AP Environmental Science Unit 8: Aquatic and Terrestrial Pollution Practice Exam

Assessment for Unit 8: Aquatic and Terrestrial Pollution

Estimated Time: 60 minutes

Exam Details

Questions: 35 total (35 multiple choice)
Time: 60 minutes (recommended)
Topics Covered: Unit 8: Aquatic and Terrestrial Pollution
Format: Multiple Choice questions matching real exam difficulty
Scoring: Instant results with detailed explanations

A. Multiple-Choice Questions (35 Questions)

Select the one best answer for each question.

1. **1. [Skill: 2 | Topic: 8.1]** A watershed monitoring team measured nitrate concentration in a stream downstream of an agricultural area. The data below were collected at the same site. | Day | Weather/Event | Nitrate (mg/L) | |---|---|---| | 1 | Dry (no rain for 5 days) | 2.1 | | 2 | Dry | 2.0 | | 3 | Heavy rainstorm | 8.6 | | 4 | Light rain | 6.9 | | 5 | Dry | 2.4 | Which of the following is the most likely classification of the nitrate pollution source responsible for the spike on Days 3 and 4?

(A)Point source pollution from a single waste-discharge pipe releasing nitrate-rich effluent(B)Nonpoint source pollution from fertilizer runoff carried over the land into the stream during precipitation events(C)Point source pollution from a smokestack depositing nitrate through dry deposition directly into the stream(D)Nonpoint source pollution from an underwater spring releasing naturally high-nitrate groundwater only during storms

2. **2. [Skill: 1 | Topic: 8.1]** A city environmental agency is trying to reduce pollution entering a river. Four potential contributors are listed below. 1. A wastewater treatment plant that releases treated effluent through a single outfall pipe 2. Oil and heavy metals washed from many streets and parking lots during storms 3. Pesticides that drift and later wash off from multiple residential lawns 4. Sediment carried into storm drains from multiple construction sites across the city Which option correctly identifies the contributors that are **point sources** of pollution?

(A)1 only(B)2 and 4 only(C)1 and 3 only(D)1, 2, 3, and 4

3. **3. [Skill: 4 | Topic: 8.1]** A student reads the following statement in a local newspaper: > “Because stormwater enters the river through storm drains, urban runoff is a point source of pollution.” Which of the following best evaluates the statement using the correct distinction between point and nonpoint sources?

(A)The statement is correct because storm drains are single, identifiable discharge points, so urban runoff is always a point source.(B)The statement is incorrect because urban runoff originates from many diffuse locations, so it is classified as a nonpoint source even if it later moves through storm drains.(C)The statement is correct because any pollutant that reaches a river through a pipe must be classified as a point source regardless of where it originated.(D)The statement is incorrect because point sources can only come from factories, and storm drains are not industrial facilities.

Refer to the figure below.

4. 1. [Skill: 4.A | Topic: 8.10] [Image Cue]: Bar graph, "Energy Use for Manufacturing (per metric ton of product)", x-axis: Material (Aluminum, Glass), y-axis: Energy use (GJ per metric ton). Bars show: Aluminum—Virgin production 150 GJ, Recycled production 10 GJ; Glass—Virgin production 20 GJ, Recycled production 15 GJ. A city is deciding which recycling program to prioritize in order to reduce overall energy demand from manufacturing. Based on the graph, which statement best supports a decision the city could make and also reflects a common drawback of recycling?

(A)Prioritize aluminum recycling because it provides much larger energy savings than glass recycling; however, recycling programs can be costly and energy-intensive due to collection, transport, and processing.(B)Prioritize glass recycling because it provides much larger energy savings than aluminum recycling; however, recycling always costs less than using virgin materials.(C)Prioritize aluminum recycling because it uses more energy than producing aluminum from virgin ore; however, recycling reduces the demand for minerals.(D)Prioritize glass recycling because recycling eliminates the need for mining and therefore requires no energy input beyond consumer drop-off.

5. 2. [Skill: 1.A | Topic: 8.10] A school cafeteria begins collecting fruit and vegetable scraps and placing them in an on-site composting system. After several months, the school uses the finished material in the campus garden beds. Which of the following best describes the process and identifies a likely drawback the school may need to manage?

