2017
AP Environmental
Science
Sample Student Responses
and Scoring Commentary
Inside:
• Free Response Question 1
• Scoring Guideline
• Student Samples
• Scoring Commentary
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AP® ENVIRONMENTAL SCIENCE
2017 SCORING GUIDELINES
Question 1
Read the following article from the Fremont Daily Times and answer the questions that follow.
(a) Describe TWO effects that ingesting microbeads has on aquatic organisms.
(2 points: 1 point for each correct description of an effect of microbeads on aquatic organisms.)
• Microbeads fill or block the digestive tract
• Organisms accumulate toxic chemicals (PCBs, dioxins) from microbeads, leading to long-term
health effects
(b) Dr. Ewoldsen states that nitrates pose different threats to aquatic ecosystems than microbeads do.
Describe how nitrate levels can negatively affect water quality in some aquatic ecosystems.
(2 points: 1 point for a correct description of the ecosystem response to increased nitrate levels
and 1 point for a correct description of the effect of increased algal growth on water quality. The
effect on water quality must be linked to response to increased nitrate levels to earn point.)
Response to increased nitrate Effect on water quality
levels
• Cause excessive algal growth or • Algae die and microbes deplete the water of
algal blooms available oxygen (DO) during decomposition
• Cause cultural eutrophication of algae (hypoxic/anoxic conditions)
• Speed eutrophication process • Algal blooms increase turbidity
• Algal blooms lead to reduced light
penetration
• Algal blooms cause taste/odor problems
(c) While wastewater treatment plants are ineffective at removing microbeads, they are very effective
at removing large pieces of plastic waste and other pollutants.
(i) Identify one way large pieces of plastic are removed from wastewater during primary
treatment.
(1 point for a correct identification of one way plastics are removed during primary treatment.)
Physical mechanism for removing plastics from the liquid component of wastewater, such as
• Screens/Sieves • Skimmers
• Settling • Filters
• Nets • Manual removal
(ii) Prior to discharge, wastewater is often disinfected. Identify one technique commonly used to
disinfect wastewater.
(1 point for a correct identification of one technique used to disinfect wastewater.)
• Chlorination • Ozonation
• Treatment with ultraviolet • Membrane filtration
(UV) light (reverse osmosis and ultrafiltration)
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AP® ENVIRONMENTAL SCIENCE
2017 SCORING GUIDELINES
Question 1 (continued)
(iii) Sludge or biosolids produced during the wastewater treatment process can be spread on
agricultural fields. Identify one advantage and one disadvantage of this practice.
(2 points: 1 point for a correct identification of an advantage of spreading sludge and 1 point for a
correct identification of a disadvantage of spreading sludge.)
Advantage Disadvantage
• Used as fertilizer • Foul odors
• Increases crop yields/crop revenue • Surface water and groundwater
• Improves soil quality contamination by nutrients, heavy metals,
• Reduces need for disposal of sludge/biosolids pharmaceuticals, hormones, pathogens
in landfills or by incineration • Soil contamination by heavy metals,
• Generates revenue from sale of pharmaceuticals, hormones, pathogens
sludge/biosolids • Crop contamination by heavy metals,
• May be less expensive than commercial pharmaceuticals, pathogens
fertilizer • Lack of public acceptance
• May be least expensive disposal option
(d) Coastal ecosystems are threatened by other human activities in addition to wastewater disposal.
Mangrove swamps are one such threatened ecosystem.
(i) Provide one reason why mangrove trees are being removed by humans.
(1 point for a correct reason for why mangrove trees are being removed by humans.)
• Establishing aquaculture facilities (fish and shrimp farming)
• Expanding agriculture
• Developing coastal areas (e.g., marinas, condos, resorts, infrastructure)
• Harvesting mangroves for wood products, including paper pulp
• Burning mangroves for energy/charcoal production
• Removing mangroves for aesthetic reasons (to improve views)
• Removing trees to increase access to coastal waters
(ii) Identify one ecosystem service provided by intact mangrove ecosystems.
(1 point for a correct identification of an ecosystem service provided by intact mangroves.)
• Shoreline stabilization/protection (e.g., storm surge, tsunami, wave action)
• Commercial fisheries
• Nursery grounds for aquatic organisms
• Biodiversity preservation
• Flood control
• Groundwater recharge
• Sediment/nutrient retention
• Nutrient cycling
• Absorption of carbon dioxide and release of oxygen
• Purification of water, air
• Ecotourism/tourism/recreational opportunities
• Protection from saltwater intrusion
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1A 1 of 2
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1A 2 of 2
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1B 1 of 1
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1C 1 of 2
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1C 2 of 2
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AP® ENVIRONMENTAL SCIENCE
2017 SCORING COMMENTARY
Question 1
Overview
This question was intended to have students describe the impact of various pollutants on aquatic organisms
and on water quality, to identify and describe common methods of sewage (wastewater) treatment, and to
demonstrate an understanding of the importance of mangrove swamps, an example of an ecosystem
threatened by human activities. Students were asked to read the document provided and describe the
impacts of ingesting microbeads on aquatic organisms. This concept was drawn from VI. Pollution,
B. Impacts on the Environment and Human Health, 2. Hazardous Chemicals in the Environment of the topic
outline. Students were then asked to describe how nitrates, a different water pollutant, can negatively affect
water quality in some aquatic ecosystems.
