1 question, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 1
Arctic foxes grow brown fur in summer and white fur in winter. Which statement best explains how one fox can produce both fur colors?
Answer and reasoning
AWinter cold causes mutations in its fur-color genes each year, and these mutations reverse in summer. A student who thinks the environment changes phenotype by changing genes picks this. The genotype stays the same; only its expression changes.
BThe fox decides to grow white fur each winter because it needs camouflage in the snow. A student who explains traits by purpose picks this. The change is a response to environmental cues, not a decision, even though white fur is useful in snow.
CIts genotype stays the same, but seasonal changes in its environment change gene expression in its fur cells.Correct The fox's alleles do not change between seasons. Environmental cues that change with the seasons alter which genes are expressed in the cells that produce fur, so the same genotype produces two phenotypes: an example of phenotypic plasticity.
DEach winter, natural selection removes foxes with brown-fur alleles, so the foxes turn white. A student who confuses a change in one individual with evolution of a population picks this. The same fox changes color each season; no alleles are removed.
In preparation: 0 of 1 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
5.5.A.1 Phenotypic plasticity Fix
Phenotypic plasticity
The ability of one genotype to produce different phenotypes in different environmental conditions.
Genotype
The set of alleles an individual carries for one or more genes. Environmental conditions during an individual's life do not change its genotype in a directed way.
Phenotype
The observable expression of an individual's traits, which results from its genotype acting in a particular environment.
Environmental influence on gene expression
Environmental conditions such as temperature, light, day length or chemical signals can change whether, when or how much a gene is expressed, and so change the phenotype without changing the DNA sequence.
Temperature-dependent sex determination
In some reptiles, the sex of an offspring is determined by the temperature at which the egg is incubated during development, rather than by sex chromosomes.
Genetically identical individuals
Individuals with the same genotype, such as cuttings or other clones of one plant. Comparing them in different environments shows the effect of environment with genotype held constant.
Phenotype–environment graph
A graph that plots a measured phenotype of each genotype against an environmental variable; differences along one genotype's line show plasticity, and lines that cross show that the genotype with the largest value depends on the environment.
Percent change
The change in a value divided by the original (reference) value, multiplied by 100.
Students often think When an environmental condition changes an organism's phenotype, it does so by changing its genes, for example by causing mutations or changing its alleles. In fact Not in the examples of phenotypic plasticity. The environment changes how the existing genotype is expressed or acts, not the DNA sequence of the genes. Environmental agents that do cause mutations (such as some chemicals or radiation) do so at random, not to produce a particular phenotype.
Students often think A trait that an organism develops because of its environment is passed on to its offspring. In fact Generally no. A phenotype produced by the environment does not change the alleles in the gametes, so offspring inherit the genotype, not the parent's environmentally produced phenotype; in examples such as flower color in soil of different pH or fur color in Himalayan rabbits, the offspring's phenotype depends on its own environment.
6 more questions. Every wrong answer here is a real mistake students make, and you see why it is wrong as soon as you answer.
Question 1 of 6
A gardener takes several cuttings from one hydrangea plant, so the cuttings are genetically identical. The cuttings planted in acidic soil produce blue flowers, and those planted in alkaline soil produce pink flowers. Which statement about these plants is correct?
Answer and reasoning
AAlkaline soil caused mutations in the flower-color genes of the cuttings planted in it. A student who thinks an environment changes phenotype by changing genes picks this. Soil pH changes the color the existing genotype produces; the cuttings' genotypes are unchanged.
BThe cuttings share one genotype, but the soil they grow in affects their flower-color phenotype.Correct The cuttings came from one plant, so they have the same genotype. Their different flower colors show phenotypic plasticity: the same genotype produces different phenotypes in different soil conditions.
CSeeds from the pink-flowered cuttings will grow into pink-flowered plants in any soil they are planted in. A student who thinks environmentally produced traits are inherited picks this. Offspring inherit alleles, not the pink color produced by alkaline soil; their color will depend on their own soil.
DEach cutting chose the flower color that would best attract pollinators in its soil. A student who explains traits by purpose picks this. The color change is a response of the plant's cells to soil conditions, not a choice.
In Himalayan rabbits, the enzyme that makes dark fur pigment is active at the cooler temperatures of the ears, nose, feet and tail but inactive at the warmer temperature of the rest of the body, where fur grows white. A patch of white fur is shaved from a rabbit's back, and an ice pack is kept on the patch while the fur regrows. The rabbit is later mated with another Himalayan rabbit. Which outcome is predicted?
Answer and reasoning
AThe new fur on the patch would be dark, and the rabbit's offspring would all have dark fur on their backs. A student who thinks environmentally produced traits are inherited picks this. The ice pack changed the phenotype of one patch, not the alleles passed to offspring.
BThe new fur on the patch would be white, because the rabbit's fur-color genotype has not been changed. A student who thinks phenotype is fixed by genotype alone picks this. The genotype is unchanged, but the enzyme it codes for is active in cool skin, so the fur grows dark.
CThe new fur on the patch would be dark, but the rabbit's offspring would have the usual pattern.Correct Cooling the skin lets the pigment enzyme work, so the regrowing fur is dark. The rabbit's alleles are unchanged, so its offspring inherit the same genotype and develop the usual pattern: dark fur only on the cool extremities.
