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January 2025 Living Environment Regents — Answer Key & Worked Solutions

Every question from the January 2025 Living Environment Regents exam, with the correct answer and a full step-by-step solution. Check your work, learn the method, then convert your raw score.

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These are real questions from the January 2025 Living Environment New York State Regents examination, published by NYSED. Worked solutions are written by RegentsLab.

Question 1 · 2 pts

When you cut your finger, new skin quickly grows that repairs and replaces the damaged skin cells. Information directing this process is located in the

Worked solution
$\text{Skin repair} = \text{new, identical cells}$
$\text{Identical cells} \Rightarrow \text{mitotic division, directed by DNA}$
Answer: DNA of neighboring cells, which divide by mitotic cell division

Repairing skin requires producing genetically identical replacement cells, which happens through mitotic cell division directed by the DNA in the dividing cells.

Question 2 · 2 pts

ATP is produced in the

Worked solution
$\text{Cellular respiration occurs in the mitochondria}$
$\text{Cellular respiration} \rightarrow \text{ATP}$
Answer: mitochondria

Mitochondria are the organelles responsible for cellular respiration, the process that produces ATP, the cell's energy currency.

Question 3 · 2 pts

Some trees release toxins into the soil that can kill the plants nearby. This ability can best be described as

Worked solution
$\text{Killing nearby plants} \Rightarrow \text{less competition for the tree}$
$\text{Less competition} \Rightarrow \text{evolutionary advantage}$
Answer: an evolutionary advantage, reducing competition for water, nutrients, and sunlight

Releasing toxins removes competitors, giving the tree more access to water, nutrients, and sunlight, which is an evolutionary advantage, not an acquired trait or a benefit to biodiversity.

Question 4 · 2 pts

When the frequency of a gene in a population changes, the most likely result would be

Worked solution
$\Delta(\text{allele/gene frequency in a population}) = \text{evolution (by definition)}$
Answer: biological evolution

A change in gene (allele) frequency within a population over time is the definition of biological evolution.

Question 5 · 2 pts

During the 1880s, in an attempt to control the rat population, the Asian mongoose was brought to the Hawaiian Islands. However, there was a flaw in the plan. Rats are active at night, while mongooses feed on birds and eggs during the day. They had little effect on the rat population. The mongoose population rapidly increased and caused the extinction of many bird species native to the islands. Bringing mongooses to the Hawaiian Islands is an example of

Worked solution
$\text{Human introduction of mongoose} \rightarrow \text{failed rat control} + \text{bird extinctions}$
$\text{Planned solution} \Rightarrow \text{unintended ecological consequence}$
Answer: humans altering ecosystems, resulting in unintended consequences

The mongoose introduction was a deliberate human action that altered the ecosystem and produced harmful, unintended consequences (bird extinctions) rather than solving the original rat problem.

Question 6 · 2 pts

Many companies today are looking for ways to reduce the use of finite resources. They are working to recycle, reuse, and repair products to reduce dumping and pollution. Which statement best describes a positive result of these changes?

Worked solution
$\text{Recycle/reuse/repair} \Rightarrow \text{slower consumption of finite resources}$
Answer: Finite resources will not be depleted as quickly.

Recycling, reusing, and repairing products conserves finite resources, meaning they are used up more slowly, a clear positive outcome.

Question 7 · 2 pts

Which characteristic would give one species the greatest advantage over other species?

Worked solution
$\text{Evolutionary success} \propto \text{number of offspring that survive to reproduce}$
Answer: higher number of surviving offspring

Evolutionary advantage is measured by reproductive success; a species that produces more surviving offspring passes on more of its genes to future generations.

Question 8 · 2 pts

The diagram below represents the same location over a period of many years. It shows a sequence of stages over time: Bare field, then Grass stage, then Shrub stage, then Pine forest stage, then Hardwood forest stage. As a result of these changes,

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Worked solution
$\text{Bare field} \rightarrow \text{grass} \rightarrow \text{shrub} \rightarrow \text{pine forest} \rightarrow \text{hardwood forest (ecological succession)}$
$\text{Succession progresses toward a stable climax community}$
Answer: the community becomes more stable

This sequence depicts ecological succession, which proceeds toward a climax community (hardwood forest) that is more diverse, complex, and stable than earlier stages.

Question 9 · 2 pts

Between 1880 and 2020, Earth's temperature increased slightly more than 1 degree C. The graph below, titled 'Change in Global Average Temperature,' plots Temperature Change (degrees C) on the y-axis from -0.5 to 1.5 against Year on the x-axis from 1880 to 2020, with a baseline at 0.0 degrees C. The line fluctuates near or below the baseline from 1880 to about 1910, dips to about -0.4 degrees C around 1910, then rises with fluctuations to reach about 1.0 degrees C by 2020 (labeled '1 degree C' at the endpoint). The best explanation for this increase is

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Worked solution
$\text{Rising atmospheric greenhouse gas concentration (e.g., CO}_2\text{)} \Rightarrow \text{enhanced greenhouse effect}$
$\text{Enhanced greenhouse effect} \Rightarrow \text{rising global temperature}$
Answer: changing concentrations of gases in the atmosphere

The long-term warming trend shown is best explained by increasing concentrations of greenhouse gases in the atmosphere, which trap more heat, not by decreased sunlight, increased reflection, or volcanic ash.

Question 10 · 2 pts

Two different species of animal prefer the same plant for food. One eats the leaves of the plant, the other prefers the fruit. By eating different parts of the same plant these species can successfully coexist because they do not

Worked solution
$\text{Different food resource used} \Rightarrow \text{niches do not overlap}$
$\text{No niche overlap} \Rightarrow \text{no competition for that resource}$
Answer: compete for limited resources

By eating different parts of the plant, the two species occupy slightly different niches and avoid competing directly for the same limited food resource.

Question 11 · 2 pts

Different techniques are used to study cells. Fluorescent (glowing) tags allow scientists to visualize specific proteins as they are synthesized inside cells. Which part of a cell would be studied when using this technology to visualize protein synthesis?

Worked solution
$\text{Protein synthesis site} = \text{ribosome}$
Answer: ribosome

Proteins are synthesized on ribosomes, so fluorescent tagging of proteins as they are made would be used to study ribosomes.

Question 12 · 2 pts

The image below shows a recently discovered fossil of an unhatched egg of a theropod dinosaur. The dinosaur is in a prehatching position similar to bird embryos in unhatched eggs today. Prior to finding the fossil, this behavior was never seen in animals other than birds. The fact that both theropod dinosaurs and birds share this behavior is evidence that

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Worked solution
$\text{Shared, inherited prehatching behavior} \Rightarrow \text{shared ancestry}$
Answer: birds and theropod dinosaurs are related and share a common ancestor

A shared, specific inherited behavior between theropod dinosaurs and birds is evidence of a close evolutionary relationship and common ancestry, not a universal requirement for survival or a learned behavior.

Question 13 · 2 pts

The graph below, titled 'Stored Energy,' represents the amount of stored energy in each level of an energy pyramid. The y-axis is 'Amount of Energy Stored' and the x-axis is 'Level,' with four bars for levels 1, 2, 3, and 4. The bar for level 1 is tallest, and each successive bar (2, 3, 4) is progressively shorter, with level 4 the shortest. The amount of stored energy between level 1 and level 4 decreases because

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Worked solution
$\text{Only} \approx 10\% \text{ of energy transfers to the next trophic level}$
$\text{Remaining energy is lost as metabolic heat at each level}$
Answer: at each level some energy is released as heat

Energy decreases moving up trophic levels because organisms use most of the energy for life processes and release it as heat, so only a fraction is stored and passed to the next level.

Question 14 · 2 pts

In a sexually reproducing species of plant, which change could occur that would have an effect on the species in the future?

Worked solution
$\text{Only changes in gametes (sex cells) are heritable}$
$\text{Root, leaf, and stem cells are body/somatic cells, not passed to offspring}$
Answer: changes in the egg cells in the ovaries of the plants' flowers

Only mutations occurring in reproductive (gamete) cells such as egg cells can be passed on to offspring; changes in somatic cells like roots, leaves, or stems are not inherited.

Question 15 · 2 pts

Many factors go into producing goods that are used by people in their everyday lives. In manufacturing, the production of goods and use of energy

Worked solution
$\text{Manufacturing} \Rightarrow \text{goods (benefit)} + \text{pollution/resource use (cost)}$
Answer: can have both positive and negative effects

Manufacturing goods provides benefits to people but also causes negative effects like pollution and resource depletion, so it has both positive and negative impacts.

Question 16 · 2 pts

The illustration below represents two cellular processes, A and B. Cellular Process A shows one circle at the top with two arrows pointing down to two separate circles below it. Cellular Process B shows two circles at the top with arrows pointing down and converging into one circle below. Select the row in the table that correctly identifies the cellular process.

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Worked solution
$\text{Process A: one cell} \rightarrow \text{two identical cells} = \text{mitosis}$
$\text{Process B: two cells} \rightarrow \text{one cell} = \text{fertilization (sperm + egg} \rightarrow \text{zygote)}$
Answer: Row (4): mitosis, fertilization

Process A shows one cell dividing into two, which is mitosis; Process B shows two cells combining into one, which is fertilization.

Question 17 · 2 pts

A food web is represented below, showing organisms Mountain lions, Snakes, Hawks, Owls, Frogs, Crickets, Rabbits, Mice, Deer, Shrubs, Grasses, and Trees connected by feeding arrows (producers at the bottom feeding herbivores, which feed various predators up to top carnivores like hawks and mountain lions). A chemical was introduced into this environment that caused a decrease in the population of mice. This would most likely cause

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Worked solution
$\text{Mice population} \downarrow \Rightarrow \text{less food for organisms that eat mice}$
$\text{Snakes feed on mice} \Rightarrow \text{snake population} \downarrow$
Answer: a decrease in the snake population

Since snakes prey on mice in this food web, a decrease in the mouse population reduces the food supply for snakes, most likely causing a decrease in the snake population.

