U2 FRQ Practice
Master AP Environmental Science Unit 2 FRQs: strategies for biodiversity, ecological tolerance, and disturbance questions, with worked examples and scoring tips.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on U2 FRQ Practice, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Unit 2 concepts — biodiversity, island biogeography, ecological tolerance, and disturbance/succession — are exam favorites because they connect easily to data sets, graphs, and real-world scenarios. The AP Environmental Science exam rarely asks you to simply define these terms; instead it wants you to apply them to a described ecosystem, defend a claim, or interpret a figure.
This lesson is not about re-learning the content from U2.1 through U2.3. It is about converting what you already know into points on the free-response section. You will learn how to decode task verbs, structure a response that graders can score quickly, and avoid the vague answers that cost students easy points.
This lesson is not about re-learning the content from U2.1 through U2.3. It is about converting what you already know into points on the free-response section. You will learn how to decode task verbs, structure a response that graders can score quickly, and avoid the vague answers that cost students easy points.
How AP FRQs Test Unit 2 Content
The AP Environmental Science exam has three free-response questions worth 10 points each. Unit 2 content most often appears in the design an investigation FRQ or the data analysis FRQ, but it can appear anywhere. A single prompt might give you a table of species counts on islands of different sizes, then ask you to calculate species richness, explain island biogeography, and propose a conservation action.
Graders use a rubric with specific earning statements. You do not get partial credit for sounding knowledgeable — you earn a point only if your sentence matches what the rubric requires. That means each answer must be a complete, standalone claim with a mechanism.
The biggest score killer is answering a different question than the one asked. Underline the task verb and the specific subject before writing.
Graders use a rubric with specific earning statements. You do not get partial credit for sounding knowledgeable — you earn a point only if your sentence matches what the rubric requires. That means each answer must be a complete, standalone claim with a mechanism.
| FRQ type | Typical Unit 2 task | What earns the point |
|---|---|---|
| Data analysis | Read a graph of tolerance ranges | Correct trend plus environmental reason |
| Design investigation | Test how disturbance affects diversity | Testable hypothesis, variables, control |
| Doc-based/scenario | Explain succession after a fire | Named stage plus process |
Decoding Task Verbs
Every FRQ sentence begins with a directive word that tells you exactly how much to write. Matching your answer length and depth to the verb is the single most reliable way to gain points.
Identify or State wants a single fact — one word or phrase. Do not explain; just name it. Describe wants characteristics or a step-by-step account. Explain requires a cause-and-effect mechanism: use the word "because" or "which causes." Calculate demands the setup, the numbers, and the correct units — always show your work so a math slip still earns setup credit. Justify or Make a claim asks you to take a position and defend it with reasoning.
A frequent error is over-answering an "identify" and under-answering an "explain." Give exactly what the verb requests, then move on to protect your time.
Identify or State wants a single fact — one word or phrase. Do not explain; just name it. Describe wants characteristics or a step-by-step account. Explain requires a cause-and-effect mechanism: use the word "because" or "which causes." Calculate demands the setup, the numbers, and the correct units — always show your work so a math slip still earns setup credit. Justify or Make a claim asks you to take a position and defend it with reasoning.
| Verb | You must provide | Common Unit 2 use |
|---|---|---|
| Identify | One term/value | Name a limiting factor |
| Describe | Details or steps | Describe primary succession |
| Explain | Mechanism (cause→effect) | Why small islands hold fewer species |
| Calculate | Work + units | Percent change in richness |
| Justify | Claim + evidence | Argue which reserve design is better |
Structuring Unit 2 Answers That Score
Answer in the order the prompt lists the parts, and label them (a), (b), (c) to match. Never bury a scoring answer inside a paragraph — put the earning sentence first, then support it.
For biodiversity and island biogeography questions, always connect to the two drivers: island size (extinction rate) and distance from mainland (immigration rate). A rubric-friendly sentence sounds like: "The larger island supports greater species richness because larger area lowers extinction rates by supporting bigger populations."
For ecological tolerance questions, reference the tolerance curve: an optimal range, zones of physiological stress, and zones of intolerance. Tie the organism's distribution to a specific abiotic factor such as temperature, salinity, or pH.
For disturbance and succession questions, distinguish primary succession (starts on bare rock/lava, no soil, begins with pioneer species like lichens) from secondary succession (soil remains after fire or farming, faster recovery). Name the disturbance and the resulting change in the community.
