AP Environmental Science Unit 1 practice questions
Try 10 multiple-choice questions from Unit 1 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
Both biomes receive substantial precipitation, yet tropical rainforests have much higher biodiversity. Which best explains the difference?
Year-round warm temperatures sustain continuous productivity and specialized niches
Higher precipitation alone always produces greater biodiversity in tropical forests
Tropical forests have deeper richer soils that directly support higher species diversity
Periodic wildfires in temperate forests reduce diversity while humid tropics avoid fires
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Answer: (A)
Year-round warmth enables continuous photosynthesis and faster nutrient cycling, producing more specialized niches. Temperate seasonality forces dormancy and periodic resource bottlenecks that limit species coexistence.
Question 2
Hunting reduced sea otters in a kelp forest, urchin numbers boomed, and kelp was overgrazed. Which best explains how resource availability drove this change in species interactions?
Otter removal lifts predation, urchins overconsume kelp until kelp limits them.
Urchins do not outcompete otters because otters are predators of urchins.
Kelp fluctuations alone do not explain the directional urchin boom after otter loss.
Urchin persistence requires kelp, so kelp depletion halts their population growth.
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Answer: (A)
Predation kept urchin numbers low, so removing otters allows urchins to expand. Expanded urchin grazing depletes kelp and converts forests to barrens, showing resource limitation shapes interactions.
Question 3
In a temperate forest, oak and hickory trees produce different nuts eaten by squirrels and jays. Oaks yield harder, tannin-rich nuts while hickories yield softer, more palatable nuts. Squirrels prefer and cache hickory nuts, while jays can crack oak nuts efficiently. Which best explains how resource partitioning reduces competition between these bird and mammal species?
Each species specializes on different nut types based on feeding morphology.
Different body sizes do not prevent competition for the same food resources.
High nut abundance is not implied and partitioning reduces competition under scarcity.
Partitioning promotes coexistence by reducing niche overlap rather than creating dominance.
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Answer: (A)
Resource partitioning occurs when species specialize on different resource types, reducing direct competition. Squirrels use softer hickory nuts while jays crack tannin-rich oak nuts, so each species accesses different food resources.
Question 4
A parasitic wasp lays eggs inside caterpillars and the larvae consume and kill the host. Wasp populations boom when caterpillars are abundant and crash when caterpillars are scarce. Which best explains this tight link?
Wasp reproduction depends on caterpillar hosts, so host availability limits populations.
Wasps and caterpillars compete for the same plant resources, driving linked cycles.
Wasp populations cycle from internal density effects like disease independent of host availability.
Wasps outcompete other predators and maintain stable numbers regardless of caterpillar abundance.
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Answer: (A)
Wasp reproduction requires caterpillar hosts for egg laying and larval development. When hosts are abundant wasp numbers rise, and when hosts decline reproduction fails and populations fall.
Question 5
Zebras eat tall coarse grasses and wildebeest eat short fine grasses. After drought reduces grass production by 80%, both populations fall, but wildebeest decline more. Which best explains this difference?
Wildebeest lose their preferred short fine grasses first and decline more.
Zebras are larger so they would be expected to decline more during drought.
Higher wildebeest reproductive volatility causes larger crashes under environmental stress.
Different grass preferences mean digestive efficiency does not explain the decline.
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Answer: (A)
Resource specialization becomes a liability when a preferred food is lost. Wildebeest rely on short fine grasses that droughts deplete first while zebras can eat coarser grasses that persist longer.
Question 6
Clownfish shelter among anemone tentacles and gain protection while anemones receive nutrients from clownfish waste. Experiments show anemones grow slower and get sicker without clownfish, while clownfish are quickly eaten without anemones. How does resource availability influence this symbiosis?
Each species supplies essential resources the other needs, forming mutualism.
Their association reflects learned behavior rather than resource exchange.
The anemone parasitizes the clownfish and harms it for shelter.
They compete for the same food so coexistence depends on sufficient prey.
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Answer: (A)
Both species exchange limiting resources that increase fitness: clownfish supply nutrients and anemones provide shelter and protection. Experimental separations reduce growth and survival, showing the exchanged resources constrain each species' fitness.
Question 7
In a tide pool ecosystem, sea stars and sea urchins both feed on kelp. Sea stars are predators of sea urchins, but sea urchins are more efficient kelp grazers and can consume kelp faster than sea stars can consume urchins. When sea star populations decline due to disease, urchin populations initially increase. However, kelp biomass decreases so severely that both urchin and sea star populations subsequently decline. Which of the following best explains why the sea star population declines despite the removal of disease pressure?
Urchin populations increased unchecked and overgrazed kelp, depleting the resource base that sea stars indirectly depend on through their urchin prey.
The disease that initially killed sea stars mutated to affect urchins, causing urchin populations to decline and eliminating sea star food sources.
Sea stars require kelp as a direct food source and cannot survive on urchin meat alone, so kelp depletion causes sea star starvation.
Increased urchin populations produce chemical compounds that inhibit sea star reproduction, preventing population recovery even after disease declines.
