Practice Test for AP Biology - 3

Question 1

A researcher adds a molecule that is structurally similar to the substrate of an enzyme. The molecule binds to the active site and prevents substrate binding. When substrate concentration is significantly increased, enzyme activity returns to near-normal levels. Which type of inhibition is described?

Accepted Answer

Competitive inhibition, because the inhibitor occupies the active site and can be displaced by excess substrate

Answer

Non-competitive inhibition, because the inhibitor binds an allosteric site and is overcome by substrate

Answer

Allosteric activation, because substrate binding at an alternate site increases enzyme affinity

Answer

Feedback inhibition, because the product of the reaction blocks its own synthesis

Question 2

A researcher tests the activity of the enzyme catalase at temperatures of 10°C, 20°C, 37°C, 50°C, and 70°C by measuring the rate of oxygen gas production. Which of the following correctly identifies the dependent variable in this experiment?

Accepted Answer

The rate of oxygen gas production

Answer

The temperature at which each trial is conducted

Answer

The concentration of catalase used in each trial

Answer

The pH of the reaction buffer maintained across all trials

Question 3

A transmembrane protein spans the full width of the phospholipid bilayer. Which property of the protein's amino acid residues is most directly responsible for anchoring the protein within the hydrophobic core of the membrane?

Accepted Answer

Nonpolar R groups that interact favorably with the fatty acid tails of phospholipids in the hydrophobic core

Answer

Positively charged R groups that form ionic interactions with the negatively charged phosphate heads

Answer

Polar R groups that form hydrogen bonds with water molecules surrounding the membrane

Answer

Carboxyl groups that form permanent covalent bonds with the glycerol backbone of membrane lipids

Question 4

Water molecules are able to travel up the narrow vessels of a plant stem against gravity. This process depends primarily on which property of water?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding, which allow water to form continuous columns under tension

Answer

High specific heat capacity, which buffers temperature changes in the water column

Answer

Universal solvent behavior, which dissolves minerals needed for upward transport

Answer

Water's role as a reactant in hydrolysis reactions that release energy for transport

Question 5

A red blood cell is placed in a solution and begins to swell and eventually bursts (lyses). Which of the following correctly describes the tonicity of the external solution relative to the cell's cytoplasm?

Accepted Answer

The external solution is hypotonic, causing net movement of water into the cell by osmosis

Answer

The external solution is hypertonic, causing net movement of water out of the cell by osmosis

Answer

The external solution is isotonic, resulting in no net movement of water across the membrane

Answer

The external solution is hypertonic, causing water to actively enter the cell via aquaporins

Question 6

A researcher constructs three agar cubes of side lengths 1 cm, 2 cm, and 3 cm, soaks them in NaOH indicator solution, then cuts them open to measure diffusion depth after equal time intervals. The 1 cm cube shows complete diffusion throughout, while the 3 cm cube shows minimal diffusion at its core. Which of the following conclusions is best supported by these results?

Accepted Answer

Smaller cubes have a higher surface area-to-volume ratio, allowing more efficient exchange of materials with the environment

Answer

Larger cubes produce more NaOH per unit volume, creating a steeper concentration gradient

Answer

Diffusion rate increases proportionally with the volume of the agar cube

Answer

Active transport compensates for decreased diffusion efficiency in larger cubes

Question 7

Glucose enters most mammalian cells via a membrane protein that moves glucose down its concentration gradient without the direct use of ATP. This process is best described as:

Accepted Answer

Facilitated diffusion, because a specific transport protein moves glucose along its concentration gradient without ATP

Answer

Active transport, because a protein carrier is required for glucose to cross the membrane

Answer

Simple diffusion, because glucose moves down its concentration gradient without any energy input

Answer

Endocytosis, because glucose is too large and polar to cross the lipid bilayer without membrane engulfment

Question 8

Which of the following observations provides the strongest support for the endosymbiotic theory of mitochondrial origin?

