Loading test…

AP Biology Hard practice

15 questions

Header banner

Hard practice

0 of 15 answered

~9 min left

Question 1

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 2

Researchers studying gene regulation find that a eukaryotic gene is highly expressed in liver cells but completely silenced in neurons despite both cell types having identical genomic DNA. Which combination of mechanisms could best explain this tissue-specific expression pattern?

A.Different DNA sequences in liver vs. neuron genomes encoding different versions of the geneB.Liver-specific activator transcription factors and neuron-specific DNA methylation silencing the gene's promoterC.Alternative splicing that produces a functional protein only in liver cellsD.Ribosomes in neurons are unable to translate liver-specific mRNAs

Question 3

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 4

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 5

Genomic imprinting results in differential expression of a gene depending on whether it was inherited from the mother or the father. The Igf2 gene in mice is only expressed from the paternal chromosome. If an Igf2 deletion is inherited from the father, the offspring will lack Igf2 expression entirely. What would happen if the same deletion were inherited from the mother?

A.The offspring would also lack Igf2 expression because the deletion removes the coding sequence regardless of parent of originB.The offspring would have normal Igf2 expression because the paternal allele (which is expressed) is still intactC.The offspring would overexpress Igf2 because losing maternal repression amplifies paternal expressionD.The offspring would show the deletion phenotype in maternal tissues only

In-content ad

Question 6

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 7

Apoptosis (programmed cell death) is triggered in a cell with extensive DNA damage. Which of the following best describes why apoptosis is preferable to continued cell division in this scenario?

A.Apoptosis recycles all cellular components into new cells more efficiently than mitosisB.Continued division of damaged cells risks transmitting mutations to daughter cells, potentially creating tumor cellsC.DNA damage prevents the cell from completing S phase, so apoptosis allows other cells to divide in its placeD.Apoptosis sends chemical signals that directly reprogram neighboring cells to replicate the damaged cell's genome

Question 8

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

Question 9

The phosphorus cycle, unlike the carbon and nitrogen cycles, lacks a significant atmospheric reservoir. What are the primary environmental consequences of this difference?

A.Phosphorus cycles very rapidly between organisms and the atmosphere, making it rarely limitingB.Phosphorus cycles slowly through geological weathering and is often the limiting nutrient in aquatic ecosystemsC.Phosphorus volatilizes from soil and is replenished regularly by precipitation, similar to nitrogenD.Phosphorus is more abundant than nitrogen in most ecosystems because it does not escape to the atmosphere

Question 10

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

In-content ad

Question 11

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

Question 12

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 13

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 14

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 15

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

AP Biology Hard practice — Free with Answer Explanations | Test Practice Hub