AP Environmental Science Unit 8 practice questions
Try 10 multiple-choice questions from Unit 8 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
An agricultural engineer in California's Central Valley writes: 'Center-pivot irrigation systems efficiently deliver water to crops, but the water returned to the Sacramento-San Joaquin Delta is significantly warmer than when withdrawn. Installing heat-exchange systems to cool return water before discharge would reduce thermal pollution but would increase operational costs by 15% and reduce farmer profitability. Farmers should not be required to absorb these costs when the primary responsibility for thermal pollution lies with power plants and industrial facilities.' Which stakeholder perspective does this statement most clearly represent?
Agricultural producers prioritizing economic viability and cost-minimization over pollution reduction.
Environmental regulators seeking to distribute thermal pollution responsibility equitably across all industries.
Aquatic ecosystem advocates concerned about dissolved oxygen depletion in the Delta.
Water treatment specialists focused on maintaining safe drinking water quality in the Delta.
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Answer: (A)
The engineer advocates for farmers by arguing they should not bear cooling costs, framing thermal pollution responsibility as belonging elsewhere. This reveals a perspective that prioritizes agricultural economic interests and treats environmental mitigation as an unfair burden on farming operations. The argument assumes farmers' profitability concerns should outweigh their thermal pollution contributions, characteristic of agricultural industry stakeholders.
Question 2
Researchers measured mercury in water, zooplankton, small fish, and large predatory fish over one year. If they exclude water and sample only organisms at each trophic level, how would this change most likely affect their ability to assess biomagnification?
Can measure biomagnification between trophic levels but lose the water baseline
Organism mercury levels would remain unchanged but lose environmental context
They could no longer determine if biomagnification occurred without water data
Excluding water does not improve accuracy and reduces contextual understanding
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Answer: (A)
This preserves organism-to-organism comparisons so trophic biomagnification can be demonstrated. Removing water eliminates the abiotic baseline needed to quantify magnification from the environment to apex predators.
Question 3
In a coastal ecosystem, agricultural runoff raises phytoplankton biomass by 300%. Zooplankton briefly increase but then crash after two weeks. Why did zooplankton decline despite abundant food?
Decomposition of the algal bloom consumes oxygen, causing hypoxia that kills zooplankton
Predator response is too slow and indirect to explain the rapid zooplankton crash
Zooplankton cannot consume an ecosystem-wide 300% phytoplankton increase in two weeks
Algal blooms usually lower diversity, so reduced food quality is unlikely to cause collapse
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Answer: (A)
Decomposition fuels bacterial respiration which depletes dissolved oxygen and creates hypoxia. Zooplankton cannot tolerate low-oxygen conditions, so they die even when food remains abundant.
Question 4
Researchers kept seawater at pH 8.1, 7.9, 7.7, and 7.5 and measured pteropod shell dissolution. Why include multiple pH levels rather than only current pH and one future pH?
Reveal the dose-response curve and detect gradual versus threshold effects.
Increase sample size and thereby improve experimental statistical power.
Determine pteropod pH habitat preference under laboratory conditions.
Compensate for the small sample size by adding more data points.
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Answer: (A)
Using intermediate pH values shows whether shell dissolution changes gradually or jumps at a threshold. A gradient lets researchers model dose-response relationships and infer mechanisms that a two-point comparison cannot reveal.
Question 5
An agricultural region increases synthetic fertilizer use by 40% over five years. River phosphorus rises from 0.05 to 0.35 mg/L. Summer algal blooms cover 15% of a downstream lake and bottom dissolved oxygen falls to 2 mg/L in July and August. Which best describes the environmental problem?
Excess phosphorus runoff causes eutrophication leading to algal blooms and hypoxia.
Direct phosphorus poisoning kills fish rather than causing nutrient-driven eutrophication.
Phosphorus build-up in soils reduces future fertilizer effectiveness and crop yields.
Atmospheric phosphorus deposition combines with runoff to overwhelm the lake's buffering.
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Answer: (A)
Eutrophication occurs when excess phosphorus fuels algal growth and decomposition consumes oxygen, producing hypoxia. The fertilizer increase, higher river phosphorus, extensive summer blooms, and 2 mg/L bottom DO fit this nutrient-driven mechanism.
Question 6
A lake receives 85 percent of its phosphorus from agricultural runoff and 15 percent from wastewater. Over five years algal blooms expand from 2 percent to 18 percent of the surface and bottom-water dissolved oxygen falls from 6 to 1 mg per L. Sediment cores show increasing phosphorus accumulation. Which statement best describes the environmental problem and its relation to phosphorus reservoirs?
Excess phosphorus causes eutrophication and moves into long-term sediment storage.
Sedimentation does not permanently remove phosphorus because it can be remobilized.
Agricultural runoff is the primary source because it supplies 85 percent of inputs.
Efficient recycling is not indicated by blooms and falling oxygen levels.
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Answer: (A)
Excess phosphorus drives eutrophication and excess biomass settles into sediments. Accelerating sediment accumulation shows phosphorus leaving active cycling and entering long-term storage faster than the lake can process it.
Question 7
Agricultural nitrogen causes an algal bloom. Dead algae sink and decompose. Why do bottom waters become oxygen-depleted?
Decomposer respiration consumes oxygen and stratification prevents surface mixing.
