AP® Environmental Science 2025 FRQ Set 1: Detailed Solutions
A Note from Your APES Educator: Welcome! This guide provides a detailed walkthrough of the 2025 Set 1 Free-Response Questions. Success in AP Environmental Science requires you to understand complex environmental systems, analyze data, evaluate solutions, and perform calculations. For each question, we'll break down the prompt, devise a strategy, and present a model answer that demonstrates the skills required for a high score.
Chickadees, Nonnative Plants, and Biodiversity
A. Describe one reproductive strategy used by a K-selected species such as the chickadee.
One reproductive strategy used by K-selected species like the chickadee is providing a high degree of parental care to their offspring. This often involves parents feeding and protecting their young for an extended period after birth or hatching, which increases the offspring's chance of survival to reproductive age.
B. Based on the information provided, explain how a decrease in spider populations could affect a lower trophic level.
A decrease in spider populations could lead to an increase in the population of insects, which are at a lower trophic level. According to the provided food chain, spiders are predators that consume insects. If the number of spiders decreases, there will be less predation on the insect population, allowing the insect population to grow larger.
C. Based on the data in Figure 1, identify the number of spiders per sample at 25% nonnative plants.
Based on the data in Figure 1, the number of spiders per sample at 25% nonnative plants is 1.0.
D. Based on the data in Figure 1, describe the trend in the number of insects per sample in relation to the percentage of nonnative plants.
Based on Figure 1, there is a negative correlation between the percentage of nonnative plants and the number of insects per sample. As the percentage of nonnative plants in an area increases, the average number of insects found there decreases.
E. Scientists hypothesized that the population of chickadees would be stable or growing with fewer than 25% nonnative plants. Describe one way that the data in Figure 2 support this hypothesis.
The data in Figure 2 support this hypothesis because at percentages of nonnative plants below 25%, the line representing the chickadee population growth rate is at or above the replacement level (r=0). A growth rate of zero indicates a stable population, while a rate above zero indicates a growing population. Therefore, the data show the population is stable or growing when nonnative plants make up less than 25% of the habitat.
F. i. Identify a likely scientific question for the students’ investigation of ant diversity.
A likely scientific question is: "How does the frequency of mowing affect the species richness of ants in a grassy habitat?"
F. ii. Identify the dependent variable in the students’ investigation.
The dependent variable is the species richness of ants, measured by the number of different ant species found in the traps at each site.
G. i. Explain why the ant community of the unmowed grassland would be more likely to recover from a disturbance, such as a flood or fire, than the ant community in the mowed urban park would.
The ant community in the unmowed grassland would be more likely to recover from a disturbance because it has higher species richness (a component of biodiversity). The table shows the grassland has five ant species, while the urban park has only three. An ecosystem with higher biodiversity is more resilient because it has a greater variety of species with different traits and ecological roles. This increases the probability that some species will survive the disturbance and be able to repopulate the area, or that the loss of one species can be compensated for by another with a similar function.
G. ii. Explain how the results of the investigation could have been altered if students had measured ant biodiversity at a paved playground rather than in the grassland.
If the students had measured ant biodiversity at a paved playground, they likely would have found an even lower species richness compared to both the grassland and the urban park. A paved surface represents a highly degraded habitat with very little soil, vegetation, or food sources available to support a diverse ant community. Therefore, the difference in biodiversity between the mowed urban park and the new site (playground) would have been much smaller, or the playground might have had no ants at all, altering the conclusion of the study.
H. Describe one effect that a paved road in a forest can have on animal species such as deer or bears.
One effect of a paved road is habitat fragmentation, which can act as a barrier to movement for large animals like deer or bears. The road can divide a large, continuous habitat into smaller, isolated patches, restricting the animals' ability to roam across their full territory to find food, water, or mates. This can lead to smaller, less genetically diverse populations in the fragmented patches, making them more vulnerable to disease or local extinction.
