Learn Extracted exam questions AP Biology 2026 Free Response
2026 Free Response
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Molecules known as dinucleoside polyphosphates, a type of nucleotide, are signaling molecules that accumulate in plant cells during dry or stressful conditions.
The following information applies to parts B, C, and D.
Stomata are pores on the surface of leaves that open when exposed to light and regulate the flow of carbon dioxide, oxygen, and water vapor in and out of a plant. In response to dry environmental conditions, many plants close their stomata, which reduces water loss.
Scientists hypothesized that the dinucleoside polyphosphates $\text{Ap}_4\text{A}$ and $\text{Cp}_4\text{C}$ bind to DORN1 receptors on the plasma membrane of plant cells and initiate signaling cascades that cause stomata to close. The scientists exposed plants to light to open the stomata and then placed samples of the leaves in buffer alone or in buffer containing one of three different compounds: $\text{Ap}_4\text{A}$, $\text{Cp}_4\text{C}$, or abscisic acid (ABA), a molecule that causes stomata to close.
The scientists measured the size of the stomata in each sample and calculated their sizes relative to the size of the stomata in the sample kept in buffer alone, as shown in Figure 1.
Figure 1. Effect of $\text{Ap}_4\text{A}$, $\text{Cp}_4\text{C}$, and ABA on Relative Stomatal Size (Error Bars Represent $\pm \text{SE}_{\bar{x}}$)
[Bar graph; y-axis "Relative Size of Stomata (width/length)" from 0.0 to 1.1 in increments of 0.1; x-axis "Treatment" with four bars: Buffer, $\text{Ap}_4\text{A}$, $\text{Cp}_4\text{C}$, ABA. Approximate bar heights with error bars: Buffer $\approx 1.0 \pm 0.05$; $\text{Ap}_4\text{A} \approx 0.65 \pm 0.05$; $\text{Cp}_4\text{C} \approx 0.62 \pm 0.05$; ABA $\approx 0.70 \pm 0.05$.]
Describe the three structural components of a nucleotide.
Identify the dependent variable in the scientists' first experiment.
Based on Figure 1, describe the relative size of the stomata in the $\text{Cp}_4\text{C}$ treatment group as compared with the size of the stomata in the group treated with buffer alone.
Justify the use of buffer alone as a control in the scientists' experiments.
In a second experiment, the scientists used plants that were identical to those in the first experiment except that the gene encoding the DORN1 receptor was mutated. The scientists repeated the procedure of the first experiment. Their results are shown in Figure 2.
Figure 2. Effect of $\text{Ap}_4\text{A}$, $\text{Cp}_4\text{C}$, and ABA on Relative Stomatal Size in DORN1 Mutants (Error Bars Represent $\pm \text{SE}_{\bar{x}}$)
[Bar graph; y-axis "Relative Size of Stomata (width/length)" from 0.0 to 1.2 in increments of 0.1; x-axis "Treatment" with four bars: Buffer, $\text{Ap}_4\text{A}$, $\text{Cp}_4\text{C}$, ABA. Approximate bar heights with error bars: Buffer $\approx 1.0 \pm 0.05$; $\text{Ap}_4\text{A} \approx 1.1 \pm 0.1$; $\text{Cp}_4\text{C} \approx 0.70 \pm 0.05$; ABA $\approx 0.60 \pm 0.05$.]
Justify the scientists' treating one sample of leaves with ABA in the experiments.
Based on Figure 2, describe the difference between the effects of $\text{Ap}_4\text{A}$ and $\text{Cp}_4\text{C}$ treatments on the size of stomata in plants with mutated DORN1 receptors.
Activation of DORN1 receptors induces plant cells to produce certain molecules that cause the stomata to close. Based on the data in Figures 1 and 2 for cells treated with $\text{Ap}_4\text{A}$, predict the relative production of the molecules by DORN1-mutated cells in comparison to the production by nonmutated cells.
