AP Environmental Science Unit 9 practice questions
Try 10 multiple-choice questions from Unit 9 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
Researchers quantified nitrous oxide emissions from agricultural soil by measuring gas concentrations in chambers placed over fertilized plots immediately after nitrogen fertilizer application and again 7 days later. If they modified the procedure to measure nitrous oxide concentrations daily for 30 days following fertilizer application, how would this change most likely affect their understanding of nitrous oxide emission patterns?
Peak emission rates would be identified, revealing the temporal dynamics of nitrous oxide production following fertilizer application.
Total nitrous oxide emissions would appear lower because daily measurements would average out the high initial emissions.
Nitrous oxide emissions would be shown to remain constant throughout the 30-day period, indicating stable microbial activity.
The study would become invalid because daily disturbance of the soil chambers would prevent accurate measurement of natural emissions.
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Answer: (A)
Increasing sampling frequency from two timepoints to daily measurements over 30 days captures the full emission trajectory. Nitrous oxide production from fertilizer-amended soil follows a predictable pattern: rapid initial production as microbes metabolize the nitrogen fertilizer, followed by declining emissions as substrate becomes depleted. Daily sampling reveals this peak and subsequent decline, providing mechanistic understanding of how agricultural practices generate nitrous oxide pulses. The original two-timepoint design would miss the peak entirely if it occurred between measurements.
Question 2
Researchers investigating the relationship between livestock farming practices and atmospheric methane levels collected air samples monthly from above 12 dairy farms and 12 grain farms in the same region over two years. All farms had similar soil types and climate conditions. Which of the following best describes the research method used in this study?
Observational field study comparing methane emissions across different agricultural practices
Controlled laboratory experiment testing the effect of livestock diet on methane production
Longitudinal study tracking individual animals to measure their personal methane contributions
Comparative survey using self-reported farm management data to estimate methane emissions
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Answer: (A)
Recognizing this as an observational study requires identifying that researchers measured naturally occurring differences in farming practices rather than manipulating variables. The study compares two groups (dairy vs. grain farms) selected for their existing practices, with careful matching of confounding variables (soil, climate), which is characteristic of observational field research designed to identify correlations between agricultural type and methane emissions.
Question 3
Scientists measuring nitrous oxide emissions from agricultural soils collected samples at depths of 0–15 cm, 15–30 cm, and 30–60 cm from 20 randomly selected locations across a corn field treated with nitrogen fertilizer. Samples were collected monthly for one growing season. Which of the following aspects of this sampling design most directly addresses the variability in nitrous oxide production across different soil conditions?
Collecting samples at multiple depths to account for stratification of nitrous oxide production in soil layers
Using 20 randomly selected locations to ensure that all corn plants in the field are represented equally
Collecting samples monthly throughout the growing season to measure how nitrous oxide changes with crop growth
Applying nitrogen fertilizer uniformly across the field to standardize the nitrous oxide source
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Answer: (A)
Stratified sampling by depth directly addresses the reality that nitrous oxide production varies with soil conditions that change vertically—oxygen availability, microbial activity, and nitrogen concentration differ at different depths. By sampling multiple depths at each location, researchers capture the heterogeneity of nitrous oxide sources within the soil profile, improving the reliability of emission estimates compared to sampling only surface soil.
Question 4
Researchers measured wetland methane using 30-minute chambers and continuous sensors 2 meters above the surface. Why does combining both methods yield more reliable data than either alone?
Chambers give precise local fluxes while sensors capture continuous temporal trends
Chambers are more accurate so sensors can be adjusted using chamber values
Sensors cannot measure methane accurately so chambers provide the only reliable data
Multiple methods reduce replication needs so researchers sample fewer locations
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Answer: (A)
Chamber sampling yields precise local flux measurements while sensors record continuous temporal variation. Together they provide high-resolution local data and comprehensive temporal-spatial coverage for validation and broader inference.
Question 5
Researchers measured nitrous oxide emissions from plots treated with two fertilizers, synthetic urea and organic compost. Each treatment had six replicate plots and weekly gas sampling for eight weeks. Why does using six replicate plots per treatment strengthen conclusions about the fertilizers' effects on nitrous oxide emissions?
Multiple replicates reduce random variation by averaging natural soil heterogeneity.
Replicates are repeats of the same treatment not different fertilizer types.
Replication addresses variability within treatments rather than guaranteeing full field coverage.
Larger sample sizes increase power but replication primarily reveals treatment variability.
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Answer: (A)
Replication reduces the influence of plot-to-plot differences by averaging results across varied soils. Six replicates let researchers estimate mean emissions and determine whether observed differences between fertilizers exceed random variation.
