• 56 questions

APES Unit 2 Practice Test

Unofficial AP Environmental Science Unit 2 practice test on The Living World: Biodiversity, from genetic diversity to succession.

Which three levels make up the biodiversity of an ecosystem?

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Unofficial practice questions, not affiliated with the College Board. Bank checked October 14, 2026.

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All 56 questions

Topic 2.1: Introduction to biodiversity 10

  • A forest is cut into small, separate patches. Besides specialists, which animals are likely to decline? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.4
  • A hurricane strikes two coastal forests. One has many tree species and the other only a few. Which is more likely to recover? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.3
  • A large area of habitat is slowly lost. Which kind of species tends to disappear first? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.4
  • A new disease reaches two populations of the same plant. Population A is genetically diverse; population B is nearly uniform. Which is more likely to survive? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.2
  • A river valley holds forest, marsh, meadow and open water within a few square kilometers. Which level of biodiversity is high here? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.1
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Topic 2.1: Introduction to biodiversity, continued

  • Hunting cut the northern elephant seal to about 30 animals in the 1890s. What lasting mark does such a bottleneck leave on a species? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.2; fact read in Wikipedia, "Population bottleneck"
  • In one wolf population, individuals carry many different versions of the genes for coat color and disease resistance. Which level of biodiversity is this? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.1
  • Plot A holds 4 species with 25 individuals each. Plot B holds 6 species: 95 individuals of one and 1 of each of the other five. Which plot has the higher species richness? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.5
  • What does species richness measure? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.5
  • Which three levels make up the biodiversity of an ecosystem? College Board, AP Environmental Science Course and Exam Description, topic 2.1, essential knowledge ERT-2.A.1

Topic 2.2: Ecosystem services 7

  • A coastal marsh takes carbon dioxide out of the air and stores the carbon in its soil. Which category of ecosystem service is this? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.B.1; fact read in Wikipedia, "Ecosystem service"
  • A forest supplies timber and a river supplies drinking water and fish. Which category of ecosystem service is this? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.B.1; fact read in Wikipedia, "Ecosystem service"
  • A wetland beside a town is drained and built over. Floods in the town then get worse and cost more to repair. What does this show? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.C.1
  • Heavy pesticide use kills most of the wild bees near an orchard. What consequence shows the loss of an ecosystem service? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.C.1; fact read in Wikipedia, "Ecosystem service"
  • Soil organisms cycle nutrients that every plant in a forest depends on. Which category of ecosystem service is this? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.B.1; fact read in Wikipedia, "Ecosystem service"
  • Visitors hike, camp and watch birds in a national forest. Which category of ecosystem service is this? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.B.1; fact read in Wikipedia, "Ecosystem service"
  • What are the four categories of ecosystem services? College Board, AP Environmental Science Course and Exam Description, topic 2.2, essential knowledge ERT-2.B.1

Topic 2.3: Island biogeography 7

  • A generalist species from the mainland is introduced to an island of specialist birds. What is the main risk to the birds? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.E.1
  • A patch of forest is left standing in the middle of a wide area of farmland. Why can island biogeography be applied to it? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.D.1; fact read in Wikipedia, "Insular biogeography"
  • Four islands have the same climate. Which is expected to hold the most species? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.D.1; fact read in Wikipedia, "Insular biogeography"
  • How did most islands first get their plants and animals? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.D.2
  • Two islands are the same size. Why is the one farther from the mainland expected to hold fewer species? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.D.2; fact read in Wikipedia, "Insular biogeography"
  • What does island biogeography study? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.D.1
  • Why have many island species evolved to be specialists? College Board, AP Environmental Science Course and Exam Description, topic 2.3, essential knowledge ERT-2.E.1

Topic 2.4: Ecological tolerance 6

  • Each organism has a minimum, a maximum and an optimum for a factor such as temperature. Where along that range is a population expected to do best? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.1; fact read in Wikipedia, "Shelford's law of tolerance"
  • In ecology, what does the tolerance of an organism describe? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.1
  • The salinity of an estuary swings widely after a dam changes the river's flow. Which species is most at risk? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.1
  • Suppose a fish survives in water from 4 °C to 20 °C and does best near 12 °C. A heat wave holds its stream at 24 °C. What does ecological tolerance predict? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.1
  • To which of these can ecological tolerance be applied? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.2
  • Which list holds only conditions for which organisms have a range of tolerance? College Board, AP Environmental Science Course and Exam Description, topic 2.4, essential knowledge ERT-2.F.1

Topic 2.5: Natural disruptions to ecosystems 8

  • A river floods its banks every spring when the snow melts. Which word describes the timing of this disruption? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.2
  • A wildfire burns a mountain forest in summer. A herd of elk moves to an unburned valley and returns the next spring. What is this an example of? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.6
  • About 21,000 years ago, at the height of the last ice age, sea level was about 125 meters lower than it is today. Why? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.4; fact read in Wikipedia, "Last Glacial Maximum"
  • How can the environmental effects of a natural disruption, such as a large volcanic eruption, compare with those of human-made disruptions? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.1
  • Over geological time, what has happened to sea level when the amount of glacial ice on Earth shrank? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.4
  • What commonly follows a major environmental change or upheaval? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.5
  • Which statement about Earth's climate over geological time is correct? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.3
  • Which three words does the course use for the timing of Earth system processes? College Board, AP Environmental Science Course and Exam Description, topic 2.5, essential knowledge ERT-2.G.2