(A)Composting converts organic matter into a fertilizer-like soil amendment; if the pile is not managed properly, odors and rodents may become an issue.(B)Composting converts mixed waste into new plastic products; a likely drawback is increased groundwater contamination from leachate.(C)Composting sterilizes waste into an inert solid; a likely drawback is decreased soil nutrient availability when it is applied.(D)Composting removes hazardous metals from electronic devices; a likely drawback is increased formation of photochemical smog.

6. 3. [Skill: 6.A | Topic: 8.10] A county government proposes a three-part solid-waste plan: 1) Create an e-waste collection and recycling program for discarded phones, computers, and batteries. 2) Increase the use of waste-to-energy incineration to reduce the volume of municipal solid waste going to landfills. 3) After closure of an older landfill, cap it and restore habitat so the site can be used as a public park. Which option correctly pairs TWO parts of the plan with the environmental concern each most directly addresses?

(A)Part 1—reduces odors and rodents; Part 2—prevents hazardous metals from leaching into groundwater(B)Part 2—eliminates the need for recycling by turning all materials into reusable products; Part 3—prevents all future methane production(C)Part 1—reduces the risk of lead and mercury leaching from landfills into groundwater; Part 3—mitigates long-term landfill impacts by restoring habitat and repurposing the site as parkland(D)Part 1—reduces the need for landfill liners; Part 3—converts organic matter into fertilizer

Refer to the figure below.

7. [Skill: SP 4 (Analyze Data) | Topic: 8.11] A municipal wastewater treatment plant measured water quality at four points during treatment. Results are shown below. [Image Cue]: Table, "Wastewater Quality Through Treatment Steps"; Columns: Sampling point (Influent, Step 1, Step 2, Step 3, Step 4/Final effluent), BOD (mg/L), TSS (mg/L), Dissolved inorganic nutrients (nitrate + phosphate, mg/L), Fecal coliform (counts/100 mL). Data: Influent—BOD 250, TSS 220, nutrients 12, coliform 1,000,000. Step 1—BOD 180, TSS 60, nutrients 12, coliform 1,000,000. Step 2—BOD 25, TSS 20, nutrients 11, coliform 100,000. Step 3—BOD 10, TSS 10, nutrients 2, coliform 100,000. Step 4—BOD 10, TSS 10, nutrients 2, coliform 150. Which step most clearly represents tertiary treatment?

(A)Step 1(B)Step 2(C)Step 3(D)Step 4

8. [Skill: SP 1 (Concept Explanation) | Topic: 8.11] A wastewater treatment facility uses an activated-sludge system during secondary treatment. During one week, a mechanical problem reduces aeration in the secondary treatment tank, causing dissolved oxygen levels to drop substantially. The plant observes that the effluent leaving the secondary treatment tank has a higher BOD than normal. Which statement best explains the observed increase in BOD?

(A)With less aeration, aerobic bacteria break down less organic matter, so more oxygen-demanding material remains in the water.(B)With less aeration, large solids cannot settle out in the primary clarifier, increasing suspended solids and BOD.(C)With less aeration, disinfectants (such as chlorine) can no longer kill bacteria, increasing BOD.(D)With less aeration, tertiary treatment cannot remove nutrients, increasing BOD because nitrates are oxygen-demanding material.

9. [Skill: SP 6 (Argumentation) | Topic: 8.11] A town’s wastewater treatment plant currently uses primary treatment, secondary treatment, and then chlorination before discharge to a river. Monitoring shows: - Low BOD in the final effluent - Persistently high nitrate and phosphate concentrations in the final effluent - Occasional spikes in fecal coliform counts after heavy rain events Which proposed upgrade would best address BOTH the nutrient problem and the pathogen problem?

(A)Install finer screens at the plant inlet to remove smaller debris and improve primary treatment.(B)Increase aeration time in the secondary tank to further reduce BOD.(C)Add a tertiary nutrient-removal step (ecological or chemical) and add UV (or ozone) disinfection prior to discharge.(D)Eliminate disinfection to protect aquatic organisms from exposure to chlorine.