Dead algae stop photosynthesizing so they no longer produce oxygen.
Nitrogen fuels algal growth but does not directly consume dissolved oxygen.
Reduced light limits deep photosynthesis but decomposition uses most bottom oxygen.
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Answer: (A)
Decomposer respiration consumes dissolved oxygen while stratification blocks mixing with oxygen-rich surface waters. Oxygen is used faster than it can be replenished, producing hypoxia in bottom waters.
Question 8
Which statement best explains the relationship between nutrient loading, algal growth, and oxygen depletion in this lake?
Nutrient runoff stimulates algal growth, which increases decomposition of dead algae by bacteria, consuming dissolved oxygen and creating hypoxic conditions that exceed the ecosystem's oxygen-based carrying capacity.
Nutrient runoff stimulates algal growth, which increases oxygen consumption through algal respiration at night, depleting dissolved oxygen and creating hypoxic conditions that exceed the ecosystem's oxygen-based carrying capacity.
Nutrient runoff stimulates algal growth, which increases decomposition of dead algae by bacteria, consuming dissolved oxygen until the ecosystem stabilizes at a new equilibrium with lower oxygen levels.
Nutrient runoff stimulates algal growth, which increases decomposition of dead algae by bacteria during seasonal turnover events, temporarily consuming dissolved oxygen and creating hypoxic conditions that recover when nutrient inputs decrease.
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Answer: (A)
The graph shows the inverse relationship between algal biomass and dissolved oxygen, indicating eutrophication. Excess nutrients promote algal blooms; when algae die, bacterial decomposition consumes oxygen faster than it can be replenished, creating hypoxia. This demonstrates how exceeding the ecosystem's capacity to process nutrients leads to oxygen depletion and die-off of oxygen-dependent organisms. The correct answer traces the causal chain shown in the visual.
Question 9
Over 10 years a lake's phosphorus rose from 15 to 68 µg/L, chlorophyll-a rose from 3.2 to 24.1 µg/L, and bottom dissolved oxygen fell from 6.8 to 1.2 mg/L. Which conclusion is best supported?
Nutrient loading caused eutrophication with algal bloom and bottom-water hypoxia.
Increased sunlight not nutrients primarily drove the phytoplankton increase.
Phytoplankton biomass remained stable despite higher phosphorus inputs.
Observed changes reflect a flowing river system that prevents oxygen loss.
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Answer: (A)
The data show eutrophication driven by excess phosphorus leading to an algal bloom and oxygen loss. Phosphorus rose 4.5-fold and chlorophyll-a rose 7.5-fold, then bottom oxygen dropped to 1.2 mg/L consistent with decomposition-driven hypoxia.
Question 10
A freshwater lake receives nitrogen and phosphorus inputs from agricultural runoff, wastewater treatment, and urban stormwater totaling 500 metric tons of nitrogen and 80 metric tons of phosphorus annually. The lake's natural nutrient cycling processes remove approximately 120 metric tons of nitrogen and 15 metric tons of phosphorus per year through sedimentation and denitrification. Algal biomass has increased 400% over 15 years, and summer dissolved oxygen levels have declined from 8 mg/L to 2 mg/L. Which environmental problem best describes this situation?
Nutrient loading exceeds the lake's assimilative capacity, causing eutrophication that stimulates algal growth and subsequent oxygen depletion
Thermal pollution from power plants has reduced dissolved oxygen solubility, creating hypoxic conditions independent of nutrient loading
Invasive zooplankton species have consumed native algae, reducing primary productivity and causing the observed oxygen depletion through respiration
The lake is experiencing natural eutrophication as it ages, with nutrient accumulation and oxygen depletion occurring independent of human nutrient inputs
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Answer: (A)
Nutrient inputs (500 N, 80 P metric tons/year) far exceed removal capacity (120 N, 15 P metric tons/year), creating net accumulation that drives eutrophication. The 400% algal increase and oxygen decline from 8 to 2 mg/L demonstrate the mechanism: excess nutrients fuel algal blooms that deplete oxygen when decomposed. Students must connect the nutrient budget imbalance to the observed ecological consequences.
What's on the AP Environmental Science Unit 8 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 4262 multiple-choice questions and 52 FRQs written for Unit 8, Aquatic & Terrestrial Pollution.
Practice AP Environmental Science Unit 8 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Design an Investigation (16 questions)
- FRQ 2 – Analyze and Interpret Quantitative Data (19 questions)
- FRQ 3 – Analyze an Environmental Problem Doing Calculations (17 questions)
Review Unit 8 before you start
- 8.1 Sources of Pollution
- 8.2 Human Impacts on Ecosystems
- 8.3 Endocrine Disruptors
- 8.4 Human Impacts on Wetlands and Mangroves
- 8.5 Eutrophication
- 8.6 Thermal Pollution
- 8.7 Persistent Organic Pollutants (POPs)
- 8.8 Bioaccumulation and Biomagnification
- 8.9 Solid Waste Disposal
- 8.10 Waste Reduction Methods
- 8.11 Sewage Treatment
- 8.12 Lethal Dose 50% (LD50)
- 8.13 Dose Response Curve
- 8.14 Pollution and Human Health
- 8.15 Pathogens and Infectious Diseases