Unit 8 · 7–10% of the exam Beta

Unit 8 practice test: Aquatic and Terrestrial Pollution

12 exam-style questions from the unit, free, with an explanation for every option. Most have four answer choices, as on the real exam, and a few ask you to type a calculation with its units; sets share one data table, graph, model or passage.

Covers: Sources of Pollution; Human Impacts on Ecosystems; Endocrine Disruptors; Human Impacts on Wetlands and Mangroves; Eutrophication; Thermal Pollution; Persistent Organic Pollutants (POPs); Bioaccumulation and Biomagnification; Solid Waste Disposal; Waste Reduction Methods; Sewage Treatment; Lethal Dose 50% (LD50); Dose Response Curve; Pollution and Human Health; Pathogens and Infectious Diseases.

Data

Mercury in one species of fish by age

Average methylmercury in the muscle of walleye from one lake, by age (invented data for practice). Advisories often limit meals of fish above about 0.3 ppm.
Fish age (years)Average length (cm)Methylmercury (ppm)
2250.08
4380.18
6470.31
8540.46
10600.62

1. What happens to methylmercury in the walleye as they age?

  1. It falls as the fish get older
  2. It stays about the same from age to age
  3. It rises as the fish get older
  4. It rises until 6 years, then falls
Show the answer

It rises with age, from 0.08 ppm at 2 years to 0.62 ppm at 10 years: older fish have had more years to take in and store mercury.

  • It falls as the fish get older: The values rise with age.
  • It stays about the same from age to age: It increases nearly eightfold.
  • Correct: It rises as the fish get older: Right: from 0.08 to 0.62 ppm.
  • It rises until 6 years, then falls: It keeps rising at 8 and 10 years.

2. The walleye data show one species at one level of the food chain. Which process do they illustrate?

  1. Biomagnification: rise from one trophic level to the next
  2. Bioaccumulation: build-up in one organism over its life
  3. Eutrophication: nutrients causing algal blooms
  4. Thermal pollution: heat lowering oxygen
Show the answer

Bioaccumulation is the build-up of a substance in one organism over its lifetime, faster than it is removed. Biomagnification is the rise from one trophic level to the next.

  • Biomagnification: rise from one trophic level to the next: The table compares ages of one species, not trophic levels.
  • Correct: Bioaccumulation: build-up in one organism over its life: Right: same species, rising with age.
  • Eutrophication: nutrients causing algal blooms: Mercury is not a nutrient.
  • Thermal pollution: heat lowering oxygen: The data are about mercury, not temperature.

3. A state issues advice for anglers on this lake. Which advice best fits the data?

  1. Eat smaller walleye and limit meals of large ones
  2. Eat the largest walleye, since they are the healthiest
  3. Eat as much walleye as you like, of any size
  4. Cook walleye longer to remove the mercury
Show the answer

Walleye from about 6 years (about 47 cm) and older are at or above 0.3 ppm, so limiting meals of large walleye and favoring smaller ones lowers mercury intake.

  • Correct: Eat smaller walleye and limit meals of large ones: Right: fish above about 47 cm reach 0.3 ppm or more.
  • Eat the largest walleye, since they are the healthiest: The largest fish carry the most mercury.
  • Eat as much walleye as you like, of any size: The older fish exceed the advisory level.
  • Cook walleye longer to remove the mercury: Cooking does not remove methylmercury, which is bound in muscle.

Data

Phosphorus and algae in five lakes

Total phosphorus and summer algae in five lakes in one region (invented data for practice)
LakeLand around the lakeTotal phosphorus (µg/L)Summer algae (chlorophyll, µg/L)Water clarity (m)
Crystalforest827.5
Birchforest and cabins1554.8
Millpasture40181.9
Cornrow crops85450.8
Towncity and lawns110620.5

4. What relationship do the five lakes show between phosphorus and algae?

  1. More phosphorus goes with less algae
  2. Phosphorus and algae are not related
  3. More phosphorus goes with more algae
  4. Algae are highest in the forest lakes
Show the answer

Lakes with more phosphorus have more algae: from 8 µg per L and 2 µg per L of chlorophyll in Crystal Lake to 110 and 62 in Town Lake.

  • More phosphorus goes with less algae: Town Lake has the most of both.
  • Phosphorus and algae are not related: They rise together across all five lakes.
  • Correct: More phosphorus goes with more algae: Right: algae rise steadily with phosphorus.
  • Algae are highest in the forest lakes: The forest lakes have the least algae.

5. Why does water clarity fall as phosphorus rises?

  1. Phosphorus is a dark powder that stains the water
  2. More phosphorus feeds algae that cloud the water
  3. Clear lakes are deeper, so they hold less phosphorus
  4. Fish stir up the bottom in lakes with more phosphorus
Show the answer

More phosphorus feeds more algae, which cloud the water. Crystal Lake is clear to 7.5 m; Town Lake, green with algae, only to 0.5 m.

  • Phosphorus is a dark powder that stains the water: Dissolved phosphate is not what clouds the water; the algae are.
  • Correct: More phosphorus feeds algae that cloud the water: Right: clarity falls as algae rise.
  • Clear lakes are deeper, so they hold less phosphorus: Depth is not in the table; the link is through algae.
  • Fish stir up the bottom in lakes with more phosphorus: The table gives no fish data.

6. Which lake is most likely oligotrophic?

  1. Crystal Lake, clear and low in nutrients
  2. Town Lake, which has the most phosphorus
  3. Corn Lake, beside fields of row crops
  4. Mill Lake, beside grazed pasture land
Show the answer

An oligotrophic lake is low in nutrients, with little algae and clear water. Crystal Lake has the least phosphorus (8), least algae (2) and clearest water (7.5 m).