10. [Skill: 1.A | Topic: 8.12] A toxicologist exposes groups of laboratory mice to different single (one-time) oral doses of a pesticide. The scientist reports that the pesticide has an $LD_{50}$ of 18 mg/kg for the mice. Which of the following best defines the reported $LD_{50}$ value?

(A)The dose of the pesticide that will kill 50% of all organisms exposed to it, regardless of species(B)The dose of the pesticide that is lethal to 50% of a population of the tested species under the conditions of the experiment(C)The minimum dose of the pesticide that causes any measurable harmful effect in an individual organism(D)The dose of the pesticide that causes a 50% reduction in growth or reproduction in the tested species

11. [Skill: 3.A | Topic: 8.12] A student conducts a dose-response experiment using the same species of fish and a single, short-term exposure to a chemical. The results are shown below. Dose (mg/kg): 5, 10, 15, 20 Percent mortality: 0%, 40%, 60%, 90% Based on the data, what is the best estimate of the chemical’s $LD_{50}$ for this fish species?

(A)10 mg/kg(B)12.5 mg/kg(C)15 mg/kg(D)20 mg/kg

12. [Skill: 1.A | Topic: 8.12] Two different chemicals are tested using single-dose exposures on the same species under the same laboratory conditions. Chemical X: $LD_{50}$ = 4 mg/kg Chemical Y: $LD_{50}$ = 40 mg/kg Which conclusion is best supported by the $LD_{50}$ data?

(A)Chemical X is more acutely toxic than Chemical Y because a smaller dose is lethal to 50% of the population(B)Chemical Y is more acutely toxic than Chemical X because it has a higher $LD_{50}$ value(C)Chemical X and Chemical Y have the same acute toxicity because both can kill 50% of the population(D)Chemical Y is more acutely toxic than Chemical X because it takes a larger dose to kill 50% of the population

Refer to the figure below.

13. [Skill: 2.B | Topic: 8.13] A toxicology lab exposed two groups of mice to different doses of two pesticides, Pesticide A and Pesticide B. The mortality results are summarized in a dose-response graph. Which of the following conclusions is best supported by the dose-response curves?

(A)Pesticide A is more toxic than Pesticide B because Pesticide A has a lower LD50.(B)Pesticide B is more toxic than Pesticide A because Pesticide B has a lower threshold dose.(C)Pesticide A is less toxic than Pesticide B because Pesticide A reaches 100% mortality at a lower dose.(D)Pesticide B is more toxic than Pesticide A because Pesticide B has a steeper slope near the middle of the curve.

Refer to the figure below.

14. [Skill: 2.B | Topic: 8.13] Scientists tested a noncarcinogenic industrial solvent for its effect on tadpole development. The dose-response curve shows the percentage of tadpoles with abnormal development at different solvent concentrations. Based on the curve, which statement best identifies the threshold and its regulatory relevance?

(A)The threshold is the concentration at which 50% of tadpoles show abnormal development; it is used to calculate LD50.(B)The threshold is the lowest concentration at which abnormal development begins to increase above 0%; regulators can use it (with a safety factor) to set an allowable exposure limit.(C)The threshold is the concentration at which 100% of tadpoles show abnormal development; it indicates the safest concentration for exposure.(D)There is no threshold because any exposure to a toxic chemical causes harm; therefore the curve cannot be used to set any exposure limit.

15. [Skill: 2.A | Topic: 8.13] A stream near an agricultural area is contaminated with dissolved copper from runoff. A toxicity test exposed groups of 20 juvenile fish to different copper concentrations for 96 hours. Results are shown in the table. Copper concentration (mg/L): 0, 2, 4, 6, 8 Number dead (out of 20): 0, 2, 8, 14, 19 Assuming mortality increases approximately linearly between 4 mg/L and 6 mg/L, what is the approximate LD50 for copper in this test?

(A)About 3.0 mg/L(B)About 4.7 mg/L(C)About 5.5 mg/L(D)About 6.0 mg/L

Refer to the figure below.