The DORN1 receptor transmits signals that result in an increase in the transcription of genes involved in plant defenses. The scientists then developed DORN1-mutant plants in which the DORN1 receptor lacked most of its intracellular domain.
In cells homozygous for this mutation, predict the effect of $\text{Ap}_4\text{A}$ treatment on transcription of the genes involved in plant defenses relative to the effect of $\text{Ap}_4\text{A}$ on nonmutated cells.
Justify your prediction.
Eukaryotic cells use small interfering RNA (siRNA) molecules that regulate the expression of certain genes by binding to complementary sequences in target mRNAs. This binding causes the protein AGO2 to cleave the target mRNAs. As a result of the cleavage, the mRNAs are not translated.
The following information applies to parts B, C, and D.
To investigate the role of AGO2 in the cleavage of mRNA transcribed from two genes, Gene $G$ and Gene $H$, scientists determined the amount of Gene $G$ and Gene $H$ mRNA produced in cells with three different AGO2 genotypes:
- Homozygous for the wild-type AGO2 protein ($AGO2^{+/+}$)
- Heterozygous for the allele encoding a nonfunctional AGO2 protein ($AGO2^{+/-}$)
- Homozygous for the allele encoding a nonfunctional AGO2 protein ($AGO2^{-/-}$)
The scientists then calculated the amount of Gene $G$ and Gene $H$ mRNA produced from cells of each genotype relative to that in $AGO2^{+/+}$ cells. These results are shown in the table.
Relative Average Amounts of Gene $G$ and Gene $H$ mRNA in Cells with Different AGO2 Genotypes
| mRNA in $AGO2^{+/+}$ Cells $\pm \text{SE}_{\bar{x}}$ | mRNA in $AGO2^{+/-}$ Cells $\pm \text{SE}_{\bar{x}}$ | mRNA in $AGO2^{-/-}$ Cells $\pm \text{SE}_{\bar{x}}$ | |
|---|---|---|---|
| Gene $G$ | $1.0 \pm 0.1$ | $0.9 \pm 0.4$ | $1.5 \pm 0.5$ |
| Gene $H$ | $1.0 \pm 0.1$ | $2.0 \pm 0.1$ | $3.0 \pm 0.4$ |
Describe one location where ribosomes are found in eukaryotic cells.
Using the template in the space provided for your response, construct a bar graph that represents the data in the table. Your graph should be appropriately plotted and labeled.
Based on the table, determine all the cells in which the amount of Gene $G$ mRNA produced is statistically the same as the amount in the cells with the $AGO2^{+/+}$ genotype.
Based on the table, describe the relationship between the number of wild-type copies of the AGO2 gene and the amount of Gene $H$ mRNA in the cells.
Based on the data in the table for Gene $H$, calculate the percent by which the average amount of mRNA in $AGO2^{-/-}$ cells increases compared with that in $AGO2^{+/-}$ cells.
The scientists claim that siRNA binding and AGO2 cleavage of mRNAs play a greater role in the regulation of Gene $H$ expression than in the regulation of Gene $G$ expression. Based on the table, support the scientists' claim.
Anaphase I of meiosis is blocked in mice with the $AGO2^{-/-}$ genotype. Scientists hypothesize that the block in meiosis occurs because the continued presence of a spindle-fiber stabilizing protein prevents the chromosomes from separating. Based on the table, explain how the $AGO2^{-/-}$ genotype could cause this effect on the dividing cells.
Cyanide is a chemical that affects the enzyme cytochrome c oxidase (CCO), a key enzyme in the mitochondrial electron transport chain. At high cyanide concentrations, CCO activity is much lower than when no cyanide is present. At low concentrations of cyanide, CCO activity is slightly higher than when no cyanide is present, as shown in Table 1.
