AP Environmental Science FRQ Practice

Practice FRQ 1 of 22

1. A freshwater lake ecosystem supports multiple trophic levels. Phytoplankton are photosynthetic organisms that form the base of the food web. Zooplankton are small animals that consume phytoplankton. Small fish consume zooplankton, and large fish consume small fish, as shown in the following food chain: Phytoplankton → Zooplankton → Small fish → Large fish. Scientists studied how nutrient availability affects primary productivity and energy transfer through the food web.

A. Describe one step in the phosphorus cycle that occurs in aquatic ecosystems.

B. Based on the food chain provided (Phytoplankton → Zooplankton → Small fish → Large fish), explain how an increase in phytoplankton biomass would affect the small fish population.

Figure 1. Phosphorus Concentration vs. Phytoplankton Biomass and Zooplankton Abundance (same vertical scale)

Create a clean, black-and-white dual-line graph with a single shared set of axes (NOT dual y-axes). No gridlines.

Axes (required):
- X-axis label centered below axis: "Phosphorus concentration (μg/L)".
- X-axis numerical range: from 0 to 50.
- X-axis tick marks and labels: 0, 10, 20, 30, 40, 50 (ticks every 10 μg/L). Ensure each tick has a short tick mark and the number printed below it.
- Y-axis label rotated vertically along the left side: "Relative abundance (organisms/L)".
- Y-axis numerical range: from 0 to 100.
- Y-axis tick marks and labels: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 (ticks every 10 organisms/L). Ensure each tick has a short tick mark and the number printed to the left.
- Origin labeling: the intersection of the axes must be labeled "0" (visible at the bottom-left corner where both axes meet).
- Add arrowheads on the positive (right) end of the x-axis and on the positive (top) end of the y-axis.

Legend/series labeling (required for unambiguous identification):
- Include a legend box in the upper-left interior of the plotting area.
- Legend entries:
1) "Phytoplankton biomass" shown as a solid black line with filled circular markers.
2) "Zooplankton abundance" shown as a solid medium-gray line with filled square markers.

Data and exact plotted heights (must match these values exactly at the shown x-ticks):
- At x=0 μg/L:
- Phytoplankton marker sits exactly halfway between y=10 and y=20, indicating 15.
- Zooplankton marker sits exactly two units below y=10, indicating 8.
- At x=10 μg/L:
- Phytoplankton marker sits exactly halfway between y=30 and y=40, indicating 35.
- Zooplankton marker sits exactly two units above y=20, indicating 22.
- At x=20 μg/L:
- Phytoplankton marker sits exactly two units below y=60, indicating 58.
- Zooplankton marker sits exactly two units below y=40, indicating 38.
- At x=30 μg/L:
- Phytoplankton marker sits exactly halfway between y=70 and y=80, indicating 75.
- Zooplankton marker sits exactly two units above y=50, indicating 52.
- At x=40 μg/L:
- Phytoplankton marker sits exactly two units below y=90, indicating 88.
- Zooplankton marker sits exactly four units above y=60, indicating 64.
- At x=50 μg/L:
- Phytoplankton marker sits exactly halfway between y=90 and y=100, indicating 95.
- Zooplankton marker sits exactly two units above y=70, indicating 72.

Line/curve shape description (required):
- Each series is drawn as a polyline made of straight-line segments connecting its six markers in order from left to right (no smoothing). This prevents the curve from drifting off the exact values.

Curve behavior by segment (required):
- Phytoplankton biomass line:
- From 0→10 μg/L: straight line rising from 15 to 35.
- From 10→20 μg/L: straight line rising from 35 to 58.
- From 20→30 μg/L: straight line rising from 58 to 75.
- From 30→40 μg/L: straight line rising from 75 to 88.
- From 40→50 μg/L: straight line rising from 88 to 95.
- Visual slope pattern constraint: the line’s slope is largest in the first two segments and becomes smaller in later segments (rises with decreasing slope overall).
- Zooplankton abundance line:
- From 0→10 μg/L: straight line rising from 8 to 22.
- From 10→20 μg/L: straight line rising from 22 to 38.
- From 20→30 μg/L: straight line rising from 38 to 52.
- From 30→40 μg/L: straight line rising from 52 to 64.
- From 40→50 μg/L: straight line rising from 64 to 72.
- Visual slope pattern constraint: the line rises throughout and also shows decreasing slope from left to right.

Critical math constraints:
- No maxima, minima, discontinuities, or asymptotes: both series increase strictly monotonically from x=0 to x=50.
- The phytoplankton line must remain above the zooplankton line at every shown x-tick (no intersections).