ENSO and its Effects
A. Identify the sea surface condition for the eastern equatorial area of the Pacific Ocean illustrated in Figure 1.
The sea surface condition for the eastern equatorial area of the Pacific Ocean is cooler than average ocean water.
B. Based on the information in Figure 1, identify the climate phenomenon associated with the sea surface conditions shown in the equatorial area of the Pacific Ocean.
The climate phenomenon shown is La Niña. This is indicated by the cooler-than-average water in the eastern Pacific and the stronger-than-normal trade winds.
C. Based on the information in Figure 2, describe a difference in climate patterns between the regions A and B.
In region A (the Pacific Northwest), there is a decreased chance of precipitation and it is warmer than average. In contrast, in region B (the southeastern United States), there is an increased chance of precipitation and it is cooler than average.
D. Describe one reason why there is an increased risk of flooding in urban areas during extended periods of precipitation.
Urban areas have an increased risk of flooding because they have large amounts of impervious surfaces, such as roads, sidewalks, and rooftops. These surfaces prevent rainwater from infiltrating into the ground, leading to a high volume of surface runoff that can overwhelm storm drain systems and cause flooding.
E. Propose a realistic solution a city could implement to decrease the risk of flooding in urban areas.
A realistic solution is to increase the amount of permeable surfaces by installing permeable pavement for parking lots and sidewalks or by creating green spaces like parks and rain gardens.
F. Justify the solution proposed in part E by providing an additional advantage other than a reduction in the risk of flooding.
Installing permeable surfaces and green spaces not only reduces flooding but also helps to recharge groundwater aquifers. By allowing rainwater to infiltrate into the ground instead of running off into storm drains, these solutions help replenish the local groundwater supply, which can be an important source of drinking water for the city.
G. Describe one difference between the climate of a temperate seasonal forest and that of a savanna.
A temperate seasonal forest experiences four distinct seasons with significant temperature variation, including warm summers and cold winters with freezing temperatures. A savanna, being a tropical biome, has consistently warm temperatures year-round and is characterized by distinct wet and dry seasons rather than temperature-based seasons.
H. Identify the ecological process that occurs following a forest fire that leaves the soil intact.
The ecological process that occurs is secondary succession.
I. Describe one way burning forests contribute to atmospheric pollution.
Burning forests releases large amounts of particulate matter (soot and ash) into the atmosphere. These fine particles can travel long distances, reduce air quality, and cause respiratory problems in humans and other animals.
J. Describe one sustainable forestry practice that could be used to reduce the occurrence or severity of forest fires.
One sustainable forestry practice is conducting prescribed burns (or controlled burns). This involves intentionally setting small, low-intensity fires under controlled conditions to clear out accumulated dead vegetation, small trees, and undergrowth from the forest floor. This reduces the amount of fuel available for a potential wildfire, making any future fires less severe and easier to control.
Air Pollution, Transportation, and Energy Use
A. Identify an anthropogenic source of particulate matter, other than from motor vehicles.
An anthropogenic source of particulate matter is the burning of coal in power plants for electricity generation.
B. Describe one way a vapor recovery nozzle is used to reduce atmospheric pollution.
A vapor recovery nozzle captures gasoline vapors (volatile organic compounds, or VOCs) that escape from the gas tank during refueling. The nozzle has a rubber boot that creates a seal and a system that sucks the vapors back into the underground storage tank, preventing them from being released into the atmosphere where they can contribute to the formation of smog.
C. Explain how a decrease in the number of people commuting to work in their personal vehicles could lead to a reduction in acid rain.
A decrease in commuting could reduce acid rain because personal vehicles burn gasoline, which releases nitrogen oxides (NOx) into the atmosphere. In the atmosphere, nitrogen oxides react with water, oxygen, and other chemicals to form nitric acid, a major component of acid rain. Fewer cars on the road would mean lower emissions of NOx, leading to less formation of nitric acid and thus a reduction in acid rain.
D. Calculate the percent change in gas mileage between the gasoline-powered SUV and the hybrid SUV based on the data provided. Show your work.