The next part of the question evaluated student understanding of wastewater treatment. Students were
asked to identify one way large objects, such as plastic, could be removed during primary wastewater
treatment and to then identify one common technique to disinfect wastewater prior to discharge.
Additionally, students were asked to identify one advantage and one disadvantage of spreading biosolids
(sludge) on agricultural fields. These concepts were drawn from VI. Pollution, subtopic A. Pollution Types,
section 3.Water Pollution of the topic outline.
Students were then asked to demonstrate their knowledge of the importance of ecosystem diversity and
the threat of human activities to ecosystems using the mangrove forest as an example of a threatened
coastal ecosystem. Students were asked to provide a reason as to why humans remove mangrove tress and
to identify an ecosystem service provided by intact mangrove forests. These concepts were drawn from
II. The Living World, subtopic C. Ecosystem Diversity of the topic outline.
Sample: 1A
Score: 10
The student earned 2 points in part (a): 1 point for describing that microbeads “can block the digestive
tracts of fish” and 1 point for describing the “bioaccumulation of toxins such as DDT” as a second effect of
ingesting microbeads. The student earned 2 points in part (b): 1 point for describing that “when nitrate
levels are high, more algae can bloom” and 1 point for describing how when algae dies, “decomposition
may occur. This dramatically reduces D.O. (or dissolved oxygen) levels.” This response demonstrates the
link between algal blooms and the negative effect on water quality, reduced levels of dissolved oxygen.
The student earned 1 point in (c)(i) for stating “bar screens” as a method to remove large pieces of plastic
from wastewater during primary treatment. The student earned 1 point in (c)(ii) for identifying that
“chlorination is often used to disinfect wastewater.” The response earned 2 points in (c)(iii): 1 point for
identifying “the use of waste as fertilizer” as one advantage to spreading biosolids on agricultural fields
and 1 point for identifying that biosolids “naturally contain elements, such as nitrogen and phosphorus,
which, when introduced to an aquatic system, can promote eutrophication.” The response clearly
identifies how specific chemicals in the biosolids runoff can contaminate surface water as the
disadvantage. The response earned 1 point in (d)(i) for identifying “Mangrove trees are removed by humans
in order for humans to build on mangrove swamps.” The response earned 1 point in (d)(ii) for identifying
that “intact mangrove ecosystems filter water” as an ecosystem service.
Sample: 1B
Score: 8
The student earned 1 point in part (a) for describing that microbeads “fill up the organisms [sic] stomach.”
No additional point was earned because PCBs are not described as toxic chemicals that impact the
long-term health of aquatic organisms. The response earned 2 points in part (b): 1 point for describing how
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AP® ENVIRONMENTAL SCIENCE
2017 SCORING COMMENTARY
Question 1 (continued)
high nitrate levels “allow for algae to flourish” as a description of an algal bloom and 1 point for describing
that the algae “form a layer that blocks out sunlight” negatively impacting water quality. The student
earned 1 point in (c)(i) for identifying that “metal grates block large pieces of plastic from moving further
into the sewage treatment process.” The student earned 1 point in (c)(ii) for identifying chlorine as a
disinfectant. The student earned 1 point was earned in (c)(iii) for identifying one advantage of using
biosolids as “less synthetic fertilizers have to be used.” No additional point was earned for the
disadvantage given because a specific pollutant is not identified in the runoff. The student earned 1 point
in (d)(i) for identifying coastal development, by stating that mangroves may be removed “to build a dock.”
The response earned 1 point in (d)(ii) for identifying the ecosystem service of sediment retention because
“Intact mangroves keep the soil in place and prevent soil erosion.”
Sample: 1C
Score: 6
The student earned 1 point in part (a) for describing that microbeads “can cause blockages in the digestive
tracts of aquatic organisms.” No additional point was earned because PCBs are not described as toxic
chemicals that impact long-term health. The student earned 1 point in part (b) for describing an algal
bloom. No additional point was earned because the response does not include the intermediate step of
decomposition leading to hypoxic zones. The student earned 1 point in (c)(i) for identifying the use of
filters as a method to remove large pieces of plastic. The student earned 1 point in (c)(iii) for identifying
that biosolids “provides organic fertilizer” as an advantage. No additional point was earned for identifying
a disadvantage because a specific compound in the runoff is not identified. The student earned 1 point in
(d)(i) for identifying that mangrove trees are removed by humans “in an attempt to develop the land.” The
student earned 1 point in (d)(ii) for identifying “the natural filtration of water” as an ecosystem service
provided by mangroves.
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