Styling constraints:
- Keep marker sizes large enough that the exact y-positions relative to the 10-unit y-ticks are visually readable.
- No extra text inside the plot besides the legend and axis labels/tick numbers.

C. Based on the data in Figure 1, identify the zooplankton abundance at a phosphorus concentration of 20 μg/L.

D. Based on the data in Figure 1, describe the relationship between phosphorus concentration and phytoplankton biomass.

Figure 2. Energy Transfer Efficiency vs. Phosphorus Concentration with 10% Reference Line

Create a clean, black-and-white single-line graph with one data series and one horizontal dashed reference line. No gridlines.

Axes (required):
- X-axis label centered below axis: "Phosphorus concentration (μg/L)".
- X-axis numerical range: from 0 to 50.
- X-axis tick marks and labels: 0, 10, 20, 30, 40, 50 (ticks every 10 μg/L).
- Y-axis label rotated vertically along the left side: "Energy transfer efficiency (%)".
- Y-axis numerical range: from 0 to 20.
- Y-axis tick marks and labels: 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 (ticks every 2%).
- Origin labeling: the axes intersection must be labeled "0" at the bottom-left.
- Add arrowheads on the positive (right) end of the x-axis and on the positive (top) end of the y-axis.

Data series (energy transfer efficiency):
- Plot filled circular markers at each x-tick (0, 10, 20, 30, 40, 50).
- The marker heights must match these exact y-values:
- At x=0: y=4 (marker lies exactly on the labeled tick 4).
- At x=10: y=6 (marker lies exactly on the labeled tick 6).
- At x=20: y=8 (marker lies exactly on the labeled tick 8).
- At x=30: y=11 (marker lies exactly halfway between labeled ticks 10 and 12).
- At x=40: y=13 (marker lies exactly halfway between labeled ticks 12 and 14).
- At x=50: y=15 (marker lies exactly halfway between labeled ticks 14 and 16).

Line/curve shape description (required):
- Connect the markers with straight-line segments (polyline), not a smooth curve, so the line passes exactly through each marker.
- Overall, the polyline rises monotonically from left to right with no dips.

Curve behavior by segment (required):
- From 0→10: straight line rising from 4 to 6.
- From 10→20: straight line rising from 6 to 8.
- From 20→30: straight line rising from 8 to 11.
- From 30→40: straight line rising from 11 to 13.
- From 40→50: straight line rising from 13 to 15.
- Slope constraint: the increase per 10 μg/L is largest between 20→30 (a rise of 3), and is smaller (a rise of 2) in the other segments.

10% reference line (required):
- Draw a horizontal dashed line across the entire plot at y=10 (exactly on the labeled tick 10).
- Place a small label near the right side of this dashed line reading: "10%".

Critical math constraints:
- The data line must be below the dashed 10% line at x=0, x=10, and x=20.
- The data marker at x=30 must be clearly above the dashed 10% line (since it is at 11).
- All markers at x=40 and x=50 must also be above the dashed 10% line.
- No maxima/minima/discontinuities/asymptotes: strictly increasing throughout.

Legend (optional but allowed; if included must be unambiguous):
- If a legend is present, put it in the upper-left and include two entries:
- "Energy transfer efficiency" shown as solid black line with filled circles.
- "10% reference" shown as dashed line.

Styling constraints:
- Keep the dashed reference line visually distinct (thin dashed) from the solid data line (medium thickness).
- Ensure tick labels are large enough to read the difference between 10 and 12, and that the 11%, 13%, and 15% markers are visibly at midpoints between the adjacent labeled ticks.

E. Scientists hypothesized that energy transfer efficiency would be greater than 10% when phosphorus concentration exceeds 30 μg/L. Describe how the data in Figure 2 support this hypothesis.

i. Identify a likely scientific question for the students' investigation of aquatic invertebrate diversity.

ii. Identify the independent variable in the students' investigation.

Site	Species A	Species B	Species C	Species D	Species E	Species F
Forested stream	X	X	X	X	X	X
Agricultural stream	X		X

i. Explain why the invertebrate community of the forested stream would be more resilient to environmental stress, such as a drought or pollution event, than the invertebrate community in the agricultural stream would.

ii. Explain how the results of the investigation could have been altered if students had measured invertebrate biodiversity in a stream receiving treated wastewater discharge rather than in the forested stream.

H. Describe one negative effect that eutrophication can have on dissolved oxygen levels in the lake ecosystem.