AP Biology full-length mock. The whole syllabus, at the real length.

The figure shows part of a leaf cell. In the chloroplast, O₂ is released into the space inside the thylakoids. Some of this O₂ diffuses to the matrix of the mitochondrion in the same cell. How many membranes, each a single phospholipid bilayer, must an O₂ molecule cross on this path, and how does it cross them?

A researcher digests a circular plasmid with two restriction enzymes, A and B, either alone or together, and separates the resulting fragments by gel electrophoresis alongside a DNA size ladder. The sizes of the fragments detected in each lane are listed in the table.

Based on the number of fragments produced by enzyme B alone, how many recognition sites for enzyme B are present in this circular plasmid?

Enzyme A alone produces a single 6000-bp band from the circular plasmid, and no smaller fragments appear in that lane. What does this single-band result indicate about enzyme A's recognition sites in the plasmid?

The enzyme B digest is repeated, but the reaction is stopped early, so some plasmid molecules have been cut only once by enzyme B while the rest have been cut completely. Which band would appear in this lane in addition to the 3500-bp and 2500-bp bands?

A population of bacteria lives in a hot spring. A mutation produces a version of a key metabolic enzyme whose active site keeps its shape at 65 °C, whereas the ancestral enzyme denatures near 50 °C. How does this molecular variation most likely affect the population over time?

Once peas are harvested, an enzyme in them slowly breaks down the compounds that give them their green color and fresh flavor. Food scientists divided one batch of freshly harvested peas into three lots. Lot 1 was frozen at −18 °C. Lot 2 was blanched (dipped in water at 100 °C for 2 minutes), cooled, and then frozen at −18 °C. Lot 3 was blanched in the same way but not frozen. An extract was made from lots 1 and 2 after 6 months of frozen storage, and from lot 3 on the day it was blanched, and the activity of the enzyme in each extract was measured at 25 °C with an excess of its substrate. The results are shown in Table 1.

During the 6 months in the freezer, lot 1 changed only slowly in color and flavor, and lot 2 did not change. After thawing, the peas of lot 1 lost much of their green color and fresh flavor within a day at room temperature, but the peas of lot 2 did not. Which explanation is best supported by this information?

The graph shows the rate of an enzyme-catalyzed reaction at increasing substrate concentrations with no inhibitor and in the presence of two inhibitors, P and Q, each at a fixed concentration. All other conditions were held constant.

At a substrate concentration of 2 mmol dm⁻³, inhibitors P and Q each reduce the rate to about half of the uninhibited rate. Which statement best describes how their effects compare at 16 mmol dm⁻³?

Which statement best describes how inhibitor Q reduces the rate of reaction?

The concentration of inhibitor P is doubled and the experiment is repeated. Which change in the curve for P is predicted?

The figure shows the free-energy change (ΔG) of each step in a four-step pathway that breaks down compound A to compound E in a cell; each step is catalyzed by a different enzyme. Under the conditions in the cell, making ATP from ADP and inorganic phosphate (Pᵢ) has ΔG = +30 kJ/mol. The cell can make ATP only by coupling its synthesis to an individual step of the pathway. What is the greatest number of ATP molecules the cell could make for each molecule of A broken down to E?

A sample of double-stranded DNA is analyzed and found to contain 22% adenine. Based on complementary base pairing, what are the expected percentages of thymine, guanine, and cytosine in this sample?

In water, almost every glucose molecule is in one of two ring forms, α and β, which differ only in whether the –OH group on carbon 1 points below or above the ring. The ring can open, at the bond between carbon 1 and the oxygen atom in the ring, and then close again, and each time it closes it can form either ring. Pure crystals of each form were dissolved in water at 25 °C, and the percentage of the dissolved glucose in the α form was measured for 6 hours. The results are shown in the figure.

