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AP Environmental Science practice questions

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Question 1The Living World: Ecosystems

Which process converts atmospheric nitrogen gas into forms that producers can use?

  1. Transpiration
  2. Cellular respiration
  3. Nitrogen fixation Correct answer.
  4. Photosynthesis

Explanation

Nitrogen fixation is carried out by bacteria (some free-living, some in root nodules) that reduce atmospheric N2 to ammonia, which can then be incorporated into organic molecules. The other listed processes move water, carbon, or energy rather than making nitrogen bioavailable.

Question 2The Living World: Ecosystems

In a food web, organisms that consume both producers and primary consumers are best described as:

  1. Detritivores
  2. Omnivores Correct answer.
  3. Apex predators
  4. Primary producers

Explanation

An omnivore feeds at more than one trophic level, eating both producers and consumers. Detritivores specialize in dead organic matter, while apex predators occupy the top of a chain and producers photosynthesize.

Question 3The Living World: Ecosystems

Which biome is characterized by permafrost, low-growing vegetation, and a very short growing season?

  1. Chaparral
  2. Temperate deciduous forest
  3. Tundra Correct answer.
  4. Tropical rainforest

Explanation

Tundra occurs at high latitudes or elevations where permafrost and cold temperatures limit plant growth to a brief summer. The other biomes listed have warmer climates, deeper soils, and longer growing seasons.

Question 4The Living World: Ecosystems

Which statement best describes the role of decomposers in an ecosystem?

  1. They fix atmospheric carbon into glucose.
  2. They break down dead organic matter and release nutrients. Correct answer.
  3. They transfer energy directly to top predators.
  4. They convert solar energy into chemical energy.

Explanation

Decomposers such as bacteria and fungi break down dead organisms and waste, releasing inorganic nutrients back to the soil and water for reuse by producers. Energy conversion and carbon fixation are functions of producers.

Question 5The Living World: Ecosystems

A grassland food chain has 20,000 kcal of energy in the producer level. Using the ten percent rule, about how much energy is available to the secondary consumers?

  1. 2 kcal
  2. 20 kcal
  3. 2,000 kcal
  4. 200 kcal Correct answer.

Explanation

Applying the ten percent rule twice: 20,000 kcal × 0.10 gives 2,000 kcal at primary consumers, and × 0.10 again gives 200 kcal at secondary consumers. Each transfer loses roughly ninety percent of energy as heat and metabolism.

Question 6The Living World: Ecosystems

Two species of warbler feed in different parts of the same tree, avoiding direct competition. This is an example of:

  1. Resource partitioning Correct answer.
  2. Competitive exclusion
  3. Primary succession
  4. Mutualism

Explanation

Resource partitioning occurs when species divide a shared resource, such as feeding zones, so they can coexist. Competitive exclusion would instead result in one species being eliminated locally.

Question 7The Living World: Ecosystems

In a predator-prey relationship, which pattern is typically observed over time?

  1. Predator and prey populations remain perfectly constant.
  2. Predator peaks lag behind prey peaks. Correct answer.
  3. Predator numbers rise while prey numbers rise identically.
  4. Prey peaks lag behind predator peaks.

Explanation

Because predators depend on prey abundance, predator populations typically peak shortly after prey populations peak. The delay reflects the time needed for predator reproduction in response to increased food.

Question 8The Living World: Ecosystems

Which of the following is a key characteristic of a species classified as a generalist?

  1. It feeds on a single host species.
  2. It tolerates a narrow range of environmental conditions.
  3. It has a broad niche and can use many resources. Correct answer.
  4. It lives only in undisturbed habitats.

Explanation

Generalists have broad ecological niches, tolerating varied conditions and using many resource types, which helps them persist in changing environments. Specialists, by contrast, have narrow niches.

Question 9The Living World: Ecosystems

In the carbon cycle, which process moves carbon from living organisms back to the atmosphere?

  1. Nitrogen fixation
  2. Photosynthesis
  3. Sedimentation
  4. Cellular respiration Correct answer.

Explanation

Cellular respiration by organisms oxidizes organic carbon and releases carbon dioxide to the atmosphere. Photosynthesis removes carbon dioxide, while the other options involve nitrogen or long-term burial.

Question 10The Living World: Ecosystems

Which factor most directly limits primary productivity in the open ocean over large areas?

