Answer Key & Rubric

AP Environmental Science — Full Practice Exam: Answer Key

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Section I: Multiple-Choice Answer Key with Explanations

Unit 1: Ecosystems (Q1–8)

1. 100 kcal. Applying the 10% rule: producers = 10,000 kcal → primary consumer = 1,000 kcal → secondary consumer = 100 kcal.

2. Phosphorus cycle. Unlike carbon, nitrogen, sulfur, and water, phosphorus has no significant atmospheric reservoir. It cycles through rocks, soil, water, and organisms.

3. Denitrification. Denitrifying bacteria convert nitrates back to N2 gas in anaerobic conditions. Nitrification converts ammonia to nitrate. Nitrogen fixation converts N2 to ammonia.

4. The energy available to herbivores after plants have used some energy for their own respiration. NPP = GPP − respiration. It represents the energy stored in plant tissue available to consumers.

5. Producers (primary producers). Energy pyramids are always upright — producers have the most energy, and energy decreases at each successive level.

6. Cellular respiration. All organisms (plants, animals, bacteria) release CO2 through respiration. Photosynthesis removes CO2.

7. Rocks/minerals (sedimentary rock). Phosphorus is found primarily in phosphate rock. It enters the cycle through weathering.

8. Recycling nutrients back into the soil. Decomposers break down dead organic matter, returning essential nutrients (nitrogen, phosphorus, carbon) to the soil for producers to use.

Unit 2: Biodiversity (Q9–16)

9. Ecosystem diversity. Ecosystem diversity refers to the variety of habitats, communities, and ecological processes within a geographic area.

10. A small island far from the mainland. Small islands have higher extinction rates; islands far from the mainland have lower immigration rates. This combination yields the lowest species richness.

11. Habitat loss. The destruction, degradation, and fragmentation of habitat is the single greatest threat to biodiversity worldwide.

12. A keystone species. Keystone species have a disproportionately large effect on community structure relative to their abundance (e.g., sea otters, wolves, beavers).

13. Community-based conservation. In situ strategies engage local communities in sustainable resource management, providing economic incentives for conservation.

14. Harm (or "take") endangered species or destroy their critical habitat. The ESA prohibits the "take" of listed species, which includes harassing, harming, pursuing, hunting, shooting, wounding, killing, trapping, capturing, or collecting.

15. Found naturally in only one geographic area. Endemic species have restricted ranges and are particularly vulnerable to extinction because they cannot be found anywhere else.

16. Zebra mussels. Native to the Caspian Sea region, zebra mussels were introduced to the Great Lakes in the 1980s via ballast water. They outcompete native species, clog water intake pipes, and alter ecosystems.

Unit 3: Populations (Q17–28)

17. Carrying capacity. K represents the maximum population size that the environment can sustain indefinitely.

18. Type I. Type I survivorship curves show high survival early and late in life, with most mortality occurring in old age. Characteristic of K-selected species with parental care.

19. 20 per 1,000, or 2.0%. RNI = CBR − CDR = 30 − 10 = 20 per 1,000 = 2.0%.

20. Disease transmission. Disease spreads more easily in dense populations, making it density-dependent. Natural disasters and weather events are density-independent.

21. r-selected. r-selected species produce many offspring with little parental care, short lifespans, and rapid maturation. Examples: insects, rodents, dandelions.

22. Birth rates and death rates as a country develops economically. The DTM describes the shift from high birth/death rates (Stage 1) through rapid growth (Stage 2–3) to low birth/death rates (Stage 4–5).

23. Rapid population growth in the future. The wide base means many young people who will reach reproductive age, ensuring continued population growth.

24. The average number of children a woman will bear during her lifetime. Replacement-level TFR is approximately 2.1 in developed countries.

25. 35 years. Using the Rule of 70: Doubling time = 70 / 2 = 35 years.

26. Stage 2. In Stage 2, death rates drop rapidly due to improved medicine, sanitation, and food supply, while birth rates remain high, causing rapid growth.

27. Density-dependent factors. Predator-prey cycles occur because predation is density-dependent: more prey → more predators → fewer prey → fewer predators.

28. 1,080 individuals per year. dN/dt = 0.3 × 1,000 × [(5,000 − 1,000)/5,000] = 300 × 0.8 = 240. Correction: Using the logistic equation: dN/dt = rN × (K−N)/K = 0.3 × 1000 × (5000−1000)/5000 = 300 × 0.8 = 240 individuals per year.

Unit 4: Earth Systems (Q29–40)

29. Slide past each other horizontally. Transform boundaries involve horizontal movement. No crust is created or destroyed. Example: San Andreas Fault.

30. A horizon. The A horizon (topsoil) is the most productive layer, rich in humus, nutrients, microorganisms, and plant roots.

31. Clockwise. The Coriolis effect deflects water to the right in the Northern Hemisphere, creating clockwise rotation of ocean gyres.

32. Weaken or reverse. During El Niño, trade winds weaken, allowing warm water to flow eastward toward South America.

33. Metamorphic rock. Metamorphic rocks form from existing rocks transformed by heat and pressure. Igneous rocks form from cooling magma; sedimentary from compacted sediments.