Once carbon 1 of a glucose unit is joined to another unit by a glycosidic linkage, the ring of that unit can no longer open. Disaccharide G is made of two glucose units: carbon 1 of unit 1 is joined by an α linkage to carbon 4 of unit 2, and carbon 1 of unit 2 is not joined to anything. A solution of G, freshly made with unit 2 in the β form, is kept at 25 °C for 24 hours with no enzyme present. Which prediction is best supported?

The ribosomes of all cells contain RNA. When the sequence of one ribosomal RNA is compared across thousands of species of bacteria, archaea, and eukaryotes, most regions of the molecule differ widely among species. One stretch of about 20 nucleotides, at the site where the ribosome joins amino acids into a chain, is almost identical in every species. Which explanation accounts for both observations?

A child is born with three copies of chromosome 21 (trisomy 21). Chromosome analysis shows the extra chromosome 21 was contributed by the egg. This condition most commonly arises when a chromosome pair fails to separate properly during gamete formation. The failure of homologous chromosomes (or sister chromatids) to separate during meiosis is called ______, and by itself it produces a gamete that has ______.

Mature nerve cells and many other specialized cells in the human body stop dividing and remain in a nondividing state, carrying out their normal functions but not progressing through the cell cycle. This nondividing state is best described as which of the following?

A suspension of the single-celled green alga Chlamydomonas reinhardtii was sealed in a chamber at 25 °C in a medium holding a large reserve of dissolved CO₂, and the concentration of dissolved O₂ was recorded while the light was changed, as shown in the figure. At 55 minutes, with the dim light still on, compound C was added. Compound C stops the mitochondrial electron transport chain and has no effect on the chloroplasts. Assume that the algae respire at the same rate in light and in darkness. Which prediction for the next 10 minutes is best supported?

When a DNA copy of the protein-coding sequence of the human insulin gene is inserted into bacterial cells, the bacteria transcribe and translate it and make a polypeptide with exactly the amino acid sequence that human cells make from that gene. Which conclusion about the hereditary machinery of these two very different organisms is best supported?

Eukaryotic cells contain ribosomes free in the cytosol and ribosomes bound to the endoplasmic reticulum (ER). Researchers used electron micrographs to count the ribosomes in two types of cell, A and B, from the same animal, and recorded what percent of each cell's ribosomes were bound to the ER. Table 1 shows the mean values. A student studying the table writes: "Cell type A must be the one secreting large quantities of protein, because it has twice as many ribosomes as cell type B, and ribosomes are where proteins are made."

Which statement best identifies the flaw in the student's reasoning?

The graph shows a person's blood glucose concentration over 12 hours, with the times of three meals marked by arrows. Which feature of the graph is the best evidence that blood glucose is regulated by negative feedback?

The following table gives the amino acid or signal specified by several mRNA codons. Use it to answer the questions in this set.

The mRNA 5'-AUG UUU GAA AAG UGC UAA-3' is added to a cell-free translation system that contains ribosomes, all of the amino acids, and tRNAs for every codon in the table except GAA: no tRNA in the system can pair with GAA. Which outcome is expected?

Four different single-base substitutions each change one codon of the mRNA 5'-AUG UUU GAA AAG UGC UAA-3' as shown below. Which substitution is a silent (synonymous) mutation that does not change the polypeptide?

A mutation changes the fourth codon (AAG) of the mRNA 5'-AUG UUU GAA AAG UGC UAA-3' into UAG. Which of the following best describes the effect on the polypeptide and on the resulting phenotype?

Cultured cells respond to hormone G, which binds a receptor on the cell surface and starts a signaling cascade inside the cell. Researchers exposed cultures to six concentrations of G and measured the percentage of the cells' receptors that had G bound and the size of the cells' response, expressed as a percentage of the largest response the cells can give. The results are shown in Table 1.

The researchers then treated cells with a drug that binds permanently to 80 percent of the receptors, so that G cannot bind them; the other receptors are unaffected. Which prediction about the response of the treated cells to 100 nM G is best supported by the data?

