Middle School Science Quiz: Traits Affect Populations

20 questions · exam conditions

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Traits Affect PopulationsQuestion 1 of 20

A population of flowering plants has trait variation in flower tube length: short or long. A pollinator shift occurs: over 6 years, long-tongued moths become more common than short-tongued bees. Seed counts show that in years with more moths, long-tube plants produce more seeds than short-tube plants. Trait frequencies change from Year 0 to Year 6: short-tube 70% to 40%, long-tube 30% to 60%. Traits can affect population outcomes. Which claim about traits is incorrect based on the evidence?

Long-tube plants increased in the population because they produced more seeds when moths were the main pollinators.

The shift in pollinators is evidence that the environment can change which traits lead to higher reproductive success.

Short-tube plants became rare because each plant changed its tube length during its lifetime to match the moths.

The data show a change in trait frequencies over time in the plant population.

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Middle School Science Quiz

Middle School Science Quiz: Traits Affect Populations

Practice Traits Affect Populations in Middle School Science with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Traits Affect Populations, giving you a quick way to practice the rules, question types, and explanations that matter most for Middle School Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Long-tube plants increased in the population because they produced more seeds when moths were the main pollinators.
The shift in pollinators is evidence that the environment can change which traits lead to higher reproductive success.
Short-tube plants became rare because each plant changed its tube length during its lifetime to match the moths. (correct answer)
The data show a change in trait frequencies over time in the plant population.

Explanation: The core skill is evaluating claims about how traits influence population outcomes, identifying which are supported or incorrect based on evidence. Populations of flowering plants include varied traits, such as short or long flower tubes, allowing different interactions with pollinators like bees or moths. Evidence from seed counts and trait frequency data shows long-tube plants increasing from 30% to 60% over six years as moth pollinators became dominant, indicating a population shift. To check, verify if claims align with evidence of reproductive success differences rather than individual changes. A misconception is that plants alter their own traits during life and pass those changes on, but population changes occur through inherited traits and selection. Population traits shift over generations as plants with long tubes produce more seeds with moth pollinators, leading to higher representation. This differential success causes advantageous traits to spread in the population.

Question 2

A population of bacteria contains two trait types: antibiotic-resistant (R) and non-resistant (N). The environment includes an antibiotic in the water for 8 weeks. Population counts were measured:

Week 0: R = 5% (50 cells), N = 95% (950 cells) Week 4: R = 40% (400 cells), N = 60% (600 cells) Week 8: R = 90% (900 cells), N = 10% (100 cells)

Traits can affect population outcomes. Which claim about traits is incorrect based on the evidence?

The resistant trait became more common because resistant bacteria survived and reproduced more in the antibiotic environment, changing the population over many generations.
There was trait variation in the population at Week 0, and that variation is important for explaining the later change in trait frequency.
Most non-resistant bacteria turned into resistant bacteria because they were exposed to the antibiotic, so the trait frequency changed mainly by individuals changing traits. (correct answer)
The antibiotic environment is consistent with the increase in the resistant trait frequency over time.

Explanation: This question tests understanding how traits affect populations by identifying an incorrect claim about bacterial resistance. Populations contain individuals with varied traits—here, bacteria that are either resistant or non-resistant to antibiotics—and this variation existed before the antibiotic was introduced (5% were already resistant at Week 0). The evidence shows a dramatic shift from 5% resistant to 90% resistant over 8 weeks in the presence of antibiotics, indicating strong selection pressure. To find the incorrect claim, look for statements that contradict how traits actually change in populations. A critical misconception is that individuals can change their traits during their lifetime (option C claims non-resistant bacteria "turned into" resistant bacteria), but antibiotic resistance is a genetic trait that bacteria either have or don't have—they cannot acquire it by exposure. Population traits shift over generations because individuals with advantageous traits—here, resistant bacteria—survive and reproduce in the antibiotic environment while non-resistant bacteria die, leading to rapid changes in trait frequency through differential survival, not through individuals changing their traits.

Question 3

A population of rabbits shows trait variation in coat color: white or brown. The habitat has patchy snow in winter for several years. A researcher records the trait frequencies: Year 0: white 50%, brown 50% Year 4: white 30%, brown 70% Predator observations show hawks catch white rabbits more often than brown rabbits in patchy snow conditions. Traits can affect population outcomes. Which prediction about population traits is supported if patchy snow continues for the next 4 years?

