Practice Test 26 - AP Biology

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

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1. A student tracks alleles on a homologous chromosome pair with genes G and H linked on the same chromosome. One homolog is GH and the other is gh. The student predicts that a crossover between G and H in prophase I will produce gametes containing Gh and gH chromatids. The student then asks what must physically occur for those gametes to form. Which event is required at the chromosomal level to generate Gh and gH chromatids?
2. A plant cell has a large central vacuole whose lumen is more acidic than the surrounding cytosol. An enzyme that hydrolyzes stored proteins has maximal activity at pH 5 and low activity at pH 7. When the vacuolar membrane (tonoplast) is disrupted, the vacuolar pH rises toward cytosolic pH and protein hydrolysis slows. Which conclusion is best supported about how compartmentalization affects this cellular function?
3. This development of pesticide resistance in Colorado potato beetles is an example of continuing evolution because it demonstrates which of the following?
4. Researchers tested an RNA-world hypothesis using a ribozyme (catalytic RNA) that can join short RNA fragments. In a reaction containing only RNA fragments, $\mathrm{Mg^{2+}}$, and the ribozyme, longer RNA strands accumulated over time. In a control lacking the ribozyme, fragment length remained unchanged. Which conclusion is best supported by these results about early genetic systems?
5. A small pond experiences rapid air-temperature changes between day and night, yet measurements show the pond water temperature changes more slowly than the surrounding air. Water molecules are polar, with partial negative charge near oxygen and partial positive charge near hydrogen. Hydrogen bonds form between neighboring water molecules due to these partial charges. When water warms, energy is absorbed before molecules can move freely because some energy disrupts hydrogen bonds; when water cools, hydrogen bonds re-form and release energy. These molecular interactions influence how quickly water's temperature changes. Which statement best describes the molecular reason the pond resists rapid temperature change?
6. A freshwater protist has an internal solute concentration of 300 mOsm and is suddenly transferred to a medium of 50 mOsm. The membrane is permeable to water but not to the major intracellular solutes. Within minutes, the cell volume increases. If no pumps or channels change activity during this interval, which outcome is most likely for water movement across the membrane?
7. A plant cell is placed in a hypertonic solution. After several minutes, the plasma membrane pulls away from the cell wall, but the cell wall retains its shape. Which feature best explains why the wall maintains the overall cell outline?
8. A phospholipid bilayer separates two solutions. The bilayer interior is nonpolar and resists entry of molecules that are polar or charged. Compare two molecules of similar size: acetone (polar due to a carbonyl group) and hexane (nonpolar hydrocarbon). Neither molecule is ionized in this context. The membrane contains no proteins. Which molecule would most likely have greater permeability through the bilayer?
9. On early Earth, amphipathic molecules could accumulate in shallow water. In an experiment, fatty acids in water spontaneously formed membrane-bound vesicles. When RNA nucleotides were added, vesicles trapped them inside; vesicles in plain water did not contain nucleotides after rinsing. Which conclusion is best supported by the evidence about early life origins?
10. A researcher isolates nuclear RNA from a eukaryotic cell and detects two versions of an RNA from the same gene. Version 1 contains exon 1–exon 2–exon 3. Version 2 contains exon 1–exon 3, with exon 2 absent; DNA sequencing confirms the gene's exon 2 is intact. Both RNAs share identical sequences at the exon 1/exon 3 junction where present. Which explanation best accounts for production of version 2 at the molecular level?
11. Two animal cell types are compared. Cell type X has many mitochondria with densely folded inner membranes; cell type Y has fewer mitochondria with less folded inner membranes. The inner mitochondrial membrane contains proteins that carry out electron transport and establish a proton gradient used to produce ATP. Which outcome is most likely in cell type X compared with cell type Y under the same conditions?
12. In a eukaryotic cell, enzymes for fatty acid breakdown are located inside peroxisomes, where reactions produce hydrogen peroxide (H2O2). Catalase, also inside peroxisomes, converts H2O2 to water and oxygen. When peroxisomal membranes are experimentally disrupted, H2O2 accumulates in the cytosol and other enzymes show decreased activity. No changes occur in nuclear DNA. Which feature best explains how compartmentalization affects cellular efficiency in this scenario?
13. Two double-stranded DNA samples have equal length. Sample 1 has more G–C pairs than sample 2. Which statement best describes a molecular consequence?
14. A rabbit breeder selects only rabbits with very long ears to breed. Ear length is influenced by alleles R (longer) and r (shorter). After seven generations, the average ear length increases, but the breeder notices fewer distinct ear-length categories in the population than at the start. No rabbits are introduced from outside. Which outcome is most likely regarding genetic variation for ear length?
15. A membrane protein transports Na+ from the cytosol (10 mM) to the extracellular fluid (145 mM). When ATP is present, Na+ efflux occurs; when ATP is removed, Na+ efflux stops immediately. A nonhydrolyzable ATP analog binds the protein but does not support transport. The membrane remains intact, and Na+ channels are blocked to prevent diffusion. Which mechanism best explains Na+ movement across the membrane?
16. A researcher increases the size of a spherical cell while keeping membrane permeability and external conditions constant. The cell produces a waste molecule at a constant rate per unit volume, and waste leaves by diffusion across the membrane. As radius increases, the internal waste concentration rises. Which explanation best accounts for the relationship between radius and internal waste concentration?
17. A signaling molecule binds to a G protein–coupled receptor (GPCR) on a muscle cell. In untreated cells, the Gα subunit rapidly exchanges GDP for GTP after ligand binding. In cells treated with a drug that prevents GDP release from Gα, the ligand still binds the GPCR but downstream second-messenger levels do not change. Which of the following best explains why the drug blocks early signal transduction?
18. In a flowering plant, tall stems (T) are completely dominant to short stems (t). A true-breeding tall plant (TT) is crossed with a short plant (tt). All offspring receive one allele from each parent. The phenotype of each offspring depends on whether it has at least one T allele. Which genotype will be present in all offspring of this cross?
19. A freshwater protist contains a contractile vacuole that periodically fills and then expels water to the outside of the cell. The surrounding pond water has a lower solute concentration than the cytosol. Which outcome is most likely if the contractile vacuole stops functioning?
20. A cell releases signaling molecule K that binds to receptors on many nearby cells. A second molecule, J, is released simultaneously and binds K in the extracellular space, forming a complex that cannot bind the receptor. When J is present, the response to K decreases. Which of the following best explains the decreased response?

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