16. [Skill: 4.A | Topic: 8.14] A public health department investigates whether air pollution is associated with respiratory illness. The department collects the following data for 6 weeks in the same city. [Image Cue]: Line graph, "Weekly Average Tropospheric Ozone vs. Emergency Room (ER) Respiratory Visits". X-axis: Week (1–6). Left Y-axis: Tropospheric ozone (ppb). Right Y-axis: ER respiratory visits (number of visits). Data points (ozone ppb by week): 35, 40, 55, 60, 45, 50. Data points (ER visits by week): 80, 85, 120, 130, 95, 105. Key trend: ER visits generally increase during weeks with higher ozone. Which of the following best explains why it can still be difficult to establish a definitive cause-and-effect relationship between tropospheric ozone levels and the increase in respiratory ER visits in the city?

(A)Higher ozone concentrations can occur at the same time as other factors (such as particulate matter, allergens, smoking rates, or viral infections) that also affect respiratory health, making it difficult to isolate ozone as the single cause.(B)Tropospheric ozone is not associated with respiratory effects; it only affects aquatic organisms, so the observed pattern must be coincidental.(C)Ozone levels cannot be measured reliably in urban areas, so the data are not usable for any conclusions.(D)Because the data show a positive correlation, ozone must be the direct cause of increased respiratory illness in the city.

17. [Skill: 1.A | Topic: 8.14] A state environmental agency releases a summary describing several recent public health concerns: • Community A reported an outbreak of severe intestinal illness after heavy rain caused overflow from a wastewater system into a nearby river used for recreation. • Community B reported multiple cases of a rare cancer among workers who renovated an older building without specialized protective equipment. • Community C issued air-quality alerts during several hot, sunny afternoons, and local clinics noted more patients with coughing and worsened asthma symptoms. Which of the following options correctly links each community’s health concern to the most likely pollutant source?

(A)A: untreated sewage in waterways; B: asbestos exposure; C: elevated tropospheric ozone(B)A: elevated tropospheric ozone; B: untreated sewage in waterways; C: asbestos exposure(C)A: asbestos exposure; B: elevated tropospheric ozone; C: untreated sewage in waterways(D)A: agricultural fertilizer runoff; B: lead paint exposure; C: stratospheric ozone depletion

Refer to the figure below.

18. [Skill: 4.A | Topic: 8.15] A public health agency tracked a mosquito-borne viral disease in a mountainous region over 15 years. The agency noted that the disease had historically been absent above 1,500 m elevation. [Image Cue]: Line graph, "Temperature Change and Disease Cases at High Elevation (1,500–2,000 m)", x-axis = Year (2010–2024), left y-axis = Mean summer temperature (°C), right y-axis = Reported disease cases (cases per 100,000). Key trend: mean summer temperature increases from about 18°C to 21°C; reported cases increase from ~0–1 to ~25–30, with the rise in cases lagging slightly behind the temperature increase. Which of the following best explains the most likely cause of the increase in disease cases at higher elevations?

(A)Warming temperatures allow mosquito vectors to survive and reproduce at higher elevations, expanding disease transmission into areas where it was previously uncommon.(B)Higher elevation communities develop stronger immune systems over time, leading to higher reported disease cases due to improved detection.(C)Increased ultraviolet radiation at higher elevations directly increases viral replication rates inside humans, causing more infections.(D)The virus becomes less adapted to humans as temperatures increase, leading to more severe symptoms and therefore more reported cases.

19. [Skill: 1.A | Topic: 8.15] A nongovernmental organization (NGO) is designing a health intervention for a low-income community in sub-Saharan Africa. The community has (1) frequent diarrheal disease outbreaks during the rainy season and (2) high rates of malaria. Local observations include: - Many households collect drinking water from a river that receives untreated sewage upstream. - Open ditches and uncovered containers create areas of standing water near homes. Which pair of interventions would most directly address the primary environmental transmission pathways for BOTH health problems described?

(A)Distribute insecticide-treated bed nets and drain/cover sources of standing water near homes.(B)Build or improve sanitary waste disposal and provide reliable access to treated (filtered/chlorinated) drinking water.(C)Build or improve sanitary waste disposal and provide reliable access to treated (filtered/chlorinated) drinking water; AND distribute insecticide-treated bed nets and reduce standing water near homes.(D)Encourage residents to boil food thoroughly and switch to drought-tolerant crops to reduce exposure to agricultural pests.

