Rucete ✏ AP Biology In a Nutshell
20. The Basics of Ecology — Practice Questions 2
This chapter explores how organisms adapt to environmental changes and how energy and matter flow through ecosystems via trophic structures.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. What type of signal do electric fish like knifefish use to locate prey?
(A) Chemical
(B) Tactile
(C) Electrical
(D) Visual
Answer
(C) — Electric fish use electrical signals to detect movement and locate prey in murky environments.
2. Which of the following is most likely to exhibit kleptoplasty?
(A) Starfish
(B) Coral polyp
(C) Sea slug
(D) Eel
Answer
(C) — Some sea slugs retain chloroplasts from algae they consume, allowing temporary photosynthesis.
3. What would likely happen to a lizard placed in a consistently cold environment without access to sunlight?
(A) Its body temperature would remain stable
(B) Its metabolism would increase
(C) It would become sluggish and potentially die
(D) It would shiver to generate heat
Answer
(C) — As an ectotherm, a lizard depends on environmental heat and would slow down or die without warmth.
4. Which of the following explains why trophic pyramids typically have a broad base and narrow top?
(A) Organisms grow smaller as they evolve
(B) Biomass decreases due to loss of energy at each trophic level
(C) Only plants store energy
(D) Carnivores produce more waste than herbivores
Answer
(B) — Each step in the pyramid involves energy loss as heat, so less energy supports higher levels.
5. In bottom-up regulation, which of the following would most directly cause a collapse of a marine food web?
(A) Overfishing top predators
(B) Decrease in dissolved oxygen
(C) Herbicide runoff killing phytoplankton
(D) Introduction of invasive zooplankton
Answer
(C) — Loss of phytoplankton, the base producers, disrupts energy input for the whole food web.
6. Which of the following best defines a poikilotherm?
(A) An animal that maintains constant body temperature
(B) An animal whose body temperature fluctuates with the environment
(C) An animal with a fixed metabolic rate
(D) An animal that sweats to cool down
Answer
(B) — Poikilotherms do not regulate internal temperature, so their body heat depends on the external environment.
7. What is the likely short-term response of an endotherm to cold weather?
(A) Hibernation
(B) Fur color change
(C) Vasoconstriction and shivering
(D) Estivation
Answer
(C) — Endotherms shiver and reduce blood flow to extremities to conserve heat in cold conditions.
8. Which of the following best describes a biotic factor in an ecosystem?
(A) Soil pH
(B) Ambient temperature
(C) Predation by a hawk
(D) Wind speed
Answer
(C) — Biotic factors include living components, such as predators and prey relationships.
9. What is the ultimate source of energy for nearly all ecosystems on Earth?
(A) Geothermal vents
(B) Heat from Earth's core
(C) The Sun
(D) Decomposition
Answer
(C) — Most ecosystems rely on solar energy, captured by producers during photosynthesis.
10. Which group of organisms contributes most to primary productivity in the ocean?
(A) Sharks
(B) Kelp
(C) Coral
(D) Phytoplankton
Answer
(D) — Microscopic phytoplankton photosynthesize and form the base of the marine food web.
11. Which term describes the total amount of energy fixed by autotrophs in an ecosystem?
(A) Net primary productivity
(B) Gross primary productivity
(C) Biomass conversion rate
(D) Energy yield
Answer
(B) — GPP is the total energy captured by autotrophs before accounting for their respiration.
12. What characteristic distinguishes detritivores from decomposers?
(A) Detritivores consume live prey
(B) Detritivores ingest dead material; decomposers externally digest it
(C) Decomposers are always fungi
(D) Decomposers eat only plant tissue
Answer
(B) — Detritivores consume dead material directly (e.g., earthworms), while decomposers secrete enzymes to break it down externally (e.g., fungi, bacteria).
13. Why do ectothermic animals bask in the sun?
(A) To avoid predators
(B) To digest food faster
(C) To raise body temperature and become active
(D) To synthesize vitamins
Answer
(C) — Ectotherms rely on environmental heat to regulate activity, often basking to warm up.
14. What trophic level does a cow occupy when it grazes on grass?
(A) Primary producer
(B) Primary consumer
(C) Secondary consumer
(D) Decomposer
Answer
(B) — Cows are herbivores, consuming producers, which places them in the primary consumer level.
15. Which of the following describes behavioral thermoregulation?
(A) Sweating
(B) Hibernating
(C) Adjusting enzyme expression
(D) Curling into a ball to reduce heat loss
Answer
(D) — Changing body posture is a behavioral method for retaining or losing heat.