DThe cold would cause a mutation, so the patch would grow dark fur at every later molt. A student who thinks the environment changes phenotype by mutating genes picks this. Once the ice pack is removed, later fur on the warm back would grow white again.
In a hypothetical species of turtle, eggs from the same population were incubated at different constant temperatures, and the sex of each hatchling was recorded. The graph shows the percentage of hatchlings that were female. Which statement is supported by the data?
Answer and reasoning
ABetween 26 °C and 31 °C, the percentage of females rose from near 0% to near 100%.Correct At 26 °C, 2% of hatchlings were female, and at 31 °C, 96% were, so across this range the percentage rose from near 0% to near 100%. Outside it, the percentage changed little.
BEach 1 °C rise in temperature raised the female percentage by the same amount. A student who assumes increasing trends are linear picks this. The percentage did not change from 24 to 25 °C but rose by 30 points from 29 to 30 °C.
CHigher temperature changed which sex chromosomes the developing turtles had inherited. A student who thinks the environment changes phenotype by changing genes picks this. Temperature affected development of the embryos; the data say nothing about chromosomes, and genes are inherited at fertilization, before incubation.
DEggs incubated at 40 °C would all hatch as female turtles of this species. A student who extends a trend beyond the data picks this. No eggs were incubated above 34 °C, so the data cannot say what would happen at 40 °C.
Working Read the points: 26 °C → 2%, 31 °C → 96%. Steps: 24→25: 0; 25→26: +2; 26→27: +6; 27→28: +17; 28→29: +25; 29→30: +30; 30→31: +16; 31→32: +4; then 0. The steps are not equal. Highest temperature measured: 34 °C.
Fish of a hypothetical species living in clear, shallow water have darker skin than those living in deep water. A student hypothesizes that the darker skin is caused by greater exposure to ultraviolet (UV) light rather than by genetic differences. Which experiment would best test this hypothesis?
Answer and reasoning
ACatch wild fish from shallow water and from deep water, and compare their skin darkness. A student who thinks comparing wild groups is enough picks this. The two wild groups may differ genetically, so a difference in skin darkness could not be attributed to UV light.
BRaise all of the siblings under the same high UV light, and then measure their skin darkness. A student who thinks one treated group is enough picks this. With no low-UV group, there is nothing to compare the result with.
CRaise siblings at two water temperatures under the same UV light, and compare their skin darkness. A student who thinks changing any condition tests the hypothesis picks this. The hypothesis is about UV light, so UV light is the variable that must differ between groups.
DAssign siblings at random to high-UV and low-UV tanks, and compare their skin darkness.Correct Assigning siblings at random to the two tanks spreads genetic differences evenly, and the tanks differ only in UV light. A darker skin in the high-UV group would then be attributable to UV exposure.
Cuttings from a single plant of a hypothetical perennial species were planted at a low-elevation site and a high-elevation site. The graph shows the mean height of the plants at each site after two years. By what percentage was the mean height at high elevation lower than the mean height at low elevation?
Answer and reasoning
A33% A student who divides the difference by the high-elevation value picks this: 15/45 × 100 = 33%. The comparison is with the low-elevation mean, 60 cm.
B25%Correct The cuttings are genetically identical, so the difference is environmental. Percent change is measured from the low-elevation (reference) value: (60 − 45)/60 × 100 = 25% lower.
C75% A student who divides the new value by the reference picks this: 45/60 × 100 = 75%, which is the proportion of the height reached, not the reduction.
D15% A student who reports the difference in centimeters as the percent change picks this. The difference is 15 cm, which is 25% of 60 cm.
Working Low elevation = 60 cm, high elevation = 45 cm. Difference = 60 − 45 = 15 cm. Percent lower = 15/60 × 100 = 25%.
Researchers grew three lines of a hypothetical plant species, X, Y and Z, at three temperatures. All plants within a line are genetically identical. The graph shows the mean height of each line at each temperature. Which statement is supported by the graph?
Answer and reasoning
AEach line's height changed with temperature, and which line grew tallest depended on the temperature.Correct Every line had a different mean height at different temperatures, so each genotype shows phenotypic plasticity. Line Y was tallest at 15 °C and line X at 25 °C, so the ranking of the genotypes depends on the environment.
BHigher temperatures changed the plants' genotypes, and these genetic changes caused the differences in height. A student who thinks the environment changes phenotype by changing genes picks this. Each line's genotype is the same at every temperature; temperature changes the phenotype it produces.
CLines X and Y must carry the same alleles for height, because they grew to the same mean height at 20 °C. A student who infers genotype from one phenotype picks this. X and Y respond to temperature in opposite ways, so they differ in alleles affecting height; their lines simply cross at 20 °C.
DEach line of plants chose the height that best suited the temperature at which it grew. A student who explains traits by purpose picks this. Height changed because temperature affected each genotype's growth, not because the plants chose a suitable height.
Compiled from the AP Biology Course and Exam Description (effective Fall 2025) and our question bank · Specialist review in progress. How these pages are made · Free, no account