A misconception that costs points: writing that "biodiversity is good for the ecosystem" without a mechanism. Instead specify why — greater genetic and species diversity increases resilience and the chance some species survive environmental change.
For biodiversity and island biogeography questions, always connect to the two drivers: island size (extinction rate) and distance from mainland (immigration rate). A rubric-friendly sentence sounds like: "The larger island supports greater species richness because larger area lowers extinction rates by supporting bigger populations."
For ecological tolerance questions, reference the tolerance curve: an optimal range, zones of physiological stress, and zones of intolerance. Tie the organism's distribution to a specific abiotic factor such as temperature, salinity, or pH.
For disturbance and succession questions, distinguish primary succession (starts on bare rock/lava, no soil, begins with pioneer species like lichens) from secondary succession (soil remains after fire or farming, faster recovery). Name the disturbance and the resulting change in the community.
A misconception that costs points: writing that "biodiversity is good for the ecosystem" without a mechanism. Instead specify why — greater genetic and species diversity increases resilience and the chance some species survive environmental change.
Managing Data, Graphs, and Calculations
Unit 2 FRQs love quantitative hooks. Species richness is a simple count of different species; species evenness describes how balanced their populations are. If asked to compare two communities with the same number of species, the one with more even population sizes has higher diversity.
When a percent-change calculation appears, use . Always carry units through and box or clearly state the final answer. Graders scan for the number and the unit together.
When reading a tolerance graph, describe the trend before interpreting it: state whether the population peaks at an intermediate value (optimal range) and declines at the extremes. Then connect the pattern to a stressor. For a graph of the intermediate disturbance hypothesis, note that diversity is highest at moderate disturbance frequency because low disturbance lets competitors dominate while high disturbance eliminates all but the hardiest species.
Do not describe the axes back to the grader as your whole answer — that earns nothing. Turn the data into an environmental claim.
When a percent-change calculation appears, use . Always carry units through and box or clearly state the final answer. Graders scan for the number and the unit together.
When reading a tolerance graph, describe the trend before interpreting it: state whether the population peaks at an intermediate value (optimal range) and declines at the extremes. Then connect the pattern to a stressor. For a graph of the intermediate disturbance hypothesis, note that diversity is highest at moderate disturbance frequency because low disturbance lets competitors dominate while high disturbance eliminates all but the hardiest species.
Do not describe the axes back to the grader as your whole answer — that earns nothing. Turn the data into an environmental claim.
Key terms
- Species Richness.
- The number of different species present in a community; a common calculation target on Unit 2 FRQs.
- Species Evenness.
- How similar the population sizes of the different species are; high evenness raises overall diversity.
- Island Biogeography.
- Model predicting species number from island size (affects extinction) and distance to mainland (affects immigration).
- Ecological Tolerance.
- The range of an abiotic condition an organism can survive, with an optimal range flanked by stress and intolerance zones.
- Primary Succession.
- Community development beginning on bare surfaces with no soil, started by pioneer species like lichens.
- Secondary Succession.
- Faster community recovery on land where soil remains after a disturbance such as fire or abandoned farming.
- Intermediate Disturbance Hypothesis.
- Idea that species diversity peaks at moderate levels of disturbance frequency or intensity.
- Task Verb.
- The directive word (identify, describe, explain, calculate, justify) that defines how much detail an FRQ answer requires.
Worked example
A researcher surveys two islands off a coastline. Island A is 50 km from the mainland and 200 hectares; Island B is 5 km from the mainland and 200 hectares. Island A has 24 bird species and Island B has 40 bird species. (a) Identify which island has greater species richness. (b) Explain, using island biogeography, why the two islands differ in richness. (c) Calculate the percent difference in species richness between Island B and Island A.
Part (a) uses the verb "identify," so give one fact: Island B has greater species richness with 40 species compared to 24. No explanation is needed here.
Part (b) uses "explain," so provide a mechanism. Because both islands are the same size, area and extinction rate are held constant, so the difference must come from distance to the mainland. Island B is only 5 km away, so it has a higher immigration rate — birds can more easily colonize it because the shorter distance is easier to cross. Island A, at 50 km, receives fewer colonizing species, so immigration is lower and richness is lower. Notice the answer names the driver (distance), the affected rate (immigration), and the resulting outcome.
Part (c) uses "calculate," so show the setup and units. Using , we get . State the final answer clearly: Island B has about 67% more bird species than Island A. Showing the fraction protects setup credit even if the arithmetic slips.