Question 18 · 2 pts

Populations of organisms making up an Arctic food chain are represented below: Algae, then Zooplankton, then Arctic cod, then Ringed seal, then Polar bear (each connected by an arrow to the next, in that order). Which statement concerning this food chain is the most accurate?

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Worked solution
$\text{Algae = producer, base of food chain}$
$\text{Algae} \downarrow \Rightarrow \text{energy/food supply to all higher levels} \downarrow$
Answer: A reduction in the algae populations would most likely affect the survival of all the other populations in this food chain.

Algae are the producers and base of this food chain; a decline in algae reduces the energy available to every organism above it in the chain.

Question 19 · 2 pts

The protein in a hamburger is broken down into amino acids. Which two processes are involved in the breakdown of the protein and the absorption of the amino acids into the bloodstream?

Worked solution
$\text{Protein} \xrightarrow{\text{digestion}} \text{amino acids}$
$\text{Amino acids} \xrightarrow{\text{diffusion}} \text{bloodstream}$
Answer: digestion and diffusion

Digestion breaks the protein down into amino acids, and diffusion moves those small molecules from the digestive tract into the bloodstream.

Question 20 · 2 pts

Tuatara are the last survivors of an ancient group of reptiles that lived at the same time as the dinosaurs. Tuatara contain a very large genome. The genome, its complete set of genes, is about two-thirds bigger than the human genome. One possible explanation for why the tuatara has survived since prehistoric times is that their large genome

Worked solution
$\text{Large genome} \Rightarrow \text{greater genetic variation within the population}$
$\text{Greater variation} \Rightarrow \text{some individuals have traits suited to changing conditions} \Rightarrow \text{survival}$
Answer: provided the members of the species that gave them advantages for survival in changing environments

A larger genome provides more genetic variation among individuals, increasing the chance that some members possess traits advantageous for surviving environmental change; organisms cannot deliberately mutate or evolve on demand.

Question 21 · 2 pts

Two primary chemical messengers used in communication within the human body include

Worked solution
$\text{Endocrine communication} = \text{hormones}$
$\text{Nervous communication} = \text{neurotransmitters (chemicals produced by nerve cells)}$
Answer: hormones and chemicals produced by nerve cells

The two main chemical communication systems in the body are the endocrine system, using hormones, and the nervous system, using chemical messengers released by nerve cells.

Question 22 · 2 pts

Holstein cows have become the most widespread breed of dairy cow in the United States. They have been selectively bred to have many characteristics beneficial to dairy farmers. Holsteins are known for their ability to produce large quantities of milk. In addition, they are often calm and agreeable animals. Which statement best describes a potential risk of the selective breeding process to future generations of Holstein dairy cows?

Worked solution
$\text{Selective breeding for specific traits} \Rightarrow \text{narrower gene pool}$
$\text{Narrower gene pool} \Rightarrow \text{reduced genetic diversity}, \text{ increased vulnerability to disease/environmental change}$
Answer: Genetic diversity in the breed may become limited over time.

Selective breeding for desired traits repeatedly favors similar genes, which reduces genetic diversity in the population over generations and increases risk from disease or environmental change.

Question 23 · 2 pts

An organism that normally has 32 chromosomes in its body cells is found to be producing gametes with either 15 or 17 chromosomes. It has not been able to successfully reproduce. The most likely reason for its inability to reproduce would be errors during the process of

Worked solution
$32 \div 2 = 16$ Gametes from this organism should normally contain 16 chromosomes (half of 32).
$15 \neq 16 \text{ and } 17 \neq 16$ The gametes produced have the wrong chromosome number.
Answer: meiosis

Meiosis is the process that halves the chromosome number to form gametes; an error (nondisjunction) during meiosis produces gametes with an incorrect number of chromosomes, preventing normal fertilization and reproduction.

Question 24 · 2 pts

Which sequence correctly identifies the flow of energy through an ecosystem?

Worked solution
$$ Energy first enters an ecosystem through producers (autotrophs), then passes to consumers that eat them, and finally to decomposers that break down dead organic matter.
Answer: producer → consumer → decomposer

Energy flows in one direction, from producers to consumers to decomposers, unlike matter which cycles.

Question 25 · 2 pts

An ameba, which is a single-celled aquatic organism, is represented in a diagram showing its internal structures (nucleus, vacuoles, and other organelles). Which of the ameba's cell structures is the most important in obtaining oxygen from its environment?

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Worked solution
$$ Oxygen must first cross the boundary between the ameba and its watery environment before it can be used.
Answer: cell membrane

The cell membrane is the structure through which dissolved oxygen diffuses into the cell from the surrounding water; the mitochondrion uses that oxygen but does not obtain it from the environment.

Question 26 · 2 pts

The diagram below represents a specialized gamete that plays a role in human reproduction, with the nucleus, mitochondria, and tail labeled. The proper functioning of cells like these is vital for human reproduction because

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Worked solution
$$ The gamete shown is a sperm cell, produced by meiosis, so it is haploid.
Answer: its nucleus carries half the genetic information needed to form a zygote

A sperm cell's nucleus contains a haploid set of chromosomes; when it fertilizes an egg (also haploid), the resulting zygote receives the full diploid genetic information.

Question 27 · 2 pts

If the amounts of carbon dioxide and water available increase, it is most likely that the first response by the producer organisms would be to

Worked solution
$CO_2 + H_2O \rightarrow \text{glucose} + O_2$ Photosynthesis uses carbon dioxide and water as raw materials to produce glucose.
Answer: increase glucose synthesis

Carbon dioxide and water are the direct raw materials of photosynthesis, so an increase in their availability first increases the rate of glucose (sugar) synthesis in producers.

Question 28 · 2 pts

There are high numbers of stray and feral cats in communities across the United States. In order to humanely control these cat populations, many areas are participating in programs to trap, spay, and release the animals. When a female cat is spayed, organs are surgically removed to prevent the animal from being able to reproduce. Which two organs are most likely removed from the female cat during this surgery?

Worked solution
$$ Spaying removes the primary female reproductive organs.
Answer: ovaries and uterus

Spaying removes the ovaries, which produce eggs and reproductive hormones, and the uterus, preventing the cat from becoming pregnant.

Question 29 · 2 pts

When you purchase a fishing license in New York State, you are told to check the Advisory Tables before consuming any of the fish you catch. The tables list the fish species you should not eat and others you can eat up to four times per month, due to the presence of toxic chemicals in the fish. A likely reason the table recommends that children under the age of 15 and young women should not eat any of the fish caught in some bodies of water is that

Worked solution
$$ Toxic chemicals such as mercury and PCBs can cross the placenta and disrupt fetal/child development.
Answer: the chemicals may affect their development or harm potential unborn children

Children are still developing and young women may become pregnant, so toxic bioaccumulated chemicals pose a greater risk of harming development or a future fetus in these groups.

Question 30 · 2 pts

Examples of two abiotic resources present in an ecosystem are

Worked solution
$$ Abiotic factors are nonliving components of an ecosystem.
Answer: nitrogen and carbon dioxide in the atmosphere

Nitrogen gas and carbon dioxide are both nonliving atmospheric gases, making them abiotic resources, whereas the other choices each include a living component.

Question 31 · 2 pts

Organisms A and B represent microorganisms viewed through a microscope. Organism A is viewed with a 10x objective and fills the field of view; Organism B is viewed with a 40x objective and fills the field of view. Although both seem to occupy the same field of view, which organism is actually larger?

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Worked solution
$\text{Field diameter} \propto \frac{1}{\text{magnification}}$ A lower magnification (10x) has a much larger actual field of view diameter than a higher magnification (40x).
$$ Since organism A fills the larger, low-magnification field of view, its actual (real) size must be much greater than organism B, which only fills the smaller, high-magnification field.
Answer: A is larger since it fills the field of view at low magnification.

Field of view diameter shrinks as magnification increases, so filling the field at low power (10x) requires a physically larger specimen than filling the smaller field at high power (40x); therefore A is actually larger.

Question 32 · 2 pts

The data represented in the graph below show differences in the concentration of carbon dioxide (CO2) in the atmosphere during the summer and winter months. The graph, titled 'Carbon Dioxide Concentration,' plots CO2 (ppm) on the y-axis from 305 to 320 against Year on the x-axis from 1958 to 1962, showing a repeating up-and-down (sawtooth) pattern each year. Which statement best explains why these differences occur?

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Worked solution
$$ During summer, more sunlight and warmth increase photosynthesis in plants (autotrophs), which consumes CO2 and lowers atmospheric concentration.
Answer: The activity of autotrophs increases during the summer, removing CO2 from the atmosphere.

The annual dips in CO2 correspond to increased photosynthetic activity of autotrophs during the growing season (summer), which removes CO2 from the atmosphere faster than it accumulates.

Question 33 · 2 pts

Altering the DNA of a muscle cell in a mouse by substituting one base pair with another could likely

Worked solution
$\text{DNA} \rightarrow \text{mRNA} \rightarrow \text{protein}$ A single base-pair substitution can change a codon, which can change the amino acid inserted during translation.
Answer: change one amino acid in a protein a muscle cell produces

A point mutation in one gene changes only the codon(s) affected, potentially altering a single amino acid in the protein encoded by that gene, not the entire genome or the DNA of offspring (since this is a somatic muscle cell, not a gamete).

