellular receptor. How does this differ from signaling through a membrane-bound receptor tyrosine kinase (RTK)?

A.Steroid hormones signal faster because they do not require a receptorB.Steroid signaling directly alters gene expression without a second messenger; RTK signaling uses a phosphorylation cascade in the cytoplasmC.RTK signaling requires the hormone to enter the nucleus, whereas steroid hormones act only at the plasma membraneD.Both pathways use cAMP as a second messenger to transmit their signals

Question 5

A scientist discovers a novel inhibitor that competes with NAD⁺ at the active site of isocitrate dehydrogenase in the Krebs cycle. If this inhibitor is added to a cell, which of the following best predicts the downstream effects?

A.NADH production increases and ATP yield per glucose risesB.Isocitrate accumulates, the Krebs cycle slows, and overall ATP yield from aerobic respiration decreasesC.The cell shifts entirely to glycolysis with no change in total ATP outputD.Pyruvate oxidation accelerates to compensate for reduced Krebs cycle activity

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Question 6

A ribosome is reading an mRNA strand and reaches the codon 5′-UAA-3′. What happens at this point in translation?

A.A tRNA carrying the amino acid tyrosine enters the A siteB.A release factor binds the A site, and the completed polypeptide is releasedC.The ribosome shifts back one nucleotide and re-reads the codonD.mRNA is degraded immediately to recycle the nucleotides

Question 7

Mycorrhizal fungi form associations with plant roots, providing phosphorus to the plant in exchange for carbohydrates. Which type of species interaction does this represent?

A.Commensalism (+/0): the fungus benefits and the plant is unaffectedB.Mutualism (+/+): both the fungus and the plant benefit from the associationC.Parasitism (+/−): the fungus benefits and the plant is harmedD.Amensalism (0/−): the fungus is unaffected and the plant is harmed

Question 8

Which of the following BEST illustrates evidence for common ancestry?

A.Bird wings and bat wings have similar bone structures despite different evolutionary origins.B.Whales, humans, and dogs all share the same set of bones in their forelimbs (homologous structures).C.Eyes evolved independently in vertebrates and cephalopods.D.Sharks and dolphins both have streamlined bodies for swimming.

Question 9

In a C₃ plant, the Calvin cycle consumes ATP and NADPH to fix CO₂. Under conditions of high light intensity but a sudden drop in CO₂ concentration (stomata close due to drought), which of the following would be expected?

A.RuBP levels decrease because the Calvin cycle continues to consume it at the same rateB.ATP and NADPH accumulate while RuBP builds up, and photorespiration may increaseC.The light reactions slow down because there is less demand for ATP and NADPHD.Glucose production increases because the Calvin cycle is no longer limited by light

Question 10

A group of ecologists introduces a new predator (wolves) into an ecosystem that previously had none. Over the following years, the deer population declines and vegetation in the riparian zone recovers. Beaver populations also increase as vegetation returns. The wolves did not directly interact with beavers. This is an example of which ecological phenomenon?

A.Bottom-up regulation, where primary producers drive changes in higher trophic levelsB.A trophic cascade, where predator addition triggers indirect changes through multiple trophic levelsC.Competitive exclusion between wolves and beavers for shared resourcesD.Character displacement between deer and beavers due to increased competition

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Question 11

An enzyme lowers the activation energy of a reaction. Which of the following best describes how the enzyme accomplishes this?

A.By adding energy to the reactants to push the reaction forwardB.By stabilizing the transition state, reducing the energy required to reach itC.By permanently bonding to the substrate and forming a new productD.By increasing the temperature of the reaction environment

Question 12

A mutation in a proto-oncogene converts it to an oncogene, causing the encoded growth factor receptor to be constitutively active (always 'on') regardless of whether a ligand is bound. Which of the following best explains why this promotes uncontrolled cell division?

A.The constitutively active receptor signals the cell to skip checkpoints by degrading p53B.The receptor continuously transmits growth and division signals even without a growth factor ligandC.The receptor migrates into the nucleus and directly activates cell cycle genesD.The receptor recruits additional copies of itself, increasing the number of functional receptors

Question 13

A signaling molecule binds a receptor on Cell A, triggering a phosphorylation cascade that activates a transcription factor. The transcription factor enters the nucleus and upregulates a gene encoding a secreted inhibitory protein. This protein then binds receptors on Cell A itself, reducing receptor activity. What type of signaling and feedback does this describe?