Topic 2.6: Adaptations 5

  • A field is sprayed with the same pesticide every year. After many years most of the insects survive the spray. What best explains this? College Board, AP Environmental Science Course and Exam Description, topic 2.6, essential knowledge ERT-2.H.1
  • A species' environment changes suddenly. By the course description, what are the choices open to its individuals? College Board, AP Environmental Science Course and Exam Description, topic 2.6, essential knowledge ERT-2.H.2
  • On what kind of trait does natural selection act? College Board, AP Environmental Science Course and Exam Description, topic 2.6, essential knowledge ERT-2.H.1
  • Who or what adapts by natural selection, and over what span of time? College Board, AP Environmental Science Course and Exam Description, topic 2.6, essential knowledge ERT-2.H.1
  • Why is a very rapid environmental change harder for a species to survive than a slow one? College Board, AP Environmental Science Course and Exam Description, topic 2.6, essential knowledge ERT-2.H.1

Topic 2.7: Ecological succession 13

  • A fire burns a forest to the ground but leaves the soil in place, and plants return. Which type of succession is this? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.1; fact read in Wikipedia, "Secondary succession"
  • A lichen that is sensitive to air pollution disappears from the trees near a growing city. Used this way, what is the lichen? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.3; fact read in Wikipedia, "Bioindicator"
  • Along one coast the sea otters, which prey on kelp-grazing sea urchins, die out. What is likely to become of the kelp forest there? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.2; fact read in Wikipedia, "Keystone species"
  • How does a keystone species differ from an indicator species? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.3
  • Lava cools into bare rock with no soil, and living things slowly colonize it. Which type of succession is this? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.1; fact read in Wikipedia, "Secondary succession"
  • Pioneer species move into an unoccupied habitat and adapt to its conditions over a long time. What can this lead to? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.J.1
  • Soil deepens on a site in primary succession as organic matter decomposes. What happens to species diversity there over the same time? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.J.2; fact read in Wikipedia, "Primary succession"
  • What are the two main types of ecological succession? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.1
  • What earns a species the label keystone? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.2
  • Which organisms are often the first pioneers on bare rock? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.J.1; fact read in Wikipedia, "Pioneer species"
  • Which three measures of an ecosystem does succession change over time, by the course description? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.J.2
  • Why are frogs and toads often used as indicator species for chemical pollution? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.3; fact read in Wikipedia, "Bioindicator"
  • Why is secondary succession usually faster than primary succession? College Board, AP Environmental Science Course and Exam Description, topic 2.7, essential knowledge ERT-2.I.1; fact read in Wikipedia, "Secondary succession"

How this list was compiled: Our own questions, written to Unit 2 (The Living World: Biodiversity) of the College Board's AP Environmental Science Course and Exam Description, effective fall 2026, https://apcentral.collegeboard.org/media/pdf/ap-environmental-science-course-and-exam-description.pdf, read 2026-10-14: topics 2.1 to 2.7. The rule behind each answer was read on 2026-10-14 in the essential knowledge statement of the course description named under the question; the named examples (a seal, an otter, lichens, frogs, islands, the last ice age, the kinds of ecosystem service) were read in the Wikipedia articles named. Licence: Own work. Short quotations from the public documents named under each question.

How it works

This APES Unit 2 practice test has 56 questions of our own on The Living World: Biodiversity, the second unit of AP Environmental Science. It is unofficial: the College Board owns AP and did not write, review or endorse these questions.

Read the full guide

What Unit 2 covers

The College Board's course description, effective fall 2026 and read October 14, 2026, gives Unit 2 seven topics and no weights among them, so the spread is ours: biodiversity (10 questions), ecosystem services (7), island biogeography (7), ecological tolerance (6), natural disruptions (8), adaptations (5) and ecological succession (13).

Pairs the unit asks you to tell apart

The description says students often confuse the unit's terms, such as biodiversity and genetic diversity. Genetic diversity is one of biodiversity's three levels: the variety of genes within one population. A keystone species shapes its community; an indicator species reports on it.

  • Species richness is a count of species. A plot with more individuals is not a richer plot.
  • Individuals never adapt by natural selection. Populations do, over generations.

Questions and answers

What is Unit 2 in AP Environmental Science?

The Living World: Biodiversity, the second of nine units. It carries 6 to 8% of the multiple-choice section, by the College Board's course page, and the description allows about 11 to 12 class periods.

What should an APES Unit 2 study guide cover?

An AP Environmental Science Unit 2 study guide needs the terms of seven topics: genetic, species and habitat diversity; the four ecosystem services; island biogeography; ecological tolerance; periodic, episodic and random disruptions; natural selection; and succession, with keystone, indicator and pioneer species.

What is the difference between primary and secondary succession?

Primary succession begins where there is no soil, such as new volcanic rock, and pioneers such as lichens must help build it. Secondary succession begins on soil left after a disturbance such as a fire, so it is usually faster.

What are the four types of ecosystem services?

Provisioning services are goods such as food, water and timber. Regulating services control climate, floods and disease. Cultural services are recreation and other non-material benefits. Supporting services, such as nutrient cycling, make the other three possible.

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