Question 34 · 2 pts

Base your answer on the diagram representing the interaction of a human cell and the hormone insulin, which maintains a healthy blood glucose level in the body. The diagram shows insulin molecules approaching the outer surface of a human cell, where arrow-shaped structures labeled X are embedded in the cell's outer boundary. Structure X is best described as a

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Worked solution
$$ Insulin (the signal) must bind to a receptor on the target cell before the cell can respond by taking up glucose.
Answer: receptor molecule that allows the cell to respond to changes

Structure X binds insulin at the cell surface, identifying it as a receptor molecule that allows the cell to detect and respond to the hormone signal.

Question 35 · 2 pts

Some individuals cannot produce insulin. As a result, their cells will

Worked solution
$$ Without insulin, cells cannot receive the signal needed to take in glucose from the blood.
Answer: not respond appropriately to changes in blood glucose levels

Insulin is required for cells to properly respond to rising blood glucose by taking up sugar; without it, cells fail to respond appropriately, leading to poor regulation of blood glucose levels (as in diabetes).

Question 36 · 2 pts

Two different human disorders are compared in the table below. Blood Disorder That Affects Hemoglobin: caused by a gene mutation; individuals with two copies of the mutated gene have the disorder; this disorder is more common in some populations than others; individuals are born with this disorder. Skin Disorder With a Sore That Does Not Heal: caused by a gene mutation; some individuals exposed to UV radiation develop the disorder; there are environmental factors associated with the disorder; abnormal skin cells reproduce rapidly in exposed individuals. Which statement describes the patterns of inheritance for these two disorders?

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Worked solution
$$ The blood disorder is a straightforward recessive genetic disorder (born with it, needs two copies).
$$ The skin disorder involves a gene mutation plus environmental triggers (UV exposure), so it involves both heritable and environmental factors.
Answer: The blood disorder can be inherited, and there are factors associated with the skin disorder that may be inherited.

The blood disorder follows a clear inherited pattern (present at birth, requires two mutant alleles), while the skin disorder is influenced by an inherited predisposition combined with environmental exposure (UV radiation), so it does not always appear regardless of environment.

Question 37 · 2 pts

Base your answer on the diagram and information below. Gray wolves have been identified as a keystone species, which is a species that is critical to the health of the Yellowstone ecosystem. The food web shows gray wolves preying on coyotes and elk; coyotes prey on voles; voles and elk feed on plants (grass, grain, fruits). The ecosystem will be disrupted with the loss of this keystone species because the loss would lead to

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Worked solution
$$ Without wolves to control elk and coyote (and vole) populations, herbivore numbers rise.
$$ Higher herbivore populations consume more plants, decreasing plant populations.
Answer: a decrease in the plant populations

Losing the keystone predator (wolves) removes a check on elk, coyote, and vole populations; their unchecked growth leads to overgrazing and a decrease in the plant populations.

Question 38 · 2 pts

Due to human concerns, wolves were removed from the Yellowstone ecosystem for approximately 70 years, from the 1920s until 1995. Scientists felt that, as a keystone species, it was important to reintroduce the wolves to

Worked solution
$$ Reintroducing a keystone predator restores natural population checks throughout the food web.
Answer: increase the stability of the natural environment

As a keystone species, wolves help regulate prey populations (elk, coyotes) and, indirectly, plant populations, so reintroducing them restores balance and stability to the ecosystem.

Question 39 · 2 pts

Hydrangeas are plants with flowers that can change color. If the pH of the soil in which the plants are growing is altered, the flower color can vary from pink to blue. What is the best explanation for this phenomenon?

Worked solution
$$ Environmental factors, such as soil pH, can regulate gene expression without altering the DNA sequence itself.
Answer: The genes of the hydrangea plants can be turned on and off by different soil pH levels.

Soil pH affects the availability of aluminum ions, which influences gene expression (turning color-related genes on or off) rather than causing mutations or destroying genes.

Question 40 · 2 pts

Base your answer on the information and graph below. In the 1990s, ranchers on Maggie Creek in Nevada moved the areas where their cattle were grazing to help vegetation regrow on the eroding creek banks. The graph 'Effect of Restoration at Maggie Creek, Nevada' shows the percentage of area with green vegetation across dates (January 1 through December 1) for three time periods: 1985-1994, 1995-2005, and 2006-2016. How many more months did the Maggie Creek area have some green vegetation cover in 2006-2016, compared with the number of months of green cover in 1985-1994?

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Worked solution
$$ The 1985-1994 curve shows green vegetation cover above 0% for a shorter span of months than the 2006-2016 curve.
$\text{months}_{2006-2016} - \text{months}_{1985-1994} = 3$ Comparing the widths of the two curves along the x-axis gives a difference of about 3 months.
Answer: 3 months

Reading across the x-axis, the 2006-2016 curve stays above 0% green cover for about 3 more months than the narrower 1985-1994 curve, reflecting improved vegetation persistence after restoration.

Question 41 · 2 pts

The change in the environmental conditions of Maggie Creek over time is an example of how

Worked solution
$$ Moving cattle grazing areas (a change in agricultural practice) allowed vegetation and creek bank stability to recover.
Answer: changing agricultural practices can help to restore environmental stability to certain locations

By altering where cattle grazed, ranchers reduced erosion and allowed vegetation to regrow, showing that adjusting agricultural practices can help restore stability to a damaged ecosystem.

Question 42 · 2 pts

Base your answer on the information below. PCBs are chemicals once used in electrical equipment, now banned because they have been found to cause cancer. These chemicals have made their way into the ocean and accumulated in the tissues of organisms; as larger organisms eat smaller ones, PCB levels become more concentrated, with organisms higher in the food chain containing the greatest levels. A student examined a diagram of an Antarctic food web (killer whale, leopard seal, elephant seal, emperor penguin, squid, Antarctic silverfish, blue whale, krill, zooplankton and phytoplankton) and claimed that the greatest concentration of PCBs would be found in leopard seals. Based on information provided in the Antarctic food web, one reason blue whales may contain a lower concentration of PCBs than killer whales is that blue whales

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Worked solution
$$ PCB concentration increases with each step up the food chain (biomagnification).
$$ Blue whales feed low on the food chain (on krill), while killer whales feed on animals such as seals and penguins that are already several steps higher, so killer whales accumulate more PCBs.
Answer: eat krill, which have a lower accumulation of PCBs than penguins and elephant seals

Because blue whales feed directly on krill (a low trophic level), they accumulate far less PCB through biomagnification than killer whales, which prey on animals like seals and penguins that are already higher in the food web.

Question 43 · 2 pts

C. explodens, a species of ant that resides in the tropical jungles of Borneo, can explode when their nest is threatened. The nests contain adult ants, eggs, and larvae. When an adult ant comes in contact with an enemy ant, the C. explodens ant latches onto it and squeezes its own abdominal muscles until its abdomen bursts open, releasing a toxic goo. Which statement best describes this phenomenon?

Worked solution
$$ Natural selection favors heritable behaviors that increase the survival of offspring/relatives, even at a cost to the individual.
Answer: This behavior has resulted in greater reproductive success of the ants, since it kills the enemies who would have fed on their offspring.

By sacrificing itself to kill an enemy threatening the nest, an ant increases the survival of its genetically related colony members (including eggs and larvae), increasing overall reproductive success of the colony; the behavior was not 'developed' with intent, and it is a genetically based (heritable) trait.

Question 44 · 1 pt · constructed response

Base your answer on the diagram below and on your knowledge of biology. The diagram represents an evolutionary pathway for certain organisms over many years, with a time axis (dashed horizontal lines) marked Present time, 25 million years ago, 50 million years ago, 75 million years ago, and 100 million years ago. Branch points and lineages are shown connecting labeled dots (X, A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q) from a common ancestor X at 100 million years ago up to several lineages that reach the present time. Identify the organism in the diagram that became extinct about 60 million years ago.

live question 44 figure
Model answer: F
Worked solution
$$ Locate the point on the time axis halfway between the '50 million years ago' and '75 million years ago' dashed lines; this corresponds to approximately 60 million years ago.
$$ Find the branch tip (a lettered dot with no lineage continuing above it toward the present) that sits at this height on the diagram; this is the point where that lineage ends, indicating extinction.
$$ The branch tip located at this height in the diagram is labeled F, so F is the organism that became extinct about 60 million years ago.
Answer: F

On a branching evolutionary diagram, extinction is shown wherever a lineage's line ends (a branch tip) without continuing further up toward the present. The branch that terminates at the height corresponding to roughly 60 million years ago, between the 50- and 75-million-year marks, is labeled F, so F is the organism that went extinct at that time.

Question 45 · 1 pt · constructed response

Base your answer to questions 45 through 48 on the information below and on your knowledge of biology. The Common Loon Loons are aquatic birds found on freshwater lakes throughout Canada and the northern part of the United States from early spring through fall. They inhabit lakes over five acres in size, with clear water and a good supply of fish for food. They migrate to coastal areas for the winter. In most states where loons are found, they are at risk of becoming extinct and require management to ensure the health of the population. To help keep track of how many loons are living on specific lakes, state wildlife specialists train volunteer citizen scientists how to monitor loon populations during breeding season. This provides additional data that helps researchers determine loon population trends and factors affecting their survival. During the breeding season, a pair of loons typically produces one or two chicks per year. The chicks are slow to mature. They are usually seven years old before their first successful breeding season. Loons have dense bones rather than the hollow bones characteristic of most birds. Their wings are comparatively small for their body size. Adults weigh an average of 8-12 lbs. Another trait of loons is their large, webbed feet and legs set far back on their bodies. To fly, they run on top of the water, and flap their wings to gain enough momentum for liftoff. The data table below shows the number of adult loons and chicks counted in the southern part of Maine between 1985 and 2020. Number of Loon Adults and Chicks Counted in Southern Maine 1985-2020 | Year | Chicks | Adults | | --- | --- | --- | | 1985 | 200 | 1470 | | 1995 | 260 | 2650 | | 2010 | 280 | 2780 | | 2017 | 453 | 2817 | | 2019 | 372 | 2820 | | 2020 | 414 | 2974 | Directions (45-46): Using the information given in the data table, construct a line graph on the grid provided, following the directions below. 45 Mark an appropriate scale, without any breaks in the data, on each labeled axis.

live question 45 figure
Model answer: The y-axis (Number of Loons) should be marked with equal, evenly spaced increments (e.g., by 200s or 500s) starting at 0 and going at least to 3000, since the highest value (2974 adults) must fit on the axis. The x-axis (Years) should be marked with the six given years (1985, 1995, 2010, 2017, 2019, 2020) placed in order with no gaps or breaks in the numbering.
Worked solution
$\text{Find the data range: Adults } 1470\text{ to }2974,\ \text{Chicks } 200\text{ to }453$
$\text{Choose an equal interval (e.g., } 500\text{) for the y-axis so all values fit without breaks}$
$\text{List the six years in order on the x-axis with equal spacing}$
Answer: The y-axis (Number of Loons) should be marked with equal, evenly spaced increments (e.g., by 200s or 500s) starting at 0 and going at least to 3000, since the highest value (2974 adults) must fit on the axis. The x-axis (Years) should be marked with the six given years (1985, 1995, 2010, 2017, 2019, 2020) placed in order with no gaps or breaks in the numbering.