20. **1. [Skill: SP4 (Data Analysis) | Topic: 8.2]** A coastal monitoring station recorded nutrient and dissolved oxygen (DO) data in an estuary before and after a major rainstorm. **Data (surface water):** - **Day 1 (before storm):** Nitrate = 0.4 mg/L; DO = 7.8 mg/L - **Day 5 (after storm):** Nitrate = 3.2 mg/L; DO = 2.1 mg/L Within a week after the storm, residents reported fish kills in the estuary. Which of the following best explains the most likely cause of the low DO conditions?

(A)Nutrient runoff increased algal growth, and decomposition of the excess biomass increased oxygen demand, lowering DO.(B)Warmer stormwater raised water temperature, and warmer water always contains more dissolved oxygen, increasing fish mortality.(C)Sediment runoff increased water clarity, increasing photosynthesis and causing DO to drop sharply.(D)Hydrocarbons from an oil spill coated fish gills, directly lowering DO in the water column.

21. **2. [Skill: SP4 (Data Analysis) | Topic: 8.2]** A researcher measured mercury concentrations in organisms from the same aquatic food web. **Measured mercury concentrations (ppm):** - Water: 0.0002 ppm - Phytoplankton: 0.02 ppm - Zooplankton: 0.10 ppm - Small fish: 0.60 ppm - Large predatory fish: 2.5 ppm Which of the following best explains both (i) why mercury concentrations increase at higher trophic levels and (ii) why mercury in aquatic systems can be especially toxic?

(A)Mercury biomagnifies because consumers ingest contaminated prey; in water, bacteria convert elemental mercury into methylmercury, which is highly toxic.(B)Mercury biomagnifies because organisms excrete mercury more quickly at higher trophic levels; elemental mercury is the most toxic form because it is unstable.(C)Mercury concentrations increase because mercury is diluted as it moves up the food chain; bacteria convert methylmercury into elemental mercury, reducing toxicity.(D)Mercury concentrations increase because larger fish absorb mercury directly from water through gills; mercury is toxic primarily because it lowers dissolved oxygen levels.

Refer to the figure below.

22. [Skill: 2.A | Topic: 8.3] A research team sampled water from three sites along a river: Site 1 (upstream of a wastewater treatment plant), Site 2 (immediately downstream of the plant), and Site 3 (20 km downstream). The team measured the concentration of ethinylestradiol (a synthetic estrogen used in oral contraceptives) and recorded the percent of male fish exhibiting intersex characteristics (presence of egg cells in testicular tissue). [Image Cue]: Scatter plot, "Intersex Characteristics vs. Ethinylestradiol Concentration"; x-axis: Ethinylestradiol concentration (ng/L) for Sites 1–3; y-axis: Percent of sampled male fish with intersex characteristics (%). Data trend: Site 1 has near 0 ng/L and ~0% intersex; Site 2 has highest concentration and highest % intersex; Site 3 has intermediate concentration and intermediate % intersex. Which of the following best describes why ethinylestradiol is considered an endocrine disruptor in this ecosystem?

(A)It interferes with hormone signaling by mimicking a natural hormone and binding to hormone receptors in fish.(B)It increases dissolved oxygen levels, altering fish respiration rates and causing tissue damage.(C)It acts as a nutrient that stimulates algal blooms, indirectly changing fish sex ratios through eutrophication.(D)It bioaccumulates in fish muscle and directly causes mortality by blocking cellular respiration.

23. [Skill: 1.A | Topic: 8.3] A biologist compares two isolated lakes that are similar in size, temperature, and nutrient levels. The primary difference is that Lake X receives runoff from agricultural fields where an endocrine-disrupting pesticide is applied; Lake Y does not receive this runoff. Over multiple breeding seasons, the biologist observes that in Lake X: - A higher proportion of male fish show feminized secondary sex characteristics. - Egg production per adult female is lower. - A greater fraction of embryos fail to develop normally. Which of the following is the most likely ecological outcome in Lake X over time if the exposure continues?

