U9 FRQ Practice
Master AP Environmental Science Unit 9 free-response questions on ozone, climate change, ocean acidification, and biodiversity with strategies, a worked FRQ, and practice.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on U9 FRQ Practice, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Unit 9 packs the biggest global-scale problems in AP Environmental Science—ozone depletion, the enhanced greenhouse effect, ocean warming and acidification, and threats to biodiversity—into a single testable theme. On the exam, these ideas rarely appear as isolated facts. Instead, they surface inside the three free-response questions (FRQs), where you must explain mechanisms, read data, propose solutions, and sometimes run calculations.
This lesson does not re-teach the science; your neighboring lessons already covered that. Instead, it trains the skill of turning what you know into full-credit FRQ responses. You will learn how AP prompts are structured, which verbs demand which kinds of answers, how to earn calculation points, and how to avoid the vague phrasing that costs students easy points.
This lesson does not re-teach the science; your neighboring lessons already covered that. Instead, it trains the skill of turning what you know into full-credit FRQ responses. You will learn how AP prompts are structured, which verbs demand which kinds of answers, how to earn calculation points, and how to avoid the vague phrasing that costs students easy points.
How Unit 9 Content Maps onto the Three FRQs
The AP Environmental Science exam always includes three 10-point FRQs, and Unit 9 topics can anchor any of them. Knowing each question's personality tells you what kind of answer to prepare.
Each part is scored on a rubric of discrete points. There is no penalty for wrong extra writing, but graders read for specific ideas, so padding wastes time. A strong Unit 9 answer names the mechanism (for example, that traps outgoing infrared radiation), connects cause to effect, and stays concrete. Because global-change topics interconnect, prompts often chain them: a question about ocean warming may also ask about biodiversity loss or a human economic impact, rewarding students who can move fluidly across the unit.
| FRQ | Official focus | What Unit 9 version looks like |
|---|---|---|
| Question 1 | Design an Investigation | Plan an experiment testing coral bleaching, CO uptake, or invasive-species spread |
| Question 2 | Analyze an Environmental Problem and Propose a Solution | Interpret a climate graph, explain a mechanism, propose and justify a mitigation strategy |
| Question 3 | Analyze an Environmental Problem, Propose a Solution, and Do Calculations | Same as Q2 but with math—emissions, warming rates, pH change, or species loss |
Decoding the Command Verbs
The single fastest way to raise an FRQ score is to answer the exact task word. AP uses a consistent set of command verbs, and each earns points differently.
Identify or State wants one specific thing—one sentence, no elaboration needed. Describe wants observable characteristics or a what-happens statement. Explain demands a cause-and-effect chain using the word because or a logical link. Calculate requires showing your setup with correct units. Justify or Propose a solution asks you to give a realistic action and explain why it works.
A common misconception is that writing more automatically earns more. It does not. If a prompt says identify one greenhouse gas, writing three does not add points, and a wrong first answer can be the one graded. Instead, spend energy where verbs demand depth. For explain prompts, always complete the causal chain. Saying warming melts ice is incomplete; saying warming melts reflective ice, which lowers albedo, so the surface absorbs more solar energy and warms further completes the loop. Underlining or clearly separating each answer part helps graders find your points and helps you confirm you addressed every task.
Identify or State wants one specific thing—one sentence, no elaboration needed. Describe wants observable characteristics or a what-happens statement. Explain demands a cause-and-effect chain using the word because or a logical link. Calculate requires showing your setup with correct units. Justify or Propose a solution asks you to give a realistic action and explain why it works.
A common misconception is that writing more automatically earns more. It does not. If a prompt says identify one greenhouse gas, writing three does not add points, and a wrong first answer can be the one graded. Instead, spend energy where verbs demand depth. For explain prompts, always complete the causal chain. Saying warming melts ice is incomplete; saying warming melts reflective ice, which lowers albedo, so the surface absorbs more solar energy and warms further completes the loop. Underlining or clearly separating each answer part helps graders find your points and helps you confirm you addressed every task.
Nailing the Calculation and Data Points
Question 3 and sometimes Question 1 include quantitative parts worth easy points—if you show work. AP awards separate points for the correct setup and the correct answer with units, so never write only a final number.
