AP Environmental Science Unit 1: The Living World: Ecosystems Practice Exam

Assessment for Unit 1: The Living World: Ecosystems

Estimated Time: 60 minutes

Exam Details

Questions: 31 total (30 multiple choice, 1 short answer)
Time: 60 minutes (recommended)
Topics Covered: Unit 1: The Living World: Ecosystems
Format: Multiple Choice, Short Answer questions matching real exam difficulty
Scoring: Instant results with detailed explanations

A. Multiple-Choice Questions (30 Questions)

Select the one best answer for each question.

Refer to the figure below.

1. [Skill: 4A | Topic: 1.1] A field ecologist monitored the populations of snowshoe hares (prey) and lynx (predator) in the same boreal forest over 10 years. Which of the following best explains the relationship shown in the graph? [Image Cue]: Line graph, "Hare and Lynx Populations Over Time"; x-axis = Year (1 to 10); y-axis = Population size (relative units). Hare line rises to a peak around Years 4–5 and then declines; lynx line also rises but peaks about 1 year after the hare peak and then declines after the hare declines. This pattern repeats as a smaller second cycle near Years 8–10.

(A)The lynx population increases after hare numbers rise because greater prey availability increases predator survival and reproduction.(B)The hare population increases after lynx numbers rise because predators provide food resources for the prey population.(C)Both populations increase at the same time because lynx and hares occupy different niches and therefore do not affect each other.(D)The lynx population peaks first because predators must increase before prey populations can grow.

2. [Skill: 1A | Topic: 1.1] Researchers observed that cleaner wrasse fish feed on parasites living on the skin and in the mouths of larger reef fish. The larger fish spend time hovering near “cleaning stations” and show fewer parasites after visits. Cleaner wrasse gain a reliable food source. Which of the following best identifies the species interaction described?

(A)Mutualism, because both species benefit from the interaction(B)Commensalism, because the larger fish benefit while the cleaner wrasse are unaffected(C)Parasitism, because the cleaner wrasse harm the larger fish by feeding on them(D)Predation, because the cleaner wrasse kill the larger fish for food

3. [Skill: 3A | Topic: 1.1] Two closely related bird species live in the same forest. Ecologists recorded where each species most often forages for caterpillars. Data summary (most common foraging location): - Species 1: outer branches in the upper canopy - Species 2: inner branches in the mid-canopy Which of the following best explains how both species can persist in the same forest over time?

(A)Resource partitioning reduces competition because each species uses a different part of the same food resource habitat.(B)Parasitism reduces competition because one species feeds on the other and lowers its population.(C)Predation reduces competition because both species hunt the same caterpillars, increasing food supply.(D)Competition increases survivorship because both species are forced to use exactly the same niche.

4. 1. [Skill: 2A | Topic: 1.10] A grassland ecosystem has an average of 20,000 kJ/m^2/year of energy captured as net primary productivity (NPP) by grasses (producers). Assuming the 10% rule applies at each trophic transfer, approximately how much energy is available to secondary consumers in this ecosystem?

(A)20,000 kJ/m^2/year(B)2,000 kJ/m^2/year(C)200 kJ/m^2/year(D)20 kJ/m^2/year

Refer to the figure below.

5. 2. [Skill: 5A | Topic: 1.10] Ecologists measured the average energy content at each trophic level in a coastal marsh food web. [Image Cue]: Bar graph, "Energy Available by Trophic Level in a Marsh"; x-axis: Producers, Primary Consumers, Secondary Consumers, Tertiary Consumers; y-axis: Energy (kJ/m^2/year). Example bar heights: Producers = 10,000; Primary Consumers = 1,200; Secondary Consumers = 130; Tertiary Consumers = 12. Key trend: steep decrease in energy at higher trophic levels. Which of the following best explains the observed decrease in energy at higher trophic levels?

(A)Energy is destroyed during trophic transfers because consumers are less efficient than producers.(B)Energy is converted to heat and becomes less available for biological work due to cellular respiration and other metabolic processes.(C)Energy accumulates in higher trophic levels because predators store all energy from their prey as new biomass.(D)Energy decreases because matter is not conserved when organisms are eaten and digested.

