AP Environmental Science FRQ Practice

♻️AP Environmental Science

Practice FRQ 1 of 221/22

1. A freshwater lake ecosystem contains phytoplankton (microscopic photosynthetic organisms), zooplankton (small animals that consume phytoplankton), small fish that eat zooplankton, and large predatory fish. Scientists studied how nitrogen availability affects the populations of organisms at different trophic levels in the lake.

A. Describe one step in the nitrogen cycle that converts atmospheric nitrogen into a form usable by plants.

B. Based on the food web described in the opening context, explain how an increase in phytoplankton biomass could affect the population of large predatory fish.

Figure 1. Nitrate concentration (mg/L) and phytoplankton biomass (g/m²) versus distance from an agricultural runoff source (km).

Create a clean dual-line graph with two data series.

Overall layout:
- White background, no gridlines.
- A rectangular plotting area occupying most of the figure.
- A legend inside the plotting area in the upper-right corner with two entries: a solid line labeled "Nitrate (mg/L)" and a dashed line labeled "Phytoplankton (g/m²)".

Axes (all required features):
- Horizontal axis label centered below the axis: "Distance from Agricultural Area (km)".
- X-axis numerical range: from 0 to 5.
- X-axis tick marks and labels: ticks at every 1 km, showing the numbers 0, 1, 2, 3, 4, 5.
- Vertical axis label rotated along the left side: "Concentration / Biomass".
- Y-axis numerical range: from 0 to 50.
- Y-axis tick marks and labels: ticks every 5 units, showing 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50.
- The origin is explicitly labeled "0" at the bottom-left intersection of the axes.
- Arrows appear on the positive ends of both axes (right end of x-axis and top end of y-axis).

Series 1: Nitrate concentration (solid line)
- Line style: solid, medium thickness, black.
- Plot the nitrate values exactly at each integer distance tick, using small filled circular markers at each distance.
- Exact values to hit at each distance (read directly above each x tick):
- At 0 km, the marker lies on the y=45 tick.
- At 1 km, the marker lies on the y=38 level (between 35 and 40, closer to 40).
- At 2 km, the marker lies on the y=28 level (between 25 and 30, closer to 30).
- At 3 km, the marker lies on the y=18 level (between 15 and 20, closer to 20).
- At 4 km, the marker lies on the y=12 level (between 10 and 15, closer to 10).
- At 5 km, the marker lies on the y=8 level (between 5 and 10, closer to 10).

Curve shape and behavior for nitrate:
- Connect the markers with straight line segments (piecewise linear), not a smoothed curve.
- The polyline is strictly decreasing across every segment from left to right.
- Each segment slopes downward; there are no flat segments, no reversals, no local maxima or minima within the interior of the x-range.
- Endpoints: the series begins at the left boundary at 0 km and ends at the right boundary at 5 km, with filled markers at both ends.

Series 2: Phytoplankton biomass (dashed line)
- Line style: dashed, medium thickness, black.
- Plot the phytoplankton values exactly at each integer distance tick, using small filled triangular markers at each distance (distinct from nitrate markers).
- Exact values to hit at each distance:
- At 0 km, the marker lies on the y=42 level (between 40 and 45, closer to 40).
- At 1 km, the marker lies on the y=36 level (between 35 and 40, slightly above 35).
- At 2 km, the marker lies exactly on the y=28 level (between 25 and 30, closer to 30).
- At 3 km, the marker lies exactly on the y=20 tick.
- At 4 km, the marker lies exactly on the y=15 tick.
- At 5 km, the marker lies on the y=12 level (between 10 and 15, closer to 10).

Curve shape and behavior for phytoplankton:
- Connect the markers with straight line segments (piecewise linear), not a smoothed curve.
- The polyline is strictly decreasing across every segment from left to right.
- No flat segments and no interior turning points.
- Endpoints: filled markers at both 0 km and 5 km.

Relationship visible in the figure:
- Both lines trend downward as distance increases, with nitrate always higher than phytoplankton at every distance tick.

No additional titles beyond the caption; all text in the image is limited to axis labels, tick numbers, and the legend entries.

C. Based on the data in Figure 1, identify the phytoplankton biomass at 3 km from the agricultural area.

D. Based on the data in Figure 1, describe the relationship between nitrate concentration and phytoplankton biomass as distance from the agricultural area increases.

Figure 2. Zooplankton density (individuals/m³) and small-fish density (individuals/m³) versus distance from an agricultural runoff source (km).

Create a clean dual-line graph with two population-density data series.

