Rucete ✏ AP Biology In a Nutshell
20. The Basics of Ecology — Practice Questions 3
This chapter explains how organisms respond to environmental stimuli and how energy and matter move through ecosystems via trophic levels and regulatory mechanisms.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following signals is most commonly used by nocturnal animals to communicate mating readiness?
(A) Visual signals
(B) Chemical signals
(C) Tactile signals
(D) Electrical signals
Answer
(B) — Nocturnal animals rely heavily on chemical signals (e.g., pheromones) due to limited visibility at night.
2. What is the function of tactile signaling in social primates?
(A) Thermoregulation
(B) Expression of dominance and bonding
(C) Hunting coordination
(D) Reproductive isolation
Answer
(B) — Primates use touch (like grooming) to maintain social bonds and establish hierarchies.
3. Why do smaller animals require more food per unit body mass compared to larger animals?
(A) They move more quickly
(B) They have higher surface area-to-volume ratios, increasing heat loss
(C) They lack internal organs for digestion
(D) They store less fat
Answer
(B) — Smaller animals lose heat faster due to a higher surface area relative to volume, requiring more energy to maintain body function.
4. Which behavior most clearly represents top-down regulation in an ecosystem?
(A) Plants die due to a drought
(B) A predator controls herbivore populations
(C) Soil nutrient loss affects plant growth
(D) Sunlight reduction limits photosynthesis
Answer
(B) — Top-down regulation occurs when predators influence the population sizes of lower trophic levels.
5. Why is kleptoplasty beneficial to the sea slug *Elysia crispata*?
(A) It increases its ability to digest prey
(B) It lets the slug use chloroplasts for photosynthesis during food scarcity
(C) It enhances camouflage
(D) It provides reproductive advantage
Answer
(B) — The sea slug stores chloroplasts from consumed algae and uses them to photosynthesize when food is unavailable.
6. Which type of behavioral adaptation is most likely in desert animals during the hottest part of the day?
(A) Seeking open sun
(B) Increased mating activity
(C) Burrowing or hiding in shade
(D) Expelling excess water
Answer
(C) — Many desert animals avoid extreme heat by becoming inactive or hiding during midday to conserve water and energy.
7. What is the main reason that energy pyramids are always upright?
(A) Decomposers exist only at the base
(B) Energy input increases with trophic level
(C) Energy is lost at each trophic level
(D) Herbivores are more efficient than carnivores
Answer
(C) — Energy is lost as heat and waste at each level, leaving less energy available for organisms higher up in the pyramid.
8. Which of the following best describes a population's response when it approaches its carrying capacity?
(A) Exponential growth
(B) Rapid extinction
(C) Logistic growth with slowed rate
(D) Immediate overshoot and collapse
Answer
(C) — As a population nears carrying capacity, growth rate slows due to limited resources, resulting in logistic growth.
9. What is one way that plants can influence the water cycle?
(A) Reducing transpiration
(B) Increasing runoff
(C) Absorbing carbon dioxide
(D) Releasing water vapor through transpiration
Answer
(D) — Through transpiration, plants release water vapor into the atmosphere, contributing to the water cycle.
10. Which organisms play a major role in decomposing organic matter in forest soils?
(A) Earthworms and fungi
(B) Herbivores
(C) Carnivorous plants
(D) Insects that consume live prey
Answer
(A) — Fungi and earthworms are key decomposers in soil ecosystems, recycling nutrients from dead material.
11. Which of the following would be a short-term physiological response to cold in endotherms?
(A) Migration
(B) Hibernation
(C) Shivering
(D) Color change
Answer
(C) — Shivering generates heat by muscle activity and is a rapid physiological response to cold in endotherms.
12. What is an example of an abiotic factor that affects aquatic ecosystems?
(A) Competition for mates
(B) Salinity levels
(C) Predator-prey interaction
(D) Decomposer activity
Answer
(B) — Salinity, a non-living physical factor, affects which species can survive in a body of water.
13. How do trophic levels relate to energy flow in ecosystems?
(A) Each level gains energy from sunlight
(B) Only top predators receive energy
(C) Energy is transferred up but decreases at each level
(D) Energy moves in a circular loop
Answer
(C) — Energy flows from producers to consumers, but most is lost as heat or used in metabolism, reducing availability up the chain.
14. Which of the following animals is most likely an ectotherm?
(A) Dolphin
(B) Bird
(C) Frog
(D) Human
Answer
(C) — Frogs rely on environmental heat and are considered ectotherms.