6. 3. [Skill: 2A | Topic: 1.10] A simplified energy model estimates that producers in a lake store 5,000,000 kJ of energy as biomass during a given year. Using the 10% rule, ecologists want to determine how many trophic levels (including producers) could be supported if a minimum of 500 kJ is required at the highest trophic level to sustain a small population of top predators. Assuming 10% energy transfer efficiency between each trophic level, what is the maximum number of trophic levels (including producers) that could be supported?

(A)3 trophic levels(B)4 trophic levels(C)5 trophic levels(D)6 trophic levels

7. [Skill: 1.A | Topic: 1.11] A marine ecologist constructs the following simplified food web for a coastal ecosystem. Arrows indicate the direction of energy transfer (from food to consumer). Producers: phytoplankton Primary consumers: zooplankton, krill Secondary consumers: anchovy (eats zooplankton), squid (eats krill) Tertiary consumers: tuna (eats anchovy and squid) Quaternary consumers: shark (eats tuna) Which organism is best classified as a tertiary consumer in this food web?

(A)Krill(B)Squid(C)Tuna(D)Phytoplankton

8. [Skill: 4.A | Topic: 1.11] A biologist studies a simple forest food web: - Oak trees produce acorns. - Mice eat acorns. - Hawks prey on mice. A nearby community eliminates hawks from the area over several years. The biologist records the following data. Table 1. Mice and oak seedling density before and after hawk removal - Before hawk removal: 20 mice per hectare; 50 oak seedlings per 100 m^2 - After hawk removal: 60 mice per hectare; 15 oak seedlings per 100 m^2 Which of the following best explains the observed changes, including the most likely feedback effect on the ecosystem over time?

(A)Removing hawks decreases mouse populations, allowing oak seedlings to increase; this is a positive feedback that stabilizes the ecosystem.(B)Removing hawks increases mouse populations, increasing acorn consumption and reducing oak seedling recruitment; the resulting decline in oak production can later reduce mouse populations, a negative feedback.(C)Removing hawks increases mouse populations, which increases oak seedling recruitment by dispersing acorns; this is a positive feedback that increases oak populations.(D)Removing hawks has no effect on oak seedlings because producers are not affected by changes in consumer populations.

Refer to the figure below.

9. [Skill: 2.A | Topic: 1.11] A lake has a food chain in which algae are consumed by zooplankton, and zooplankton are consumed by small fish. An invasive small fish species is introduced that consumes zooplankton at a high rate. A student monitors the lake for 10 weeks and creates the graph described below. Which of the following best explains the population trends shown and identifies the type of feedback loop most consistent with the data?

(A)Zooplankton decrease causes algae to increase; the resulting algal bloom lowers dissolved oxygen and later reduces fish populations, allowing zooplankton to recover—this is a negative feedback.(B)Zooplankton increase causes algae to increase; the resulting algal bloom increases dissolved oxygen and further increases fish populations—this is a positive feedback.(C)Algae decrease causes zooplankton to decrease; the resulting decrease in zooplankton allows algae to decrease further—this is a negative feedback.(D)Algae increase causes zooplankton to increase; increased grazing then increases algae even more—this is a positive feedback.

Refer to the figure below.

10. [Skill: 2.A | Topic: 1.2] A researcher creates a climograph for an unidentified terrestrial region. [Image Cue]: Climograph, "Climate of Region X"; x-axis = months (Jan–Dec), left y-axis = average monthly temperature (°C), right y-axis = average monthly precipitation (mm). Key trends: temperature stays warm year-round (about 24–27°C each month); precipitation is high every month (generally 150–300 mm) with no true dry season; total annual precipitation is about 2,500 mm. Based on the climograph, which terrestrial biome is most likely represented by Region X?