New Value (Hybrid) = 36 mpg
Old Value (Gasoline) = 22 mpg
Percent Change = [ (36 - 22) / 22 ] * 100
Percent Change = [ 14 / 22 ] * 100
Percent Change = 0.6363 * 100
Percent Change ≈ 63.6%
E. Calculate how many more miles the owner can drive in the hybrid SUV in the city than they could have driven in the gasoline-powered SUV. Show your work.
Gasoline SUV miles = 14 gallons * 22 mpg = 308 miles
Hybrid SUV miles = 14 gallons * 36 mpg = 504 miles
Difference = 504 miles - 308 miles = 196 more miles
F. Propose a realistic solution that schools could implement to decrease energy use for heating and cooling, other than a reduction in the amount of time the school building is occupied.
A realistic solution is to install a green roof. A layer of vegetation on the roof provides natural insulation, which reduces the amount of heat lost in the winter and keeps the building cooler in the summer, thereby decreasing the energy required for heating and cooling.
G. Calculate the energy use in the school building in kilowatts per year using LED light bulbs. Show your work.
There appears to be a typo in the number of bulbs in the prompt "2 8. 104". Assuming this was intended to be a number like 2,800 or a similar magnitude, the calculation would follow this setup. Let's assume the intended number was 2,800 bulbs for this example calculation.
Total Energy Use = 2,800 bulbs * 0.0085 kW/bulb * 2,340 hours/year
Total Energy Use = 23.8 kW * 2,340 hours/year
Total Energy Use = 55,692 kWh/year
(Note: The final numerical answer will depend on the correct number of bulbs from the prompt. The setup is the key part of the answer.)
AP® Environmental Science 2025 FRQ Set 2: Detailed Solutions
A Note from Your APES Educator: Welcome, environmental scientists! This guide will provide a detailed walkthrough of the 2025 Set 2 Free-Response Questions. To succeed on the AP Environmental Science exam, you must apply scientific principles, analyze data and environmental scenarios, and clearly articulate solutions and their consequences. For each question, we'll break down the prompt, devise a strategy, and present a model answer that demonstrates the skills required for a high score.
Common Terns, Sea Level Rise, and Biodiversity
A. Based on the data in the graph, identify the number of Common Tern breeding pairs in 1995.
Based on the data in the graph, the number of Common Tern breeding pairs in 1995 was 1,200.
B. Based on the data in the graph, describe the trend in the number of Common Tern breeding pairs from 1995 to 2008.
From 1995 to 2008, the overall trend in the number of Common Tern breeding pairs was a decrease. Although there were year-to-year fluctuations, the number of breeding pairs dropped from a peak of 1,200 in 1995 to approximately 600 in 2008.
C. A group of students hypothesized that sea level rise will lead to an increase in Common Tern populations. Describe one way that the data in the graph refute this hypothesis.
The data in the graph refute the hypothesis by showing a negative correlation between sea level change and the number of breeding pairs. For example, from 1998 to 2008, the sea level change (the line) generally increased, while the number of breeding pairs (the bars) showed an overall decreasing trend. This is the opposite of the hypothesized positive relationship.
D. Explain how climate change can lead to sea level rise.
Climate change leads to sea level rise primarily through the thermal expansion of ocean water. As global temperatures increase due to the greenhouse effect, the oceans absorb a significant amount of this excess heat. When water heats up, it expands in volume, causing the sea level to rise globally. A second major cause is the melting of land-based ice, such as glaciers and the Greenland and Antarctic ice sheets, which adds water to the oceans.
E. i. Identify a hypothesis that researchers are likely investigating in the wading bird study.
A likely hypothesis is: An increase in the rate of sea level rise will cause a change in the species richness of wading birds in coastal wetlands.
E. ii. Identify the dependent variable in this study.
The dependent variable is the number of wading bird species, which is a measure of species richness.