  1. Availability of nitrogen and phosphorus Correct answer.
  2. Abundance of dissolved oxygen
  3. Presence of detritivores
  4. Rate of transpiration

Explanation

Primary productivity in much of the open ocean is limited by scarce nutrients such as nitrogen and phosphorus, which are often concentrated in deeper water. Oxygen is generally not limiting for producers, and transpiration is a plant process.

Question 11The Living World: Ecosystems

After a glacier retreats, bare rock is colonized by lichens and mosses, followed later by shrubs and trees. This sequence is best described as:

  1. Primary succession Correct answer.
  2. Eutrophication
  3. Resource partitioning
  4. Secondary succession

Explanation

Primary succession begins on newly exposed substrate with no preexisting soil, such as rock left by a retreating glacier. Soil must be built by pioneer species before larger plants establish.

Question 12The Living World: Ecosystems

An ecosystem has high species richness but most individuals belong to a single dominant species. Which statement about its diversity is most accurate?

  1. Its species diversity must be zero.
  2. Its richness is low and evenness is high.
  3. Richness and evenness are always identical measures.
  4. Its evenness is low even though richness is high. Correct answer.

Explanation

Species diversity combines richness (number of species) and evenness (relative abundance). If one species dominates numerically, evenness is low even when many species are present.

Question 13The Living World: Ecosystems

Which change would most likely increase net primary productivity of a temperate forest ecosystem?

  1. A decrease in available soil nitrogen
  2. An increase in the length of the growing season Correct answer.
  3. A rise in the population of herbivores
  4. A reduction in incoming solar radiation

Explanation

Net primary productivity depends on the balance of photosynthesis and respiration, and a longer growing season allows more photosynthesis over the year. Nutrient shortages, heavy grazing, and reduced sunlight would tend to lower productivity.

Question 14The Living World: Ecosystems

A keystone predator is removed from a rocky intertidal community. Which outcome is most consistent with keystone species theory?

  1. Total species richness rises immediately and stays high.
  2. Energy transfer efficiency between trophic levels increases.
  3. Competitive exclusion among prey species changes community structure. Correct answer.
  4. The community returns to its original state without change.

Explanation

Keystone predators keep dominant competitors in check; removing them can let one prey species monopolize space or resources, altering community structure through competitive exclusion. The effect is disproportionate to the predator's abundance.

Question 15The Living World: Biodiversity

Which term describes the variety of genes, species, and ecosystems present in a region?

  1. Biodiversity Correct answer.
  2. Carrying capacity
  3. Primary productivity
  4. Trophic efficiency

Explanation

Biodiversity is the full range of biological variation, encompassing genetic diversity within species, the number of species, and the variety of ecosystems. The other terms describe population limits or energy flow, not biological variety.

Question 16The Living World: Biodiversity

A species that has an unusually large effect on community structure relative to its abundance is best described as a:

  1. Indicator species
  2. Invasive species
  3. Keystone species Correct answer.
  4. Pioneer species

Explanation

A keystone species exerts influence on community structure that is disproportionate to its biomass or numbers, such as a predator controlling herbivore populations. The other categories describe early colonizers, environmental monitors, or non-native harm-causing organisms.

Question 17The Living World: Biodiversity

Which level of biodiversity is reduced when a population loses the genetic variation that allows it to adapt to a changing climate?

  1. Genetic diversity Correct answer.
  2. Ecosystem diversity
  3. Functional diversity
  4. Species diversity

Explanation

Genetic diversity refers to variation in alleles within a population, which is the raw material for adaptation. Losing that variation reduces a population's capacity to respond to environmental change.

Question 18The Living World: Biodiversity

Which pattern of species distribution describes species richness that peaks in the tropics and declines toward the poles?

  1. Edge effect
  2. Latitudinal diversity gradient Correct answer.
  3. Species-area relationship
  4. Island biogeography

Explanation

The latitudinal diversity gradient is the well-documented pattern in which species richness is highest near the equator and decreases toward higher latitudes. It is distinct from area-based or boundary-based patterns.

Question 19The Living World: Biodiversity

According to the theory of island biogeography, which island would be expected to support the greatest equilibrium number of species?

  1. A small island close to the mainland
  2. A small island far from the mainland
  3. A large island far from the mainland
  4. A large island close to the mainland Correct answer.

Explanation

Equilibrium richness rises with island area because larger islands lower extinction rates, and rises with proximity to the mainland because nearby islands receive more colonizers. The combination of large size and short distance therefore yields the highest predicted richness.