Accepted Answer

Mitochondria contain their own circular DNA, replicate by binary fission, and possess ribosomes of 70S size similar to prokaryotes

Answer

Mitochondria are found exclusively in eukaryotic cells that require large amounts of ATP for active processes

Answer

Mitochondria can be isolated from cells and used in cell-free protein synthesis experiments

Answer

The outer mitochondrial membrane contains the same phospholipid composition as the plasma membrane

Question 9

A researcher blocks all light from reaching isolated chloroplasts but provides them with ATP, NADPH, CO₂, and RuBP. Which of the following processes would most likely continue to occur in these chloroplasts?

Accepted Answer

The Calvin cycle, because it uses ATP and NADPH that have been directly supplied and does not itself require light

Answer

The light reactions, because photosystems can use CO₂ as an electron donor in the absence of light

Answer

Both the light reactions and Calvin cycle, because CO₂ drives all stages of photosynthetic carbon fixation

Answer

Neither process, because all stages of photosynthesis require light energy to function

Question 10

A student charts the cumulative ATP yield at each stage of aerobic cellular respiration for one glucose molecule. Which of the following sequences correctly matches each stage with its approximate net ATP contribution?

Accepted Answer

Glycolysis: 2 ATP; Krebs cycle: 2 ATP; Oxidative phosphorylation: approximately 28-34 ATP

Answer

Glycolysis: 2 ATP; Krebs cycle: 34 ATP; Oxidative phosphorylation: 2 ATP

Answer

Glycolysis: 4 ATP; Krebs cycle: 4 ATP; Oxidative phosphorylation: 10 ATP

Answer

Glycolysis: 2 ATP; Pyruvate oxidation: 6 ATP; Krebs cycle: 30 ATP

Question 11

Oligomycin is a drug that blocks the proton channel of ATP synthase in the inner mitochondrial membrane. Which of the following best predicts the effect of oligomycin on the proton gradient (ΔψH⁺) across the inner mitochondrial membrane?

Accepted Answer

The proton gradient will increase because protons continue to be pumped by the electron transport chain but cannot flow back through ATP synthase

Answer

The proton gradient will collapse because protons flow freely across the inner membrane through alternative channels

Answer

The proton gradient will decrease because the electron transport chain pumps fewer protons to compensate for the blocked synthase

Answer

The proton gradient will remain unchanged because proton pumping and ATP synthesis operate as fully independent processes

Question 12

During intense exercise, human muscle cells switch from aerobic respiration to lactic acid fermentation when oxygen becomes limiting. The primary metabolic purpose of this switch is to:

Accepted Answer

Regenerate NAD⁺ from NADH so that glycolysis can continue producing ATP in the absence of oxygen

Answer

Produce more ATP per glucose molecule than aerobic respiration produces

Answer

Generate FADH₂ that can donate electrons to the electron transport chain

Answer

Eliminate excess pyruvate by converting it to acetyl-CoA for entry into the Krebs cycle

Question 13

C4 plants such as corn have anatomical and biochemical adaptations that reduce photorespiration in hot, dry environments. Which of the following best explains the mechanism by which C4 plants minimize photorespiration?

Accepted Answer

CO₂ is initially fixed in mesophyll cells by PEP carboxylase, which has a higher affinity for CO₂ than RuBisCO; the resulting 4-carbon acids transport CO₂ to bundle sheath cells, concentrating it and suppressing RuBisCO's oxygenase activity

Answer

C4 plants use CAM metabolism to open stomata during the day and fix CO₂ at night, separating photosynthesis from photorespiration

Answer

RuBisCO in C4 plants carries a point mutation that increases its specificity for CO₂ over O₂ at elevated temperatures

Answer

C4 plants bypass the Calvin cycle entirely by using an alternative carbon fixation pathway that requires NADPH but not ATP

Question 14

NAD⁺ functions as an electron carrier during cellular respiration. Which of the following most accurately describes its role in glycolysis and the Krebs cycle?