15. What role do producers play in the carbon cycle?
(A) Releasing carbon through photosynthesis
(B) Absorbing carbon dioxide to form organic molecules
(C) Fixing nitrogen into glucose
(D) Breaking down dead organisms
Answer
(B) — Producers absorb atmospheric CO₂ during photosynthesis to build sugars and other organic molecules.
16. Which process increases atmospheric carbon dioxide levels?
(A) Photosynthesis
(B) Nitrogen fixation
(C) Cellular respiration
(D) Transpiration
Answer
(C) — Cellular respiration releases CO₂ as organisms break down food for energy.
17. What is one major function of wetlands in ecosystems?
(A) Increase desertification
(B) Filter pollutants and absorb floodwaters
(C) Reduce biodiversity
(D) Increase evaporation only
Answer
(B) — Wetlands act like sponges, filtering runoff and storing water to reduce flooding and improve water quality.
18. Why are detritivores important to nutrient cycling?
(A) They store nutrients long-term
(B) They fix atmospheric nitrogen
(C) They break down waste and dead material into usable forms
(D) They consume only living tissue
Answer
(C) — Detritivores feed on dead material, helping return nutrients to the soil for reuse by producers.
19. Which of the following is a density-independent factor that can limit population growth?
(A) Disease
(B) Predation
(C) Food shortage
(D) Natural disaster
Answer
(D) — Events like hurricanes or floods affect populations regardless of their size, making them density-independent.
20. Which level of biological organization includes both biotic and abiotic components?
(A) Population
(B) Organism
(C) Community
(D) Ecosystem
Answer
(D) — An ecosystem consists of living organisms and their interactions with the nonliving environment.
21. Which trophic level is typically the largest in biomass in terrestrial ecosystems?
(A) Secondary consumers
(B) Primary producers
(C) Decomposers
(D) Tertiary consumers
Answer
(B) — Primary producers form the base of the food chain and usually contain the most biomass.
22. Which of the following is an example of a behavioral adaptation to seasonal changes?
(A) Shedding fur
(B) Estivation
(C) Production of antifreeze proteins
(D) Increased fat storage
Answer
(B) — Estivation is dormancy during hot or dry periods, a behavioral strategy for surviving seasonal extremes.
23. What defines the ecological niche of an organism?
(A) Its genetic diversity
(B) Its position in a food chain only
(C) Its role, resource use, and environmental conditions
(D) Its biomass
Answer
(C) — An organism’s niche includes everything about how it lives and interacts with its environment.
24. What process converts ammonia into nitrates that plants can absorb?
(A) Nitrogen fixation
(B) Nitrification
(C) Denitrification
(D) Ammonification
Answer
(B) — Nitrifying bacteria convert ammonia to nitrites and then nitrates that plants can use.
25. What is the role of apex predators in maintaining ecological balance?
(A) Promoting overgrazing
(B) Stabilizing prey populations and food web structure
(C) Disrupting nutrient cycling
(D) Converting solar energy into ATP
Answer
(B) — Apex predators regulate prey populations, preventing overpopulation and maintaining balance in ecosystems.
26. Which of the following best illustrates a negative feedback loop in ecological systems?
(A) Predator numbers drop, leading to a prey boom
(B) Herbivore population increases, leading to overgrazing and population crash
(C) More producers lead to more herbivores
(D) Increased sunlight causes plants to photosynthesize continuously
Answer
(B) — Overgrazing due to too many herbivores reduces available food, eventually limiting population size — a classic negative feedback.
27. In the nitrogen cycle, which process returns nitrogen gas to the atmosphere?
(A) Nitrogen fixation
(B) Ammonification
(C) Nitrification
(D) Denitrification
Answer
(D) — Denitrification converts nitrates back into nitrogen gas, releasing it to the atmosphere.
28. Why does an energy pyramid usually have fewer organisms at higher trophic levels?
(A) Competition is lower at the top
(B) There is more energy available at higher levels
(C) Energy is lost at each level, limiting population sizes
(D) Producers consume top predators
Answer
(C) — Only about 10% of energy passes from one trophic level to the next, supporting fewer organisms at higher levels.
29. What makes estuaries among the most productive ecosystems on Earth?
(A) They have little human impact
(B) Their waters are deep and nutrient-poor
(C) They receive nutrients from both rivers and oceans
(D) They are always shaded from the sun
Answer
(C) — Estuaries receive nutrient-rich input from land and sea, making them highly productive and biodiverse.
