AP Biology Full-length practice exam 3

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

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

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 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?

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?

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

During the spindle assembly checkpoint (SAC), the cell detects that one kinetochore is not attached to a spindle microtubule. Which of the following correctly describes what happens next?

In the nitrogen cycle, which group of organisms is responsible for converting ammonium ($N{H}_4^{+}$) into nitrite ($N{O}_2^{-}$) and then nitrate ($N{O}_3^{-}$)?

Disruptive selection is a type of natural selection in which:

Which type of bond holds two complementary DNA strands together in the double helix?

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?

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

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?

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?

A mutation eliminates the enzyme RuBisCO from a plant cell. Which stage of photosynthesis would be most directly affected?

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 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?

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

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

The mitochondrion has its own DNA and double membrane. This evidence best supports which hypothesis?

A buffer maintains stable pH by:

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?

Saturated and unsaturated fatty acids differ in:

Which of the following BEST illustrates evidence for common ancestry?

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

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

In humans, red-green color blindness is an X-linked recessive trait. A color-blind woman and a man with normal color vision have children. What is the expected phenotypic ratio for their sons?

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

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?

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

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

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 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?

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

The lac operon in E. coli is repressed under which of the following conditions?

Cilia and flagella in eukaryotes share which structural feature?

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?

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?

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

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 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?

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?

What is the primary role of the cytoskeleton in a eukaryotic cell?

Genetic drift has a stronger effect in:

Which structural feature distinguishes prokaryotic cells from eukaryotic cells?

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

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?

During which phase of the cell cycle is DNA replicated?

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?

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

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

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?

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 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 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 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 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 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?

An athlete sprinting at maximum effort for 8 seconds relies primarily on which metabolic process to generate ATP?