Question 6
Original practice passage
Cattle release methane during digestion. Improving productivity alone does not establish that a farm has reduced its total emissions. A climate-management plan should therefore evaluate measures that directly reduce methane, including appropriate changes to feeding practices, and measure their effects on emissions.
Background: U.S. EPA, Agriculture Sector Emissions.
Which statement best expresses the passage's main recommendation?
Evaluate and measure livestock-management measures that directly reduce methane emissions.
Assess climate progress solely by increases in the amount of agricultural output.
Exclude methane from climate planning because it is released during a natural process.
Assume every change in cattle feeding practices produces the same reduction in emissions.
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Answer: (A)
The passage recommends evaluating methane-reducing management and measuring its effects. This states its proposed action rather than a background fact.
Question 7
A wetland ecologist reports that wetlands naturally emit methane via anaerobic decomposition and that human actions alter those dynamics. Drainage removes methane sources but destroys carbon storage. Restoration increases local methane while providing flood control, water filtration, and habitat. Which sentence best expresses the ecologist's central claim?
Wetland ecosystem services justify accepting their methane emissions in sustainable management
Wetlands produce methane by anaerobic decomposition in low oxygen environments
Draining wetlands removes methane sources but destroys long term carbon storage
Restoring wetlands raises local methane emissions while providing flood control and filtration
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Answer: (A)
The passage argues that management decisions should weigh methane emissions against the broader services wetlands provide. It presents methane production as a trade off to be balanced with flood control, filtration, habitat, and carbon considerations.
Question 8
A study finds nitrous oxide rose 20 percent since pre-industrial times, mainly from agricultural nitrogen fertilizer. The researchers conclude reducing fertilizer is essential to stabilize atmospheric nitrous oxide. Which additional information would most strengthen that reasoning?
Agriculture produces most human nitrous oxide and fertilizer is the main controllable source.
Evidence that nitrous oxide levels were stable for centuries before industrial times.
Data on nitrous oxide's global warming potential and long atmospheric lifetime.
Evidence that alternative fertilizers or precision methods sustain yields with less nitrogen.
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Answer: (A)
Showing that agriculture supplies most human-caused nitrous oxide and fertilizer is the main controllable source directly links fertilizer reduction to stabilization. This closes the gap between observed increases and the claim that reducing fertilizer is essential.
Question 9
As atmospheric CO2 dissolves into surface seawater, why can organisms like pteropods and corals build calcium carbonate shells less effectively?
CO2 forms carbonic acid, lowering pH and converting carbonate to bicarbonate
Moderate pH shifts do not primarily denature proteins or halt calcification
Higher CO2 does not primarily lower oxygen or induce hypoxia stopping calcification
CO2-driven density changes are negligible and cannot compress shells mechanically
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Answer: (A)
Dissolved CO2 forms carbonic acid, increasing hydrogen ions and shifting carbonate into bicarbonate which reduces carbonate ion availability for calcification. With fewer carbonate ions, organisms cannot precipitate calcium carbonate and their shells weaken or dissolve.
Question 10
Coastal flooding increases as sea levels rise. How do melting land ice and thermal expansion both raise sea level?
Melting land ice adds ocean water while warming expands seawater volume
Melting ice does not significantly heat oceans or drive thermal expansion
Floating sea ice melting does not change sea level while land ice raises it
Warming lowers seawater density and increases its volume, raising sea level
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Answer: (A)
Melting land ice adds water mass to the oceans, directly raising sea level. Warming increases seawater volume so thermal expansion further raises sea level.
What's on the AP Environmental Science Unit 9 practice test
The standard version takes about 70 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (23 minutes)
- 1 FRQ – FRQ 1 – Design an Investigation (23 minutes)
- 1 FRQ – FRQ 2 – Analyze and Interpret Quantitative Data (23 minutes)
Questions are drawn from 2688 multiple-choice questions and 42 FRQs written for Unit 9, Global Change.
Practice AP Environmental Science Unit 9 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Design an Investigation (14 questions)
- FRQ 2 – Analyze and Interpret Quantitative Data (15 questions)
- FRQ 3 – Analyze an Environmental Problem Doing Calculations (13 questions)
Review Unit 9 before you start
- 9.1 Stratospheric Ozone Depletion
- 9.2 Reducing Ozone Depletion
- 9.3 The Greenhouse Effect
- 9.4 Increases in the Greenhouse Gases
- 9.5 Global Climate Change
- 9.6 Ocean Warming
- 9.7 Ocean Acidification
- 9.8 Invasive Species
- 9.9 Endangered Species
- 9.10 Human Impacts on Biodiversity
- Major Environmental Disasters