A.Paracrine signaling with positive feedbackB.Autocrine signaling with negative feedbackC.Endocrine signaling with negative feedbackD.Synaptic signaling with positive feedback

Question 14

A plant breeder crosses two true-breeding plants: one with red flowers and one with white flowers. All F₁ plants have pink flowers. When F₁ plants are self-fertilized, the F₂ ratio is 1 red : 2 pink : 1 white. This pattern of inheritance is best explained by which of the following?

A.Complete dominance of the red allele over the white alleleB.Incomplete dominance, where the heterozygote shows an intermediate phenotypeC.Codominance, where both alleles are fully expressed in the heterozygoteD.Epistasis between two separate genes controlling flower color

Question 15

In the light reactions, the electron transport chain between Photosystem II and Photosystem I pumps protons into the thylakoid lumen. What is the primary function of this proton gradient?

A.To reduce NADP⁺ to NADPH directlyB.To drive ATP synthesis through ATP synthase (chemiosmosis)C.To split water molecules and release oxygenD.To absorb additional photons for Photosystem I

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Question 16

If allele frequencies are not changing across generations, the population is in:

A.Genetic drift.B.Hardy-Weinberg equilibrium.C.Speciation.D.Stabilizing selection.

Question 17

During the Krebs cycle, one turn (per acetyl-CoA) produces which of the following sets of energy carriers?

A.2 NADH, 1 FADH₂, 1 ATP (or GTP)B.3 NADH, 1 FADH₂, 1 ATP (or GTP)C.3 NADH, 2 FADH₂, 2 ATPD.2 NADH, 2 FADH₂, 1 ATP (or GTP)

Question 18

Genetic drift has a stronger effect in:

A.Large populations.B.Small populations.C.Populations with high mutation rates.D.Populations under strong selection.

Question 19

A cell has a high ratio of AMP to ATP. This condition allosterically activates phosphofructokinase-1 (PFK-1), a key enzyme in glycolysis. Which of the following best explains why this regulation is adaptive?

A.It prevents overproduction of pyruvate when ATP is abundant, conserving glucoseB.It accelerates ATP production precisely when the cell's energy charge is low, restoring homeostasisC.It inhibits the Krebs cycle to prevent further energy expenditureD.It signals the cell to begin gluconeogenesis to produce more glucose from amino acids

Question 20

A woman is heterozygous for a balanced chromosomal translocation between chromosomes 14 and 21. During meiosis, if the translocated chromosome 21 and the normal chromosome 21 both segregate to the same cell, which of the following describes the result in the offspring if that cell is fertilized by a normal sperm?

A.The offspring has monosomy 21 and is unaffectedB.The offspring has an extra copy of chromosome 21 material (trisomy 21, Down syndrome)C.The offspring is a carrier of the translocation with no extra chromosome 21 materialD.The offspring has a deletion of chromosome 14 material

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Question 21

A researcher measures the carbon flux in a forest ecosystem. She finds that gross primary productivity (GPP) is 8,000 g C/m²/year and plant respiration is 3,500 g C/m²/year. She also measures that herbivores consume 1,000 g C/m²/year of plant biomass, and decomposers respire 2,500 g C/m²/year. Which of the following correctly calculates the net primary productivity (NPP) and identifies whether this ecosystem is a net carbon sink or source?

A.NPP = 4,500 g C/m²/year; the ecosystem is a carbon sink because NPP exceeds decomposer respirationB.NPP = 4,500 g C/m²/year; the ecosystem is a carbon source because total respiration exceeds GPPC.NPP = 3,000 g C/m²/year; the ecosystem is carbon neutral because NPP equals herbivore consumption plus decomposer respirationD.NPP = 8,000 g C/m²/year; plant respiration is not subtracted because it is already included in GPP

Question 22

A researcher adds an uncoupler to mitochondria. The uncoupler makes the inner mitochondrial membrane freely permeable to protons (H⁺). Which of the following would be the immediate result?

A.ATP synthesis increases because more protons flow through ATP synthaseB.The electron transport chain stops because it has no electron acceptorsC.The proton gradient collapses and ATP synthesis via oxidative phosphorylation haltsD.NADH accumulates because the Krebs cycle accelerates

Question 23

A species of bird exclusively eats large seeds. Another species of bird exclusively eats small seeds. When they are allopatric (living separately), each species occupies a range of seed sizes. When the two species are sympatric (living together), each species shifts its diet to the extremes (one eats only very large seeds; the other eats only very small seeds). This pattern is best explained by which of the following?