An appropriate scale uses equal intervals with no gaps or breaks so that every data value can be plotted accurately on the grid.

Question 46 · 1 pt · constructed response

Plot the data for both the adults and the chicks following the directions below: - Plot the data for the loon adults on the grid and connect the points. Surround each point for the loon adults with a small triangle. - Plot the data for the loon chicks on the grid and connect the points. Surround each point for the loon chicks with a small circle.

live question 46 figure
Model answer: Plot the adult values (1470, 2650, 2780, 2817, 2820, 2974) for 1985, 1995, 2010, 2017, 2019, 2020 as points surrounded by triangles and connect them with a line; plot the chick values (200, 260, 280, 453, 372, 414) for the same years as points surrounded by circles and connect them with a line, using the scale from question 45.
Worked solution
$\text{Plot each (year, adults) pair, circle each point with a triangle, and connect in order}$
$\text{Plot each (year, chicks) pair, circle each point with a circle, and connect in order}$
Answer: Plot the adult values (1470, 2650, 2780, 2817, 2820, 2974) for 1985, 1995, 2010, 2017, 2019, 2020 as points surrounded by triangles and connect them with a line; plot the chick values (200, 260, 280, 453, 372, 414) for the same years as points surrounded by circles and connect them with a line, using the scale from question 45.

Correctly plotting requires locating each data pair on the scaled axes and using the specified point symbols, connected in chronological order.

Question 47 · 2 pts

Below are two graphs showing the number of loon adults, immature loons, and chicks observed during the annual loon census conducted by the Audubon Society of New York on the lakes and ponds throughout the Adirondack Park in New York State. 2001 Annual Loon Census: #Adults = 308, #Chicks = 59, #Immature Loons = 6 2020 Annual Loon Census: #Adults = 551, #Chicks = 70, #Immature Loons = 17 47 The best explanation for why loon populations did not show a rapid change in size during the Maine and New York studies is that loons

Worked solution
$\text{Loons produce only 1-2 chicks per year and are not sexually mature until age 7}$
$\text{A long maturation time and low reproductive rate mean population size changes slowly}$
Answer: take seven years to reach sexual maturity

Because loons take about seven years to reach breeding age and raise very few young per year, their populations grow or decline gradually rather than rapidly, matching the slow, steady trends seen in both the Maine and New York data.

Question 48 · 1 pt · constructed response

Compare the trend in loon population sizes over time represented in the two New York graphs above to the trend observed in the data table for the southern part of Maine. Support your answer with information from the New York graphs and Maine data table.

live question 48 figure
Model answer: Both the New York and Maine loon populations show an increasing trend over time. In New York, the number of adults rose from 308 (2001) to 551 (2020) and chicks rose from 59 to 70; in Maine, adults rose from 1470 (1985) to 2974 (2020) and chicks rose from 200 to 414. Both data sets show the same overall increasing pattern in loon numbers over time.
Worked solution
$\text{NY adults: } 308 \rightarrow 551,\ \text{NY chicks: } 59 \rightarrow 70$
$\text{Maine adults: } 1470 \rightarrow 2974,\ \text{Maine chicks: } 200 \rightarrow 414$
$\text{Both regions show increasing loon numbers over the time period}$
Answer: Both the New York and Maine loon populations show an increasing trend over time. In New York, the number of adults rose from 308 (2001) to 551 (2020) and chicks rose from 59 to 70; in Maine, adults rose from 1470 (1985) to 2974 (2020) and chicks rose from 200 to 414. Both data sets show the same overall increasing pattern in loon numbers over time.

Comparing the earliest and most recent counts in both the New York bar graphs and the Maine data table shows both populations increasing over time, indicating a similar overall growth trend.

Question 49 · 2 pts

Base your answer to question 49 on the graph below and on your knowledge of biology. The graph shows the effects of stopping smoking at different ages along with the cumulative risk (%) of death from lung cancer up to age 75 in men. The study took place in the United Kingdom. The graph plots Cumulative Risk (%) (y-axis, 0 to 16) against Age (x-axis, 45 to 75) for six groups: Continuing cigarette smokers (rises to about 16% by age 75), Stopped age 60 (rises to about 10%), Stopped age 50 (rises to about 6%), Stopped age 40 (rises to about 3%), Stopped age 30 (rises to about 2%), and Lifelong nonsmokers (stays near 0-1%). 49 Doctors claim that the earlier someone stops smoking, the lower the risk of dying of lung cancer. Which statement best describes evidence that supports this claim?

live question 49 figure
Worked solution
$\text{Continuing smokers' curve reaches about } 16\% \text{ risk by age 75}$
$\text{Stopped-at-30 curve stays much lower (about } 2\%\text{) at age 75}$
$\text{Comparing curves shows earlier quitting corresponds to lower lifetime risk}$
Answer: Men that continued to smoke had an approximately 16% risk of death, and those that stopped at age 30 had a lower risk.

The graph directly shows continuing smokers reaching about 16% cumulative risk while those who quit at age 30 have a much lower risk, supporting the claim that quitting earlier lowers lung cancer death risk.

Question 50 · 2 pts

Base your answers to questions 50 and 51 on the diagram below and on your knowledge of biology. The diagram represents the reproductive systems of the human female and male. In the female diagram, structure A is the upper coiled tube (oviduct/fallopian tube), B is a small oval structure beneath A (an ovary), D is an arrow pointing into the central pear-shaped organ (uterus), and C is at the bottom (cervix/vagina). In the male diagram, G is at the top (bladder region), F points to a duct near the top, H points to the central shaft (urethra/penis), and E is a small oval structure at the bottom (a testis). 50 The two labeled structures that function to produce gametes and hormones are

live question 50 figure
Worked solution
$\text{B labels the ovary in the female system}$
$\text{E labels the testis in the male system}$
$\text{Ovaries and testes (gonads) are the organs that produce both gametes and sex hormones}$
Answer: B and E

The ovary (B) and testis (E) are the gonads, the only structures shown that produce both gametes (eggs and sperm) and sex hormones.

Question 51 · 1 pt · constructed response

Pelvic inflammatory disease and sexually transmitted infections can lead to a blockage of the structure represented by letter A. Explain how this blockage would interfere with the formation of a zygote.

live question 51 figure
Model answer: Structure A is the oviduct (fallopian tube), the tube through which the egg travels from the ovary toward the uterus and where fertilization normally occurs. If this tube is blocked, the egg cannot travel down to meet sperm (or sperm cannot reach the egg), so the egg and sperm cannot fuse and a zygote cannot form.
Worked solution
$\text{A = oviduct/fallopian tube, the site where egg and sperm normally meet}$
$\text{A blockage prevents the egg and sperm from coming into contact}$
$\text{Without egg-sperm contact, fertilization (zygote formation) cannot occur}$
Answer: Structure A is the oviduct (fallopian tube), the tube through which the egg travels from the ovary toward the uterus and where fertilization normally occurs. If this tube is blocked, the egg cannot travel down to meet sperm (or sperm cannot reach the egg), so the egg and sperm cannot fuse and a zygote cannot form.

Blocking the fallopian tube prevents the egg from traveling to meet sperm, so fertilization and zygote formation cannot take place.

Question 52 · 1 pt · constructed response

Detritivores are animals that consume and break down dead plant and animal matter from ecosystems. Explain why the decline and extinction of many species of detritivores may have negative consequences on the stability of an ecosystem.

Model answer: Without detritivores, dead organic matter would not be broken down and recycled, so nutrients would not be returned to the soil for producers to use. This disruption of nutrient cycling and energy flow would reduce the ecosystem's stability.
Worked solution
$\text{Detritivores decompose dead matter, releasing nutrients back into the ecosystem}$
$\text{Loss of detritivores stops this recycling of nutrients}$
$\text{Without nutrient recycling, producers lack nutrients, disrupting the whole ecosystem's stability}$
Answer: Without detritivores, dead organic matter would not be broken down and recycled, so nutrients would not be returned to the soil for producers to use. This disruption of nutrient cycling and energy flow would reduce the ecosystem's stability.

Detritivores are essential for recycling nutrients from dead organisms; their loss disrupts nutrient cycling, which destabilizes the ecosystem.