Bacterium S has channel proteins in its plasma membrane that open only when the membrane is stretched; when open, each channel lets ions and other small solutes through. Cells of the normal strain and of a mutant strain that lacks these channels, all with intact cell walls, were grown in a medium with a high solute concentration and then moved suddenly into distilled water or into fresh growth medium. In some cells, ATP synthesis was blocked for 10 minutes before the move. The table shows the percentage of cells surviving 10 minutes after the move.

Which explanation of how the normal strain survives the move into distilled water is best supported by the data?

During childbirth, stretching of the uterine wall stimulates the release of oxytocin, which increases the strength of uterine contractions. These stronger contractions stretch the uterus further, causing still more oxytocin to be released until the baby is delivered. Which term best describes this regulatory mechanism, and why?

Two populations of a wild annual plant, a Coast population and an Inland population, have been separated by a mountain range for many thousands of years. Researchers grew plants from both populations in one greenhouse. They crossed Coast plants with Inland plants to produce F1 hybrids, then crossed F1 hybrids with each other to produce F2 hybrids. They measured the percent of pollen grains that were viable in 20 plants of each group. The figure shows the mean percent of viable pollen ± 2SE for each group.

The researchers' null hypothesis is that F1 hybrids and Coast plants have the same mean percent of viable pollen. Which statement about this null hypothesis is best supported by the data?

Mice of one inbred laboratory strain are genetically identical. Researchers took 20 male mice of this strain, all born in the same week, and divided them into two groups at weaning (3 weeks old). They reared one group at 25 °C and the other at 10 °C, with the same food, cages and light schedule. When the mice were 9 weeks old, the researchers measured three traits in every mouse. The results are shown in Table 1 as mean ± 2SE.

A student claims that rearing at 10 °C caused a statistically significant change in all three traits. Which evaluation of the claim is best supported by the data in Table 1?

In a classic experiment, a plant is supplied with water containing a heavy isotope of oxygen, while its CO₂ contains only ordinary oxygen. The O₂ gas released during photosynthesis carries the heavy isotope. From which molecule does the released O₂ originate?

A student compares a molecule of DNA with a molecule of messenger RNA taken from the same cell. Which set of differences correctly distinguishes the RNA from the DNA?

Two polypeptides are each 100 amino acids long and contain exactly the same set of amino acids, but arranged in a different order. When each folds, the two proteins adopt different three-dimensional shapes and carry out different functions. Which statement best explains this outcome?

Why are ecosystems with high species diversity generally more resistant to disturbance than those with low diversity?

A bacterial population of 200 cells is growing exponentially with a per-capita growth rate r = 0.5 per hour. Using the exponential model dN/dt = rN, what is the population's growth rate at this instant?

In a grassland, grasshoppers eat the plants, and a ground-nesting bird feeds its nestlings mainly on grasshoppers. Over 8 years, ecologists measured five variables at 30 grassland sites and used a statistical model to estimate the effect of each variable on the others. In the model, a solid arrow shows a statistically significant effect, a thicker solid arrow shows a larger effect, and + shows that an increase in the first variable increases the second. A dashed arrow shows an effect that was not statistically significant.

A rancher irrigates part of this grassland every spring, adding about as much water as an unusually wet spring would bring, while summer temperature is unchanged. Based on the model, which prediction for the irrigated part is best supported?

A desert annual plant germinates after winter rain, flowers once, and dies. Some plants have hairy leaves and others have smooth leaves. The plant self-pollinates, and seeds from each form grow into plants of the same form. In one wet year and one later dry year, researchers marked 500 newly emerged seedlings of each form at the same site, recorded the percent that survived to flower, and counted the seeds produced by each flowering plant.

Which leaf form had the greater fitness in the wet year?

Suppose the next four years are wet, dry, wet, dry, and the plants in each year perform exactly as in the table for that type of year. Which pattern of change in the frequency of the smooth-leaf form is expected?

In which type of year did the two leaf forms differ more in fitness?