(A)An increase in fish population size because feminized males will compete less, reducing stress-related mortality.(B)A decrease in fish population size due to reduced reproductive success and developmental abnormalities.(C)A rapid shift to oxygen-depleted conditions because endocrine disruptors directly increase algal photosynthesis rates.(D)An increase in fish species richness because endocrine disruptors create more ecological niches by altering hormone levels.

24. [Skill: 4.B | Topic: 8.4] A county compares water-quality and streamflow conditions in a watershed during similar storm events before and after a 60% reduction in wetland area due to commercial development. The table shows average measurements taken at the same downstream monitoring station. | Condition (same storm intensity) | Peak stream discharge (m^3/s) | Nitrate concentration (mg/L) | |---|---:|---:| | Before wetland reduction | 120 | 2.0 | | After wetland reduction | 190 | 4.5 | Which of the following best explains the changes observed after the wetland reduction?

(A)Wetlands previously increased infiltration and temporary water storage, reducing flood peaks, and they also filtered or transformed nutrients, reducing nitrate concentrations.(B)Wetlands previously increased surface runoff to streams, which lowered flood peaks, and they released nitrates from sediments, which lowered nitrate concentrations.(C)Wetlands previously reduced biodiversity, which decreased decomposition rates and therefore decreased nitrate concentrations, while also increasing flood peaks.(D)Wetlands previously increased evaporation, which reduced flood peaks, and they reduced erosion, which directly removes nitrate from the water column by settling.

25. [Skill: 1.A | Topic: 8.4] A coastal region contains extensive mangrove forests that historically buffered storms and supported local fisheries. Over a decade, the following changes occur: • Portions of mangroves are cleared for waterfront commercial development. • An upstream dam is constructed on a river that previously delivered freshwater and sediment to the coast. • Shrimp harvests increase substantially, and fishing pressure rises in the nearshore area. Which of the following identifies human activities that threaten wetlands and mangroves and a likely ecological outcome most consistent with the scenario?

(A)Commercial development, dam construction, and overfishing; increased coastal flooding and loss of nursery habitat that supports fish populations.(B)Commercial development, dam construction, and overfishing; increased primary productivity in mangroves due to higher nutrient delivery from the dam and increased shoreline stability.(C)Dam construction only; increased sediment delivery to mangroves and expansion of mangrove habitat into deeper coastal waters.(D)Overfishing only; increased mangrove area due to reduced grazing pressure on mangrove roots and decreased storm-surge risk.

Refer to the figure below.

26. 1. [Skill: 4.A | Topic: 8.5] A lake was monitored for one week before and two weeks after a major rainstorm. The storm caused runoff from nearby land to enter the lake. The table shows average measurements taken at the same location and depth. [Image Cue]: Data table, "Lake Water Quality Before and After Storm Runoff". Columns: Time period; Nitrate (mg/L); Phosphate (mg/L); Algal biomass (chlorophyll-a, µg/L); Dissolved oxygen (mg/L). Rows: Week before storm: 0.4, 0.03, 6, 8.5. Week 1 after storm: 1.8, 0.18, 28, 4.2. Week 2 after storm: 1.2, 0.12, 10, 2.8. Key trend: Nutrients spike after storm, algal biomass peaks in week 1 then declines, dissolved oxygen decreases steadily into hypoxic levels. Several fish kills were observed during Week 2 after the storm. Which of the following best explains the fish kills observed in Week 2?

(A)Nutrient enrichment caused an algal bloom; when algae died, microbial decomposition consumed dissolved oxygen, creating hypoxic conditions.(B)Runoff increased water salinity, causing fish to experience osmotic stress and die.(C)Runoff lowered the pH of the lake, directly dissolving fish gill tissue and causing immediate mortality.(D)Runoff warmed the lake, increasing the dissolved oxygen concentration and leading to gas bubble disease in fish.

27. 2. [Skill: 1.A | Topic: 8.5] A coastal estuary receives water from a river that drains a watershed containing both farmland and a city. Over the past decade, the estuary has experienced seasonal hypoxic conditions. A local government is considering four actions to reduce eutrophication and hypoxia in the estuary: I. Upgrade the city’s wastewater treatment plant to remove more nitrogen and phosphorus before discharge. II. Require farmers to apply more fertilizer each spring to increase crop yields. III. Install vegetated buffer strips between crop fields and nearby streams. IV. Replace phosphate-containing detergents with phosphate-free detergents in the city. Which set of actions would most directly reduce the anthropogenic nutrient inputs that cause eutrophication in the estuary?