White rabbits will likely increase back to 50% because populations always return to their original trait frequencies.
Brown coat color will likely become even more common because brown rabbits are caught less often, so they are more likely to survive and reproduce over generations. (correct answer)
Each white rabbit will likely turn brown during its lifetime to avoid being caught, increasing brown frequency without reproduction differences.
Trait frequencies will not change because only the strongest single rabbit matters for the population's survival.

Explanation: The core skill is predicting future population trait changes based on evidence of how traits affect outcomes in specific environments. Populations of rabbits include varied traits, such as white or brown coats, which can impact visibility to predators in different habitats. Evidence from trait frequency data shows brown coats increasing from 50% to 70% over four years in patchy snow, with hawks catching white rabbits more often. To check, evaluate if predictions consider ongoing differential survival and reproduction rates from the evidence. A misconception is that populations always revert to original trait balances regardless of conditions, but shifts depend on sustained environmental pressures. Population traits shift over generations as brown rabbits, less visible in patchy snow, survive and reproduce more. This differential success can make brown coats even more common if conditions persist.

Question 4

A population of birds has variation in beak depth: shallow (S) and deep (D). A drought reduces the number of small soft seeds, leaving mostly large hard seeds for several years. Bird counts show:

Before drought: 70% S, 30% D After 3 years: 40% S, 60% D After 6 years: 20% S, 80% D

Which explanation best connects traits to the population change using the evidence?

Deep beaks likely helped birds eat the remaining hard seeds, so birds with deep beaks produced more offspring and the deep-beak trait increased in frequency over generations. (correct answer)
Birds with shallow beaks decided to eat harder seeds, which caused their beaks to become deeper and then the population changed.
The drought instantly changed the beak depth of most birds, so the trait distribution shifted within a single season.
Beak depth is only about appearance and does not affect feeding, so the shift in beak types is unrelated to the seed change.

Explanation: The core skill is connecting trait variation to population changes using evidence from environmental shifts. Populations include varied traits, like shallow and deep beaks in birds, which affect abilities such as seed consumption during droughts. Evidence shows population change in beak depth percentages over years, with deep beaks increasing as hard seeds dominate. A checking strategy involves examining if trait shifts align with survival advantages in the changed environment. A common misconception is that individuals modify their own traits intentionally or instantly. Generally, beneficial traits become more common through higher reproduction rates of those individuals. Consequently, population traits evolve over generations via differential success driven by trait-environment fit.

Question 5

A population of plants has variation in stem height: short (S) and tall (T). In a windy coastal area, storms become more frequent over 15 years. Plant surveys show:

Year 0: 40% S, 60% T Year 5: 55% S, 45% T Year 10: 70% S, 30% T Year 15: 80% S, 20% T

Which prediction about population traits is supported if frequent storms continue for the next 10 years?

The percent of short-stem plants will likely continue to increase because the data show the short-stem trait becoming more common over time in the stormy environment. (correct answer)
All tall plants will immediately become short within one generation because storms force individual plants to change their height trait.
The trait distribution will stay exactly 40% short and 60% tall because populations cannot change trait frequencies over time.
Short stems will become common only if the tallest single plant controls reproduction for the whole population.

Explanation: The core skill is making predictions about population traits based on trends in evidence from environmental patterns. Populations include varied traits, like short and tall stems in plants, affecting stability in windy conditions. Evidence shows population change with short stems increasing in frequency over years of frequent storms. A checking strategy is to extrapolate from data trends, assuming continued conditions favor the same trait. A misconception is expecting instant trait changes in all individuals rather than gradual shifts. Generally, traits enhancing survival in storms become more prevalent through reproduction. Over generations, this differential success alters the population's trait distribution toward more adaptive forms.

Question 6

A population of fish has variation in tolerance to low oxygen: high tolerance (H) and low tolerance (L). A lake becomes polluted, lowering oxygen levels for many years. Fish surveys show:

Year 0: 25% H, 75% L Year 6: 50% H, 50% L Year 12: 78% H, 22% L

Which statement about population change is supported by the evidence?