34. Temperature decreasing with altitude. The troposphere has a lapse rate of approximately 6.5°C per km. Weather occurs here.

35. Sulfide minerals in exposed rock reacting with water and oxygen. Pyrite (FeS2) oxidizes to form sulfuric acid (H2SO4), which contaminates water.

36. Fresh water. Water is renewable through the water cycle. Fossil fuels, minerals, and topsoil are nonrenewable on human timescales (though water can be overdrawn locally).

37. Tropical rainforest regions. Shifting cultivation is practiced in tropical areas where nutrient-poor soils require farmers to move periodically.

38. Stratosphere. The ozone layer is located in the stratosphere (15–50 km altitude), where it absorbs harmful UV radiation.

39. A desert or arid climate. At 30°N, the descending air of the Hadley cell creates high-pressure zones with dry conditions. Cold ocean currents on western coasts further reduce moisture.

40. Descending air at 30°N and 30°S creates high-pressure zones with dry conditions. In the Hadley cell, air rises at the equator and sinks at ~30° latitude, creating desert conditions.

Unit 5: Land and Water Use (Q41–52)

41. Biomagnification. Biomagnification is the increase in concentration of a substance at each trophic level due to the 10% rule and fat-soluble toxins.

42. Drip irrigation. Drip irrigation delivers water directly to plant roots with 90–95% efficiency. Flood (~50%), spray (~75%).

43. Clear-cutting. All trees are removed, causing maximum habitat destruction and soil erosion.

44. It requires wild-caught fish for feed, resulting in a net protein loss. Carnivorous farmed fish need fishmeal, meaning more wild fish are caught to produce less farmed fish.

45. Crop rotation. Rotating crops reduces pest buildup, maintains soil nutrients, and prevents soil depletion.

46. The National Environmental Policy Act (NEPA). NEPA requires environmental impact assessments for federally funded or permitted projects.

47. Loss of crop genetic diversity. High-yield varieties replaced diverse traditional varieties, making crops more vulnerable to pests and disease.

48. Low-density development spreading into rural areas, automobile dependency, and loss of farmland.

49. Desertification, soil compaction, and loss of native vegetation. Overgrazing exceeds the land's carrying capacity, degrading the ecosystem.

50. Bottom trawling. Trawls dragged along the seafloor destroy benthic habitats.

51. Approximately 70%. Agriculture accounts for the largest share of global freshwater withdrawals.

52. It combines biological, cultural, and limited chemical controls. IPM uses a multifaceted approach to minimize pesticide use while managing pest populations.

Unit 6: Energy Resources (Q53–64)

53. Coal. Coal has the highest carbon content per unit energy (~100 kg CO2/million BTU vs. 56 for natural gas).

54. Approximately 1.3:1. Corn ethanol barely produces more energy than is invested in its production. Wind is ~18:1, coal ~30:1.

55. Geothermal energy. Geothermal provides continuous, weather-independent baseload power, unlike solar and wind.

56. Carbon capture and storage (CCS). CCS captures CO2 from emission sources and stores it underground in geological formations.

57. Intermittency and visual/noise impact. Wind doesn't blow consistently; turbines can cause visual and noise complaints and bird/bat mortality.

58. Normal operation. Nuclear plants produce very little CO2 while operating. Most emissions come from construction and uranium processing.

59. Energy storage. Pumped storage acts like a giant battery, storing energy during low-demand periods and generating during peak demand.

60. LED bulbs. LEDs use ~75% less energy than incandescent bulbs and last much longer.

61. 15–25%. Solar PV capacity factors are limited by daylight hours, cloud cover, and seasonal variation.

62. Natural gas. Natural gas emits ~45% less CO2 than coal per unit energy, making it a transitional fuel.

63. It achieves 80–90% total efficiency by capturing waste heat. Conventional plants waste ~60% of energy as heat; cogeneration uses that heat for heating.

64. Contamination of groundwater with fracking chemicals and methane leaks. Fracking can also cause small seismic events and requires large water volumes.

Unit 7: Atmospheric Pollution (Q65–72)

65. Secondary pollutant. Ozone is not emitted directly; it forms from reactions between NOx and VOCs in sunlight.

66. Industrial smog (London-type). Formed from SO2 + particulates + moisture + cold temperatures. Common in coal-burning cities in winter.

67. It traps pollutants near the surface, preventing vertical dispersion. Warm air above cool air creates a lid that prevents pollutants from rising and dispersing.

68. Scrubbers. Flue gas desulfurization scrubbers spray limestone slurry to capture SO2 before it leaves the stack.

69. Developing countries. Biomass (wood, dung) burned indoors for cooking and heating in poorly ventilated homes affects ~3 billion people.

70. Lead (Pb). Lead emissions dropped >99% after leaded gasoline was phased out in the 1970s–1980s.

71. Dry deposition. Acid deposition includes dry particles and gases that settle on surfaces, not just precipitation.

72. Cap-and-trade. The Acid Rain Program set an emissions cap and allowed companies to trade allowances.

Unit 8: Aquatic and Terrestrial Pollution (Q73–78)

73. The amount of oxygen consumed by bacteria to decompose organic matter in water. High BOD indicates polluted water with excess organic waste.