(A)I and II only(B)I and III only(C)II and IV only(D)III and IV only

28. [Skill: 4.A | Topic: 8.6] A coal-fired power plant uses once-through cooling and discharges heated water into a nearby river. Students measure water temperature and dissolved oxygen (DO) upstream and 2 km downstream of the discharge point. Data collected at 3:00 p.m. on the same day: - Upstream: 18°C; DO = 9.2 mg/L - Downstream: 26°C; DO = 6.3 mg/L Soon after, anglers report that several fish species are crowding near the river surface downstream. Which of the following best explains the fish behavior observed downstream?

(A)The warmer downstream water holds less dissolved oxygen, so fish move toward the surface where oxygen from the atmosphere is more available.(B)The warmer downstream water holds more dissolved oxygen, so fish move toward the surface to avoid oxygen toxicity.(C)The warmer downstream water causes dissolved oxygen to increase, so fish move toward the surface to avoid higher temperatures.(D)The downstream dissolved oxygen is lower because the river is colder there, which reduces oxygen solubility and stresses fish.

Refer to the figure below.

29. [Skill: 1.A | Topic: 8.6] A manufacturing facility releases waste heat into a freshwater lake during summer months. The lake supports trout, which require relatively high levels of dissolved oxygen (DO). [Image Cue]: Line graph, "Dissolved Oxygen vs. Water Temperature"; x-axis: Water temperature (°C) from 0 to 30; y-axis: Dissolved oxygen (mg/L) from 0 to 14; key trend: DO decreases as temperature increases (e.g., ~14 mg/L at 0°C, ~9 mg/L at 20°C, ~7 mg/L at 30°C). Based on the relationship shown, which of the following outcomes is most likely in the lake near the discharge site?

(A)Trout populations will likely decline near the discharge site because warmer water lowers dissolved oxygen availability needed for respiration.(B)Trout populations will likely increase near the discharge site because warmer water increases dissolved oxygen availability needed for respiration.(C)Algal growth will immediately stop near the discharge site because warmer water prevents photosynthesis in aquatic producers.(D)Aquatic organisms will be unaffected because temperature changes do not influence dissolved oxygen concentrations in water.

Refer to the figure below.

30. [Skill: 4.A | Topic: 8.7] [Image Cue]: Bar graph, "DDT Concentration by Trophic Level in a Coastal Food Web". X-axis: Trophic level (Phytoplankton, Zooplankton, Small Fish, Large Fish, Seabird). Y-axis: DDT concentration (ng/g lipid). Data (approx.): Phytoplankton 0.2, Zooplankton 1, Small Fish 8, Large Fish 40, Seabird 120. Trend: concentration increases sharply at higher trophic levels. A researcher measured DDT concentrations in organisms from a coastal ecosystem and normalized the results to lipid (fat) content, as shown in the graph. Which of the following best explains the pattern shown?

(A)DDT is water-soluble, so it is diluted as organisms move to higher trophic levels.(B)DDT is fat-soluble, so it biomagnifies as predators consume many contaminated prey.(C)DDT causes eutrophication, which increases biomass at higher trophic levels and raises concentrations.(D)DDT is a nutrient required by top predators, so it is stored at higher concentrations in their tissues.

31. [Skill: 1.A | Topic: 8.7] A monitoring station in northern Alaska detects PCBs in snowpack and in the fatty tissues of Arctic foxes, even though PCBs have not been manufactured locally. Investigators determine that prevailing winds often arrive from industrial regions thousands of kilometers to the south. Which statement best explains why PCBs can be found far from their original source regions?

(A)PCBs rapidly biodegrade into harmless products, allowing them to spread widely without impacting organisms.(B)PCBs are synthetic carbon-based chemicals that persist and can be transported long distances by wind and water before being redeposited.(C)PCBs are heavy metals that sink quickly in the atmosphere and therefore accumulate only near factories.(D)PCBs are highly reactive gases that break down quickly, so they can only reach the Arctic through animal migration.