High-oxygen tolerance likely increased in frequency because fish with that trait survived and reproduced more in low-oxygen conditions over multiple generations. (correct answer)
The pollution caused most individual fish to gain high-oxygen tolerance during their lives, so the population changed without reproduction.
Because the lake changed, the trait variation was not needed; the same trait would increase even if all fish started identical.
The only evidence needed is that oxygen levels changed; trait data are not useful for explaining population outcomes.

Explanation: The core skill is using evidence to support statements about how traits drive population changes in altered environments. Populations include varied traits, such as high and low oxygen tolerance in fish, crucial for survival in polluted waters. Evidence shows population change with high-tolerance fish percentages rising over years of low oxygen. To check statements, verify if they align with data indicating generational increases via reproduction. One misconception is that pollution directly modifies individuals without needing initial variation. In general, advantageous traits spread because tolerant individuals reproduce more. This results in population trait shifts over generations due to differential success in challenging conditions.

Question 7

A population of snails has variation in shell banding: banded (B) and unbanded (U). In a shaded forest, birds hunt snails by sight. Scientists record both the environment and trait frequencies over time.

Environment: forest stays shaded for 10 years Year 0: 60% B, 40% U Year 5: 48% B, 52% U Year 10: 30% B, 70% U

Which claim about traits and population outcomes is incorrect based on the evidence?

The change in trait frequencies over time suggests that one shell-banding trait may be linked to survival and reproduction in the shaded forest environment.
Traits can affect population outcomes because trait differences can change which individuals survive and reproduce, shifting trait frequencies over generations.
Because the forest stayed shaded, the rise in unbanded snails is consistent with unbanded shells being harder for birds to see in that environment.
The population changed because the snails chose to remove bands when they noticed birds, so individuals changed their trait in response to danger. (correct answer)

Explanation: The core skill is identifying incorrect claims about traits and population outcomes based on environmental and frequency data. Populations include varied traits, like banded and unbanded shells in snails, affecting visibility to predators in shaded areas. Evidence shows population change with unbanded shells increasing over years in a stable forest. A checking strategy is to compare claims against evidence supporting generational rather than individual changes. A misconception is that organisms actively choose to alter their traits in response to threats. Generally, traits influencing survival shift frequencies through reproduction. This leads to population adaptations over generations via differential success of better-suited individuals.

Question 8

A population of mice has variation in fur color: brown (B) and gray (G). The habitat is mostly brown soil. A new predator arrives that hunts by sight. Over 8 years, scientists record:

Year 0: 55% B, 45% G Year 4: 70% B, 30% G Year 8: 85% B, 15% G

What evidence links trait variation to population change most directly?

The predator chose to hunt gray mice because gray fur is a worse trait, so the change happened for moral reasons rather than survival and reproduction.
The habitat is brown soil, so the environment alone explains the change without needing to consider fur-color traits.
The increase in brown fur over time shows a trait frequency change in the population that is consistent with brown fur reducing detection by a sight-based predator. (correct answer)
Gray mice became brown after the predator arrived, which is why the percent of brown mice increased.

Explanation: The core skill is linking evidence of trait variation directly to observed population changes in response to predators. Populations include varied traits, such as brown and gray fur in mice, influencing visibility in specific habitats. Evidence shows population change through increasing brown fur percentages over years after a sight-based predator arrives. To check linkages, analyze if trait frequency shifts correspond to reduced detection risks. One misconception is attributing changes solely to the environment without considering trait roles. In general, traits that improve survival lead to more offspring inheriting them. Thus, populations experience trait shifts over generations due to the differential reproductive success of better-camouflaged individuals.

Question 9

A population of insects has variation in pesticide tolerance: tolerant (T) and not tolerant (N). A farmer applies the same pesticide each season. The percent tolerant changes:

Season 1: 10% T Season 2: 25% T Season 3: 55% T Season 4: 85% T

A student says: "The pesticide caused the insects to become tolerant because they were exposed to it." Which evaluation is best supported by the population data?

The student's claim is supported because the pesticide is the only cause of any population change, so traits do not matter.
The student's claim is not supported; the data are more consistent with tolerant insects leaving more offspring over generations, increasing the frequency of the tolerance trait. (correct answer)
The student's claim is supported because exposure makes most individuals change their traits, and population data always show individual change.
The student's claim is supported because tolerant insects are "better," and populations become better over time regardless of evidence.

