Practice Test 37 - AP Biology

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. A deer population in a fenced reserve was estimated each year: Year 1 = 120, Year 2 = 180, Year 3 = 250, Year 4 = 290, Year 5 = 300, Year 6 = 298. Vegetation surveys showed increasing browse damage after Year 3. Which pattern best illustrates the deer population growth shown by the data?
2. A researcher observes a cell at the G1 checkpoint. The cell has a DNA content of 2C and unreplicated chromosomes. The researcher then damages the DNA and notes that the cell does not enter S phase during the experiment. Later, a different cell with no DNA damage passes the same checkpoint and enters S phase, increasing DNA content toward 4C. No other phases are manipulated. Which outcome is most likely for the first cell during the observation period?
3. Two cell types from the same plant—leaf mesophyll cells and root hair cells—are grown in identical conditions. DNA sequencing shows the cells have the same genome. When exposed to light, mesophyll cells show high levels of mRNA for a photosystem protein, while root hair cells show little to none; root hair cells instead show high levels of mRNA for a membrane transporter. Which explanation best accounts for these differences in mRNA abundance?
4. A lab tests two polysaccharides made of glucose: Polymer M is unbranched and forms a tight helix; Polymer N is highly branched with many short chains. When iodine solution is added, M produces a deep blue color while N produces a reddish-brown color. The color change occurs because iodine molecules fit into helical cavities of certain polymers. Which structural feature best explains the deep blue result for M?
5. Cellulose and starch are both polymers of glucose. In cellulose, adjacent monomers are connected by $β(1\to4)$ glycosidic bonds, producing straight chains that align closely. In starch (amylose), monomers are connected by $α(1\to4)$ bonds, producing a helical chain. A plant cell wall sample resists stretching when pulled, even when hydrated. Which molecular feature best explains the wall's tensile strength at the polymer level?
6. Genetically identical hydrangea plants were grown in pots with different soil pH. Plants in acidic soil produced blue flowers, while plants in basic soil produced pink flowers. DNA sequencing of a pigment gene was identical in both groups. Which explanation best accounts for the different flower colors under different soil pH conditions?
7. A weed population in soybean fields is exposed to the same herbicide each spring. Seeds are collected and genotyped yearly at a locus with alleles H (herbicide resistance) and h. Over 9 years, allele H increases from 0.08 to 0.61, while planting density and field size stay similar. Which observation best demonstrates evolution occurring in this weed population?
8. DNA replication is semiconservative: each daughter DNA molecule contains one parental strand and one newly synthesized strand. Replication depends on strand separation and complementary base pairing (A–T, G–C) as polymerase builds new DNA 5′→3′. A researcher grows cells for one generation in medium containing a heavy isotope of nitrogen, then transfers them to light nitrogen for one generation and isolates DNA. Which DNA composition is most likely after the first generation in light nitrogen?
9. A researcher amplifies a 220-bp region of a gene using PCR with primers flanking the region. After 30 cycles, the products are run on an agarose gel stained to visualize DNA. The negative control (no template DNA) shows no bands. Patient 1 shows a single band at ~220 bp. Patient 2 shows no visible band at any size. The thermocycler settings and reagents were identical for both patients. Which explanation best accounts for Patient 2's gel result?
10. A fish population has genetic variation at a locus affecting toxin resistance: allele R (resistant) and r (nonresistant). A factory begins releasing a toxin into the river, and within 8 generations the frequency of R increases from 0.10 to 0.46. Researchers find no evidence of increased mutation rate at this locus. Which statement best explains how genetic variation enabled the population-level change?
11. In a species of mouse, black fur (B) is completely dominant to brown fur (b). A black-furred mouse with genotype Bb is crossed with a brown-furred mouse with genotype bb. Each offspring receives one allele from each parent. Assume this trait is controlled by one gene and that dominance is complete. Which proportion of offspring is expected to have brown fur?
12. Researchers create two liposomes. Liposome M contains phospholipids with short fatty acid tails; Liposome N contains phospholipids with longer tails. Both lack transport proteins. The hydrophobic tails form the interior barrier, and small nonpolar molecules cross by simple diffusion. The liposomes are placed in a solution containing a small nonpolar dye, and dye entry is measured over time. Which feature best explains why dye enters Liposome M faster than Liposome N?
13. A large population of wildflowers has two alleles at a pigment locus, $R$ and $r$. Before a drought, $p(R)=0.60$. After three years of drought, surveys show $p(R)=0.82$. Field data indicate plants with genotype $RR$ and $Rr$ produce more seeds than $rr$ during drought years, and the population size remains large. Which factor most directly explains the observed allele frequency change?
14. In a large moth population, allele $D$ at a wing-color locus has frequency 0.50. Over ten generations, $p(D)$ remains near 0.50, but genotype surveys show heterozygotes ($Dd$) consistently have higher survival than either homozygote. Population size is large, and there is no immigration. Which evolutionary process most likely explains the stable intermediate allele frequency?
15. In a desert ecosystem, a shrub species produces abundant nectar that attracts ants. Ants patrol the shrub and are observed attacking caterpillars feeding on shrub leaves. Experimental shrubs with ants excluded by sticky barriers show higher caterpillar abundance and increased leaf damage compared with control shrubs with ants present. Nectar production and water availability are similar between treatments. Which interaction best explains the relationship between the shrub and the ants in this system?
16. A eukaryotic cell line is engineered so the 5′ splice site consensus sequence at the exon 1–intron 1 boundary is mutated, while all other splice signals remain unchanged. After transcription, nuclear RNA is analyzed. Compared with wild type, the predominant RNA species retains intron 1 sequences but does not retain intron 2 sequences, and exon 2 and exon 3 are still joined. Transcription initiation and elongation rates are unchanged. Which explanation best accounts for the selective retention of intron 1?
17. Cells respond to ligand G only when G is presented on the surface of a neighboring cell, not when purified soluble G is added to the medium. The receptor for G is on the responding cell's membrane. Which of the following best explains why soluble G fails to signal?
18. A student claims the nucleus originated when an ancient bacterium was engulfed and became the nuclear compartment. However, in a cell lineage being studied, the nuclear envelope is continuous with an internal membrane network, and both membranes have similar lipid composition to the plasma membrane. The nuclear compartment contains linear chromosomes and no bacterial-like ribosomes. Which evidence best supports an alternative origin of the nuclear envelope?
19. A river changed course and formed a wide channel that separated a population of small mammals into east-bank and west-bank populations. Ten thousand years later, the two populations have different allele frequencies at many loci. When individuals are captured and placed together in a large outdoor pen, mating occurs and embryos form, but nearly all embryos die before birth. Field surveys show no natural crossings of the river. Which process most directly explains how speciation began in these mammals?
20. In a population of 2,000 rabbits, allele $B$ frequency at a fur locus is 0.40. A road is built that splits the habitat into two isolated subpopulations of equal size with no migration. After 30 generations, subpopulation 1 has $B=0.18$ and subpopulation 2 has $B=0.63$, and no consistent fitness differences among genotypes are detected. Which process most likely produced the different allele frequencies?

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