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Answer: (A)
Understanding indirect resource effects requires recognizing that sea stars depend on kelp availability not directly (they don't eat it) but indirectly through their prey. When sea stars decline, urchin populations explode and overgraze kelp. The resulting kelp depletion reduces urchin population size and condition, eliminating the resource (healthy urchin prey) that sea stars require. This demonstrates how resource availability influences species interactions across multiple trophic levels—sea stars' survival depends on maintaining urchin populations, which requires adequate kelp. The removal of predation pressure paradoxically leads to resource depletion that harms the predator.
Question 8
In a forest ecosystem, two species of squirrels occupy the same geographic area. Red squirrels cache nuts in underground burrows during fall, while gray squirrels bury nuts individually in shallow soil. After an unusually wet winter causes widespread soil waterlogging, many cached nuts rot and become unusable. Red squirrel populations remain relatively stable, but gray squirrel populations decline significantly. Which of the following best explains this differential population response?
Red squirrels' burrow caching strategy provided better protection from waterlogging than gray squirrels' shallow burial method, preserving more usable food resources.
Gray squirrels are larger animals requiring more food, so they depleted their cached food supplies faster than smaller red squirrels during the wet winter.
Waterlogging created anaerobic soil conditions that killed gray squirrels through direct exposure to toxic compounds, while red squirrels avoided these conditions by remaining in burrows.
Red squirrels and gray squirrels compete for the same nut resources, but red squirrels outcompeted gray squirrels by consuming more nuts before waterlogging occurred.
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Answer: (A)
Understanding resource partitioning requires recognizing that species using resources differently experience different consequences when environmental conditions change. Red squirrels' deep burrow caching and gray squirrels' shallow burial represent different strategies for storing the same resource (nuts). The waterlogging event differentially affects these strategies—deep burrows remain drier than shallow soil, preserving red squirrel food caches while destroying gray squirrel caches. This demonstrates how resource availability (usable cached nuts) is influenced by both species' ecological strategies and environmental conditions, producing different outcomes for species with different resource acquisition and storage methods.
Question 9
In a coral reef ecosystem, a symbiotic relationship exists between corals and zooxanthellae (photosynthetic algae living in coral tissues). When water temperatures increase by 3°C above normal, corals expel their zooxanthellae in a process called bleaching. Coral survival depends on rapidly reestablishing the symbiosis with zooxanthellae. Which of the following best explains why corals cannot survive long-term without zooxanthellae despite being able to feed on plankton?
Zooxanthellae provide the majority of coral energy through photosynthetic products, and plankton feeding alone cannot supply sufficient energy to meet coral metabolic demands.
Zooxanthellae produce chemical compounds that corals require for skeleton formation, and without these compounds, corals cannot build or maintain their calcium carbonate structures.
Bleached corals lose the ability to capture plankton because zooxanthellae produce enzymes necessary for plankton digestion.
Temperature increase directly damages coral tissues, making them unable to process any food source, including plankton.
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Answer: (A)
Understanding mutualistic symbiosis requires recognizing that both partners depend on resource exchange—in this case, energy resources. Corals evolved to depend primarily on energy from zooxanthellae photosynthesis rather than plankton capture alone. While corals retain the ability to feed on plankton, this mechanism cannot provide sufficient energy to sustain coral metabolism and growth. The mutualistic relationship represents a resource dependency where zooxanthellae provide the primary energy resource. Bleaching eliminates this resource, causing coral starvation despite the theoretical availability of plankton. This demonstrates how resource availability through mutualistic partnerships fundamentally influences species survival.
Question 10
A parasitic fungus reduces oak acorn production by 60%. Blue jays that depend on acorns decline while wood-boring beetles that feed on dead and weakened oak wood increase. Which best explains these divergent population trends?
Fungal infection increases dead wood for beetles and reduces acorn supply to jays.
Beetles benefit from increased dead wood, not from generalist diet flexibility.
Fungal infection kills wood insects and lets jays thrive on increased insect prey.
Jays and beetles use different resources and do not compete directly.
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Answer: (A)
The fungus weakens trees and lowers acorn production while creating more dead wood that beetles use. Beetles therefore gain resources and increase while acorn-dependent jays decline.
What's on the AP Environmental Science Unit 1 practice test
The standard version takes about 70 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (23 minutes)
- 1 FRQ – FRQ 1 – Design an Investigation (23 minutes)
- 1 FRQ – FRQ 2 – Analyze and Interpret Quantitative Data (23 minutes)
Questions are drawn from 1142 multiple-choice questions and 38 FRQs written for Unit 1, The Living World: Ecosystems.
Practice AP Environmental Science Unit 1 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Design an Investigation (11 questions)
- FRQ 2 – Analyze and Interpret Quantitative Data (9 questions)
- FRQ 3 – Analyze an Environmental Problem Doing Calculations (18 questions)
Review Unit 1 before you start
- 1.1 Introduction to Ecosystems
- 1.2 Terrestrial Biomes
- 1.3 Aquatic Biomes
- 1.4 The Carbon Cycle
- 1.5 The Nitrogen Cycle
- 1.6 The Phosphorous Cycle
- 1.7 The Hydrologic Cycle
- 1.8 Primary Productivity
- 1.9 Trophic Levels
- 1.10 Energy Flow and the 10% Rule
- 1.11 Food Chains and Food Webs