A.Competitive exclusion, where one species is eliminated from the shared habitatB.Character displacement, where competition drives evolutionary divergence in resource useC.Resource partitioning without evolutionary change, where the species simply exploit different microhabitatsD.Mutualism between the two species, where each benefits by avoiding competition over seeds

Question 24

Which of the following is the direct product of glycolysis when one molecule of glucose is completely processed?

A.2 acetyl-CoA, 2 ATP, 2 NADHB.2 pyruvate, 2 ATP (net), 2 NADHC.4 pyruvate, 4 ATP, 4 NADHD.2 pyruvate, 36 ATP, 2 NADH

Question 25

An invasive grass species is introduced to a prairie ecosystem and rapidly spreads, outcompeting native grasses. Native insect species that depend on native grasses for food and reproduction begin to decline. Which of the following best describes the mechanism by which the invasive grass is harming native insects?

A.The invasive grass directly predates on native insectsB.Habitat and food resource loss from competitive displacement of native plants causes indirect harm to dependent insectsC.The invasive grass produces toxins that directly kill native insectsD.Native insects voluntarily migrate away because they prefer habitats with lower plant diversity

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Question 26

Loss-of-function mutations in both copies of the Rb (retinoblastoma) gene lead to uncontrolled cell division. Based on the role of Rb protein in the cell cycle, explain which checkpoint is affected and how.

A.The G₂/M checkpoint is affected; loss of Rb allows cells to enter mitosis with unreplicated DNAB.The G₁/S checkpoint is affected; loss of Rb constitutively releases E2F, driving unscheduled S phase entryC.The spindle assembly checkpoint is affected; Rb normally prevents kinetochore assemblyD.All checkpoints are simultaneously inactivated because Rb coordinates all CDK-cyclin pairs

Question 27

A cell with a high rate of protein secretion would be expected to have an abundance of:

A.Lysosomes.B.Smooth ER.C.Rough ER and Golgi apparatus.D.Peroxisomes.

Question 28

Which functional group is most likely to ionize and donate a proton at physiological pH (~7.4)?

A.Hydroxyl (

- O H

).B.Methyl (

- C H_{3}

).C.Carboxyl (

- C O O H

).D.Amino (

- N H_{2}

Question 29

A scientist is studying a gene located on the X chromosome. She crosses a wild-type female (X^+ X^+) with a mutant male (X^m Y). She then crosses the F₁ females with wild-type males. What phenotypic ratio would be expected in F₂ males?

A.All F₂ males are wild-typeB.1/2 wild-type : 1/2 mutant malesC.All F₂ males are mutantD.3/4 wild-type : 1/4 mutant males

Question 30

During the light-dependent reactions of photosynthesis, which molecule directly receives the electrons energized by absorbed photons?

A.NADPHB.The primary electron acceptor within the photosystemC.ATP synthaseD.Carbon dioxide

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Question 31

In a Hardy-Weinberg population, the frequency of the recessive phenotype is $0.16$ . What is the frequency of the heterozygous genotype?

0.16

0.36

0.48

0.64

Question 32

If a freshwater plant is placed in a hypertonic salt solution, what will happen to its cells?

A.Cells will burst (lyse).B.Cells will swell with water.C.Cells will plasmolyze, with the membrane pulling away from the wall.D.Cells will remain unchanged due to the cell wall.

Question 33

A woman with blood type A (genotype I^A i) and a man with blood type B (genotype I^B i) have four children. Based on ABO blood type genetics, which of the following combinations of blood types is possible among their four children?

A.All four children have blood type ABB.Children with blood types A, B, AB, and O are all possibleC.Only blood types A and B are possible because both parents have dominant allelesD.Only blood types AB and O are possible in a 1:1 ratio

Question 34

Which level of protein structure is determined by hydrogen bonding between backbone amine and carbonyl groups?

A.Primary structure.B.Secondary structure.C.Tertiary structure.D.Quaternary structure.

Question 35

A researcher is studying two genes, A and B, in fruit flies. When the genes are on the same chromosome, they tend to be inherited together more often than expected under independent assortment. A cross yields 42% AB, 42% ab, 8% Ab, and 8% aB gametes. Which of the following best explains these results?