Explanation: The core skill is evaluating claims about trait changes in populations using supportive data from repeated exposures. Populations include varied traits, like pesticide tolerance in insects, determining survival across seasons. Evidence shows population change with tolerance percentages increasing over multiple applications. A checking strategy is to assess if claims match patterns of generational shifts rather than individual adaptations. A common misconception is that exposure alone causes individuals to gain tolerance without inheritance. Generally, tolerant variants reproduce more, increasing their frequency. Thus, population traits evolve over generations through differential reproductive success.

Question 10

A population of beetles has two shell-color traits: green and brown. After a wildfire, the ground is mostly dark ash for several years. Data from the same area show the percentage of brown beetles increased from 30% in Year 0 to 80% in Year 6. Which explanation best connects trait variation to the population change using evidence from the data and environment?

The environment alone changed the beetles into brown during Year 1, so the population became mostly brown without needing trait variation.
Brown and green beetles were both present, and brown beetles were less likely to be seen on dark ash, so over generations a larger fraction of the population had the brown trait. (correct answer)
A few of the strongest brown beetles protected the others and caused most beetles to become brown.
Beetles became brown because they needed to match the ash, and this need caused the trait to spread immediately.

Explanation: This question tests understanding how traits affect populations when environments change. Populations contain individuals with varied traits—here, green and brown beetles were both present before the wildfire. The evidence shows brown beetles increased from 30% to 80% over 6 years after dark ash covered the ground. To check the answer, consider which explanation correctly links trait variation to differential success: brown beetles would be harder for predators to see against dark ash, giving them higher survival rates. A common misconception is that environments directly change organisms' traits or that need causes immediate change. In reality, population traits shift over generations because individuals with advantageous traits (like brown color on dark ash) survive and reproduce more successfully, gradually increasing that trait's frequency in the population.

Question 11

A fish population has variation in body color: light or dark. A new predator is introduced that hunts by sight in clear water. Over 10 generations, the percent of dark fish increases from 20% to 60%. Which prediction about population traits is supported if the water becomes muddy (lower visibility) and stays muddy for many generations?

The percent of dark fish will definitely keep increasing because once a trait increases it cannot decrease.
The difference between light and dark fish may matter less in muddy water, so the trait frequencies may change more slowly or stay closer to their current values. (correct answer)
Each fish will change its body color to match the mud during its lifetime, so the population will become 100% dark within one generation.
The predator alone controls the fish colors, so fish traits do not affect population outcomes.

Explanation: This question tests predicting how traits affect populations when environments change again. Populations contain individuals with varied traits—light and dark fish coexisted, with dark fish increasing to 60% in clear water due to visual predation. The evidence suggests that in muddy water with lower visibility, color differences may matter less for survival. To evaluate predictions, consider how environmental changes affect trait advantages: if predators cannot see as well, color-based survival differences may decrease. A common misconception is that traits always continue changing in the same direction or that individuals change color during their lifetime. In reality, population traits shift over generations based on current survival advantages, so trait frequencies may stabilize or change slowly when selection pressure weakens.

Question 12

A population of island birds shows variation in beak depth: shallow or deep. A drought reduces small soft seeds, leaving mostly large hard seeds for 5 years. Data show the percent of deep-beak birds rose from 35% (Year 0) to 70% (Year 5). Which claim about traits is incorrect based on the evidence?

Because deep and shallow beaks were both present, the drought could change the trait distribution across generations.
The increase in deep-beak birds is consistent with deep beaks being linked to better feeding on hard seeds during the drought.
The population's trait distribution changed over multiple years, not instantly in a single season.
Individual birds changed their beaks from shallow to deep because hard seeds were available, causing the population percent to rise. (correct answer)

Explanation: This question tests identifying incorrect claims about how traits affect populations. Populations contain individuals with varied traits—shallow and deep beaks were both present in the bird population. The evidence shows deep-beak birds increased from 35% to 70% during a 5-year drought that left mostly hard seeds. To find the incorrect claim, look for statements that misunderstand how populations change: individual birds cannot change their physical beak structure during their lifetime. A common misconception is that organisms can alter their inherited traits based on environmental needs. In reality, population traits shift over generations because birds with deep beaks could better crack hard seeds, survived more, and left more offspring with deep beaks.