Common Unit 9 calculations include converting emissions (tons of per year), computing percent change in temperature or pH, finding rates of sea-level rise, and dimensional-analysis unit conversions. Always carry units through the whole expression; a bare number like 4.2 may lose the point even when correct, while 4.2 metric tons per year secures it.
For data-based parts, describe trends precisely. Instead of it goes up, write global average temperature rose about between 1950 and 2020. Cite specific numbers from the figure and use the axis labels. When asked to explain a trend, reference the mechanism, not just the graph shape. A frequent error is confusing correlation with the physical cause—say why rising produces the observed warming, tying data back to radiative forcing. Round only at the end, keep at least three significant figures during work, and clearly box or label your final answer so the grader cannot miss it.
Common Unit 9 calculations include converting emissions (tons of per year), computing percent change in temperature or pH, finding rates of sea-level rise, and dimensional-analysis unit conversions. Always carry units through the whole expression; a bare number like 4.2 may lose the point even when correct, while 4.2 metric tons per year secures it.
For data-based parts, describe trends precisely. Instead of it goes up, write global average temperature rose about between 1950 and 2020. Cite specific numbers from the figure and use the axis labels. When asked to explain a trend, reference the mechanism, not just the graph shape. A frequent error is confusing correlation with the physical cause—say why rising produces the observed warming, tying data back to radiative forcing. Round only at the end, keep at least three significant figures during work, and clearly box or label your final answer so the grader cannot miss it.
Building a Full-Credit Solution Paragraph
Both Question 2 and Question 3 end by asking you to propose a solution and justify it. This is where students who know the science still lose points by staying vague. A phrase like use less energy is not creditable; reduce fossil-fuel combustion by replacing coal power plants with solar and wind, which emit no during generation is.
Use a two-part template: state a specific, realistic action, then explain the environmental mechanism by which it reduces the problem. For ozone, that might be phasing out CFCs under an international agreement because CFCs release chlorine that catalytically destroys . For acidification, restoring wetlands and reducing emissions because less atmospheric dissolves into seawater and forms carbonic acid.
Watch for prompts asking for an economic or human-health consequence alongside the environmental one—these are separate points. Also anticipate the describe a drawback or trade-off part that often follows a solution; every mitigation has costs (land use, expense, intermittency), and naming one earns another point. Keep each proposal grounded in a mechanism the reader can trace from action to outcome.
Use a two-part template: state a specific, realistic action, then explain the environmental mechanism by which it reduces the problem. For ozone, that might be phasing out CFCs under an international agreement because CFCs release chlorine that catalytically destroys . For acidification, restoring wetlands and reducing emissions because less atmospheric dissolves into seawater and forms carbonic acid.
Watch for prompts asking for an economic or human-health consequence alongside the environmental one—these are separate points. Also anticipate the describe a drawback or trade-off part that often follows a solution; every mitigation has costs (land use, expense, intermittency), and naming one earns another point. Keep each proposal grounded in a mechanism the reader can trace from action to outcome.
Key terms
- Command verb.
- The task word in an FRQ prompt (identify, describe, explain, calculate, justify) that dictates the type and depth of response required for credit.
- Causal chain.
- A step-by-step link from cause to effect that fully answers an explain prompt, such as tracing rising to increased infrared absorption to warming.
- Radiative forcing.
- The change in energy balance of Earth's atmosphere caused by factors like greenhouse gases; useful language for explaining warming FRQs.
- Albedo.
- The reflectivity of a surface; central to feedback-loop explanations where melting ice lowers albedo and amplifies warming.
- Ocean acidification.
- The decrease in seawater pH as dissolved forms carbonic acid, reducing carbonate available for shell-building organisms.
- Dimensional analysis.
- A calculation method that tracks and cancels units across a conversion, ensuring the numerical answer carries the correct final unit.
- Mitigation strategy.
- A specific, realistic action proposed to reduce an environmental problem, which must be paired with the mechanism explaining its effect for full credit.
Worked example
A coastal power plant burns coal and emits carbon dioxide. Nearby, marine biologists record declining coral cover and thinning mollusk shells. (a) Describe one way the plant's emissions contribute to ocean acidification. (b) Calculate the percent decrease in shell mass if a mollusk's shell drops from 12.0 grams to 9.6 grams. (c) Propose one solution to reduce ocean acidification and explain how it works. (d) Identify one economic drawback of your proposed solution.