A.The genes assort independently because crossing over occurs between them at a frequency of exactly 50%B.The genes are linked and 16% recombination frequency indicates they are 16 cM apartC.The genes are on different chromosomes and crossing over between them produces the recombinant gametesD.Gene B is epistatic to gene A, suppressing its expression in recombinant classes

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Question 36

During meiosis, homologous chromosomes separate from each other during which phase?

A.Meiosis I, anaphase IB.Meiosis II, anaphase IIC.Meiosis I, prophase ID.Meiosis II, metaphase II

Question 37

A buffer maintains stable pH by:

A.Reacting with both added acids and bases.B.Preventing all chemical reactions in solution.C.Producing equal amounts of H

^{+}

and OH

^{-}

.D.Neutralizing only acidic solutions.

Question 38

Which of the following describes a density-independent factor that limits population growth?

A.Predation rate increases as prey population density risesB.A severe drought that kills a fixed proportion of organisms regardless of population sizeC.Disease transmission rises as individuals are crowded togetherD.Intraspecific competition for food intensifies as population density increases

Question 39

Epinephrine binds to a G protein-coupled receptor (GPCR) on a liver cell, leading to glycogen breakdown. Which of the following correctly describes the role of cAMP in this pathway?

A.cAMP acts as the first messenger that initially binds the receptorB.cAMP is a second messenger that activates protein kinase A, amplifying the signalC.cAMP directly breaks down glycogen by acting as a phosphorylase enzymeD.cAMP inhibits adenylyl cyclase to provide negative feedback immediately

Question 40

Cilia and flagella in eukaryotes share which structural feature?

A.Both are made of actin microfilaments.B.Both have a 9+2 arrangement of microtubules.C.Both are extensions of the cell wall.D.Both rotate using a proton motive force.

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Question 41

In a cross between two individuals who both carry recessive alleles for cystic fibrosis (Cc × Cc), what is the probability that their first three children are ALL unaffected?

(\frac{1}{4})^{3} = \frac{1}{64}

(\frac{3}{4})^{3} = \frac{27}{64}

\frac{3}{4}

(\frac{1}{2})^{3} = \frac{1}{8}

Question 42

A researcher uses FRET (fluorescence resonance energy transfer) to show that a receptor dimerizes upon ligand binding. They then show that a truncated receptor that cannot dimerize fails to activate downstream targets even in the presence of ligand. Which of the following mechanisms is most directly disrupted by preventing dimerization?

A.Ligand binding, because dimerization is required for the receptor to adopt a ligand-binding conformationB.Receptor autophosphorylation and kinase activation, because transphosphorylation between dimerized subunits is required to activate the kinase domainC.Second messenger release, because dimerization directly synthesizes cAMPD.Receptor endocytosis, because dimerized receptors cannot be internalized

Question 43

Which of the following best describes a ligand in cell signaling?

A.A membrane protein that spans the lipid bilayer and detects signalsB.A signaling molecule that binds specifically to a receptorC.An intracellular enzyme that amplifies a signal cascadeD.A protein released at the synapse to change membrane potential

Question 44

Which of the following correctly describes the role of decomposers in a terrestrial ecosystem?

A.They convert sunlight energy into chemical energy stored in organic moleculesB.They break down dead organic matter and return nutrients to the abiotic environmentC.They consume primary producers and transfer energy to higher trophic levelsD.They fix atmospheric nitrogen into ammonium for use by plants

Question 45

CRISPR-Cas9 is used to introduce a double-strand break in a gene. In most mammalian cells, the break is repaired by non-homologous end joining (NHEJ). Which of the following best describes a likely molecular outcome of NHEJ repair?

A.The break is repaired precisely using the sister chromatid as a template, restoring the original sequenceB.Small insertions or deletions (indels) are introduced at the cut site, often causing frameshift mutationsC.The entire chromosome containing the cut is degraded to prevent genome instabilityD.The Cas9 protein becomes integrated into the genome at the cut site

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Question 46

Scientists use bacterial transformation to introduce a gene of interest into E. coli using a plasmid vector. The plasmid contains an ampicillin resistance gene (amp^R) and a lacZ gene (which turns colonies blue on X-gal plates) into which the gene of interest has been inserted. If transformation is successful and the insert disrupts lacZ, which of the following correctly describes the transformed bacteria?

A.Ampicillin sensitive, white colonies on X-gal platesB.Ampicillin resistant, white colonies on X-gal platesC.Ampicillin resistant, blue colonies on X-gal platesD.Ampicillin sensitive, blue colonies on X-gal plates

Question 47

Polymerase chain reaction (PCR) requires a template, primers, dNTPs, and a heat-stable DNA polymerase (Taq). Which of the following is the correct sequence of steps in one PCR cycle?