Question 13

A lizard population has variation in toe-pad size: small or large. A storm removes many trees, and the habitat becomes mostly smooth rocks for 7 years. Data show the percent of large toe-pad lizards increased from 25% to 65%. Which explanation best connects trait variation to population change?

The population changed because the habitat changed, so traits did not play a role in the population outcome.
Lizards with large toe pads were already present, and if large toe pads improved gripping on smooth rocks, those lizards likely left more offspring, increasing the trait frequency over generations. (correct answer)
Each lizard grew larger toe pads after the storm, so the trait frequency increased without reproduction.
Large toe pads spread because they look more noticeable, and appearance always spreads in a population.

Explanation: This question tests understanding how traits affect populations after habitat changes. Populations contain individuals with varied traits—lizards with small and large toe pads both existed before the storm. The evidence shows large toe-pad lizards increased from 25% to 65% after the habitat became mostly smooth rocks, suggesting an advantage for gripping. To verify the answer, find the explanation that correctly links pre-existing variation to differential success in the new environment. A common misconception is that individual lizards can grow larger toe pads after environmental change. In reality, population traits shift over generations because lizards with large toe pads likely gripped smooth rocks better, survived more, reproduced successfully, and passed this trait to offspring.

Question 14

In a population of beetles, there is trait variation in shell color: green or brown. A drought changes the habitat from mostly green plants to mostly brown dry leaves for 5 years. Data show the percent of green-shelled beetles decreases from 60% (Year 0) to 25% (Year 5), while brown-shelled beetles increase from 40% to 75%. Observations also show birds catch green beetles more often than brown beetles in the brown-leaf habitat. Traits can affect population outcomes over generations. Which explanation best connects trait variation to the population change using the evidence?

A few very strong brown beetles protected the rest, so the whole population became mostly brown without changes in reproduction.
Green beetles changed their shells to brown because they needed to match the leaves, causing the trait frequency to shift.
Brown shell color was linked to lower predation in the brown-leaf habitat, so beetles with brown shells left more offspring and the brown trait became more common over generations. (correct answer)
The population changed because the environment alone forced all beetles to become brown within a single season, regardless of trait variation.

Explanation: The core skill is understanding how inherited traits can influence population changes over time in response to environmental pressures. Populations of beetles include individuals with varied traits, such as green or brown shell colors, which provide natural diversity within the group. Evidence from data shows a shift in trait frequencies, with brown-shelled beetles increasing from 40% to 75% over five years, alongside observations of higher predation on green beetles in the changed habitat. To check this, compare survival rates of different traits and see if they correlate with changes in population composition over multiple generations. A common misconception is that all individuals in a population change their traits simultaneously due to the environment, but actually, only those with advantageous traits survive and reproduce more. Population traits shift over generations as beetles with brown shells, which offer better camouflage, leave more offspring. This differential success causes the brown trait to become more prevalent in the population.

Question 15

A population of lizards shows trait variation in toe pad size: small or large. A storm increases average rainfall for 10 years, making tree branches wetter and more slippery. Data show the percent of large toe pads rises from 35% (Year 0) to 65% (Year 10). Field measurements show lizards with larger toe pads slip less often on wet branches and are observed feeding more frequently. Traits can affect population outcomes. Which explanation best connects traits to population change using the evidence?

The increase happened because the rain made all lizards grow larger toe pads, so the trait distribution changed within one generation.
The increase happened because wet branches reduced slipping for large-toe-pad lizards, leading to higher survival or reproduction and a gradual rise in that trait over generations. (correct answer)
The population changed because toe pad size is only an appearance trait and cannot affect feeding or survival.
The population changed mainly because the wet environment alone determines lizard numbers, not which traits are common.

Explanation: The core skill is connecting traits like toe pad size to population changes using evidence of environmental impacts on survival. Populations of lizards include varied traits, with individuals having small or large toe pads, influencing their ability to navigate habitats. Evidence from data shows large toe pads increasing from 35% to 65% over ten years of wetter conditions, with observations of less slipping and more feeding in large-padded lizards. To check, look for correlations between trait advantages, such as reduced slipping, and gradual frequency shifts over generations. A misconception is that environments directly modify traits in all individuals within one generation, but changes happen through inheritance and selection. Population traits shift over generations as lizards with large toe pads survive and reproduce better on slippery branches. This differential success leads to larger toe pads becoming more prevalent in the population.