Table 1. Effects of Cyanide on CCO Activity
| No Cyanide | Low Cyanide | High Cyanide |
|---|---|---|
| Normal CCO activity | Slightly increases CCO activity | Greatly decreases CCO activity |
Some strains of bacteria produce cyanide, which they then release into their environment. Other strains of bacteria do not produce cyanide. Researchers grew both types of bacteria in high-concentration nutrient medium and then isolated the medium from the bacteria. One-half of each medium sample was left at a high concentration, while the concentration of the other half was lowered.
To study the effects of cyanide on mammalian cells, researchers then added the four samples of media to the cells growing in culture dishes, as shown in Table 2. They measured ATP and lactic acid production by the mammalian cells in each of the four treatment groups.
Table 2. Experimental Design to Test Effects of Cyanide on Mammalian Cells
| Mammalian Cell Treatment Group | Cyanide in Nutrient Medium? | Concentration of Medium |
|---|---|---|
| 1 | Yes | High |
| 2 | Yes | Low |
| 3 | No | High |
| 4 | No | Low |
Describe the advantage to cells of producing ATP from one molecule of glucose by aerobic cellular respiration rather than by glycolysis alone.
Identify the two treatment groups that served as controls in the researchers' experiment.
Based on the information provided in both tables, predict the treatment group that is likely to have the highest ATP production of all four treatment groups.
The researchers claim that cells in which CCO activity is inhibited will show an increase in lactic acid production. Support the researchers' claim.
The process of meiosis enables animals that reproduce sexually to produce gametes.
Describe one characteristic of chromosome movement during Meiosis I.
Explain why chromosomes are more visible when viewed under a microscope during mitosis or meiosis than at any other time in the cell cycle.
An animal cell with two pairs of homologous chromosomes (a diploid number of four) has undergone meiosis to produce four gametes, and an error occurred at one step, as shown in the figure. One set of chromosomes is represented in white, and the other set is represented in gray.
An Animal Cell Undergoing Meiosis
[Diagram of a dividing cell (undergoing Meiosis II, anaphase-like stage) with spindle fibers, showing an error where chromosomes failed to separate properly on one side. Legend: a white/gray joined pair of sister chromatids = Chromosome 1; a smaller white/gray joined pair = Chromosome 2. In the cell: the left half shows one Chromosome 1 pair (still joined, both chromatids) plus one single Chromosome 2 chromatid; the right half shows one single Chromosome 2 chromatid and one single (unpaired) small chromatid. Four arrows point from the cell to four resulting gamete circles: gamete 1 contains three chromatids (an extra copy of Chromosome 1 plus Chromosome 2 material); gamete 2 similarly contains three chromatids; gamete 3 contains one single small chromatid; gamete 4 contains one single small chromatid. (Net effect: two gametes end up with an extra copy of Chromosome 1, and two gametes are missing a copy of Chromosome 1 - i.e., nondisjunction of Chromosome 1 during Meiosis II.)]
Assume that each gamete produced by the cell shown in the figure is fertilized by a gamete with a complete haploid set of chromosomes. Also assume gene regulation on Chromosome 1 is not affected by the number of copies of Chromosome 1 in the four resulting viable zygotes. Predict the difference in mRNA production from genes on Chromosome 1 among the four possible zygotes.
Triploidy describes a condition in which an organism has three complete sets of chromosomes in each cell. Provide reasoning to justify the claim that most organisms with triploidy cannot produce gametes with the chromosome number typical of the species.
Anole lizards throughout the Caribbean islands and Central and South America have pads of varying sizes on the bottom surfaces of their toes. The sizes of the toe pads are genetically determined and not the result of phenotypic plasticity. During storms with high winds, anoles cling to trees with the help of their toe pads. In recent years, an increase in both the number and intensity of storms has occurred across the range of anole habitats.
In 2017, two very intense storms occurred in the Caribbean islands within a month. In 2019, scientists investigated the relationship between the intense storms and the average toe pad size of the offspring of lizards that survived the storms. The scientists determined the average toe pad size of the surviving offspring and grouped their measurements into three categories: small, medium, and large toe pads. The scientists then compared the 2019 toe pad measurements with measurements recorded prior to 2017. Their data are represented in the figure.