(A)Tropical rainforest(B)Savanna(C)Temperate seasonal forest(D)Desert

11. [Skill: 1.A | Topic: 1.2] A mountain range runs parallel to a coastline. Prevailing winds blow from the ocean toward the mountains year-round. On the windward (coastal) side, forests are extensive and streams flow year-round. On the leeward side, vegetation is sparse and many streambeds are dry for most of the year. Which explanation best accounts for the observed differences in the availability of freshwater and trees for lumber on the two sides of the mountain range?

(A)A rain shadow forms as moist air rises over the mountains, cools and precipitates on the windward side, leaving drier air to descend on the leeward side.(B)Soil nutrient levels are always higher on the windward side because the ocean adds minerals directly to the soil, allowing more trees to grow.(C)Latitude differences between the two sides cause one side to receive more solar radiation, creating more freshwater and trees.(D)Nonmineral resources such as freshwater and lumber are distributed uniformly, so the differences must be due to human logging practices alone.

12. [Skill: 4.A | Topic: 1.2] Scientists compare long-term climate records and vegetation surveys in a high-latitude region. Data summary (1970 to 2020): - Mean annual temperature increased by about 2°C. - Length of the growing season increased by about 3 weeks. - Field surveys show increasing shrub cover and the appearance of young conifer trees farther north than previously recorded. Which outcome is most consistent with these observations over the next several decades, assuming warming continues?

(A)Expansion of taiga (boreal forest) into areas that were previously tundra(B)Expansion of tundra into areas that were previously taiga because warmer temperatures favor tundra plants(C)Conversion of the region into a subtropical desert because higher temperatures always reduce precipitation(D)No biome change because biome distribution is fixed and does not shift over time

Refer to the figure below.

13. [Skill: 1.A | Topic: 1.3] A regional planning agency is comparing aquatic sites as potential sources of drinking water. The agency summarizes the sites in a table. [Image Cue]: Table, "Abiotic Characteristics of Candidate Aquatic Sites", columns = Site, Average salinity (ppt), Water movement, Example description. Rows: Site 1: 0.3 ppt, flowing channel, "water moves downhill through a narrow channel"; Site 2: 33 ppt, large open basin, "deep water far from shore"; Site 3: 15 ppt, partially enclosed coastal area, "mix of freshwater and seawater". Which site is most accurately classified as a freshwater biome and therefore the most likely candidate for drinking-water supply (assuming treatment capacity is limited)?

(A)Site 1, because its very low salinity is characteristic of streams and rivers(B)Site 2, because oceans contain the largest volume of water on Earth(C)Site 3, because brackish water is a typical feature of ponds and lakes(D)Site 3, because estuaries have high nutrient levels that make water easier to purify

Refer to the figure below.

14. [Skill: 4.A | Topic: 1.3] Researchers monitored a coastal marine site during a spring phytoplankton (algal) bloom. [Image Cue]: Line graph, "Dissolved Oxygen and Dissolved Carbon Dioxide During a Bloom", x-axis = Time (days 1–10), left y-axis = Dissolved oxygen (mg/L), right y-axis = Dissolved CO_2 (mg/L). Trend: dissolved oxygen increases from day 1 to day 6, then decreases slightly by day 10; dissolved CO_2 decreases from day 1 to day 6, then increases slightly by day 10. Which statement best explains the pattern shown from day 1 to day 6?

(A)Increased photosynthesis by algae produces oxygen and consumes carbon dioxide, raising dissolved oxygen while lowering dissolved CO_2(B)Increased cellular respiration by algae produces oxygen and consumes carbon dioxide, raising dissolved oxygen while lowering dissolved CO_2(C)Reduced sunlight penetration increases photosynthesis rates, which increases both dissolved oxygen and dissolved CO_2(D)Higher salinity during the bloom causes oxygen to be generated from salt ions, increasing dissolved oxygen while decreasing dissolved CO_2

Refer to the figure below.