Question 20The Living World: Biodiversity

A forest is cleared and later recolonized by grasses, then shrubs, then fast-growing trees, and eventually mature shade-tolerant trees. This sequence is an example of:

  1. Eutrophication
  2. Primary succession
  3. Secondary succession Correct answer.
  4. Biomagnification

Explanation

Secondary succession occurs where a disturbance removes existing vegetation but soil remains, allowing rapid recolonization through the sequence described. Primary succession instead begins on bare substrate lacking soil.

Question 21The Living World: Biodiversity

Two species of warbler feed in different parts of the same tree, reducing direct competition for food. This partitioning of resources is best described as:

  1. Competitive exclusion
  2. Resource partitioning Correct answer.
  3. Mutualism
  4. Commensalism

Explanation

Resource partitioning is the division of a shared resource that allows similar species to coexist by using different portions of it. Competitive exclusion would instead drive one species to local extinction.

Question 22The Living World: Biodiversity

In a mutualistic relationship, the interaction between the two species is best characterized as:

  1. One species benefits while the other is harmed
  2. One species benefits while the other is unaffected
  3. One species is harmed while the other is unaffected
  4. Both species benefit Correct answer.

Explanation

Mutualism is a symbiotic interaction in which both participating species gain a fitness benefit, such as pollinators receiving nectar while plants receive pollination. The other descriptions correspond to parasitism or commensalism.

Question 23The Living World: Biodiversity

A non-native plant is introduced to a wetland, spreads rapidly, and displaces native vegetation because it lacks natural herbivores. This plant is best classified as:

  1. A specialist species
  2. An invasive species Correct answer.
  3. A keystone species
  4. An endemic species

Explanation

An invasive species is a non-native organism that spreads and causes ecological harm, often because it escapes the predators and competitors of its native range. Endemic and specialist species are native and often ecologically narrow.

Question 24The Living World: Biodiversity

A habitat is fragmented into several small patches. Which consequence is most directly predicted by the species-area relationship?

  1. Total species richness across the patches will decline Correct answer.
  2. Genetic diversity within patches will increase
  3. Each patch will support more species than the original habitat
  4. Edge habitat will decrease relative to interior habitat

Explanation

Smaller habitat patches support fewer species, so fragmenting a large area into small patches generally lowers total richness and increases extinction risk. Fragmentation also increases edge habitat and can reduce genetic diversity, not raise it.

Question 25The Living World: Biodiversity

A coral reef loses its herbivorous fish, and fleshy algae overgrow and smother the corals. This outcome best illustrates which concept?

  1. Primary succession on a newly formed substrate
  2. The reef has low species evenness but high richness
  3. A trophic cascade following removal of a key grazer Correct answer.
  4. Biological magnification of a persistent pollutant

Explanation

Removing an herbivore releases algae from grazing pressure, and the resulting algal overgrowth indirectly harms the coral, a chain of effects propagating through the food web known as a trophic cascade. It is not a succession or pollution process.

Question 26The Living World: Biodiversity

Which statement best explains why high genetic diversity within a population improves its long-term survival?

  1. It prevents any mutation from occurring in the population
  2. It guarantees that no individuals will experience disease
  3. It directly raises the population's carrying capacity
  4. It increases the chance that some individuals carry traits suited to new conditions Correct answer.

Explanation

Greater genetic variation means a population is more likely to contain alleles that confer tolerance to new stressors such as disease or climate shifts, supporting adaptation. It does not guarantee outcomes or change carrying capacity directly.

Question 27The Living World: Biodiversity

Two islands are equal in area, but one lies 5 km from the mainland and the other 500 km away. Based on island biogeography, which best explains the expected difference in species richness?

  1. The near island has a higher immigration rate, so it is richer Correct answer.
  2. Both islands have identical richness because area is equal
  3. The distant island has a lower extinction rate, so it is richer
  4. The distant island has a higher immigration rate, so it is richer

Explanation

At equal area, extinction rates are similar, but proximity to the mainland raises the arrival rate of new colonizers, shifting equilibrium richness upward on the near island. Distance affects immigration, not extinction, in this comparison.

Question 28The Living World: Biodiversity

A region contains many species, but one species makes up more than 90 percent of all individuals. Which description best fits this community?

  1. Low species richness and low species evenness
  2. Low species richness and high species evenness
  3. High species richness and high species evenness
  4. High species richness and low species evenness Correct answer.

Explanation

Richness counts the number of species present, while evenness describes how similar their abundances are. Many species coexisting with one overwhelmingly dominant species means richness is high but evenness is low.