F. If the researchers repeated their study, explain how this environmental change could affect the results of the study.
An increase in PCBs could lead to a decrease in the number of wading bird species due to biomagnification. As a persistent organic pollutant, PCBs accumulate in the fatty tissues of organisms. Wading birds are predators and occupy a high trophic level in the coastal food web. The concentration of PCBs would increase up the food chain, potentially reaching toxic levels in the birds. This could lead to reproductive failure, illness, or death, causing a decline in bird populations and species richness that is unrelated to sea level rise, thus confounding the results of the study.
G. Describe a regulating ecosystem service that can be provided by wetlands.
A regulating ecosystem service provided by wetlands is water purification. Wetland plants and soils act as natural filters, trapping sediments and absorbing pollutants like excess nutrients (nitrogen, phosphorus) and heavy metals from the water as it passes through, thereby improving water quality.
H. Explain how increased sediment might lead to a change in the size of the wading bird populations.
Increased sediment in the water would increase its turbidity, making the water more cloudy. Since the wading birds are visual predators that hunt for fish in shallow water, higher turbidity would make it more difficult for them to see and locate their prey. This reduction in hunting efficiency could lead to a decrease in their food intake, resulting in starvation or lower reproductive success, which would cause a decline in the size of the wading bird populations.
I. Describe an environmental problem, other than an increase in sediment, that can occur in wetlands that is associated with increased urbanization and development.
An environmental problem associated with increased urbanization near wetlands is nutrient pollution from urban runoff. Fertilizers from lawns and gardens, as well as waste from leaking septic or sewer systems, can wash into the wetland, introducing excess nitrogen and phosphorus. This can lead to cultural eutrophication, causing algal blooms that deplete dissolved oxygen and create dead zones, harming aquatic life within the wetland ecosystem.
The Serengeti, Migration, and Invasive Species
A. Based on the information in Figure 1, identify the type of plate boundary that runs beneath Serengeti National Park.
The type of plate boundary is a divergent plate boundary, as indicated by the East African Rift Valley where tectonic plates are moving apart.
B. Based on the information provided, identify the dominant biome within the Serengeti.
The dominant biome is the tropical savanna (or tropical grassland), characterized by wide-open grasslands with scattered trees and distinct wet and dry seasons.
C. Based on the information in Figure 2, identify the location in the Serengeti where wildebeest are most likely to give birth.
Based on the information that most grass growth occurs after the March-May rainy season and wildebeest give birth when new grasses are growing, they are most likely to give birth in the months immediately following the rainy season, such as June or July, in the northern part of the park near the Grumeti Game Reserve or further north.
D. Explain why resource partitioning allows for the coexistence of the wildebeest and the gazelle in the Serengeti.
Resource partitioning allows for coexistence by reducing interspecific competition between the wildebeest and gazelle. By specializing on different food sources—wildebeest consuming long grasses and gazelles consuming short grasses—the two herbivore species are not directly competing for the exact same food resource. This division of the resource allows both species to find sufficient nutrition and occupy the same habitat without one outcompeting the other to exclusion.
E. Describe one way the planned highway shown in Figure 2 could negatively affect the wildebeest population in the Serengeti.
The planned highway could cause habitat fragmentation by bisecting the wildebeests' annual migration route. This could act as a barrier, preventing them from reaching critical grazing areas or water sources, or it could lead to increased mortality from vehicle collisions as the large herds attempt to cross the road.
F. Propose a solution to the negative effect created by the planned highway described in part E.
A solution would be to construct dedicated wildlife corridors, such as overpasses or underpasses, at key points along the highway. These structures would allow the wildebeest herds to safely cross over or under the road, maintaining the connectivity of their migration route and reducing the risk of vehicle collisions.
G. Describe a characteristic of an invasive species, such as the spotted knapweed, that allows them to outcompete native species.
A common characteristic of invasive species is that they are often r-strategists that reproduce rapidly and produce a large number of offspring. This allows their population to grow quickly and spread, overwhelming native species that may have slower reproductive rates.
H. Justify the use of crop rotation as an environmental solution by providing an additional advantage, other than controlling pest populations.