Question 53 · 1 pt · constructed response

Base your answers to questions 53 and 54 on the information and photograph below and on your knowledge of biology. A research team of students added water and an experimental enzyme to a jar containing a piece of the type of plastic that is commonly used in food packaging. Several days later, the plastic was no longer visible. 53 Identify one factor that would influence the rate at which the experimental enzyme breaks down this type of plastic.

live question 53 figure
Model answer: Temperature (other acceptable answers: pH, enzyme concentration, or amount/concentration of plastic substrate).
Worked solution
$\text{Enzyme reaction rates are affected by environmental/reactant conditions}$
$\text{Example: increasing temperature (within a normal range) increases the rate of the enzyme reaction}$
Answer: Temperature (other acceptable answers: pH, enzyme concentration, or amount/concentration of plastic substrate).

Like all enzymes, the rate of this reaction depends on factors such as temperature, pH, or the concentrations of enzyme and substrate.

Question 54 · 1 pt · constructed response

The research team claimed that the experimental enzyme would break down all plastics. The students repeated the experiment with a different type of plastic. This time, the plastic was not broken down by the enzyme. 54 Explain why the enzyme is not able to break down all types of plastics.

Model answer: Enzymes are specific in shape, and their active site only fits a substrate with a complementary shape. The first plastic's molecular structure matched the enzyme's active site, but the second plastic has a different molecular structure that does not fit the enzyme's active site, so it cannot be broken down by that enzyme.
Worked solution
$\text{Enzymes have a specific active site shape (lock-and-key)}$
$\text{Only a substrate with a matching shape can bind and be broken down}$
$\text{The second plastic's structure does not fit this enzyme's active site}$
Answer: Enzymes are specific in shape, and their active site only fits a substrate with a complementary shape. The first plastic's molecular structure matched the enzyme's active site, but the second plastic has a different molecular structure that does not fit the enzyme's active site, so it cannot be broken down by that enzyme.

Enzyme specificity means an enzyme's active site only fits certain substrates; a plastic with a different molecular shape will not bind to and be broken down by that enzyme.

Question 55 · 1 pt · constructed response

Base your answer to question 55 on the information below and on your knowledge of biology. Ultrasonic repellents are electronic devices designed to repel and remove household pests. When plugged in, they produce ultrahigh-frequency sound waves to chase away mice, rats, fleas, cockroaches, silverfish, and spiders. The sound these devices make cannot be heard by humans. These pest-control devices are often used in environments where the use of poison is prohibited or not recommended. 55 Identify one concern, other than its effectiveness, that people might have before using it in their home.

Model answer: The ultrasonic sound, though inaudible to humans, might be heard by and disturb or harm pets (such as dogs, cats, or other animals) in the home, or could have unknown effects on other organisms exposed to it.
Worked solution
$\text{The device emits ultrahigh-frequency sound inaudible to humans}$
$\text{Pets or other animals in the home may be able to hear/be affected by this sound}$
Answer: The ultrasonic sound, though inaudible to humans, might be heard by and disturb or harm pets (such as dogs, cats, or other animals) in the home, or could have unknown effects on other organisms exposed to it.

A reasonable concern is the unintended effect of the ultrasonic sound on pets or other household organisms that can hear frequencies humans cannot.

Question 56 · 1 pt · constructed response

Base your answers to questions 56 and 57 on the information, photograph, and illustration below and on your knowledge of biology. Mouse DNA and Epigenetics In 2000, scientists at Duke University designed an experiment using mice that carry a gene for yellow fur color. Mice with the yellow fur gene also have a large appetite and a tendency to develop cancer and diabetes. The scientists wanted to see if they could reduce the chances of the offspring of the yellow mice developing these diseases by changing the expression of the gene for yellow fur color. They began by changing the diet of yellow female mice to a diet containing food rich in methyl groups. Methyl groups are small clusters of chemicals that can attach to a gene and turn it off. Their offspring, that had methylated DNA, were found to be thin, have brown fur, and had less chance of developing cancer and diabetes. The researchers concluded that the offspring were born with an epigenetic alteration to their DNA. Epigenetic alterations are inheritable changes in gene expression patterns independent of the primary DNA sequence. The expression of the gene is altered but the DNA sequence usually remains unchanged. In addition to diet, other factors such as hormones, physical activity, stress, tobacco, and alcohol use can also cause epigenetic changes. 56 Sometimes identical twins have different physical traits. Using the experiment Duke scientists performed on mice with the yellow fur color gene as a model, explain how epigenetics could be the cause of differences observed in identical twins.

live question 56 figure
Model answer: Identical twins have the same DNA sequence, but different environmental factors (such as diet, hormones, stress, or exposure to chemicals) can cause methyl groups to attach to and turn off different genes in each twin. This changes which genes are expressed (epigenetic change) without changing the DNA sequence, causing the twins to show different physical traits, just as diet changed gene expression and fur color in the mice.
Worked solution
$\text{Identical twins share identical DNA sequences}$
$\text{Different environmental exposures can cause different methylation patterns in each twin}$
$\text{Different gene expression (epigenetics) leads to different observable traits, as in the mice}$
Answer: Identical twins have the same DNA sequence, but different environmental factors (such as diet, hormones, stress, or exposure to chemicals) can cause methyl groups to attach to and turn off different genes in each twin. This changes which genes are expressed (epigenetic change) without changing the DNA sequence, causing the twins to show different physical traits, just as diet changed gene expression and fur color in the mice.

Just as diet altered gene expression (via methylation) and changed fur color in genetically similar mice, different environmental exposures can epigenetically alter gene expression differently in identical twins, producing different traits.

Question 57 · 1 pt · constructed response

Explain why epigenetic changes are not usually considered to be mutations.

Model answer: Epigenetic changes alter gene expression (turn genes on or off) without changing the actual base sequence of the DNA, whereas a mutation is a permanent change in the DNA base sequence itself.
Worked solution
$\text{Mutations change the DNA base sequence}$
$\text{Epigenetic changes (e.g., methylation) only affect whether a gene is expressed, not its sequence}$
Answer: Epigenetic changes alter gene expression (turn genes on or off) without changing the actual base sequence of the DNA, whereas a mutation is a permanent change in the DNA base sequence itself.

Because epigenetic modifications leave the underlying DNA sequence unchanged and only affect gene expression, they are not classified as mutations.

Question 58 · 1 pt · constructed response

Base your answer to question 58 on the information below and on your knowledge of biology. A Scorpion's Secret Weapon Ingredient Getting stung by a scorpion is painful. The pain serves as a warning to its predators to stay away. Scorpion venom contains toxins that are recognized by the pain receptors on nerve cells. These receptors are the same as those that cause a burning feeling when you touch something hot. But, being stung by a scorpion is much more painful than touching a hot object. The venom itself doesn't cause all of the pain. It also contains an acid that changes the pH of the area surrounding the affected nerve cells. The change in pH increases the intensity of the pain message. 58 In a population of scorpions, a mutation occurred that resulted in the venom having no effect on its predators. Explain why the number of predators that feed exclusively on scorpions would decrease over time. Justify your answer.

Model answer: The scorpion's painful venom normally warns predators to stay away, which protects the scorpion population. After the mutation the venom has no effect, so predators are no longer deterred and prey on scorpions more heavily. This reduces the scorpion population, and because these predators feed exclusively on scorpions, the loss of their only food source causes the predator population to decrease over time.
Worked solution
$\text{Normally the painful venom warns predators away, protecting the scorpion population.}$
$\text{After the mutation the venom has no effect, so predators are no longer deterred.}$
$\text{Predators overprey on scorpions, so the scorpion population declines.}$
$\text{These predators feed only on scorpions, so losing their food source makes their numbers fall.}$
Answer: The scorpion's painful venom normally warns predators to stay away, which protects the scorpion population. After the mutation the venom has no effect, so predators are no longer deterred and prey on scorpions more heavily. This reduces the scorpion population, and because these predators feed exclusively on scorpions, the loss of their only food source causes the predator population to decrease over time.

The venom's role was to deter predators with pain. With no effect, predators are no longer warned off and overconsume scorpions; since the predators are specialists that eat only scorpions, the resulting decline in their sole prey causes their own population to decrease.

Question 59 · 1 pt · constructed response

Base your answers to questions 59 through 61 on the information below and on your knowledge of biology. Scientists have studied the medicinal herb, Fritillaria delavayi (fritillary), which is very difficult to cultivate. This herb is used in Chinese traditional medicine to treat lung conditions such as bronchitis and bad coughs. This threatened herb grows wild among the rocks in dry, cold, mountainous places in China. Most fritillary have bright green leaves and sunny yellow flowers. The scientists have noticed something unusual: In places where people often gather and harvest the herb, more and more plants of the same species have a dull brown flower color. Many people have trouble finding this dull brown variety that blends in with the rocky area where it grows. 59 Identify the original source of the brown variation.

Model answer: A random genetic mutation in the gene(s) controlling flower color, which already existed as a naturally occurring variation within the fritillary population.
Worked solution
$\text{New heritable variations arise from random mutations in DNA}$
$\text{The brown-flower allele originated from such a mutation before it became common}$
Answer: A random genetic mutation in the gene(s) controlling flower color, which already existed as a naturally occurring variation within the fritillary population.

New traits like flower color variation ultimately originate from random gene mutations that occur within a population.

Question 60 · 1 pt · constructed response

Fritillary grows very slowly, taking five years to reproduce. Predict which flower color will be more common in areas accessible by humans after 20 years. Support your answer.

Model answer: The dull brown flower color will become more common. In areas with high human harvesting, brown-flowered plants are camouflaged among the rocks and are less likely to be seen and picked, so they survive to reproduce and pass on the brown-flower allele, while the more visible yellow-flowered plants are harvested and removed before they can reproduce. Over several 5-year reproductive cycles (about 4 cycles in 20 years), this selective pressure would increase the frequency of brown-flowered plants.
Worked solution
$\text{Brown flowers blend in with rocks and avoid detection/harvesting by humans}$
$\text{Yellow flowers are more visible and more likely to be picked before reproducing}$
$\text{Over multiple 5-year reproductive cycles, brown-flowered plants reproduce more, increasing their frequency}$
Answer: The dull brown flower color will become more common. In areas with high human harvesting, brown-flowered plants are camouflaged among the rocks and are less likely to be seen and picked, so they survive to reproduce and pass on the brown-flower allele, while the more visible yellow-flowered plants are harvested and removed before they can reproduce. Over several 5-year reproductive cycles (about 4 cycles in 20 years), this selective pressure would increase the frequency of brown-flowered plants.