  • Correct: Crystal Lake, clear and low in nutrients: Right: low nutrients, little algae, high clarity.
  • Town Lake, which has the most phosphorus: High nutrients and algae make it eutrophic, not oligotrophic.
  • Corn Lake, beside fields of row crops: Its high phosphorus and algae make it eutrophic.
  • Mill Lake, beside grazed pasture land: Its phosphorus and algae are moderate to high.

7. Why have laws such as the Clean Water Act cut point-source pollution more than nonpoint pollution?

  1. Nonpoint pollution is harmless, so laws ignore it
  2. Point sources are natural, so they shrink over time
  3. One outlet can be measured and inspected
  4. Nonpoint sources are found in other countries
Show the answer

A point source can be measured at one outlet, given a permit with limits, and checked. Nonpoint pollution comes from many owners and places, so it is hard to measure or assign.

  • Nonpoint pollution is harmless, so laws ignore it: Nonpoint pollution is now the largest source of water pollution.
  • Point sources are natural, so they shrink over time: Point sources are human outlets, such as pipes.
  • Correct: One outlet can be measured and inspected: Right: that is what makes point sources easier to control.
  • Nonpoint sources are found in other countries: Nonpoint sources are everywhere, including the United States.

8. Coral reefs are also harmed by sediment from coastal construction and farms. How does sediment harm them?

  1. It raises the water temperature to bleaching levels
  2. It adds oxygen that the coral is unable to use
  3. It makes the water too fresh for coral
  4. It blocks light from the coral's algae
Show the answer

Sediment clouds the water, blocking the sunlight the coral's algae need for photosynthesis, and it can settle on and smother the coral.

  • It raises the water temperature to bleaching levels: Sediment does not cause bleaching heat.
  • It adds oxygen that the coral is unable to use: Sediment does not add oxygen.
  • It makes the water too fresh for coral: Sediment does not lower salinity.
  • Correct: It blocks light from the coral's algae: Right: less light means less food for the coral.

9. Which of these is a known endocrine disruptor?

  1. Carbon monoxide from car exhaust
  2. Radon from rock under homes
  3. Atrazine, a widely used herbicide
  4. Sulfur dioxide from coal plants
Show the answer

Atrazine, one of the most widely used herbicides, is listed by the National Institute of Environmental Health Sciences (NIEHS) among endocrine disruptors; studies of its effects on frog sex hormones differ in how large the effect is. BPA and phthalates in some plastics are other examples.

  • Carbon monoxide from car exhaust: CO blocks oxygen in the blood; it is not a hormone disruptor.
  • Radon from rock under homes: Radon is radioactive; its harm is lung cancer.
  • Correct: Atrazine, a widely used herbicide: Right: the NIEHS lists atrazine among endocrine disruptors.
  • Sulfur dioxide from coal plants: SO2 irritates lungs and forms acid; it is not a hormone mimic.

10. Which human activity is a major cause of mangrove loss in tropical countries?

  1. Planting coral reefs on mudflats
  2. Building ski resorts in mountain forests
  3. Clearing mangroves for shrimp ponds
  4. Melting glaciers on high peaks
Show the answer

Large areas of mangrove have been cleared for shrimp farms (aquaculture ponds), along with coastal building, farming and cutting for wood.

  • Planting coral reefs on mudflats: Coral does not replace mangroves, and people do not plant it on mudflats.
  • Building ski resorts in mountain forests: Mangroves grow on tropical coasts, not mountains.
  • Correct: Clearing mangroves for shrimp ponds: Right: shrimp aquaculture has replaced large areas of mangrove.
  • Melting glaciers on high peaks: Glaciers are far from mangrove coasts.

11. How does paving a watershed add thermal pollution to its streams?

  1. Pavement adds metals that heat the water chemically
  2. Rain warms on hot pavement, then flows in
  3. Pavement blocks rain, so streams dry up and cool
  4. Paved roads release radiation that warms water
Show the answer

Dark pavement and roofs heat up in the sun. Rain running off them warms, carrying that heat into streams. Removing shade trees along banks also warms streams.

  • Pavement adds metals that heat the water chemically: The warming is from heat transfer, not chemistry.
  • Correct: Rain warms on hot pavement, then flows in: Right: hot surfaces heat the runoff.
  • Pavement blocks rain, so streams dry up and cool: Pavement sends more runoff to streams, and it is warm.
  • Paved roads release radiation that warms water: Pavement does not release radiation that heats streams.

12. Why do POPs build up in the fat of animals rather than being passed out in urine?

  1. They are too large to fit inside cells
  2. Animals use them as a source of energy
  3. They dissolve in fat, not water
  4. They turn into bone over time
Show the answer

POPs dissolve in fat, not water. Urine removes water-soluble substances, so fat-soluble POPs stay stored in fatty tissue.

  • They are too large to fit inside cells: They are small molecules; the issue is fat solubility.
  • Animals use them as a source of energy: POPs are not used for energy.
  • Correct: They dissolve in fat, not water: Right: being fat-soluble keeps them in the body.
  • They turn into bone over time: POPs are stored mainly in fat, not built into bone.

Keep going

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Practice has every question in the unit, with feedback after each one; the notes for every topic are free. Other units: Unit 1 · Unit 2 · Unit 3 · Unit 4 · Unit 5 · Unit 6 · Unit 7 · Unit 8 · Unit 9.