Question 29Populations

A population of 500 rabbits lives in a meadow. In one year, 120 are born, 40 die, 30 immigrate, and 10 emigrate. What is the population at the end of the year?

  1. 560 Correct answer.
  2. 580
  3. 600
  4. 540

Explanation

Population change equals births minus deaths plus immigration minus emigration: 120 - 40 + 30 - 10 = 100. Adding this net change to the starting population of 500 gives 560.

Question 30Populations

Which pattern of population dispersion occurs when individuals cluster near a required resource such as a watering hole?

  1. Clumped Correct answer.
  2. Uniform
  3. Geometric
  4. Random

Explanation

Clumped dispersion arises when resources are patchy or when individuals form social groups, so organisms concentrate where conditions are favorable. Uniform and random patterns reflect different spacing forces.

Question 31Populations

A population grows by a constant proportion each year regardless of its size. Which growth model does this describe?

  1. Exponential growth Correct answer.
  2. Logistic growth
  3. Carrying-capacity growth
  4. Irruptive growth

Explanation

Exponential growth assumes a constant per-capita growth rate, so the population increases by a fixed percentage each interval and the absolute increase grows with population size. Logistic growth instead slows as density rises.

Question 32Populations

In the demographic transition model, which stage is characterized by high birth rates and high death rates?

  1. Stage 4
  2. Stage 2
  3. Stage 1 Correct answer.
  4. Stage 3

Explanation

Stage 1 (preindustrial) has both high birth and high death rates, so population size stays roughly stable. Later stages see death rates fall first, then birth rates decline.

Question 33Populations

Which term describes the maximum population size an environment can sustain indefinitely?

  1. Population density
  2. Environmental resistance
  3. Biotic potential
  4. Carrying capacity Correct answer.

Explanation

Carrying capacity (K) is the largest population an environment can support given available resources and conditions. Biotic potential is the maximum reproductive rate under ideal conditions.

Question 34Populations

Which of the following is a density-independent factor affecting population size?

  1. A severe frost that kills seedlings Correct answer.
  2. Predation by a specialist predator
  3. Competition for nesting sites
  4. Spread of an infectious disease

Explanation

Density-independent factors affect a population regardless of its size; weather events like frost act the same whether the population is dense or sparse. Competition, disease, and predation intensify as density rises.

Question 35Populations

A country has a total fertility rate of 2.0 children per woman. In the absence of migration, what does this rate most likely imply for long-term population size?

  1. It will grow rapidly
  2. It will slowly decline Correct answer.
  3. It will double each generation
  4. It will stay exactly constant

Explanation

Replacement-level fertility is about 2.1 children per woman in most countries; a rate of 2.0 falls below replacement, so the population tends to decline over time absent immigration.

Question 36Populations

Which of the following best describes an age-structure diagram that is broad at the base and narrow at the top?

  1. A declining population
  2. A rapidly growing population Correct answer.
  3. An aging population with low birth rates
  4. A stable population

Explanation

A wide base indicates a large proportion of young individuals, which signals high birth rates and rapid future growth as they reach reproductive age. Narrow bases indicate decline.

Question 37Populations

A population of 2,000 deer has 400 births and 200 deaths in one year. What is the per-capita growth rate?

  1. 0.05
  2. 0.20
  3. 0.10 Correct answer.
  4. 0.30

Explanation

Per-capita growth rate equals (births - deaths) divided by population size: (400 - 200) / 2,000 = 0.10. This means the population grows by about 10% per year.

Question 38Populations

Which survivorship curve shows high mortality early in life with few individuals surviving to old age?

  1. Type III Correct answer.
  2. Type IV
  3. Type II
  4. Type I

Explanation

Type III curves show steep early mortality, typical of organisms producing many offspring with little parental care, such as many fish and insects. Type I shows low early mortality and late-life decline.

Question 39Populations

In a logistic growth model, at what population size is growth rate (number of individuals added per unit time) greatest?

  1. At half the carrying capacity Correct answer.
  2. At twice the carrying capacity
  3. Just above zero population
  4. At the carrying capacity

Explanation

Logistic growth rate peaks at K/2, where the product of population size and available resources is maximized. At K the growth rate falls to zero because resources are fully used.

Question 40Populations

Which statement best explains why a population may overshoot its carrying capacity and then crash?