74. Nitrogen. In most marine systems, nitrogen is the limiting nutrient. Phosphorus is typically limiting in freshwater.

75. Clean up contaminated hazardous waste sites. CERCLA establishes liability for polluters and funds cleanup of the most contaminated sites.

76. Source reduction. Preventing waste from being generated is the most preferred strategy, followed by reuse, recycling, composting, incineration, and landfilling.

77. Mercury. Mercury biomagnifies in aquatic food chains. Large predatory fish (tuna, swordfish) accumulate the highest concentrations.

78. Physical processes. Primary treatment uses screening and sedimentation (physical methods) to remove solids.

Unit 9: Global Change (Q79–80)

79. Fluorinated gases (e.g., SF6). Sulfur hexafluoride has a GWP of ~23,500 over 100 years, far exceeding CO2, CH4, and N2O.

80. Well below 2°C above pre-industrial levels, ideally 1.5°C. The Paris Agreement's central goal is to limit warming to these thresholds.

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Section II: Free-Response Scoring Guidelines

Question 1: Design an Investigation (10 points)

(a) — 1 point

• Independent variable: Amount/concentration of nitrogen fertilizer added to the water.
• Dependent variable: Algal growth (measured as chlorophyll concentration, algal biomass, or algal cover).

  (b) — 3 points (1 per element)

• Treatment groups should include at least three levels: no nitrogen (control), low nitrogen, high nitrogen (or similar gradient).
• Control group: water with no added nitrogen fertilizer (to establish baseline algal growth).
• Description of containers, water source, replication (multiple containers per treatment), and measurement timeline.

  (c) — 2 points (1 per variable)

• Temperature, light exposure, water source, initial algal concentration, container size, duration of experiment. (Any two.)

  (d) — 2 points

• Data collected: chlorophyll levels, algal biomass, visual algal cover at regular intervals.
• Analysis: Compare means between treatment groups using statistical tests (t-test, ANOVA). If high-nitrogen treatments show significantly more algal growth than the control, the hypothesis is supported.

  (e) — 2 points

• Limitation: Laboratory conditions may not accurately represent the lake ecosystem (complex interactions, other nutrients, water flow). Address with field monitoring alongside lab experiments.

Question 2: Environmental Problem and Solution (10 points)

(a) — 2 points (1 per cause)

• Thermal expansion of ocean water as it warms.
• Melting of land-based ice (glaciers, ice sheets in Greenland and Antarctica). Note: melting sea ice does not raise sea levels.

  (b) — 2 points (1 per consequence)

• Economic: Loss of tourism revenue from eroded beaches, damage to coastal infrastructure, loss of agricultural productivity from saltwater intrusion, reduced property values.
• Ecological: Loss of coastal wetland habitat (nurseries for fish and shellfish), saltwater intrusion killing mangroves and coastal vegetation, coastal erosion destroying nesting habitat.

  (c) — 2 points (1 per strategy)

• Reduce greenhouse gas emissions: Transition to renewable energy, improve energy efficiency.
• Reforestation/mangrove restoration: Absorb CO2 and protect coastlines.
• Each with explanation and limitation.

  (d) — 2 points (1 per strategy)

• Build sea walls or levees to protect infrastructure from flooding.
• Restore natural barriers (mangroves, barrier islands, wetlands).
• Relocate infrastructure and communities away from vulnerable coastal areas.
• Elevate buildings on stilts.
• Each with explanation.

  (e) — 2 points

• Mitigation addresses the root cause (reducing emissions to slow future sea level rise).
• Adaptation addresses the impacts that are already occurring or cannot be avoided (sea walls, relocation).
• Both are necessary because even with aggressive mitigation, some additional warming and sea level rise is already committed due to greenhouse gases already in the atmosphere.

Question 3: Calculations (10 points)

(a) — 2 points

• Energy needed per hour: 500 MW = 500 MJ/s × 3,600 s/hr = 1,800,000 MJ/hr
• At 35% efficiency, energy input needed: 1,800,000 / 0.35 = 5,142,857 MJ/hr
• Coal burned per hour: 5,142,857 / 25,000 = 205.7 tons/hr

  (b) — 2 points

• CO2 per hour: 205.7 tons coal × 2.5 tons CO2/ton coal = 514.3 tons CO2/hr

  (c) — 2 points

• CO2 per year: 514.3 × 24 × 365 = 4,505,318 tons CO2/year (approximately 4.5 million tons)

  (d) — 1 point

• With 40% removal: 4,505,318 × 0.60 = 2,703,191 tons CO2/year still released

  (e) — 2 points

• Natural gas emits 55% less CO2: 4,505,318 × 0.45 = 2,027,393 tons CO2/year

  (f) — 1 point

• Advantage: Reduced air pollution (less SO2, NOx, particulate matter than coal).
• Disadvantage: Methane leaks during extraction and transport are a potent GHG concern; fracking risks groundwater contamination.