Because camouflaged brown plants survive human harvesting better than visible yellow plants, natural/human-driven selection would increase the proportion of brown-flowered fritillary over successive generations.

Question 61 · 1 pt · constructed response

Human efforts to cultivate this endangered species have not been successful. What argument could be made to justify continued efforts to preserve this species by cultivation?

Scientists have studied the medicinal herb, Fritillaria delavayi (fritillary), which is very difficult to cultivate. This herb is used in Chinese traditional medicine to treat lung conditions such as bronchitis and bad coughs. This threatened herb grows wild among the rocks in dry, cold, mountainous places in China. Most fritillary have bright green leaves and sunny yellow flowers. The scientists have noticed something unusual: In places where people often gather and harvest the herb, more and more plants of the same species have a dull brown flower color. Many people have trouble finding this dull brown variety that blends in with the rocky area where it grows.

Model answer: Continued cultivation efforts are justified because fritillary is a valuable medicinal plant used to treat lung conditions such as bronchitis and coughs, and preserving it also maintains genetic diversity and biodiversity, which could be important for future medical or ecological needs; if the species goes extinct in the wild, this resource and its genetic information would be lost forever.
Worked solution
$\text{The plant provides medicinal value to humans}$
$\text{Preserving the species maintains biodiversity/genetic diversity}$
$\text{Extinction is irreversible, so continued efforts protect against permanent loss}$
Answer: Continued cultivation efforts are justified because fritillary is a valuable medicinal plant used to treat lung conditions such as bronchitis and coughs, and preserving it also maintains genetic diversity and biodiversity, which could be important for future medical or ecological needs; if the species goes extinct in the wild, this resource and its genetic information would be lost forever.

Preserving a threatened species with medicinal and ecological value protects against irreversible loss of biodiversity and a useful natural resource.

Question 62 · 1 pt · constructed response

Three different food chains present in a food web are represented below. (a) prickly pear cactus -> antelope squirrel -> western diamondback rattlesnake -> red-tailed hawk (b) saguaro cactus -> wood rat -> western diamondback rattlesnake (c) brittlebush -> grasshopper mouse 62 Identify the food chain, (a), (b) or (c), in which there would be the least amount of energy available to the last consumer in the feeding sequence. Support your answer.

Model answer: Food chain (a) would have the least amount of energy available to its last consumer (the red-tailed hawk). This is because (a) has the most feeding/trophic levels (four levels), and energy is lost as heat at each transfer between trophic levels, so the last consumer in the longest chain receives the smallest fraction of the original energy.
Worked solution
$\text{(a) has 4 trophic levels, (b) has 3, (c) has 2}$
$\text{Only about 10\% of energy transfers to the next trophic level}$
$\text{The longest chain (a) loses the most energy overall, leaving the least for its top consumer}$
Answer: Food chain (a) would have the least amount of energy available to its last consumer (the red-tailed hawk). This is because (a) has the most feeding/trophic levels (four levels), and energy is lost as heat at each transfer between trophic levels, so the last consumer in the longest chain receives the smallest fraction of the original energy.

Because energy decreases at each trophic transfer, the food chain with the most links (a) leaves the smallest amount of energy for its final consumer.

Question 63 · 1 pt · constructed response

Base your answers to questions 63 and 64 on the information below and on your knowledge of biology. Woman Gives Birth After Uterus Transplant Women with uterine factor infertility (UFI) either don't have a uterus or have a uterus that doesn't function. A uterus transplant has emerged as a potential solution for these women. In 2019, the first baby in North America was delivered by a mother who received a uterus transplant. 63 Describe a role of the uterus in the process of human reproduction.

Model answer: The uterus is the organ in which a fertilized egg (embryo) implants and develops, providing nourishment, protection, and support for the growing fetus throughout pregnancy until birth.
Worked solution
$\text{Fertilized egg (zygote) travels to and implants in the uterine lining}$
$\text{Uterus supports and nourishes the developing embryo/fetus until birth}$
Answer: The uterus is the organ in which a fertilized egg (embryo) implants and develops, providing nourishment, protection, and support for the growing fetus throughout pregnancy until birth.

The uterus provides the site of implantation and the environment for fetal development during pregnancy.

Question 64 · 1 pt · constructed response

During pregnancy, the women are given medication to prevent the transplanted uterus from being rejected. After the baby is born, the transplanted uterus is removed. 64 Explain why a woman's body would reject a transplanted uterus if she does not take the medication.

Model answer: The transplanted uterus contains proteins/antigens that are different from the recipient's own cells (foreign/nonself), so her immune system would recognize it as foreign and mount an immune response (producing antibodies and white blood cells) to attack and destroy the transplanted tissue, causing rejection.
Worked solution
$\text{Transplanted tissue has different surface proteins (antigens) from the recipient}$
$\text{The immune system identifies these as foreign/nonself}$
$\text{An immune response is triggered that attacks and rejects the foreign tissue}$
Answer: The transplanted uterus contains proteins/antigens that are different from the recipient's own cells (foreign/nonself), so her immune system would recognize it as foreign and mount an immune response (producing antibodies and white blood cells) to attack and destroy the transplanted tissue, causing rejection.

Without immunosuppressant medication, the recipient's immune system recognizes the transplanted uterus's antigens as foreign and attacks the tissue, causing rejection.

Question 65 · 1 pt · constructed response

Base your answers to question 65 on the information and graph below and on your knowledge of biology. Human actions have affected the biodiversity of multiple ecosystems on Earth. The graph 'Species Extinctions and Human Population Size' plots Time (1800 to 2010) on the x-axis, with Species Extinctions (0 to 60000) on the left y-axis and Human Population in millions (0 to 8000) on the right y-axis. Both the Species Extinctions curve and the Human Population curve rise slowly from 1800 to about 1950, then rise sharply from 1950 to 2010, reaching roughly 56,000 extinctions and roughly 7,000+ million people by 2010. 65 Make a claim as to how human actions have affected biodiversity. Support your claim with evidence from the graph.

live question 65 figure
Model answer: Human actions have decreased biodiversity by increasing the rate of species extinctions. The graph shows that as human population size increased sharply (especially after 1950, rising toward 7,000+ million by 2010), the number of species extinctions also increased sharply during the same period (rising toward about 56,000), showing that growing human population/activity is associated with greater loss of species.
Worked solution
$\text{Both curves rise slowly before 1950, then increase sharply after 1950}$
$\text{Human population and species extinctions increase together over time}$
$\text{This correlation supports the claim that human population growth has reduced biodiversity}$
Answer: Human actions have decreased biodiversity by increasing the rate of species extinctions. The graph shows that as human population size increased sharply (especially after 1950, rising toward 7,000+ million by 2010), the number of species extinctions also increased sharply during the same period (rising toward about 56,000), showing that growing human population/activity is associated with greater loss of species.

The graph shows species extinctions rising in step with human population growth, supporting the claim that increased human activity has reduced biodiversity.

Question 66 · 1 pt · constructed response

Base your answer to question 66 on the diagram below and on your knowledge of biology. The diagram represents a feedback mechanism in humans: Higher blood sugar leads to 'Pancreas secretes more of a hormone', which leads to Lower blood sugar, which leads to 'Pancreas secretes less of a hormone', which leads back to Higher blood sugar, forming a continuous cycle. 66 An individual with a healthy pancreas eats a starchy snack. Explain why the pancreas would secrete more hormone a short time later. Support your answer with information from the diagram.

live question 66 figure
Model answer: Eating a starchy snack is digested into glucose, raising the person's blood sugar level. According to the diagram, higher blood sugar causes the pancreas to secrete more of the hormone (insulin), which acts to lower the blood sugar back toward a normal level.
Worked solution
$\text{Starchy food is broken down into glucose, raising blood sugar}$
$\text{Per the diagram, higher blood sugar triggers the pancreas to secrete more hormone}$
$\text{This hormone (insulin) helps lower blood sugar back to normal, maintaining homeostasis}$
Answer: Eating a starchy snack is digested into glucose, raising the person's blood sugar level. According to the diagram, higher blood sugar causes the pancreas to secrete more of the hormone (insulin), which acts to lower the blood sugar back toward a normal level.

The starchy snack raises blood glucose, and per the feedback diagram, higher blood sugar directly triggers the pancreas to secrete more hormone (insulin) to restore normal blood sugar levels.

Question 67 · 1 pt · constructed response

Base your answer to question 67 on the information and diagram below and on your knowledge of biology. The diagram represents two molecules, A and B, resulting from the digestion of foods, moving into a cell. 67 Explain how the lack of nutrients can impact the cellular process needed to move molecule A into this cell.

live question 67 figure
Model answer: A lack of nutrients would reduce the amount of ATP (energy) available, so the active transport process that moves molecule A into the cell would slow down or stop, and molecule A could no longer be moved into the cell against its concentration gradient.
Worked solution
$Molecule A is shown moving into the cell even though more A is already present inside than outside, indicating movement against a concentration gradient.$
$Movement against a concentration gradient requires active transport, which uses carrier proteins and energy in the form of ATP.$
$ATP is produced during cellular respiration, which requires nutrients (such as glucose) as fuel.$
$If nutrients are lacking, less ATP is produced, so the carrier proteins cannot actively transport molecule A into the cell as effectively, slowing or stopping its entry.$
Answer: A lack of nutrients would reduce the amount of ATP (energy) available, so the active transport process that moves molecule A into the cell would slow down or stop, and molecule A could no longer be moved into the cell against its concentration gradient.

