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AP Biology Medium practice

15 questions

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Medium practice

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Question 1

During transcription in eukaryotes, which of the following modifications occurs to pre-mRNA before it exits the nucleus?

A.Introns are translated into regulatory peptides before being removedB.Addition of a 5′ cap, a 3′ poly-A tail, and splicing of intronsC.Reverse transcription to produce a complementary DNA (cDNA) copyD.Translation of the first exon to begin protein synthesis in the nucleus

Question 2

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

Question 3

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

Question 4

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 5

A point mutation changes a codon from UUU (phenylalanine) to UUA (leucine) in a translated protein. Which of the following best describes this mutation?

A.Silent mutation, because the protein is unchangedB.Missense mutation, because one amino acid is substituted for anotherC.Nonsense mutation, because a stop codon is introducedD.Frameshift mutation, because a nucleotide is inserted or deleted

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Question 6

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 7

Disruptive selection is a type of natural selection in which:

A.Both extreme phenotypes are favored over the intermediate.B.The intermediate phenotype is favored.C.Only one extreme phenotype is favored.D.All phenotypes are equally favored.

Question 8

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 9

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 10

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

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Question 11

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 12

In gel electrophoresis of DNA fragments, a researcher loads four samples and observes that one fragment migrated the farthest from the well. What does this indicate about that fragment?

A.It has the highest molecular weight and is the largest fragmentB.It is the smallest fragment in the sampleC.It has the most negative charge and is most attracted to the positive electrodeD.It contains more guanine-cytosine base pairs than the other fragments

Question 13

In chickens, feather color is controlled by two genes. Allele E (dominant) produces black feathers; allele e (homozygous recessive, ee) produces red feathers when at least one C allele is present. However, any bird homozygous recessive at the C locus (cc) is white regardless of the E locus. This is an example of recessive epistasis. When two white birds both with genotype EEcc are crossed with birds of genotype EECc, what fraction of offspring are expected to be white?

\frac{3}{4}

\frac{1}{2}

\frac{1}{4}

\frac{1}{8}

Question 14

A researcher treats dividing cells with a drug that prevents the degradation of cyclin B. Based on your knowledge of the cell cycle checkpoint system, which of the following best predicts the result?

A.Cells arrest at the G₁/S checkpoint because cyclin B is needed for S phase entryB.Cells continuously enter and cannot exit mitosis, because MPF activity remains highC.Cells skip S phase because high MPF signals that DNA is already replicatedD.DNA replication occurs multiple times per cell cycle due to continuous cyclin B signaling

Question 15

A population of rabbits in an isolated meadow is growing according to the logistic growth model. The carrying capacity (K) is 500 rabbits, and the current population size (N) is 250. Which of the following statements correctly predicts the population growth rate relative to when N = 50?

A.Growth rate is lower at N=250 than at N=50 because density-dependent factors increase as N increasesB.Growth rate is at its maximum when N=250 because N equals K/2C.Growth rate is higher at N=50 than at N=250 because fewer density-dependent constraints existD.Growth rate is equal at N=50 and N=250 because the intrinsic rate of increase (r) is constant

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