Question 16

A population of bacteria has trait variation in resistance to an antibiotic: resistant (R) or non-resistant (N). An antibiotic is added to the environment starting at Day 0 and remains present for 4 days. Population counts are recorded: Day 0: R 10%, N 90% Day 2: R 55%, N 45% Day 4: R 90%, N 10% Lab tests show R bacteria survive and reproduce in the antibiotic, while N bacteria die more often. Traits can affect population outcomes. What evidence links trait variation to the population change?

The antibiotic caused every bacterium to become resistant immediately, so trait variation was not needed.
Resistant bacteria had higher survival and reproduction in the antibiotic, which matches the increase in the resistant trait frequency over time. (correct answer)
A few resistant bacteria were the strongest individuals and directly turned nearby bacteria resistant without reproduction.
Because resistance and antibiotic use happened at the same time, the antibiotic must have caused resistance in each bacterium's body.

Explanation: The core skill is linking trait variation, like antibiotic resistance, to evidence of population changes through survival and reproduction differences. Populations of bacteria include varied traits, with some resistant and others non-resistant, providing a basis for response to environmental challenges. Evidence from population counts shows resistant bacteria increasing from 10% to 90% over four days, supported by lab tests showing their higher survival in antibiotics. To check, assess if the evidence demonstrates that pre-existing variation leads to shifts via differential reproduction, not immediate changes in individuals. A misconception is that environmental factors create new traits in all individuals at once, but changes rely on existing variation and selection. Population traits shift over generations as resistant bacteria reproduce more successfully in the presence of antibiotics. This differential success makes resistance more common in the bacterial population.

Question 17

A population of field mice shows trait variation in fur thickness: thin, medium, or thick. The region experiences colder winters for 8 years. A study records the trait distribution: Year 0: thin 40%, medium 45%, thick 15% Year 8: thin 15%, medium 50%, thick 35% Survival data during winter show thick-furred mice survive at higher rates than thin-furred mice in cold years. Traits can affect population outcomes. Which statement about population outcomes is supported by the data and evidence?

The change happened mainly because the cold weather created thick fur in the population even if no mice had thick fur at Year 0.
The population became thicker-furred because all mice grew thicker fur each winter and passed that change directly to their offspring.
The trait distribution changed because the model labels 'thin/medium/thick' caused the population to sort itself into those categories.
Thick fur became more common because mice with thick fur survived winter more often and produced more offspring over multiple generations. (correct answer)

Explanation: The core skill is recognizing how traits like fur thickness can affect survival and reproduction, leading to changes in population traits over time. Populations of field mice include varied traits, with individuals having thin, medium, or thick fur, creating diversity that interacts with environmental conditions. Evidence from survival data during colder winters shows thick-furred mice surviving at higher rates, corresponding to an increase in thick fur from 15% to 35% over eight years. To check, examine if the data links specific traits to higher offspring production and if the change occurs gradually across generations. A misconception is that animals acquire traits like thicker fur during their lifetime and pass them directly to offspring, but traits are inherited, and populations change through selection. Population traits shift over generations as mice with thick fur succeed more in cold conditions, producing more surviving offspring. This differential success results in thicker fur becoming more common in the population.

Question 18

In a population of beetles, there is variation in shell color: green or brown. The habitat is a forest floor that became darker after a wildfire, and remains dark for many years. Data were collected each year:

Year 1: green 70%, brown 30% Year 5: green 45%, brown 55% Year 10: green 20%, brown 80%

Birds hunt beetles by sight. Traits can affect population outcomes. Which explanation best connects the trait variation to the population change using the evidence?