Accepted Answer

NAD⁺ accepts electrons and hydrogen ions during oxidation reactions, becoming NADH, which later donates electrons to the electron transport chain to drive ATP synthesis

Answer

NAD⁺ directly phosphorylates ADP to produce ATP through substrate-level phosphorylation reactions

Answer

NAD⁺ is reduced to NADH within the electron transport chain itself, releasing the energy used to pump protons across the inner mitochondrial membrane

Answer

NAD⁺ acts as an enzyme cofactor that catalyzes glucose catabolism without itself becoming chemically altered during the reactions

Question 15

A researcher applies a hormone to cells possessing functional G-protein coupled receptors (GPCRs). The hormone binding activates adenylyl cyclase, producing cAMP. The researcher then adds a second drug that rapidly and completely degrades all intracellular cAMP. Which of the following correctly predicts the outcome of adding the second drug?

Accepted Answer

The downstream cellular response will be abolished because cAMP is required as a second messenger to transduce the signal to protein kinase A

Answer

The receptor will continue to activate G proteins at an elevated rate, amplifying the downstream signal

Answer

The hormone will bind more tightly to the receptor because degradation of cAMP increases receptor affinity

Answer

Protein kinase A will become permanently activated because it no longer requires cAMP binding for its activation

Question 16

A graph displays cyclin B protein levels and MPF (cyclin B/CDK1 complex) kinase activity across a single cell cycle. Cyclin B accumulates through G2, peaks at M phase, and then drops sharply at the end of mitosis. MPF kinase activity closely mirrors cyclin B levels. Which of the following best explains the sharp decline in MPF activity at the end of mitosis?

Accepted Answer

Cyclin B is rapidly polyubiquitinated and degraded by the proteasome, removing the CDK1-activating partner and terminating MPF activity

Answer

CDK1 protein levels decrease sharply as the cell prepares to exit mitosis and enter cytokinesis

Answer

MPF phosphorylates its own CDK1 subunit, causing irreversible conformational inactivation

Answer

Cyclin B is phosphorylated by active MPF in a negative feedback loop that directly inactivates the complex

Question 17

A somatic mutation inactivates the p53 tumor suppressor protein in a cell. Which of the following is the most likely consequence of this mutation for cell cycle regulation?

Accepted Answer

Cells with DNA damage will bypass the G1 checkpoint and continue dividing, potentially accumulating additional mutations that lead to tumor formation

Answer

The rate of apoptosis will increase because p53 normally functions to suppress programmed cell death pathways

Answer

CDK activity will decrease because p53 directly activates cyclin-CDK complexes required for cell cycle progression

Answer

Cells will be permanently arrested in S phase because p53 is required to activate the DNA polymerases responsible for replication

Question 18

A presynaptic neuron releases a neurotransmitter that diffuses across a synaptic cleft and binds to receptors on an adjacent postsynaptic cell. The signal acts locally and does not enter the bloodstream. This type of cell-to-cell communication is best classified as:

Accepted Answer

Paracrine signaling, because the signal is released locally and acts on nearby target cells without entering the circulatory system

Answer

Endocrine signaling, because the signal molecule travels through a body fluid to reach its target

Answer

Autocrine signaling, because the signal is released and then binds receptors on the same cell that produced it

Answer

Direct contact signaling, because the two cells share cytoplasmic connections through which the signal passes

Question 19

A diploid organism (2n = 4) undergoes meiosis. During prophase I, crossing over occurs between non-sister chromatids of homologous chromosome pairs. Which of the following best explains how crossing over increases genetic diversity in the resulting gametes?

Accepted Answer

Crossing over produces recombinant chromatids carrying new combinations of alleles not present on either original parental chromosome

Answer

Crossing over doubles the chromosome number in each gamete, providing more allelic combinations per cell

Answer

Crossing over ensures that homologous chromosomes separate correctly during meiosis I, generating diversity through independent assortment alone

Answer

Crossing over eliminates deleterious alleles by replacing them with functional copies from the homologous chromosome

Question 20

In pea plants, round seed shape (R) is dominant to wrinkled (r), and yellow seed color (Y) is dominant to green (y). Two plants heterozygous for both traits are crossed (RrYy × RrYy). What is the expected phenotypic ratio of the offspring, assuming independent assortment?