  1. Carrying capacity increases whenever the population grows
  2. Reproduction lags behind resource depletion, so the population continues growing after resources are exhausted Correct answer.
  3. Birth rates fall before resources decline
  4. Density-independent factors always prevent overshoot

Explanation

Time lags in reproduction allow a population to keep growing even as resources are being depleted, so it can exceed K and then decline sharply. Resource damage and delayed feedback drive the crash.

Question 41Populations

A population has 1,000 individuals, and 150 are added through births and immigration while 50 are lost through deaths and emigration in a year. What is the net change in population size?

  1. +100 Correct answer.
  2. +50
  3. +200
  4. -100

Explanation

Net change equals total additions minus total losses: 150 - 50 = +100 individuals. This is the population's increase over the year.

Question 42Populations

Which human activity most directly increases a region's population through immigration rather than through natural increase?

  1. Improved prenatal care in the region
  2. An increase in the region's birth rate
  3. A decline in the region's infant mortality rate
  4. Recruitment of workers by new industries in the region Correct answer.

Explanation

Immigration is movement into a population; job opportunities pull migrants into a region. Birth rates and mortality affect natural increase rather than migration.

Question 43Populations

A country's population pyramid is nearly rectangular, with similar widths at all age classes. What does this pattern indicate?

  1. Rapid population growth with high birth rates
  2. Low birth and death rates with a stable age structure Correct answer.
  3. High death rates among the elderly only
  4. A recent population crash from disease

Explanation

A rectangular pyramid indicates that each cohort is roughly the same size, consistent with low birth and death rates and a stable population. Rapid growth produces a broad base.

Question 44Populations

Which factor is most likely to increase the carrying capacity of a habitat for a herbivore species?

  1. A rise in the density of its predators
  2. An increase in the abundance of its food plants Correct answer.
  3. An increase in competition from a similar species
  4. A drought that reduces plant growth

Explanation

Carrying capacity depends on resource availability; more food raises the number of individuals the habitat can support. Predators, drought, and competitors reduce carrying capacity.

Question 45Populations

In the demographic transition model, which stage typically shows the fastest population growth?

  1. Stage 3
  2. Stage 1
  3. Stage 4
  4. Stage 2 Correct answer.

Explanation

Stage 2 combines falling death rates with still-high birth rates, producing the largest gap between births and deaths and thus the fastest growth. In Stage 3 birth rates begin to fall, narrowing the gap.

Question 46Populations

Which of the following is an example of a density-dependent factor that limits population growth?

  1. A hurricane that strikes the habitat
  2. Accumulation of toxic waste in a crowded pond Correct answer.
  3. A volcanic eruption
  4. A sudden drop in temperature

Explanation

Density-dependent factors intensify as population density rises; waste accumulation in a crowded pond worsens with more individuals. Weather and geologic events act regardless of density.

Question 47Populations

A population of 100 bacteria doubles every 20 minutes. Approximately how many bacteria are present after 2 hours?

  1. 12,800
  2. 1,200
  3. 6,400 Correct answer.
  4. 64,000

Explanation

Two hours contains six 20-minute intervals, so the population doubles six times: 100 x 2^6 = 6,400. This illustrates exponential growth.

Question 48Populations

Which of the following best describes r-selected species?

  1. They have long life spans and late maturity
  2. They produce few offspring with extensive parental care
  3. They maintain stable populations near carrying capacity
  4. They produce many offspring with little parental care Correct answer.

Explanation

r-selected species invest in large numbers of offspring with minimal care, suited to unstable environments. K-selected species instead produce few offspring with heavy investment and typically live near carrying capacity.

Question 49Populations

A population of 800 individuals has 100 births, 60 deaths, 20 immigrants, and 10 emigrants in a year. What is the per-capita growth rate?

  1. 0.125
  2. 0.0625 Correct answer.
  3. 0.05
  4. 0.075

Explanation

Net change is 100 - 60 + 20 - 10 = 50 individuals. Dividing by the starting population of 800 gives 50/800 = 0.0625 per year.

Question 50Populations

Two islands of equal area support the same species. Island A has a large, well-connected habitat patch; Island B has several small, isolated patches. Based on island biogeography theory, which prediction is most reasonable?

  1. Island A will support more species because larger connected habitat lowers extinction rates Correct answer.
  2. Island B will support more species because isolation reduces competition
  3. Both will support identical species richness because total area is equal
  4. Island B will support more species because small patches have more edge habitat

Explanation

Island biogeography theory holds that larger, less isolated habitat supports more species because immigration is higher and extinction risk is lower. Fragmentation into small isolated patches raises extinction rates.