16. What would most likely occur if decomposers were removed from an ecosystem?
(A) Producers would overgrow
(B) Nutrient cycling would stop
(C) Predators would increase
(D) Energy levels would rise
Answer
(B) — Decomposers are crucial for recycling nutrients; without them, essential elements would be locked in organic matter.
17. Why does energy decrease at higher trophic levels?
(A) Organisms become more efficient
(B) Energy is lost as heat and waste at each transfer
(C) Producers absorb more energy
(D) Predators reproduce more slowly
Answer
(B) — Most energy is used for metabolism or lost as heat before it can be passed on.
18. Which adaptation is most likely found in desert animals to prevent overheating?
(A) Insulating fat layers
(B) Large ears for heat dissipation
(C) Black fur
(D) Dense muscle tissue
Answer
(B) — Large ears increase surface area and allow heat to dissipate quickly.
19. Which behavior helps migratory birds survive seasonal environmental changes?
(A) Hibernation
(B) Burrowing
(C) Long-distance travel to warmer areas
(D) Color change
Answer
(C) — Migration allows birds to exploit better climates and food resources seasonally.
20. What is one ecological benefit of animal waste in ecosystems?
(A) Destroys pathogens
(B) Reduces predator pressure
(C) Enriches soil with nutrients
(D) Prevents erosion
Answer
(C) — Animal waste returns nutrients like nitrogen and phosphorus to the soil, promoting plant growth.
21. Why is biodiversity essential to ecosystem health?
(A) It increases light availability
(B) It stabilizes the food web and supports resilience
(C) It promotes predator dominance
(D) It reduces photosynthesis
Answer
(B) — Diverse ecosystems are more stable, resist invasions, and recover more quickly from disturbances.
22. Which process is primarily responsible for moving water from soil into the atmosphere via plants?
(A) Condensation
(B) Transpiration
(C) Precipitation
(D) Fixation
Answer
(B) — Transpiration is the evaporation of water from plant leaves, a key step in the water cycle.
23. What role do beavers play when they build dams and alter river flow?
(A) Keystone species
(B) Invasive species
(C) Decomposers
(D) Parasitic organisms
Answer
(A) — Beavers are keystone species; their dam-building creates wetlands and changes habitats for many other organisms.
24. What distinguishes a food web from a food chain?
(A) Webs include abiotic factors
(B) Chains include more species
(C) Webs show interconnected feeding relationships
(D) Chains are circular
Answer
(C) — A food web better reflects real ecosystems, where organisms feed on multiple species across levels.
25. Which event would represent a density-dependent factor limiting population growth?
(A) Drought
(B) Hurricane
(C) Predation increase due to crowding
(D) Temperature drop
Answer
(C) — Density-dependent factors become stronger as population density increases; predation is one such factor.
26. Which of the following best explains how an ecological bottleneck can reduce resilience in an ecosystem?
(A) It increases biodiversity through mutation
(B) It decreases species richness and reduces functional redundancy
(C) It boosts producer biomass
(D) It enhances gene flow between populations
Answer
(B) — Bottlenecks reduce the number of species, weakening the ecosystem’s ability to recover from future stressors.
27. What is the most likely ecological consequence of introducing a top predator to a previously isolated island ecosystem?
(A) Increased productivity
(B) Decreased nitrogen fixation
(C) Loss of native species due to disrupted food webs
(D) Enhanced soil nutrient cycling
Answer
(C) — Invasive top predators can destabilize native food webs, leading to extinction of species not adapted to predation.
28. Which trait would most likely evolve in organisms in highly seasonal environments?
(A) Constant reproductive rate
(B) Diapause or dormancy
(C) High metabolic rate year-round
(D) Reduced genetic variation
Answer
(B) — In seasonal environments, dormancy allows organisms to survive unfavorable periods and resume activity when conditions improve.
29. What is a potential consequence of reduced net primary productivity in aquatic ecosystems due to increased turbidity?
(A) Expansion of producer biomass
(B) Increased herbivore diversity
(C) Collapse of higher trophic levels
(D) Increase in photosynthetic rates
Answer
(C) — Reduced light penetration decreases photosynthesis in producers, lowering energy availability up the food chain.
30. Which scenario describes a trophic cascade triggered by mesopredator release?
(A) Apex predator controls vegetation
(B) Herbivores eat all producers
(C) Removal of apex predator allows mid-level predators to boom and suppress prey
(D) Producers die from drought
Answer
(C) — When top predators are removed, mesopredators increase, potentially overconsuming prey and unbalancing the system.
31. What condition would most directly lead to eutrophication in a freshwater lake?
(A) Reduced light availability
(B) Excess nutrient runoff from agriculture
(C) Decline in detritivores
(D) Decrease in water temperature
Answer
(B) — Runoff rich in nitrogen and phosphorus causes algal blooms, leading to oxygen depletion and aquatic life loss.