Part (b) uses "explain," so provide a mechanism. Because both islands are the same size, area and extinction rate are held constant, so the difference must come from distance to the mainland. Island B is only 5 km away, so it has a higher immigration rate — birds can more easily colonize it because the shorter distance is easier to cross. Island A, at 50 km, receives fewer colonizing species, so immigration is lower and richness is lower. Notice the answer names the driver (distance), the affected rate (immigration), and the resulting outcome.
Part (c) uses "calculate," so show the setup and units. Using , we get . State the final answer clearly: Island B has about 67% more bird species than Island A. Showing the fraction protects setup credit even if the arithmetic slips.
Practice questions
A prairie experiences fires at different frequencies across three plots. Plot 1 burns rarely, Plot 2 burns every few years, and Plot 3 burns almost annually. According to the intermediate disturbance hypothesis, which plot is expected to have the highest species diversity?
- Plot 1, because the absence of fire lets all species accumulate over time
- Plot 2, because moderate disturbance prevents competitive dominance while allowing recovery
- Plot 3, because frequent fire constantly resets the community to pioneer species
- All three plots will have equal diversity because fire is a natural disturbance
Answer: Plot 2, because moderate disturbance prevents competitive dominance while allowing recovery
The intermediate disturbance hypothesis predicts peak diversity at moderate disturbance. In Plot 1, low disturbance lets a few dominant competitors outcompete others, lowering diversity. In Plot 3, frequent fire removes all but the most disturbance-tolerant species. Plot 2's moderate fire frequency clears dominants while giving the community time to recover, maximizing coexistence.
A species of trout survives in stream temperatures between 5°C and 20°C, thrives most at about 12°C, and dies above 24°C. Describe how a tolerance curve represents this trout's response to temperature, and explain what would likely happen to the population if average stream temperature rose from 12°C to 22°C.
Answer: The tolerance curve shows an optimal range near 12°C where the population is largest, flanked by zones of physiological stress toward the temperature extremes and zones of intolerance beyond 5°C and 24°C. At 22°C the trout would be pushed into the upper stress zone, so population size would decline as individuals face heat stress, reduced reproduction, and possible migration or death, even though 22°C is not yet lethal.
A strong answer names the parts of the tolerance curve (optimal range, stress zones, intolerance zones) and ties the population change to the mechanism of physiological stress. Because 22°C sits between the optimum and the lethal limit of 24°C, the correct prediction is decline rather than immediate extinction — precision about the zone earns the point.
Which of the following best describes a difference between primary and secondary succession?
- Primary succession occurs only in aquatic ecosystems, while secondary succession occurs on land
- Primary succession begins where soil already exists, while secondary succession begins on bare rock
- Primary succession begins on surfaces lacking soil, while secondary succession begins where soil remains after a disturbance
- Secondary succession never leads to a climax community, but primary succession always does
Answer: Primary succession begins on surfaces lacking soil, while secondary succession begins where soil remains after a disturbance
Primary succession starts on bare, soil-free surfaces such as cooled lava or exposed rock and relies on pioneer species like lichens to build soil, making it slow. Secondary succession follows disturbances like fire or farming that leave soil intact, so it proceeds faster. The other options reverse these facts or make false claims about climax communities.
FAQ
- How long should my Unit 2 FRQ answers be?
- Match the task verb. An "identify" needs one phrase, while "explain" needs a full cause-and-effect sentence. Most single-point parts require just one to three sentences. Writing extra unrequested material wastes time and can bury your scoring sentence, so answer directly and move on.
- Do I need to memorize formulas for Unit 2 FRQs?
- You should know how to calculate species richness (a count), interpret evenness, and apply percent change, . Calculations reward showing your setup and units, so write the formula and plug in numbers even if you are unsure of the final arithmetic.
- What is the most common mistake on biodiversity FRQs?
- Giving a vague claim without a mechanism, such as writing "more biodiversity is better" or just restating the graph axes. Always connect your claim to a process — for example, greater diversity increases resilience because a wider range of traits means some species can survive an environmental change.
- How do I know whether a scenario is primary or secondary succession?
- Check for soil. If the prompt describes bare rock, lava, or newly exposed sand with no soil, it is primary succession and begins with pioneer species. If soil remains after a fire, flood, or abandoned farm, it is secondary succession, which recovers faster because seeds, roots, and nutrients persist.
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