Refer to the figure below.

32. [Skill: 4A | Topic: 8.8] A scientist measures the concentration of methylmercury (a persistent toxin) in a freshwater food web. [Image Cue]: Data table, "Methylmercury Concentration Across Trophic Levels". Columns: "Organism/Medium" and "Methylmercury concentration (ppm)". Rows/data: Water: 0.00002 ppm; Phytoplankton: 0.04 ppm; Zooplankton: 0.20 ppm; Small fish: 0.80 ppm; Large predatory fish: 2.5 ppm; Osprey (top carnivore): 12 ppm. Key trend: concentration increases with trophic level. Which of the following best explains the pattern shown in the data?

(A)Biomagnification occurs because the toxin becomes increasingly concentrated per unit of body tissue at higher trophic levels as predators consume many contaminated prey.(B)Biomagnification occurs because water-soluble toxins are selectively stored in fatty tissues, leading to higher concentrations in organisms at each trophic level.(C)Bioaccumulation occurs because toxins only increase in concentration when organisms consume other organisms at higher trophic levels.(D)Bioaccumulation occurs because persistent toxins are diluted at higher trophic levels due to energy loss between trophic levels.

33. [Skill: 1A | Topic: 8.8] A long-banned pesticide is discovered in sediment of a coastal marsh. The chemical is persistent and fat-soluble. Small invertebrates in the marsh have low concentrations of the pesticide, but fish-eating birds nesting nearby show reproductive failure and produce many eggs that crack during incubation. Local residents are concerned about health risks from eating fish caught in the marsh. Which of the following best connects the chemical’s properties and the observed impacts?

(A)Because the pesticide is persistent and fat-soluble, it can bioaccumulate in organisms and biomagnify in the food web, contributing to eggshell thinning in top carnivores and potential human health effects on reproductive, nervous, and circulatory systems.(B)Because the pesticide is persistent and fat-soluble, it quickly breaks down in warm-blooded animals, preventing biomagnification; the cracked eggs are most likely caused by reduced dissolved oxygen in the marsh.(C)Because the pesticide is persistent, it will biomagnify only in producers; higher trophic levels will have lower concentrations, so the bird reproductive failure is most likely unrelated to the pesticide.(D)Because the pesticide is fat-soluble, it stays dissolved in water and is readily excreted, so any health impacts in humans would be limited to short-term digestive irritation.

Refer to the figure below.

34. **1.** [Skill: 2.B | Topic: 8.9] A county is building a modern sanitary municipal landfill to reduce contamination of nearby wells. The engineering plan includes multiple layers and collection systems. [Image Cue]: Diagram, "Cross-section of a sanitary municipal landfill," showing (from bottom to top) compacted soil, an impermeable bottom liner, a perforated pipe network above the liner leading to a collection tank (leachate collection), a thick layer of compacted waste, a cap (cover) on top, a vertical well/piping system that draws gas to an energy facility (methane collection), and a storm water diversion/collection channel around the landfill. Which component is specifically designed to collect contaminated liquid that percolates through the waste and thereby reduce groundwater pollution risk?

(A)Storm water collection system(B)Leachate collection system(C)Methane collection system(D)Cap (cover) layer

35. **2.** [Skill: 4.A | Topic: 8.9] A city currently landfills most municipal solid waste. The city council is considering two alternatives: - **Option 1:** Build a high-temperature waste incinerator. - **Option 2:** Contract with a company that transports baled waste overseas for disposal, including disposal at sea. A briefing memo provides the following claims: - Claim I: “High-temperature combustion can greatly reduce the volume of solid waste, but air emissions must be controlled.” - Claim II: “Disposal at sea can create large accumulations of floating trash and harm wildlife.” Which choice correctly links each option with the environmental effect that most directly supports the claims?

(A)Option 1: Increased leachate formation; Option 2: Reduced wildlife entanglement(B)Option 1: Release of air pollutants; Option 2: Wildlife ingestion/entanglement in debris(C)Option 1: Formation of floating trash islands; Option 2: Capture of methane for energy(D)Option 1: Reduced air pollution compared with landfills; Option 2: Elimination of solid waste volume

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