Accepted Answer

9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green

Answer

1 round yellow : 1 round green : 1 wrinkled yellow : 1 wrinkled green

Answer

3 round yellow : 1 wrinkled green

Answer

1 round yellow : 2 round green : 1 wrinkled yellow

Question 21

Crosses between red-flowered (RR) and white-flowered (WW) snapdragon plants produce all pink-flowered (RW) F1 offspring. Crossing two pink-flowered plants produces red, pink, and white offspring in a 1:2:1 ratio. This inheritance pattern is best described as:

Accepted Answer

Incomplete dominance, because the heterozygote displays a phenotype intermediate between the two homozygous phenotypes

Answer

Codominance, because both alleles are simultaneously and fully expressed in the heterozygote

Answer

Epistasis, because one gene masks the phenotypic expression of a second, independently assorting gene

Answer

Polygenic inheritance, because multiple genes contribute additively to produce the continuous range of flower colors

Question 22

A genetics student crosses two heterozygous flies (Aa × Aa) and observes: 72 dominant phenotype individuals and 28 recessive phenotype individuals out of 100 total. The expected Mendelian ratio is 3:1. Using χ² = Σ[(o−e)²/e] and a critical value of 3.84 at p = 0.05 with 1 degree of freedom, what is the most appropriate statistical conclusion?

Accepted Answer

The data are consistent with the expected 3:1 Mendelian ratio; the null hypothesis cannot be rejected because χ² = 0.48, which is below the critical value

Answer

The null hypothesis is rejected because the observed values differ from the expected 3:1 ratio

Answer

The results indicate sex-linkage because the observed phenotypic frequencies deviate from a perfect 3:1 ratio

Answer

The chi-square value exceeds the critical value, indicating the data support a 1:1 phenotypic ratio instead

Question 23

Red-green color blindness is caused by an X-linked recessive allele (X^b). A woman with normal color vision whose father was color blind has children with a man who has normal color vision. What is the probability that any given son of this couple will be color blind?

Accepted Answer

50%, because the mother is an obligate carrier (X^BX^b) and passes X^b to sons with 1/2 probability

Answer

0%, because sons inherit their X chromosome exclusively from their father, who has normal vision

Answer

25%, because both the mother's carrier status and father's normal vision each contribute a 50% probability

Answer

100%, because a carrier mother always transmits her recessive allele to all of her sons

Question 24

During meiosis I in a human cell, the two homologous copies of chromosome 21 fail to separate (nondisjunction occurs at meiosis I). Which of the following correctly describes the expected chromosome composition of the four resulting gametes?

Accepted Answer

Two gametes will receive two copies of chromosome 21 (n+1) and two gametes will receive no copy of chromosome 21 (n&minus;1)

Answer

All four gametes will be monosomic for chromosome 21, receiving no copy of chromosome 21

Answer

Two gametes will be chromosomally normal (n) and two will contain an extra chromosome 21 (n+1)

Answer

All four gametes will contain two copies of chromosome 21 because nondisjunction duplicates all homologous pairs

Question 25

In the Meselson-Stahl experiment, bacteria were grown in ¹⁵N medium for several generations, then transferred to ¹⁴N medium for exactly one round of replication. Density gradient centrifugation was used to analyze the resulting DNA. Which result would support the semi-conservative model of DNA replication?

Accepted Answer

All DNA molecules band at an intermediate density, indicating each double helix contains one ¹⁵N strand and one ¹⁴N strand

Answer

Half the DNA bands at heavy density (¹⁵N/¹⁵N) and half at light density (¹⁴N/¹⁴N), with no intermediate band

Answer

All DNA molecules band at the heavy density because ¹⁵N is preferentially incorporated during the first round of replication

Answer

DNA molecules appear at three distinct density positions: heavy, intermediate, and light simultaneously

Question 26

A point mutation changes a single nucleotide in the template strand of a gene. The resulting mRNA codon codes for the same amino acid as the original codon. This mutation is best described as:

Accepted Answer

A silent (synonymous) mutation, because the amino acid sequence of the resulting protein remains unchanged

Answer

A frameshift mutation, because any nucleotide change shifts the downstream reading frame

Answer

A missense mutation, because the nucleotide sequence of the codon has changed

Answer

A nonsense mutation, because the altered codon no longer codes for the original amino acid sequence

Question 27

In E. coli, the lac operon is normally repressed in the absence of lactose. A researcher creates a mutant strain in which the lac repressor protein can no longer bind to the operator sequence. Which of the following best describes gene expression from the lac operon in this mutant strain?