A Map Representing Toe Pad Size Distributions Prior to 2017 and in 2019
[Two side-by-side maps of the Caribbean islands and northern South America, labeled "Prior to 2017" and "2019". Symbols mark average toe pad size at various island/mainland locations: circle = Small, triangle = Medium, diamond = Large.
Prior to 2017 map: Caribbean islands region shows small circles and medium triangles (two small circles near the northern islands, two medium triangles near the central islands, one medium triangle further east/south near a smaller island). Mainland South America shows small circles at several locations (one near the northern coast, one further inland, two further south).
2019 map: Caribbean islands region shows the same island locations now marked with medium triangles (hatched, labeled "1") near the northern islands, and large diamonds (solid black, labeled "2") near the central islands, and a large diamond (labeled "3") near the smaller southeastern island. Mainland South America shows darker-shaded circles at the same locations as before (one near the northern coast marked with a dark circle, region labeled "4" near an inland dark circle, two further south with dark circles).
Legend: "Average Toe Pad Size" - open diamond = Large, open triangle = Medium, open circle = Small. "Storm Intensity" - a vertical gradient bar from black (Greatest) through hatched/gray shades down to gray (Least) and white (No storms), corresponding to the shading/fill of each map symbol.]
Describe the role that changes in abiotic factors have in natural selection.
Based on the figure, explain the relationship between storm intensity and average toe pad size.
Identify the region on the 2019 map, by indicating the number, that experienced the least storm intensity.
Based on the information provided, explain how continued differences in storm intensity can apply different selective pressures on anole populations living on the Caribbean islands, eventually leading to speciation.
Many raptors in Africa are top predators and keystone species in their ecosystems. Raptor population sizes have been declining in recent years.
Scientists studied the relationship between the conversion of the raptors' natural habitat into farmland and the population sizes of raptors in those regions. They compiled raptor population size data from three different regions of Africa: Region 1, Region 2, and Region 3. In each of the regions, the scientists compared the annual percent change in the raptor population size in areas that were protected from farming (protected) with the annual percent change in areas where farming occurred (unprotected). Their results are shown in the box and whisker plot.
Median Annual Percent Change in the Population Size of Raptors in Protected and Unprotected Areas
[Box-and-whisker plot; y-axis "Annual Percent Change in Population Size" from $-14.0$ to $6.0$ in increments of $2.0$; x-axis groups: Region 1, Region 2, Region 3, each with two boxes (white = Protected area, gray = Unprotected area); a dashed horizontal reference line at $y=0$.
Region 1 - Protected area: whiskers from about $-5.0$ to $0.8$, box (IQR) from about $-2.3$ to $-0.8$, median line at about $-1.7$. Region 1 - Unprotected area: whiskers from about $-10.3$ to $0.2$, box from about $-8.2$ to $-2.3$, median line at about $-4.3$.
Region 2 - Protected area: whiskers from about $-2.2$ to $5.2$, box from about $-1.2$ to $3.4$, median line at about $0.0$. Region 2 - Unprotected area: whiskers from about $-9.4$ to $4.3$, box from about $-6.1$ to $-0.8$, median line at about $-3.0$.
Region 3 - Protected area: whiskers from about $-12.1$ to $2.3$, box from about $-7.0$ to $-1.2$, median line at about $-2.3$. Region 3 - Unprotected area: whiskers from about $-8.8$ to $2.9$, box from about $-4.2$ to $-1.1$, median line at about $-2.4$.]
Based on the box and whisker plot, identify the median annual percent change in population size in the unprotected area of Region 2.
Based on the box and whisker plot, identify the region and area that experienced the greatest median annual percent change in population size.
Researchers hypothesize that if farming is eliminated in Region 2, there will no longer be a decline in the raptor population size. Based on the data in the box and whisker plot, evaluate the researchers' hypothesis.
Based on the information provided, explain why ecosystem resilience in unprotected areas may decline over time.