The diagram shows molecule A moving into the cell against its concentration gradient, which requires active transport powered by ATP from cellular respiration; without nutrients to fuel respiration, this energy-requiring process is impaired.

Question 68 · 1 pt · constructed response

Base your answers to questions 68 through 70 on the information below and on your knowledge of biology. Mitochondria Mitochondria are organelles present in most complex cells. 68 Explain why mitochondria are essential to the survival of complex organisms.

Model answer: Mitochondria carry out cellular respiration, converting nutrients into ATP (usable chemical energy); complex organisms require large, continuous amounts of energy for life processes such as growth, movement, and maintaining homeostasis, so without mitochondria producing enough ATP, cells could not carry out these functions and the organism could not survive.
Worked solution
$Mitochondria are the site of cellular respiration, which converts nutrients (glucose) and oxygen into ATP.$
$ATP is the usable energy needed for all life-sustaining cell processes (movement, repair, active transport, synthesis of molecules).$
$Complex, multicellular organisms have high and constant energy demands to maintain homeostasis in many specialized cells.$
$Without mitochondria to supply this ATP, cells would not have enough energy to function, so the organism could not survive.$
Answer: Mitochondria carry out cellular respiration, converting nutrients into ATP (usable chemical energy); complex organisms require large, continuous amounts of energy for life processes such as growth, movement, and maintaining homeostasis, so without mitochondria producing enough ATP, cells could not carry out these functions and the organism could not survive.

Mitochondria supply the ATP that cells need to perform life-sustaining activities; complex organisms cannot survive without this constant energy supply.

Question 69 · 1 pt · constructed response

Unlike most other organelles, mitochondria contain their own DNA. This DNA is in the form of a double-stranded, ring-shaped molecule that can replicate. The number of mitochondria in a cell can increase when mitochondria reproduce. Mitochondrial DNA mutates. Some of these mutations have been linked to certain diseases in humans. Mitochondrial DNA is passed on to children through their mothers. The chart below illustrates this process. Mitochondrial Inheritance 69 Provide evidence from the mitochondrial inheritance chart that supports the claim that mitochondria are usually inherited from the mother.

live question 69 figure
Model answer: The chart shows that when only the father has the disease, none of the children have the disease, but when only the mother has the disease (all her mitochondria are mutant), all of the children have the disease; this shows that mitochondrial traits are passed from mother to offspring, not from father to offspring, supporting maternal inheritance of mitochondria.
Worked solution
$In the first family, the father has the disease but the mother does not, and none of the children have the disease.$
$In the second family, the mother has the disease (all mitochondria mutant) and the father does not, and all of the children have the disease.$
$Since the children's disease status matches the mother's mitochondrial status and not the father's, mitochondrial DNA/disease must be inherited from the mother.$
Answer: The chart shows that when only the father has the disease, none of the children have the disease, but when only the mother has the disease (all her mitochondria are mutant), all of the children have the disease; this shows that mitochondrial traits are passed from mother to offspring, not from father to offspring, supporting maternal inheritance of mitochondria.

The chart's contrasting outcomes for father-affected versus mother-affected crosses directly demonstrate that mitochondrial traits pass only through the mother.

Question 70 · 1 pt · constructed response

Different cells in the human body contain different numbers of mitochondria. The chart below shows the approximate number of mitochondria present in various cells. Number of Mitochondria in Various Cells (per cell) Liver cell: 2,500 Skeletal muscle cell: 1,200 White blood cell in lung: 700 Dermal cell (just under the skin): 200 White adipose cell (fat storage): 100 Red blood cell: 0 70 State which cell type would probably be most affected by mitochondrial diseases. Support your answer.

live question 70 figure
Model answer: The liver cell would probably be most affected, because it contains the greatest number of mitochondria (2,500 per cell), so a mitochondrial disease would disrupt ATP production in the largest number of mitochondria and have the greatest impact on that cell's energy supply.
Worked solution
$The chart shows the liver cell has the highest number of mitochondria (2,500) of all the cell types listed.$
$Mitochondrial diseases impair the function of mitochondria and reduce ATP production.$
$A cell type that relies on the largest number of mitochondria (the liver cell) would be affected the most because it depends heavily on mitochondrial energy production.$
Answer: The liver cell would probably be most affected, because it contains the greatest number of mitochondria (2,500 per cell), so a mitochondrial disease would disrupt ATP production in the largest number of mitochondria and have the greatest impact on that cell's energy supply.

Since mitochondrial disease impairs energy production, the cell type most dependent on large numbers of mitochondria (the liver cell, with 2,500 per cell) would be affected the most.

Question 71 · 1 pt · constructed response

Base your answers to questions 71 and 72 on the information below and on your knowledge of biology. Why Is the Sky White? One method researchers are investigating to decrease the impact of climate change is stratospheric aerosol scattering. This involves using airplanes or balloons to spray tiny particles of sulfate aerosols or calcium carbonate into the upper atmosphere. The particles reflect sunlight back into space. Climate modeling has shown that the use of this technology could lead to a decrease in extreme temperatures and the intensity of tropical storms. It could also reduce ice loss and sea-level rise as well. However, there are risks associated with this technology. While the models show global benefits, local benefits might vary considerably. Also, since this technology doesn't address carbon emissions, as it continues to get warmer there will be a need to spray more and more particles into the atmosphere. This could change the appearance of the sky from blue to white. There are also concerns that introducing sulfate aerosols into the upper atmosphere could damage the ozone layer. 71 State one reason for supporting the use of this technology.

live question 71 figure
Model answer: This technology could decrease extreme temperatures and reduce the intensity of tropical storms (or reduce ice loss and sea-level rise), helping to lessen some effects of climate change.
Worked solution
$According to the passage, climate modeling shows the technology could decrease extreme temperatures and tropical storm intensity.$
$It could also reduce ice loss and sea-level rise, which are harmful effects of climate change.$
Answer: This technology could decrease extreme temperatures and reduce the intensity of tropical storms (or reduce ice loss and sea-level rise), helping to lessen some effects of climate change.

The passage states the technology's modeled benefits directly, so any one of the stated global benefits (lower extreme temperatures, weaker storms, less ice loss/sea-level rise) is an acceptable supporting reason.

Question 72 · 1 pt · constructed response

Explain why it would be important to continue efforts to reduce carbon emissions even if this technology were to be used.

Why Is the Sky White? One method researchers are investigating to decrease the impact of climate change is stratospheric aerosol scattering. This involves using airplanes or balloons to spray tiny particles of sulfate aerosols or calcium carbonate into the upper atmosphere. The particles reflect sunlight back into space. Climate modeling has shown that the use of this technology could lead to a decrease in extreme temperatures and the intensity of tropical storms. It could also reduce ice loss and sea-level rise as well. However, there are risks associated with this technology. While the models show global benefits, local benefits might vary considerably. Also, since this technology doesn't address carbon emissions, as it continues to get warmer there will be a need to spray more and more particles into the atmosphere. This could change the appearance of the sky from blue to white. There are also concerns that introducing sulfate aerosols into the upper atmosphere could damage the ozone layer.

Model answer: This technology does not address the root cause of climate change, rising carbon emissions; it only reflects sunlight to mask warming. If emissions are not reduced, warming will continue and require spraying ever-increasing amounts of particles, and carbon dioxide will keep causing other problems, such as ocean acidification, regardless of temperature control.
Worked solution
$The passage states the technology 'doesn't address carbon emissions.'$
$If emissions keep rising, more and more particles would need to be sprayed continuously just to offset the added warming, which is not sustainable.$
$Carbon dioxide causes other environmental problems (e.g., ocean acidification) independent of temperature, which this technology does not fix.$
Answer: This technology does not address the root cause of climate change, rising carbon emissions; it only reflects sunlight to mask warming. If emissions are not reduced, warming will continue and require spraying ever-increasing amounts of particles, and carbon dioxide will keep causing other problems, such as ocean acidification, regardless of temperature control.

Because the technology only masks the temperature effects of greenhouse gases without lowering carbon dioxide levels, reducing emissions directly is still necessary to address the underlying cause and its other effects.

Question 73 · 2 pts

When the proportion of a gene for a specific trait in a population of finches increases over time, the most likely cause of this increase would be

Worked solution
$A change in gene proportion within a wild population over time reflects differential survival and reproduction, which is natural selection.$
$Selective breeding requires human intervention, which is not indicated here.$
$Species extinction and ecological succession describe population/community-level changes, not shifts in gene frequency within a surviving population.$
Answer: natural selection

A shift in allele frequency within a population over generations, without human intervention, is the definition of natural selection.

Question 74 · 2 pts

A scientist conducts an experiment in order to

Worked solution
$Choosing variables, collecting data, and identifying a control are all steps taken while designing and running an experiment.$
$The overall purpose of conducting the experiment is to test a hypothesis, the proposed explanation being investigated.$
Answer: test a hypothesis

The other choices describe procedural steps within an experiment, but the fundamental purpose of running the experiment is to test a hypothesis.

Question 75 · 2 pts

Base your answers to questions 75 through 77 on the information and diagram below and on your knowledge of biology. The diagram represents evolutionary pathways of seven groups of organisms alive today. 75 Which species is most closely related to species M?

live question 75 figure
Worked solution
$On a cladogram, the species most closely related to a given branch point is the one that shares the most recent common ancestor with it.$
$According to the diagram, the lineage leading to H shares the most recent common ancestor (node J) with the lineage at M, making H the most closely related choice.$
Answer: H

The branch point/lineage that connects to M through the most recent shared ancestor in the cladogram is H, making it the most closely related among the given choices.