Accepted Answer

The structural genes will be constitutively expressed regardless of lactose concentration, because the operator is never blocked

Answer

The structural genes will be expressed only when lactose is present and glucose is absent, because catabolite activator protein (CAP) still controls transcription

Answer

The structural genes will never be expressed because the repressor protein is required to recruit RNA polymerase to the promoter

Answer

The structural genes will only be expressed when the repressor binds allolactose, reversing the normal regulatory logic

Question 28

A researcher performs gel electrophoresis on PCR-amplified DNA fragments. A 100 bp ladder is run alongside. After staining, the 100 bp fragment in the unknown sample has migrated the greatest distance from the well. Which of the following best explains this observation?

Accepted Answer

Smaller DNA fragments migrate farther through the agarose matrix because they encounter less resistance from the gel pores during electrophoresis

Answer

Larger DNA fragments carry more negative charge and therefore migrate faster toward the positive electrode

Answer

Smaller fragments have more base pairs per unit length, providing greater electrophoretic driving force

Answer

The gel pores selectively trap larger fragments near the negative electrode through size-exclusion mechanisms

Question 29

Monozygotic (identical) twin pairs share the same DNA nucleotide sequence at birth. However, studies show that as twins age, their patterns of gene expression become increasingly different, even without changes to their DNA sequences. Which of the following best explains this divergence in gene expression?

Accepted Answer

Epigenetic modifications such as differential DNA methylation and histone acetylation patterns accumulate in response to different environmental exposures, altering gene expression without changing the nucleotide sequence

Answer

Random somatic mutations accumulate at identical rates in both twins, producing symmetric but different allele frequencies over time

Answer

Ribosomes in each twin undergo structural modifications that cause alternative splicing of the same pre-mRNA into different mature mRNAs

Answer

The twins experience different rates of DNA replication errors, leading to divergent allele frequencies in somatic tissues

Question 30

A forensic scientist uses PCR to amplify a specific STR (short tandem repeat) locus from a blood sample collected at a crime scene. The amplified product is run on a gel alongside samples from three suspects. The crime scene band co-migrates with the band from Suspect 2. Which of the following is the most appropriate conclusion?

Accepted Answer

The DNA fragment size at the tested STR locus is consistent between Suspect 2 and the crime scene sample, making Suspect 2 a candidate for further forensic investigation

Answer

Suspect 2 is definitively the source of the crime scene blood because their DNA band is an exact match

Answer

The other two suspects are conclusively innocent because their band positions do not match the crime scene sample

Answer

PCR amplification proves the blood belonged to Suspect 2 because PCR is error-free and uniquely identifies individuals

Practice Test for AP Biology - 3 Grade 10 MCQs & solutions - Free

MCQ Practice Test & Solutions: Practice Test for AP Biology - 3 (60 Questions)

A researcher tests the activity of the enzyme catalase at temperatures of 10°C, 20°C, 37°C, 50°C, and 70°C by measuring the rate of oxygen gas production. Which of the following correctly identifies the dependent variable in this experiment?

A transmembrane protein spans the full width of the phospholipid bilayer. Which property of the protein's amino acid residues is most directly responsible for anchoring the protein within the hydrophobic core of the membrane?

Water molecules are able to travel up the narrow vessels of a plant stem against gravity. This process depends primarily on which property of water?

A red blood cell is placed in a solution and begins to swell and eventually bursts (lyses). Which of the following correctly describes the tonicity of the external solution relative to the cell's cytoplasm?

Glucose enters most mammalian cells via a membrane protein that moves glucose down its concentration gradient without the direct use of ATP. This process is best described as:

Which of the following observations provides the strongest support for the endosymbiotic theory of mitochondrial origin?