15. [Skill: 2.B | Topic: 1.3] A fisheries scientist is comparing three offshore zones in the same ocean basin to understand why commercially valuable fish are abundant in some areas and scarce in others. [Image Cue]: Data table, "Conditions in Three Marine Zones", columns = Zone, Depth (m), Surface nutrient availability (low/medium/high), Turbidity (low/medium/high), Temperature (°C), Annual fish catch (metric tons). Rows: Zone A: 50 m, high nutrients, medium turbidity, 14°C, 12,000; Zone B: 1,500 m, low nutrients, low turbidity, 4°C, 800; Zone C: 200 m, medium nutrients, high turbidity, 22°C, 2,500. Which choice best supports the claim that nonmineral marine resources (such as fish populations) vary globally due to a combination of abiotic factors?

(A)Zone A has the highest catch, consistent with relatively shallow depth and high nutrient availability supporting higher primary productivity and food webs(B)Zone B has the lowest catch because deeper water always has higher photosynthetic rates than surface waters(C)Zone C has a moderate catch because high turbidity always increases light penetration and therefore increases fish abundance(D)All zones should have similar catches because salinity is the only abiotic factor that controls the distribution of fish

Refer to the figure below.

16. [Skill: 2.A | Topic: 1.4] [Image Cue]: Line graph, "Atmospheric CO2 Concentration Above a Temperate Forest Over 24 Hours", x-axis: Time of day (06:00, 09:00, 12:00, 15:00, 18:00, 21:00, 00:00, 03:00, 06:00 next day), y-axis: Atmospheric CO2 (ppm). Data/trend: CO2 decreases from ~415 ppm at 06:00 to ~405 ppm at 15:00, then increases steadily to ~418 ppm by 06:00 the next day. A scientist measures atmospheric carbon dioxide ($CO_2$) concentration just above a temperate forest canopy over a 24-hour period. The results are shown in the graph. Which of the following best explains the overall decrease in atmospheric $CO_2$ during the daytime and the increase during nighttime?

(A)Daytime photosynthesis by plants removes $CO_2$ from the atmosphere, while nighttime cellular respiration releases $CO_2$ to the atmosphere.(B)Daytime cellular respiration by plants removes $CO_2$ from the atmosphere, while nighttime photosynthesis releases $CO_2$ to the atmosphere.(C)Daytime decomposition of dead organic matter removes $CO_2$ from the atmosphere, while nighttime decomposition releases $CO_2$ to the atmosphere.(D)Daytime diffusion of $CO_2$ from the deep ocean removes $CO_2$ from the atmosphere, while nighttime diffusion adds $CO_2$ to the atmosphere.

17. [Skill: 5.A | Topic: 1.4] A student is comparing how long carbon is typically stored in different reservoirs. Approximate carbon residence times for several reservoirs are shown below: - Atmosphere: years to decades - Terrestrial vegetation: years to centuries - Surface ocean: decades - Deep ocean: centuries to millennia - Sedimentary carbonate rock (e.g., limestone): millions of years Based on the information, which reservoir represents the longest-term sink for carbon?

(A)Atmosphere(B)Terrestrial vegetation(C)Deep ocean(D)Sedimentary carbonate rock

Refer to the figure below.

18. [Skill: 1.A | Topic: 1.4] [Image Cue]: Two-line graph, "Fossil Fuel Combustion and Atmospheric CO2 (1750–2020)", x-axis: Year (1750 to 2020), left y-axis: Atmospheric CO2 (ppm), right y-axis: Fossil fuel carbon emissions (gigatons C per year). Key trend: both lines remain low until ~1850, then increase; strong rise after ~1950 with CO2 increasing from ~280 ppm (1750) to >410 ppm (2020). A researcher shows the graph relating fossil fuel combustion to atmospheric $CO_2$ from 1750 to 2020. Which statement best explains how fossil fuel combustion alters the natural balance of the carbon cycle?

(A)It transfers carbon from a long-term geologic reservoir into the atmosphere rapidly as $CO_2$, increasing atmospheric carbon faster than it is removed by natural processes.(B)It transfers carbon from the atmosphere into long-term geologic reservoirs by increasing sedimentation rates, decreasing atmospheric $CO_2$.(C)It increases the rate at which atmospheric $CO_2$ is converted into carbonate rock, causing atmospheric $CO_2$ to decrease over decades.(D)It converts atmospheric $CO_2$ into plant biomass permanently, increasing long-term storage in vegetation over millions of years.