32. Which of the following is most likely to occur if the rate of decomposition exceeds primary production in an ecosystem?
(A) Biomass accumulation
(B) Soil nutrient depletion
(C) Rise in oxygen levels
(D) Collapse of detritivore populations
Answer
(B) — If more nutrients are being broken down than replaced by new organic matter, the ecosystem’s fertility declines.
33. What ecological role is fulfilled when a species maintains habitat conditions that benefit other organisms without directly interacting with them?
(A) Mutualist
(B) Trophic omnivore
(C) Ecosystem engineer
(D) Keystone predator
Answer
(C) — Ecosystem engineers (like beavers or coral) modify the environment in ways that benefit many other species indirectly.
34. Which feedback mechanism occurs when increased vegetation cools local temperature and promotes more plant growth?
(A) Negative feedback
(B) Positive feedback
(C) Density-dependent limitation
(D) Homeostatic inhibition
Answer
(B) — Positive feedback amplifies effects; more vegetation leads to cooling, which supports more vegetation.
35. In energy pyramids, why are the energy values of decomposers typically not shown explicitly?
(A) Decomposers are not part of food webs
(B) Their energy contribution is negligible
(C) They act at multiple levels by recycling nutrients from all trophic stages
(D) They only consume abiotic materials
Answer
(C) — Decomposers interact with all trophic levels, making their energy role difficult to assign to a single level in the pyramid.
36. Explain why ecosystems with higher biodiversity are generally more resilient to disturbances.
Answer
Higher biodiversity increases the likelihood that some species can maintain ecosystem functions during disturbances, providing stability through functional redundancy and adaptive capacity.
37. Describe how energy flows through an ecosystem and contrast it with how matter cycles.
Answer
Energy enters as sunlight, flows through trophic levels, and exits as heat, while matter (like nutrients) is recycled continuously through biotic and abiotic components.
38. What is a keystone species and how can its removal affect an ecosystem?
Answer
A keystone species has a disproportionately large impact on ecosystem structure. Its removal can cause major shifts in species abundance or ecosystem collapse.
39. How can human-induced changes, such as deforestation, disrupt ecosystem energy flow?
Answer
Deforestation reduces primary production, alters food webs, and decreases carbon storage, disrupting energy flow and nutrient cycling across trophic levels.
40. Why is primary productivity typically higher in tropical rainforests compared to deserts?
Answer
Tropical rainforests have ample sunlight, water, and nutrients, allowing rapid photosynthesis and biomass accumulation, unlike deserts with water scarcity.
41. Describe how a trophic cascade initiated by predator removal can influence producer populations.
Answer
Without predators, herbivore populations may rise unchecked, overgrazing producers and reducing primary biomass, altering the entire ecosystem structure.
42. How does nitrogen become available to plants in ecosystems?
Answer
Specialized bacteria fix atmospheric nitrogen into ammonia or nitrates, which plants absorb through roots for protein and nucleic acid synthesis.
43. What is the ecological importance of decomposers in nutrient recycling?
Answer
Decomposers break down dead organisms, releasing essential nutrients like nitrogen and phosphorus back into the soil and water, maintaining ecosystem productivity.
44. Why might invasive species outcompete native species in a new habitat?
Answer
Invasive species often lack natural predators and can reproduce rapidly or exploit resources more efficiently, displacing native species and reducing biodiversity.
45. How does transpiration in plants influence the water cycle?
Answer
Transpiration releases water vapor from plant leaves into the atmosphere, contributing to cloud formation and precipitation in the water cycle.
46. Define the term "carrying capacity" and explain what happens when a population exceeds it.
Answer
Carrying capacity is the maximum number of individuals an environment can sustain. When exceeded, resources become limited, leading to population decline or environmental degradation.
47. What is the difference between gross and net primary productivity?
Answer
Gross primary productivity (GPP) is total energy captured by producers. Net primary productivity (NPP) is the energy left after producers use some for respiration, available to consumers.
48. How does climate change affect the distribution of ecosystems and species?
Answer
Rising temperatures and shifting precipitation patterns alter habitats, forcing species to migrate, adapt, or face extinction, and causing shifts in ecosystem boundaries.
49. Describe one way organisms behaviorally respond to environmental changes.
Answer
Animals may migrate, hibernate, or change activity patterns in response to temperature, light, or food availability to survive environmental changes.
50. How do ecosystem engineers like beavers impact biodiversity?
Answer
Beavers alter habitats by building dams, which create wetlands that support diverse plant and animal species, increasing habitat heterogeneity and overall biodiversity.