A researcher blocks all light from reaching isolated chloroplasts but provides them with ATP, NADPH, CO₂, and RuBP. Which of the following processes would most likely continue to occur in these chloroplasts?

A student charts the cumulative ATP yield at each stage of aerobic cellular respiration for one glucose molecule. Which of the following sequences correctly matches each stage with its approximate net ATP contribution?

Oligomycin is a drug that blocks the proton channel of ATP synthase in the inner mitochondrial membrane. Which of the following best predicts the effect of oligomycin on the proton gradient (ΔψH⁺) across the inner mitochondrial membrane?

During intense exercise, human muscle cells switch from aerobic respiration to lactic acid fermentation when oxygen becomes limiting. The primary metabolic purpose of this switch is to:

C4 plants such as corn have anatomical and biochemical adaptations that reduce photorespiration in hot, dry environments. Which of the following best explains the mechanism by which C4 plants minimize photorespiration?

NAD⁺ functions as an electron carrier during cellular respiration. Which of the following most accurately describes its role in glycolysis and the Krebs cycle?

A somatic mutation inactivates the p53 tumor suppressor protein in a cell. Which of the following is the most likely consequence of this mutation for cell cycle regulation?

A presynaptic neuron releases a neurotransmitter that diffuses across a synaptic cleft and binds to receptors on an adjacent postsynaptic cell. The signal acts locally and does not enter the bloodstream. This type of cell-to-cell communication is best classified as:

A diploid organism (2n = 4) undergoes meiosis. During prophase I, crossing over occurs between non-sister chromatids of homologous chromosome pairs. Which of the following best explains how crossing over increases genetic diversity in the resulting gametes?

In pea plants, round seed shape (R) is dominant to wrinkled (r), and yellow seed color (Y) is dominant to green (y). Two plants heterozygous for both traits are crossed (RrYy × RrYy). What is the expected phenotypic ratio of the offspring, assuming independent assortment?

Crosses between red-flowered (RR) and white-flowered (WW) snapdragon plants produce all pink-flowered (RW) F1 offspring. Crossing two pink-flowered plants produces red, pink, and white offspring in a 1:2:1 ratio. This inheritance pattern is best described as:

Red-green color blindness is caused by an X-linked recessive allele (X^b). A woman with normal color vision whose father was color blind has children with a man who has normal color vision. What is the probability that any given son of this couple will be color blind?

During meiosis I in a human cell, the two homologous copies of chromosome 21 fail to separate (nondisjunction occurs at meiosis I). Which of the following correctly describes the expected chromosome composition of the four resulting gametes?

A point mutation changes a single nucleotide in the template strand of a gene. The resulting mRNA codon codes for the same amino acid as the original codon. This mutation is best described as:

In E. coli, the lac operon is normally repressed in the absence of lactose. A researcher creates a mutant strain in which the lac repressor protein can no longer bind to the operator sequence. Which of the following best describes gene expression from the lac operon in this mutant strain?

A researcher performs gel electrophoresis on PCR-amplified DNA fragments. A 100 bp ladder is run alongside. After staining, the 100 bp fragment in the unknown sample has migrated the greatest distance from the well. Which of the following best explains this observation?

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Practice Test for AP Biology - 3 Grade 10 MCQs & solutions - Free

MCQ Practice Test & Solutions: Practice Test for AP Biology - 3 (60 Questions)

A researcher tests the activity of the enzyme catalase at temperatures of 10°C, 20°C, 37°C, 50°C, and 70°C by measuring the rate of oxygen gas production. Which of the following correctly identifies the dependent variable in this experiment?

A transmembrane protein spans the full width of the phospholipid bilayer. Which property of the protein's amino acid residues is most directly responsible for anchoring the protein within the hydrophobic core of the membrane?

Water molecules are able to travel up the narrow vessels of a plant stem against gravity. This process depends primarily on which property of water?

A red blood cell is placed in a solution and begins to swell and eventually bursts (lyses). Which of the following correctly describes the tonicity of the external solution relative to the cell's cytoplasm?