The use of crop rotation is justified because, in addition to disrupting pest cycles, it also improves soil health and fertility. By planting different types of crops in a field in sequential seasons (for example, alternating a nutrient-depleting crop like corn with a nutrient-fixing legume like soybeans), crop rotation helps to replenish soil nutrients naturally, reducing the need for synthetic fertilizers.
I. Describe an environmental problem associated with controlling pest populations with large amounts of pesticide.
An environmental problem is the development of pesticide resistance in the pest population. Through natural selection, individual pests that happen to have a genetic resistance to the pesticide survive and reproduce, passing on their resistant genes. Over time, the entire pest population can become resistant, rendering the pesticide ineffective and creating a "pesticide treadmill" where stronger or new chemicals are required.
J. Propose a solution to controlling pests, other than pesticides or crop rotation.
A solution is to use biological control, which involves introducing a natural predator, parasite, or pathogen of the pest species into the affected area. For example, ladybugs could be introduced to control aphid populations on crops.
Energy, Mining, and Population Growth
A. Identify a type of surface mining the company could use to access the coal.
Since the coal deposit is close to the surface and the company plans to remove overburden over a large area, they could use strip mining.
B. Describe an environmental problem associated with surface mining.
An environmental problem associated with surface mining is the creation of acid mine drainage. When minerals in the exposed rock and overburden (like pyrite) react with air and water, they can form sulfuric acid, which then leaches heavy metals from the rock. This acidic, metal-laden water can run off and pollute nearby streams and rivers, harming aquatic ecosystems.
C. Describe an environmental problem the town could experience as a result of the electricity generation at the coal-burning power plant.
Since the town is downwind, it could experience increased levels of acid deposition (acid rain). The burning of coal releases sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These pollutants can travel with the wind and react with water to form sulfuric and nitric acid, which then fall back to earth as acid rain, damaging buildings, harming forests, and acidifying lakes in and around the town.
D. Propose a realistic solution the local government could enact that would reduce the negative environmental consequences of using coal to generate electricity.
The local government could enact a policy to promote or subsidize the installation of rooftop solar panels on residential and commercial buildings throughout the town. This would diversify the town's energy sources and decrease its overall reliance on the coal-fired power plant.
E. Calculate how many pounds of coal would need to be burned to generate enough electricity to power a town with 11,000 houses for a year. Show your work.
There appears to be a typo in the prompt for the electricity usage of an average household. The value "1.064 10 kWh 4 ×" is ambiguous. Assuming it was intended to be $1.064 \times 10^4$ kWh, or 10,640 kWh, the calculation is as follows:
Total kWh = (Number of houses) * (kWh per household)
Total kWh = 11,000 houses * 10,640 kWh/household = 117,040,000 kWh
Step 2: Calculate pounds of coal needed.
Pounds of coal = Total kWh / (kWh per pound of coal)
Pounds of coal = 117,040,000 kWh / 0.88 kWh/lb
Pounds of coal = 133,000,000 lbs
F. Calculate the percent change in bird species per hectare since the power plant was installed. Show your work.
New Value = 6.0 species/hectare
Old Value = 7.5 species/hectare
Percent Change = [ (6.0 - 7.5) / 7.5 ] * 100
Percent Change = [ -1.5 / 7.5 ] * 100
Percent Change = -0.2 * 100
Percent Change = -20%
G. Assuming that the growth rate remains constant, calculate the year in which the population will reach 52,500. Show your work.
This problem requires calculating the doubling time of the population.
Doubling Time (Td) = 70 / (percent growth rate)
Td = 70 / 5.38
Td ≈ 13 years
Step 2: Determine how many doublings are needed.
The initial population is 26,250. The target population is 52,500.
52,500 / 26,250 = 2. This means the population needs to double exactly once.
Step 3: Calculate the target year.
Target Year = Initial Year + Doubling Time
Target Year = 2022 + 13 years
Target Year = 2035
The population will reach 52,500 in the year 2035.