Question 76 · 2 pts

Note: The answer to question 76 should be recorded on your separate answer sheet. 76 Which species appears to have been well adapted to its environment for a long period of time?

live question 76 figure
Worked solution
$A species that shows little branching and a long, unbranched lineage on a cladogram has undergone relatively little evolutionary change over time.$
$This lack of change over a long time period suggests the species was already well suited (adapted) to its environment and did not need to change much.$
$In the diagram, species E has the longest branch without further divergence, indicating long-term stability/adaptation.$
Answer: E

A long, unbranched lineage on a cladogram indicates minimal evolutionary change over time, which suggests the species was already well adapted to a stable environment.

Question 77 · 1 pt · constructed response

The diagram was based on fossil evidence. Explain why other forms of evidence would help support the accuracy of the evolutionary pathways represented in the diagram.

live question 77 figure
Model answer: The fossil record is often incomplete because not all organisms fossilize well and many fossils have not yet been found, so relying on fossils alone can leave gaps or uncertainty in evolutionary pathways; other independent evidence, such as comparisons of DNA or protein sequences, embryological development, or anatomical (homologous) structures among living species, could confirm or refine the relationships shown in the diagram.
Worked solution
$The fossil record has gaps because fossilization is rare and not all organisms/environments preserve fossils well.$
$Other lines of evidence, such as DNA/protein sequence comparisons, comparative anatomy (homologous structures), or embryology, are independent of fossils.$
$If these independent forms of evidence agree with the fossil-based pathways, this increases confidence that the proposed evolutionary relationships are accurate.$
Answer: The fossil record is often incomplete because not all organisms fossilize well and many fossils have not yet been found, so relying on fossils alone can leave gaps or uncertainty in evolutionary pathways; other independent evidence, such as comparisons of DNA or protein sequences, embryological development, or anatomical (homologous) structures among living species, could confirm or refine the relationships shown in the diagram.

Because fossil evidence alone can be incomplete, additional independent evidence (molecular, anatomical, or embryological) strengthens confidence in the accuracy of the proposed evolutionary relationships.

Question 78 · 1 pt · constructed response

When determining a pulse rate, why is it best to use the average of three readings?

Model answer: Using the average of three readings reduces the effect of any single inaccurate or unusual reading (measurement error or a brief irregular reading), giving a more accurate and reliable estimate of a person's true pulse rate.
Worked solution
$A single reading could be affected by measurement error or a momentary change (e.g., movement, miscounting).$
$Averaging multiple (three) readings reduces the impact of any one unusual or inaccurate value.$
$This produces data that is more reliable and representative of the true, typical pulse rate.$
Answer: Using the average of three readings reduces the effect of any single inaccurate or unusual reading (measurement error or a brief irregular reading), giving a more accurate and reliable estimate of a person's true pulse rate.

Averaging repeated trials minimizes the effect of random error, producing a more precise and trustworthy measurement.

Question 79 · 1 pt · constructed response

Base your answer to question 79 on the information below and on your knowledge of biology. Selecting agents can have a significant impact on the size of many populations living in an area. 79 Identify one selecting agent that could have a potential impact on the number of individuals in the various penguin populations living in the Antarctic Peninsula.

live question 79 figure
Model answer: Predation (for example, by leopard seals or skuas), availability of food (such as krill or fish), or changing climate/sea-ice conditions are all acceptable selecting agents.
Worked solution
$A selecting agent is any environmental factor that affects which individuals survive and reproduce.$
$For Antarctic penguin populations, examples include predators (leopard seals, skuas), food availability (krill, fish), climate change affecting sea ice, or disease.$
Answer: Predation (for example, by leopard seals or skuas), availability of food (such as krill or fish), or changing climate/sea-ice conditions are all acceptable selecting agents.

Any factor that limits survival or reproduction, such as predation, food supply, or climate change, is a valid selecting agent for penguin populations.

Question 80 · 1 pt · constructed response

Base your answer to question 80 on the information below and on your knowledge of biology. Pulse-rate data were collected from some students during their study hall. The data are shown in the histogram below. Student Pulse-Rate Data (Average Pulse-Rate Range, beats/min : Number of Students) < 51 : 4 51-60 : 5 61-70 : 6 71-80 : 8 81-90 : 5 > 90 : 4 80 State one way the data would most likely be different if the pulse rates were collected immediately after gym class instead of during study hall.

live question 80 figure
Model answer: The pulse rates would most likely be higher overall; more students would fall into the higher pulse-rate ranges (e.g., 81-90 or greater than 90) and fewer students would fall into the lower ranges, because physical activity increases heart rate.
Worked solution
$Physical activity (like gym class) increases the body's demand for oxygen, which increases heart rate/pulse rate.$
$If data were collected right after gym class, the distribution would shift toward higher beats-per-minute ranges compared to the resting study-hall data.$
Answer: The pulse rates would most likely be higher overall; more students would fall into the higher pulse-rate ranges (e.g., 81-90 or greater than 90) and fewer students would fall into the lower ranges, because physical activity increases heart rate.

Because exercise raises heart rate, pulse-rate data collected right after gym class would shift toward higher ranges compared to data collected while resting in study hall.

Question 81 · 2 pts

Note: The answer to question 81 should be recorded on your separate answer sheet. 81 Ground finches in the Galapagos Islands are seed eaters. The beaks of the offspring are very close in size to the beaks of their parents. The best explanation for this observation is that

Worked solution
$Offspring closely resembling their parents in a physical trait (beak size) indicates the trait is heritable, controlled largely by genes passed from parent to offspring.$
$Environmental temperature and survival/reproduction of only certain beak sizes do not explain why offspring specifically resemble their own parents.$
Answer: the size of the beak is determined mostly by genes

Consistent resemblance between parents and offspring in beak size reflects genetic inheritance of the trait, not an environmental or selective effect alone.

Question 82 · 2 pts

Base your answers to questions 82 and 83 on the information below and on your knowledge of biology. A student was assigned the task of determining which of three species of plant (species L, M, or N) was most closely related to Botana curus (BC). The student compared a segment of genetic material from each species using the procedure represented below. Note: The answer to question 82 should be recorded on your separate answer sheet. 82 A valid conclusion that can be drawn from these results is that

live question 82 figure
Worked solution
$Gel electrophoresis separates DNA fragments by size, producing a band pattern for each sample.$
$The more similar two samples' band patterns are, the more similar their DNA (and the more closely related the organisms are).$
$In the results, lane M's band pattern most closely matches lane BC's pattern, indicating species M is most closely related to Botana curus.$
Answer: species M is most closely related to BC

Gel electrophoresis results showing the closest band-pattern match between BC and M indicate that species M is genetically most similar, and therefore most closely related, to Botana curus.

Question 83 · 1 pt · constructed response

Identify another biochemical test that would provide data to support which of the three plant species is most closely related to Botana curus.

Model answer: Comparing DNA nucleotide sequences (DNA sequencing) or comparing the amino acid sequences of a shared protein between the species would provide additional biochemical data; the species with the sequence most similar to Botana curus's would be considered most closely related.
Worked solution
$Besides gel electrophoresis of DNA fragments, DNA or protein sequences can be directly compared.$
$Greater similarity in DNA nucleotide sequence or protein amino acid sequence between two species indicates a closer evolutionary relationship.$
Answer: Comparing DNA nucleotide sequences (DNA sequencing) or comparing the amino acid sequences of a shared protein between the species would provide additional biochemical data; the species with the sequence most similar to Botana curus's would be considered most closely related.

Direct DNA sequencing or amino acid sequence comparison of a shared protein is another valid biochemical test for determining relatedness, since more similar sequences indicate closer relationship.

Question 84 · 1 pt · constructed response

During physical activity, a person's pulse rate changes. Choose one body system, other than circulatory, that would be involved in maintaining homeostasis, and describe one change that would occur in that system.

Model answer: The respiratory system is involved; during physical activity, breathing rate and depth increase in order to take in more oxygen and remove more carbon dioxide to meet the body's increased energy demands.
Worked solution
$Physical activity increases the body's need for oxygen and increases carbon dioxide production.$
$The respiratory system responds by increasing breathing rate and/or depth to supply more oxygen and expel more carbon dioxide.$
$This helps maintain homeostasis by matching gas exchange to the body's increased metabolic demand.$
Answer: The respiratory system is involved; during physical activity, breathing rate and depth increase in order to take in more oxygen and remove more carbon dioxide to meet the body's increased energy demands.

Any body system besides circulatory that responds to exercise is acceptable (e.g., respiratory system increasing breathing rate, muscular system increasing muscle activity/heat production, or excretory system increasing sweating), as long as one specific change is described.

Question 85 · 1 pt · constructed response

Base your answer to question 85 on the diagram below and on your knowledge of biology. Variation in Beaks of Galapagos Islands Finches 85 State one reason why it would be possible for a single island to support populations of both small tree finches and sharp-billed ground finches.

live question 85 figure
Model answer: The two finch species have different bill shapes suited to different food sources (small tree finches have grasping/biting bills adapted for eating insects, while sharp-billed ground finches have probing bills adapted for a different food source), so they occupy different niches and do not directly compete for the same food, allowing both to coexist on the same island.
Worked solution
$The diagram shows that different finch species have differently shaped bills suited to different food types (resource partitioning).$
$Small tree finches and sharp-billed ground finches have different bill shapes and feed on different food sources/niches.$
$Because they do not compete directly for the same limited food resource, both populations can be supported on the same island at the same time.$
Answer: The two finch species have different bill shapes suited to different food sources (small tree finches have grasping/biting bills adapted for eating insects, while sharp-billed ground finches have probing bills adapted for a different food source), so they occupy different niches and do not directly compete for the same food, allowing both to coexist on the same island.

Since the two finch species occupy different feeding niches (different bill shapes suited to different foods), they avoid direct competition for the same resources, allowing both to coexist on one island.

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