Glucose enters most mammalian cells via a membrane protein that moves glucose down its concentration gradient without the direct use of ATP. This process is best described as:

Which of the following observations provides the strongest support for the endosymbiotic theory of mitochondrial origin?

A researcher blocks all light from reaching isolated chloroplasts but provides them with ATP, NADPH, CO2, and RuBP. Which of the following processes would most likely continue to occur in these chloroplasts?

A student charts the cumulative ATP yield at each stage of aerobic cellular respiration for one glucose molecule. Which of the following sequences correctly matches each stage with its approximate net ATP contribution?

Oligomycin is a drug that blocks the proton channel of ATP synthase in the inner mitochondrial membrane. Which of the following best predicts the effect of oligomycin on the proton gradient (ΔψH+) across the inner mitochondrial membrane?

During intense exercise, human muscle cells switch from aerobic respiration to lactic acid fermentation when oxygen becomes limiting. The primary metabolic purpose of this switch is to:

C4 plants such as corn have anatomical and biochemical adaptations that reduce photorespiration in hot, dry environments. Which of the following best explains the mechanism by which C4 plants minimize photorespiration?

NAD+ functions as an electron carrier during cellular respiration. Which of the following most accurately describes its role in glycolysis and the Krebs cycle?

A somatic mutation inactivates the p53 tumor suppressor protein in a cell. Which of the following is the most likely consequence of this mutation for cell cycle regulation?

A presynaptic neuron releases a neurotransmitter that diffuses across a synaptic cleft and binds to receptors on an adjacent postsynaptic cell. The signal acts locally and does not enter the bloodstream. This type of cell-to-cell communication is best classified as:

A diploid organism (2n = 4) undergoes meiosis. During prophase I, crossing over occurs between non-sister chromatids of homologous chromosome pairs. Which of the following best explains how crossing over increases genetic diversity in the resulting gametes?

In pea plants, round seed shape (R) is dominant to wrinkled (r), and yellow seed color (Y) is dominant to green (y). Two plants heterozygous for both traits are crossed (RrYy × RrYy). What is the expected phenotypic ratio of the offspring, assuming independent assortment?

Crosses between red-flowered (RR) and white-flowered (WW) snapdragon plants produce all pink-flowered (RW) F1 offspring. Crossing two pink-flowered plants produces red, pink, and white offspring in a 1:2:1 ratio. This inheritance pattern is best described as:

Red-green color blindness is caused by an X-linked recessive allele (Xb). A woman with normal color vision whose father was color blind has children with a man who has normal color vision. What is the probability that any given son of this couple will be color blind?

During meiosis I in a human cell, the two homologous copies of chromosome 21 fail to separate (nondisjunction occurs at meiosis I). Which of the following correctly describes the expected chromosome composition of the four resulting gametes?

A point mutation changes a single nucleotide in the template strand of a gene. The resulting mRNA codon codes for the same amino acid as the original codon. This mutation is best described as:

In E. coli, the lac operon is normally repressed in the absence of lactose. A researcher creates a mutant strain in which the lac repressor protein can no longer bind to the operator sequence. Which of the following best describes gene expression from the lac operon in this mutant strain?

A researcher performs gel electrophoresis on PCR-amplified DNA fragments. A 100 bp ladder is run alongside. After staining, the 100 bp fragment in the unknown sample has migrated the greatest distance from the well. Which of the following best explains this observation?

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A researcher blocks all light from reaching isolated chloroplasts but provides them with ATP, NADPH, CO₂, and RuBP. Which of the following processes would most likely continue to occur in these chloroplasts?

Oligomycin is a drug that blocks the proton channel of ATP synthase in the inner mitochondrial membrane. Which of the following best predicts the effect of oligomycin on the proton gradient (ΔψH⁺) across the inner mitochondrial membrane?

NAD⁺ functions as an electron carrier during cellular respiration. Which of the following most accurately describes its role in glycolysis and the Krebs cycle?

Red-green color blindness is caused by an X-linked recessive allele (X^b). A woman with normal color vision whose father was color blind has children with a man who has normal color vision. What is the probability that any given son of this couple will be color blind?