The wildfire directly changed many green beetles into brown beetles, so the population color percentages shifted within the same generation.
The population became mostly brown because the forest floor got darker; the environment alone changes trait frequencies even if survival and reproduction are the same for both colors.
The population became mostly brown because the strongest individual beetles were brown and forced the others out of the habitat.
Brown shell color likely reduced detection by birds on the darker ground, so brown beetles survived and reproduced more over many generations, increasing the brown trait frequency. (correct answer)

Explanation: This question tests understanding how traits affect populations through differential survival and reproduction. Populations contain individuals with varied traits—here, beetles with green or brown shells—and these variations can lead to different outcomes when environments change. The evidence shows a gradual shift from mostly green beetles (70%) to mostly brown beetles (80%) over 10 years after the forest floor darkened, which indicates population change across multiple generations. To check your answer, look for an explanation that connects the trait (shell color) to survival differences (bird predation) and shows change over generations, not within individuals. A common misconception is that individuals change their traits in response to the environment (like option A suggests), but traits are inherited and individuals cannot change from green to brown. Population traits shift over generations because individuals with advantageous traits—in this case, brown beetles that are harder for birds to see on dark ground—survive and reproduce more successfully, gradually increasing the frequency of their trait in the population.

Question 19

A population of finches shows variation in beak depth: shallow or deep. A drought reduces the number of soft seeds for 6 years; mostly hard seeds remain. Researchers recorded survival of juveniles to adulthood and the adult beak trait frequency.

Survival during drought:

Shallow beaks: 30% survive
Deep beaks: 70% survive

Adult trait frequency:

Before drought: shallow 60%, deep 40%
After 6 years: shallow 25%, deep 75%

Traits can affect population outcomes. Which statement about population change is supported by the evidence?

Most individual finches changed their beaks from shallow to deep during the drought, causing the adult trait frequency to shift quickly.
Deep-beaked finches had higher survival in the drought conditions, so over generations the frequency of deep beaks increased in the adult population. (correct answer)
The beak-depth change happened because the drought made all finches equally likely to survive, and trait frequencies always drift toward 75% deep beaks.
Because hard seeds were present, deep beaks must be the morally "better" trait, so the population became mostly deep-beaked.

Explanation: This question tests understanding how traits affect populations through differential survival during environmental challenges. Populations contain individuals with varied traits—here, finches with shallow or deep beaks—and these variations result in different survival rates when conditions change. The evidence shows that during a drought with mostly hard seeds, deep-beaked finches had much higher survival (70%) compared to shallow-beaked finches (30%), and over 6 years the adult population shifted from mostly shallow-beaked to mostly deep-beaked. To verify the correct answer, look for an explanation that connects survival differences to reproduction and population change over generations. A common misconception is that individual finches can change their beak depth during their lifetime (option A), but beak depth is an inherited trait that doesn't change within an individual. Population traits shift over generations because individuals with traits that improve survival—here, deep beaks for cracking hard seeds—are more likely to survive to adulthood and pass on their traits, gradually increasing the frequency of beneficial traits in the population.

Question 20

A population of fish shows variation in body pattern: striped or spotted. The environment becomes murkier due to long-term runoff and stays murky. Data:

Visibility tests (percent detected by predators in a tank with murky water):

Striped: 30% detected
Spotted: 60% detected

Trait frequency in the lake:

Start: striped 40%, spotted 60%
After 9 years: striped 70%, spotted 30%

Traits can affect population outcomes. Which prediction about population traits is supported if the murky conditions continue for many more years?

The population will likely continue to increase the striped trait frequency because striped fish are detected less often and may leave more offspring over time. (correct answer)
The population will return to 40% striped because trait frequencies always reset to their original values after 10 years.
All individual spotted fish will become striped within one generation because the water is murky.
The trait frequencies will not change further because only the environment determines populations, and traits do not affect survival or reproduction.

Explanation: This question tests understanding how traits affect populations by making predictions based on evidence. Populations contain individuals with varied traits—here, fish with striped or spotted patterns—and these variations affect detection by predators in different water conditions. The evidence shows that in murky water, striped fish are detected only 30% of the time compared to 60% for spotted fish, and over 9 years the population has already shifted from 40% to 70% striped. To make a supported prediction, consider whether the selection pressure (predator detection in murky water) will continue and what that means for trait frequencies. A common misconception is that trait frequencies automatically reset or that all individuals will change their patterns (options B and C), but traits are inherited and population changes occur through differential survival over generations. Population traits shift over generations because individuals with traits that reduce predation—here, stripes that provide better camouflage in murky water—survive more often and leave more offspring, so if murky conditions persist, the striped trait frequency will likely continue to increase as striped fish maintain their survival advantage.