19. **1. [Skill: 4.A | Topic: 1.5]** A student compares the approximate size of major nitrogen reservoirs and notes the dominant form of nitrogen in each reservoir. > **Data summary (approximate):** > - Atmosphere: very large reservoir; mostly $N_2(g)$ > - Living biomass (plants/animals/microbes): smaller reservoir; organic N in proteins and nucleic acids > - Soil inorganic N: relatively small reservoir; $NH_4^+$ and $NO_3^-$ > - Surface water inorganic N: very small reservoir; $NO_3^-$ and dissolved organic N Which statement is best supported by the data summary and the nitrogen-cycle model described in AP Environmental Science?

(A)Because $N_2$ is abundant in the atmosphere, most plants can directly absorb $N_2(g)$ through their leaves and use it to build proteins.(B)The atmosphere is the major reservoir of nitrogen, and many non-atmospheric reservoirs store nitrogen compounds for relatively short periods of time.(C)Soil inorganic nitrogen is the major reservoir of nitrogen because it contains $NH_4^+$ and $NO_3^-$, the forms most organisms use directly.(D)Nitrogen moves primarily from plants to the atmosphere by nitrification, which converts organic nitrogen into $N_2(g)$.

Refer to the figure below.

20. **2. [Skill: 2.A | Topic: 1.5]** A diagram of the nitrogen cycle includes five labeled arrows representing transformations among nitrogen forms. [Image Cue]: Diagram, "Key Transformations in the Nitrogen Cycle", boxes labeled "$N_2(g)$ (atmosphere)", "$NH_3/NH_4^+$ (soil)", "$NO_2^-$ (soil)", "$NO_3^-$ (soil)", and "Organic N (plant biomass)". Arrows are labeled 1 through 5 showing: 1) $N_2 \rightarrow NH_3/NH_4^+$, 2) $NH_4^+ \rightarrow NO_2^-$, 3) $NO_2^- \rightarrow NO_3^-$, 4) $NO_3^- \rightarrow N_2$, 5) $NO_3^- \rightarrow$ Organic N (in plants). Which set correctly matches each labeled arrow with the primary nitrogen-cycle process?

(A)1 = nitrification; 2 = fixation; 3 = assimilation; 4 = ammonification; 5 = denitrification(B)1 = fixation; 2 = nitrification; 3 = nitrification; 4 = denitrification; 5 = assimilation(C)1 = assimilation; 2 = denitrification; 3 = ammonification; 4 = nitrification; 5 = fixation(D)1 = ammonification; 2 = assimilation; 3 = fixation; 4 = denitrification; 5 = nitrification

21. **3. [Skill: 1.A | Topic: 1.5]** A wetland restoration project aims to reduce nitrate ($NO_3^-$) concentrations in runoff water entering a lake. After restoration, monitoring shows that nitrate levels in water leaving the wetland are lower than nitrate levels in water entering the wetland. Which nitrogen-cycle process most directly explains the reduction in nitrate as water passes through the wetland?

(A)Denitrification by anaerobic bacteria converting $NO_3^-$ into $N_2(g)$, returning nitrogen to the atmosphere(B)Nitrogen fixation converting atmospheric $N_2(g)$ into $NH_3$, increasing nitrogen available for plant uptake(C)Nitrification converting $NH_4^+$ into $NO_3^-$, reducing the toxicity of ammonia in wetland soils(D)Ammonification converting organic nitrogen in detritus into $NH_3/NH_4^+$, reducing dissolved nitrate in the water

22. 1. [Skill: 4A | Topic: 1.6] A researcher summarizes the approximate distribution of phosphorus in an Earth system model. Reservoir (global) — Approximate phosphorus stored (gigatons) - Phosphate minerals in rock and marine sediments — 1,000,000 - Soils — 300 - Living biomass — 3 - Dissolved phosphate in the ocean — 90 Based on the data, which reservoir is the largest sink (major long-term reservoir) of phosphorus in the phosphorus cycle?