A student wrote two statements about bacteria.
Statement 1: "When a bacterium divides by binary fission, its chromosome is copied exactly, so all the cells descended from one bacterium have identical DNA."
Statement 2: "Because bacteria reproduce asexually, a bacterial cell can never gain genes from another bacterium."
Which of the following best evaluates the student's statements?

Cells of a cultured line release a growth signal, G, and carry receptors for G; a cell divides only when G binds its receptors. Researchers also made two mutant lines: line M makes no G but has normal receptors, and line N makes normal G but has no receptors for G. Cells were spread so sparsely that no cell was near another, and in one dish line M cells were given medium taken from a crowded culture of line N. The percentage of cells that divided within 2 days is shown in the table. Which conclusion is best supported by the data?

In aerobic respiration, most ATP is produced by oxidative phosphorylation rather than by substrate-level phosphorylation in glycolysis and the Krebs cycle. What directly powers ATP synthase during oxidative phosphorylation?

A population of 500 beetles is reduced to 12 individuals by a flood, then recovers to 500 over several generations. Compared with the original population, the recovered population is most likely to show

Purple loosestrife, introduced to North American wetlands, grows rapidly and forms dense stands that crowd out native cattails and sedges, reducing food and nesting habitat for native wildlife. Which statement best describes its effect as an invasive species?

Cells of a cultured line respond to signal L, which binds a receptor on the cell surface. Researchers gave the cells three 1-minute pulses of fresh medium containing the same concentration of L, washing the cells after each pulse, and recorded the peak response to each pulse. When the pulses were 10 minutes apart, the second and third responses were 58% and 31% of the first. When the pulses were 60 minutes apart, they were 96% and 94% of the first. In cells treated with drug D, which stops a cell from taking proteins of its plasma membrane into the cell in vesicles, pulses 10 minutes apart gave second and third responses of 97% and 95% of the first. Which explanation is best supported by these results?

According to the endosymbiotic hypothesis, mitochondria and chloroplasts each descend from a free-living prokaryote that was taken in by a host cell. As each organelle evolved, many of its genes moved into the host cell's nucleus, where they stay even in a line of descendants that later loses the organelle. Researchers studied 400 species of single-celled eukaryotes drawn from all the major lines of eukaryotes. In every species, the mitochondrial DNA is most similar to the DNA of one group of aerobic bacteria; in every species that has chloroplasts, the chloroplast DNA is most similar to the DNA of cyanobacteria, which are photosynthetic bacteria. No species was found that has chloroplasts but no mitochondria. Table 1 summarizes the results.

Which sequence of events is best supported by the data?

Snowshoe hares grow a brown coat in summer and a white coat in winter. Researchers randomly assigned hares from one population to two rooms held at the same constant temperature (20 °C). In Room 1 the daily light period stayed at 16 hours; in Room 2 it was shortened gradually to 8 hours over several weeks. Only the hares in Room 2 molted into a white coat. Which conclusion is best supported by these results?

A lysosome contains hydrolytic enzymes that work best at a pH of about 5, which is more acidic than the surrounding cytoplasm (pH ~7). Which statement best explains how the lysosome maintains this internal environment?

Settlers brought rats and a small predatory mammal to an island on which no ground-hunting mammals had ever lived. Within a century, most of the island's ground-nesting bird species had become extinct, although the birds' forest habitat and food supply changed little. On a nearby continent, where such mammals are native, related ground-nesting birds have persisted alongside them for millions of years. Which explanation best accounts for the extinctions on the island?

A hillside meadow grows on soil poor in nitrogen, and the growth of its plants is limited by the nitrogen supply. Clover, a plant whose root partners add nitrogen to the soil, did not grow in the meadow. Ecologists sowed clover seed into 10 plots in the meadow and left 10 similar plots unsown. Table 1 shows measurements in the unsown plots and in the sown plots 2 and 15 years after sowing; the unsown plots changed little over the 15 years.

Which statement best describes how adding clover changed the structure of the meadow community?

In a certain plant, purple flower color (P) is dominant to white (p). Two plants heterozygous for flower color are crossed. What proportion of the offspring is expected to be white-flowered?