Part (a) is a describe/explain task, so complete the mechanism. Atmospheric from burning coal dissolves into seawater and reacts with water to form carbonic acid, which lowers pH and reduces the carbonate ions mollusks need to build shells. Naming the acid and the pH drop secures the point.
Part (b) is a calculation—show the setup. Percent decrease . Write both the setup and the final answer with the percent unit; a bare 20 risks losing the answer point.
Part (c) needs a specific action plus mechanism. Replace the coal plant with solar generation because solar produces electricity without releasing , so less carbon dioxide enters the atmosphere and dissolves into the ocean, slowing acidification. Vague answers like pollute less earn nothing.
Part (d) wants an economic drawback, a distinct point. The high upfront capital cost of building solar infrastructure, or the expense of decommissioning the existing plant, is creditable. One clear trade-off is enough.
Part (b) is a calculation—show the setup. Percent decrease . Write both the setup and the final answer with the percent unit; a bare 20 risks losing the answer point.
Part (c) needs a specific action plus mechanism. Replace the coal plant with solar generation because solar produces electricity without releasing , so less carbon dioxide enters the atmosphere and dissolves into the ocean, slowing acidification. Vague answers like pollute less earn nothing.
Part (d) wants an economic drawback, a distinct point. The high upfront capital cost of building solar infrastructure, or the expense of decommissioning the existing plant, is creditable. One clear trade-off is enough.
Practice questions
An FRQ prompt reads: Explain how the enhanced greenhouse effect leads to rising global temperatures. Which response would earn the explain point?
- Greenhouse gases are bad for the environment and cause pollution
- There are more greenhouse gases in the atmosphere now than before
- Greenhouse gases like absorb outgoing infrared radiation and re-emit it toward Earth, trapping heat and raising surface temperature
- Temperatures have been going up since the Industrial Revolution
Answer: Greenhouse gases like absorb outgoing infrared radiation and re-emit it toward Earth, trapping heat and raising surface temperature
An explain prompt requires a cause-and-effect mechanism. Only this choice traces how gases absorb and re-emit infrared energy to trap heat. The others describe a trend or make a vague judgment without linking cause to effect, so they would not earn the point.
A data table shows atmospheric rising from 315 ppm in 1958 to 420 ppm in 2020. Calculate the percent increase over this period and show your work.
Answer: About 33.3 percent
Set up the percent-change formula: . Showing the subtraction and division earns the setup point, and reporting the value with a percent sign earns the answer point. Writing only 33 without work risks losing credit even though it is close.
Propose one solution to reduce stratospheric ozone depletion and explain how it works.
Answer: Enforce an international phase-out of chlorofluorocarbons (CFCs) because CFCs release chlorine atoms that catalytically destroy ozone; eliminating them reduces the chlorine available to break down .
Full credit requires a specific, realistic action plus the mechanism. The Montreal Protocol style phase-out is a valid action, and connecting it to chlorine's catalytic destruction of ozone provides the required cause-and-effect justification. Simply saying stop using harmful chemicals would be too vague for the point.
FAQ
- How many FRQs are on the AP Environmental Science exam and how long do I have?
- The exam includes three free-response questions, each worth 10 points, and you have 70 minutes total for the section—roughly 22 minutes each. Question 1 is designing an investigation, Question 2 analyzes a problem and proposes a solution, and Question 3 adds calculations.
- Do I lose points for writing extra or incorrect information on an FRQ?
- There is no direct penalty for extra correct or neutral writing, but graders may read only your first answer to a prompt. If you list several answers and the first is wrong, you can lose the point. Answer precisely and avoid contradicting yourself.
- How do I earn full credit on calculation parts?
- Always show your setup, carry units through every step, and clearly label your final answer. AP typically awards one point for the correct setup and another for the correct answer with units, so a bare number without work often loses half the available credit.
- What is the most common mistake on Unit 9 solution prompts?
- Being too vague. Answers like reduce pollution or use clean energy do not earn points. You must name a specific action and explain the environmental mechanism by which it reduces the problem, and often identify a trade-off or drawback as a separate point.
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The Crimsora tutor teaches U9 FRQ Practice live — explaining on a whiteboard, asking you questions, and adapting to where you get stuck.