A.Annealing → Denaturation → ExtensionB.Denaturation → Annealing → ExtensionC.Extension → Denaturation → AnnealingD.Denaturation → Extension → Annealing

Question 48

During DNA replication, which enzyme synthesizes new DNA strands by adding nucleotides complementary to the template strand?

A.HelicaseB.DNA polymeraseC.PrimaseD.Ligase

Question 49

A particular organism lives in an environment with abundant light and CO₂ but very little inorganic phosphate (Pi). Which of the following processes would be most severely limited?

A.Carbon fixation by RuBisCOB.ATP synthesis and regeneration of RuBP in the Calvin cycleC.Absorption of photons by chlorophyllD.Splitting of water molecules in Photosystem II

Question 50

Which structural feature distinguishes prokaryotic cells from eukaryotic cells?

A.Prokaryotes lack a membrane-bound nucleus.B.Prokaryotes lack ribosomes.C.Prokaryotes lack DNA.D.Prokaryotes lack a cell membrane.

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Question 51

Which of the following is an example of a hydrophobic interaction?

A.Salt dissolving in water.B.Phospholipid tails clustering inward in a bilayer.C.Hydrogen bonding between water and DNA bases.D.Ionic attraction between Na

^{+}

and Cl

^{-}

Question 52

Two genes, R and S, are located 20 cM apart on chromosome 3. An individual with genotype RS/rs (in coupling) mates with an rs/rs individual. A student predicts the offspring will show a 1:1 ratio of parental to recombinant phenotypes. Is the student correct, and what is the actual expected ratio of all four phenotypic classes?

A.Correct; 50% parental (RS and rs) and 50% recombinant (Rs and rS)B.Incorrect; expected ratio is 40% RS : 40% rs : 10% Rs : 10% rSC.Incorrect; all offspring are parental (RS or rs) because genes on the same chromosome never recombineD.Incorrect; expected ratio is 25% RS : 25% rs : 25% Rs : 25% rS because genes >10 cM apart assort randomly

Question 53

Which of the following is NOT one of Darwin's four conditions for natural selection?

A.Variation among individuals.B.Heritability of traits.C.Differential reproductive success.D.An external designer that selects favorable traits.

Question 54

Which transport mechanism requires both a protein channel and ATP?

A.Simple diffusion.B.Facilitated diffusion.C.Active transport.D.Osmosis.

Question 55

Two populations of finches are separated by a mountain range. Over thousands of generations they evolve different beak shapes and can no longer interbreed. This is an example of:

A.Sympatric speciation.B.Allopatric speciation.C.Polyploidy speciation.D.Convergent evolution.

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Question 56

Which of the following best explains why water is described as a polar molecule?

A.Water has equal numbers of hydrogen and oxygen atoms.B.Oxygen is more electronegative than hydrogen, creating an uneven distribution of charge.C.Water has a linear molecular geometry.D.The hydrogen atoms are double-bonded to oxygen.

Question 57

Transcription factors bind to specific DNA sequences in the promoter or enhancer regions of eukaryotic genes. A mutation abolishes the binding of an activator transcription factor to an enhancer 10,000 bp upstream of the gene's transcription start site. Which of the following best predicts the effect on gene expression?

A.No effect, because enhancers must be adjacent to the promoter to functionB.Gene expression decreases or is abolished because the activator can no longer stimulate RNA polymerase II recruitmentC.Gene expression increases because the enhancer normally inhibits the geneD.The mutation affects only transcription in embryonic cells because enhancers are only active during development

Question 58

In pea plants, round seed shape (R) is dominant over wrinkled (r), and yellow seed color (Y) is dominant over green (y). Two plants both heterozygous for both traits are crossed. What fraction of the offspring is expected to have round yellow seeds?

\frac{1}{4}

\frac{9}{16}

\frac{3}{16}

\frac{1}{2}

Question 59

A polysaccharide and a polypeptide both contain monomers linked by which type of reaction?

A.Hydrolysis reaction (water added).B.Dehydration synthesis (water removed).C.Oxidation reaction.D.Reduction reaction.

Question 60

Saturated and unsaturated fatty acids differ in:

A.Whether the carbon chain has any double bonds.B.Whether they contain glycerol.C.Whether they are esters or acids.D.Number of carboxyl groups.

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