When epinephrine binds a receptor on a liver cell, a G protein activates adenylyl cyclase, which produces cAMP; cAMP then activates protein kinase A, ultimately causing glycogen to be broken down into glucose that is released into the blood. Which of the following events represents the transduction stage of this signaling pathway?

The pedigree shows the inheritance of a rare autosomal recessive disorder. Shaded symbols are affected individuals. II-4 married into the family and has no family history of the disorder; assume he does not carry the recessive allele. Use A and a for the alleles.

What is the probability that II-3 is a carrier of the recessive allele?

What is the probability that III-1 is a carrier of the recessive allele?

Ecologists followed a population of a leaf-feeding moth in one forest for six years. Each spring they estimated the density of the caterpillars, and then they recorded the percentage of those caterpillars killed by parasitoid wasps, which lay their eggs inside caterpillars, and the percentage killed by heavy summer rainstorms, which wash caterpillars off the leaves.

Which mortality factor could keep this moth population near a stable density over many years, and why?

A green alga makes two membrane lipids, K and L. One of the two lipids contains phosphorus but no sulfur; the other contains sulfur but no phosphorus. Cells grown in a complete medium were transferred at day 0 either to a medium without phosphate, the only source of phosphorus, or to a medium without sulfate, the only source of sulfur; the two media were otherwise identical to the complete medium. The figure shows the amount of each lipid per cell over the next 8 days.

Cells from the same culture are transferred to a medium that lacks both phosphate and sulfate. Which prediction is best supported by the data?

A soil bacterium grows well in a medium that contains only water and these substances: glucose (C₆H₁₂O₆), ammonium chloride (NH₄Cl), potassium phosphate (KH₂PO₄), magnesium sulfate (MgSO₄), and traces of a few metal ions. The bacterium can take up and break down glucose, glycerol (C₃H₈O₃), and the amino acid glycine (C₂H₅NO₂). Which single change to the medium would most reduce the number of new cells that the medium can support?

Strains of a soil bacterium differ in how many copies they carry of the gene for an enzyme that breaks down a toxic compound. Strains with four copies make about four times as much of the enzyme as strains with one copy. Which outcome is most likely when both strains grow in soil that contains the toxic compound?

A biologist compares a bacterial cell with a plant cell using electron microscopy. Which structural difference best reflects the greater compartmentalization of the eukaryotic cell?

When two protist species that require the same food resource are grown together in one culture, one species consistently drives the other to local extinction, even though each species thrives when grown alone. This outcome best illustrates which of the following?

A food scientist measured the melting points of six pure fatty acids that differ in the number of carbon atoms in the chain and in the number of carbon to carbon double bonds (C=C) it contains. A fatty acid is solid at 25 °C if its melting point is above 25 °C, and liquid if its melting point is below 25 °C. The results are shown in Table 1.

A student claims: “Whether a fatty acid is solid or liquid at 25 °C depends only on whether its chain has a C=C double bond. Fatty acids with no double bond are solid, and fatty acids with a double bond are liquid.” Which evaluation of the claim is best supported by the data?

In the 1800s, botanists knew that the living contents of a plant cell lose water and shrink in a concentrated sugar solution, but not which part of the cell controls what passes into it. Model 1 proposed that the cell wall is the selectively permeable boundary of the cell. Model 2 proposed that a thin boundary around the living contents, just inside the wall, is the selectively permeable boundary. A botanist placed living leaf cells in a concentrated sucrose solution colored with a blue dye whose molecules are about the size of sucrose molecules. Under the microscope, the living contents of each cell shrank away from the wall, the space between the wall and the shrunken contents filled with blue solution, and no blue color appeared in the contents themselves. How does this observation bear on the two models?

At deep-sea hydrothermal vents where no sunlight penetrates, bacteria oxidize hydrogen sulfide (H₂S) to fix carbon into organic molecules, and tube worms and other animals depend on these bacteria. Which statement best describes how energy enters this community?