(A)Soils, because they are the main location where producers absorb phosphate(B)Living biomass, because organisms incorporate phosphorus into DNA and ATP(C)Phosphate minerals in rock and marine sediments, because most phosphorus is stored in rocks/sediments over long timescales(D)Dissolved phosphate in the ocean, because aquatic ecosystems require continual phosphate input

23. 2. [Skill: 1A | Topic: 1.6] A lake located downstream of agricultural fields experiences frequent algal blooms after heavy rain events. Water tests show a sharp increase in dissolved phosphate (PO_4^{3-}) following storms. Which of the following best explains how phosphorus is most likely entering the lake in this scenario?

(A)Volatilization of phosphorus compounds into the atmosphere followed by deposition into the lake(B)Surface runoff and erosion transporting phosphate from soils and fertilizers into streams that flow into the lake(C)Biological nitrogen fixation converting atmospheric phosphorus gas into plant-available phosphate(D)Denitrification by bacteria releasing phosphate from the lake into the atmosphere

24. 3. [Skill: 2B | Topic: 1.6] A simplified phosphorus cycle diagram (not shown) includes the following labeled reservoirs: "Phosphate in rock," "Phosphate in soil," "Phosphate in water," and "Phosphorus in organisms." One arrow is unlabeled and points from "Phosphate in water" to "Phosphate in rock". Which process best labels the unlabeled arrow from "Phosphate in water" to "Phosphate in rock"?

(A)Evaporation and condensation, transferring phosphorus to the atmosphere before returning it to rock(B)Sedimentation and burial of phosphorus-containing particles, forming sediments and eventually phosphate-bearing rock(C)Cellular respiration, releasing phosphorus from organisms directly into phosphate minerals(D)Transpiration, moving phosphorus from water into rock through plant water loss

25. [Skill: 4A | Topic: 1.7] A student is analyzing global water storage using the table below. Global Water Reservoirs (approximate percent of all water on Earth) - Oceans: 96.5% - Ice caps and glaciers: 1.74% - Groundwater: 1.69% - Lakes: 0.013% - Atmosphere: 0.001% Which of the following conclusions is best supported by the data?

(A)The oceans are the primary reservoir of water on Earth, while ice caps/glaciers and groundwater store much smaller amounts.(B)Ice caps and glaciers store more water than the oceans because they are made of solid water.(C)The atmosphere is the primary reservoir of water because it is the source of precipitation.(D)Lakes store more water than groundwater because lakes are visible at Earth’s surface.

Refer to the figure below.

26. [Skill: 2A | Topic: 1.7] [Image Cue]: Line graph, "Solar Energy and Evaporation Over an Ocean Surface"; x-axis = Time of day (6:00, 9:00, 12:00, 15:00, 18:00); y-axis = Rate (relative units). Two lines: (1) Solar energy intensity rises from 6:00 to peak at 12:00 then declines by 18:00; (2) Evaporation rate closely follows the same pattern (lowest at 6:00, highest near 12:00–15:00, then decreases). Which statement best explains the relationship shown in the graph in terms of the hydrologic cycle?

(A)Solar energy drives evaporation by providing the heat needed to change liquid water into water vapor.(B)Evaporation increases when ocean salinity decreases because freshwater evaporates faster than saltwater.(C)Solar energy directly increases precipitation by forcing water vapor to fall as rain.(D)Evaporation peaks at midday because groundwater is released to the ocean through infiltration.

27. [Skill: 4 | Topic: 1.8] A researcher measured productivity in two ecosystems during the same year. The values below are expressed in $kcal/m^{2}/yr$. Ecosystem 1: Gross primary productivity (GPP) = 25,000; Respiration by producers (R) = 15,000 Ecosystem 2: Gross primary productivity (GPP) = 12,000; Respiration by producers (R) = 5,000 Based on these data, which of the following correctly compares the net primary productivity (NPP) of Ecosystem 1 and Ecosystem 2?