Overall layout:
- White background, no gridlines.
- Single plotting area with a legend inside the plotting region in the upper-right corner.
- Legend entries: solid line labeled "Zooplankton (individuals/m³)" and dashed line labeled "Small fish (individuals/m³)".

Axes (all required features):
- Horizontal axis label centered below the axis: "Distance from Agricultural Area (km)".
- X-axis numerical range: from 0 to 5.
- X-axis tick marks and labels: ticks every 0.5 km, labeled 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0.
- Vertical axis label rotated along the left side: "Population Density (individuals/m³)".
- Y-axis numerical range: from 0 to 180.
- Y-axis tick marks and labels: ticks every 20 units, labeled 0, 20, 40, 60, 80, 100, 120, 140, 160, 180.
- The origin is explicitly labeled "0" at the bottom-left intersection of the axes.
- Arrows appear on the positive ends of both axes.

Series 1: Zooplankton (solid line)
- Line style: solid, medium thickness, black.
- Use small filled circular markers at each distance where data are given.
- Plot markers exactly at the following distances and densities (each marker vertically aligned over its stated distance tick):
- 0 km at 45
- 1 km at 95
- 2 km at 165
- 3 km at 120
- 4 km at 85
- 5 km at 55

Curve shape and behavior for zooplankton:
- Connect markers with straight line segments (piecewise linear), not a smoothed curve.
- From 0 to 2 km the polyline rises in two increasing segments, reaching a single highest point at the 2 km tick.
- At the 2 km tick, the curve has a sharp peak because the piecewise line changes from rising to falling (no rounded top).
- From 2 to 5 km the polyline decreases across every segment with no secondary peaks.
- Endpoints: filled markers at both 0 km and 5 km.

Series 2: Small fish (dashed line)
- Line style: dashed, medium thickness, black.
- Use small filled square markers at each distance where data are given (distinct from zooplankton markers).
- Plot markers exactly at the following distances and densities:
- 0 km at 15
- 1 km at 45
- 2 km at 75
- 2.5 km at 85 (this point lies exactly above the 2.5 tick mark, halfway between 2 and 3)
- 3 km at 65
- 4 km at 42
- 5 km at 25

Curve shape and behavior for small fish:
- Connect markers with straight line segments (piecewise linear), not a smoothed curve.
- The line increases from 0 km through 2.5 km, reaching a single highest point at the 2.5 km tick.
- At 2.5 km, the line forms a sharp peak (piecewise corner) because it switches from increasing to decreasing at that marker.
- The line then decreases steadily from 2.5 km to 5 km with no additional turning points.
- Endpoints: filled markers at both 0 km and 5 km.

Visual comparison requirement:
- The zooplankton peak occurs at the 2 km tick at 165, and the small-fish peak occurs at the 2.5 km tick at 85; both peaks are clearly visible and separated horizontally.

No additional titles beyond the caption; all text in the image is limited to axis labels, tick numbers, and the legend entries.

E. Scientists hypothesized that zooplankton populations would be highest at intermediate distances from the agricultural area where phytoplankton availability is sufficient but nitrate toxicity is reduced. Describe one way that the data in Figure 2 support this hypothesis.

F. Primary productivity is the rate at which photosynthetic organisms convert solar energy into chemical energy through photosynthesis. A group of students wanted to investigate how light intensity affects phytoplankton primary productivity. They collected water samples containing phytoplankton from a local lake and placed equal volumes of the sample into five clear bottles. They placed each bottle at a different depth in the lake to expose them to different light intensities: 0 meters (100% light), 1 meter (75% light), 2 meters (50% light), 3 meters (25% light), and 4 meters (10% light). After 6 hours, students measured the dissolved oxygen concentration in each bottle as an indicator of photosynthetic rate.

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

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

Location	Species 1	Species 2	Species 3	Species 4	Species 5	Species 6	Species 7
Near agricultural runoff (0 km)	X	X
Far from runoff (5 km)		X	X	X	X	X	X

G. The data from a separate phytoplankton diversity investigation are shown in the following table. An 'X' in the table indicates that the species was present at that location.

i. Explain why the phytoplankton community located far from the agricultural runoff (5 km) would be more resilient to environmental disturbances than the community near the runoff source (0 km).

ii. Explain how excessive nitrogen from agricultural runoff can lead to decreased dissolved oxygen levels in the lake, negatively affecting fish populations.

H. Describe one way that removing wetlands through development could affect water quality in a downstream lake ecosystem. Aquatic ecosystems provide important ecosystem services. Wetlands adjacent to lakes can filter nitrogen from runoff before it enters the lake.