Part 2 — Answer key

Compare your answers after you have finished Part 1.

1. In a simple food chain, primary consumers obtain their energy directly from producers.
   True
2. Red blood cells are placed in a strongly hypertonic NaCl solution. What happens to the cells over the next few minutes?
   They lose water and become crenated
3. In a culture of mammalian cells, diffusion of a small uncharged polar molecule across the plasma membrane suddenly becomes much slower, even though the concentration gradient is unchanged. Which change most plausibly explains this observation?
   An increase in membrane thickness
4. In humans, mitochondrial DNA is inherited equally from both parents.
   False
5. A population of deer exhibits logistic growth in a fenced reserve. When the population size reaches the carrying capacity of the reserve, which condition is most likely to be true?
   Birth rate equals death rate and population size stabilizes
6. In eukaryotic cells, translation of a newly synthesized protein always begins on ribosomes that are already bound to the rough endoplasmic reticulum.
   False
7. A healthy person begins to hyperventilate due to anxiety. What is the primary effect on arterial blood CO₂ and pH after several minutes?
   CO₂ decreases and pH increases
8. A man with blood type AB has a child with a woman with blood type O. Which blood type can their child not have?
   Type AB
9. A plant that is heterozygous for two genes (AB/ab) is testcrossed with a plant that is homozygous recessive (ab/ab). The progeny show many AB and ab individuals, but far fewer Ab and aB individuals than expected under independent assortment. Which genetic phenomenon best explains this pattern?
   Genetic linkage
10. A long-distance runner begins intense exercise. Within the first few minutes, which of the following physiological changes are directly mediated by activation of the sympathetic nervous system? Select all that apply.
    Dilation of pupils; Decreased blood flow to the digestive tract; Increased heart rate
11. An enzyme is studied in vitro. When a competitive inhibitor is added, the maximal reaction velocity is unchanged, but a higher substrate concentration is required to reach half-maximal velocity. Which change in kinetic parameters is most consistent with these data?
    Km increases, Vmax unchanged
12. Stabilizing selection tends to reduce phenotypic variation within a population by favoring intermediate trait values over extremes.
    True
13. In a sexually reproducing diploid species, which processes directly increase genetic diversity among offspring in a single generation? Select all that apply.
    Independent assortment of homologous chromosome pairs during metaphase I; Random fertilization between different gametes; Crossing over between homologous chromosomes during prophase I
14. A neurotoxin selectively blocks voltage-gated K⁺ channels in neurons but leaves Na⁺ channels intact. How will an action potential recorded from a poisoned neuron differ from a normal one?
    It will fail to depolarize above 0 mV
15. A newly synthesized lysosomal hydrolase is correctly translated and enters the lumen of the rough ER, but it fails to reach lysosomes and is instead secreted from the cell. Which specific signal or modification was most likely missing?
    A farnesylation motif for membrane anchoring
16. A bacterial population contains rare cells that can grow at low concentrations of a new antibiotic. After several days of treatment, almost all surviving cells show this low-level resistance. Which process best explains the shift in the population?
    Directional selection on standing genetic variation
17. A researcher knocks out the TP53 gene (encoding p53) in a human cell line. After exposure to intense DNA-damaging radiation, which cellular responses are directly impaired by loss of p53? Select all that apply.
    Transcriptional induction of DNA repair genes; Activation of apoptosis pathways; Cell cycle arrest at the G1/S checkpoint
18. Arrange the following events in the correct order for the production and secretion of a typical soluble protein that is exported from a eukaryotic cell.
    Correct order: Transcription of the coding gene in the nucleus → Capping, splicing, and polyadenylation of the primary RNA transcript → Co-translational translocation into the rough endoplasmic reticulum → Processing and sorting in the Golgi apparatus → Packaging into secretory vesicles and fusion with the plasma membrane
19. A small bird species is endemic to a remote island and is now threatened by the introduction of a predatory snake. Which features of the bird population are most likely to increase its risk of extinction under this new predation pressure? Select all that apply.
    Lack of evolved defenses against terrestrial predators; Highly restricted geographic range; Small effective population size
20. Isolated mitochondria are supplied with succinate, ADP, and inorganic phosphate. Oxygen consumption and ATP synthesis begin. When the uncoupler dinitrophenol (DNP) is added, what happens relative to the initial state?
    ATP synthesis decreases while oxygen consumption increases
21. A group of fish in a deep lake splits into multiple reproductively isolated species without obvious physical barriers. Which processes could most directly generate such sympatric speciation in this scenario? Select all that apply.
    Disruptive selection on mating preferences linked to coloration; Polyploidization events within the population; Strong assortative mating based on feeding depth
22. A child with features of Down syndrome has a karyotype in which one extra copy of chromosome 21 is fused to chromosome 14, while one normal chromosome 14 and one normal chromosome 21 are also present. Which chromosomal abnormality best describes this situation?
    Robertsonian translocation