(A)Ecosystem 1 has higher NPP than Ecosystem 2 because $25{,}000 - 15{,}000 = 10{,}000$, which is greater than $12{,}000 - 5{,}000 = 7{,}000$.(B)Ecosystem 2 has higher NPP than Ecosystem 1 because $12{,}000 - 5{,}000 = 7{,}000$, and Ecosystem 1 has zero NPP when respiration is high.(C)Ecosystem 1 has higher NPP than Ecosystem 2 because NPP is calculated as $GPP + R$, so $25{,}000 + 15{,}000$ is greater than $12{,}000 + 5{,}000$.(D)Both ecosystems have the same NPP because productivity is measured per unit area per unit time, which makes values comparable and therefore equal.

Refer to the figure below.

28. [Skill: 3 | Topic: 1.8] [Image Cue]: Line graph, "Light Availability and Photosynthesis with Depth in a Lake"; x-axis = Depth (m) from 0 to 40; left y-axis = Percent of surface light (%) from 100 to 0; right y-axis = Photosynthesis rate (relative units). The light curve declines steeply: ~100% at 0 m, ~30% at 10 m, ~10% at 20 m, ~2% at 30 m, ~0% by 40 m. The photosynthesis curve peaks near 5 m, declines by 20 m, and approaches 0 by 30–40 m. A class is investigating why primary productivity differs with depth in an aquatic ecosystem. Using the graph, which statement best explains the primary productivity pattern observed with increasing depth?

(A)Primary productivity decreases with depth because less visible light penetrates water, limiting photosynthesis; many aquatic producers have adaptations (such as accessory pigments) that help capture available wavelengths.(B)Primary productivity decreases with depth because dissolved oxygen becomes unavailable, preventing photosynthesis from occurring in deeper water.(C)Primary productivity increases with depth because higher pressure forces more $CO_2$ into solution, increasing the rate of photosynthesis.(D)Primary productivity decreases with depth because cellular respiration increases in deeper water, which directly increases GPP and lowers NPP.

Refer to the figure below.

29. [Skill: 4.A | Topic: 1.9] [Image Cue]: Bar graph, "Energy Available at Successive Trophic Levels in a Grassland". X-axis: Trophic level (Producers, Primary consumers, Secondary consumers, Tertiary consumers). Y-axis: Energy available (kJ/m^2/yr). Data bars: Producers = 20000, Primary consumers = 2000, Secondary consumers = 200, Tertiary consumers = 20. Key trend: approximately 10% of energy is available at each higher trophic level. A student analyzes the graph and claims that the pattern demonstrates why ecosystems require a continuous inflow of energy. Which of the following best supports the student’s claim?

(A)Because most energy is converted to heat during metabolic processes at each trophic level, energy availability decreases at higher trophic levels and must be continually replaced by new energy input (such as sunlight).(B)Because matter is destroyed at each trophic level, producers must continually create new matter from sunlight to maintain ecosystem structure.(C)Because energy is recycled by decomposers back to producers, energy availability remains constant over time unless new matter enters the ecosystem.(D)Because tertiary consumers store the most biomass, the highest trophic level requires the greatest energy input to maintain ecosystem structure.

30. [Skill: 1.A | Topic: 1.9] A class sets up a sealed (closed) terrarium containing soil, decomposers (bacteria and fungi), small herbivorous insects, and several plants. The terrarium is placed under a grow light that provides energy but does not add any matter. Over several weeks, the mass of plant tissue increases, insect populations persist, and dead leaves accumulate and then decompose. Which statement best explains how matter and energy behave in this terrarium?

(A)Energy and matter both cycle within the terrarium, so neither requires any external input once the terrarium is sealed.(B)Energy enters as light and ultimately leaves as heat, while matter is conserved and repeatedly recycled among organisms and the soil.(C)Energy is recycled by decomposers back into the grow light, while matter enters the terrarium from outside as new biomass forms.(D)Matter is gradually lost from the terrarium as heat, while energy is conserved and remains available to higher trophic levels.

B. Short Answer Questions (1 Question)

Answer all parts of each question. Answers must be in essay form. Outlines or lists alone are not acceptable.

Question 31:

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