30. Which of the following is a long-term adaptation to cold environments in animals?
(A) Shivering
(B) Growing thicker fur during winter
(C) Migration
(D) Evolution of compact body shape to reduce heat loss
Answer
(D) — Bergmann’s rule explains that animals in cold climates tend to have compact bodies to conserve heat — a long-term adaptation.
31. Which statement best describes primary productivity in open ocean ecosystems?
(A) It is uniformly high across all regions
(B) It is highest in deep water areas
(C) It is limited by nutrient availability despite abundant sunlight
(D) It increases with depth
Answer
(C) — Though sunlight is available, open oceans often lack nutrients, limiting primary productivity.
32. What is likely to happen in an ecosystem where a non-native herbivore has no natural predators?
(A) The food web becomes more efficient
(B) Top predator populations increase
(C) Overgrazing reduces plant diversity and disrupts balance
(D) Photosynthesis increases across all species
Answer
(C) — Without checks, the invasive herbivore can overconsume plants, altering the ecosystem structure.
33. Which of the following organisms is both a primary and secondary consumer?
(A) Deer
(B) Eagle
(C) Bear
(D) Mouse
Answer
(C) — Bears eat both plants (primary consumer role) and animals (secondary consumer role), making them omnivores.
34. How does an energy pyramid differ from a biomass pyramid in aquatic systems?
(A) They are always identical
(B) Biomass pyramids can be inverted, but energy pyramids are always upright
(C) Energy pyramids can be inverted
(D) Energy pyramids exclude decomposers
Answer
(B) — In aquatic systems, producers like phytoplankton may have low biomass but high turnover, inverting the biomass pyramid — but energy flow still decreases up levels.
35. Which process best explains how carbon is returned from the atmosphere into long-term geological storage?
(A) Combustion
(B) Erosion
(C) Sedimentation and fossilization
(D) Transpiration
Answer
(C) — Carbon from dead organisms can become trapped in sediments and eventually form fossil fuels or rock deposits over geologic time.
36. Explain how energy transfer limits the number of trophic levels in an ecosystem.
Answer
Because only about 10% of energy is passed on at each level, there isn’t enough energy to support many levels, typically limiting ecosystems to 4–5 trophic levels.
37. Describe the role of decomposers in the cycling of matter.
Answer
Decomposers break down dead organisms and waste, releasing nutrients back into the soil and water for use by producers, completing the nutrient cycle.
38. How does an organism’s surface area-to-volume ratio affect thermoregulation?
Answer
Organisms with higher surface area-to-volume ratios lose heat more easily, requiring behavioral or physiological adaptations to maintain body temperature.
39. Why is photosynthesis critical to ecosystem energy flow?
Answer
Photosynthesis captures solar energy and converts it into chemical energy stored in glucose, which serves as the energy source for all higher trophic levels.
40. What ecological consequences can result from the removal of a top predator?
Answer
Removing top predators can cause prey populations to grow unchecked, potentially leading to overgrazing, collapse of vegetation, and disruption of food webs.
41. Define the term “carrying capacity.”
Answer
Carrying capacity is the maximum population size that an environment can sustainably support given the available resources.
42. What distinguishes an ecosystem from a community?
Answer
An ecosystem includes both biotic (living) and abiotic (nonliving) components, while a community includes only the interacting populations of living organisms.
43. How do invasive species alter native ecosystems?
Answer
Invasive species often outcompete native species for resources and lack natural predators, disrupting population dynamics and reducing biodiversity.
44. Describe how water moves through plants during transpiration.
Answer
Water is absorbed by roots, transported through xylem, and evaporated from leaf surfaces, pulling more water upward in a continuous flow.
45. How can climate change affect primary productivity?
Answer
Changes in temperature and precipitation can stress producers, alter growing seasons, and reduce photosynthetic rates, decreasing productivity in many ecosystems.
46. What is ecological succession?
Answer
Ecological succession is the gradual change in species composition of a community over time, often following disturbance or the formation of new habitat.
47. Why is nutrient cycling essential for ecosystem sustainability?
Answer
Nutrient cycling ensures that essential elements like nitrogen and phosphorus are reused and remain available to support primary producers and other organisms.
48. How do behavioral adaptations help organisms survive extreme environments?
Answer
Behavioral adaptations such as migration, hibernation, and burrowing help organisms avoid harsh conditions and conserve energy or water.
49. What is the function of stomata in plant leaves?
Answer
Stomata regulate gas exchange by allowing CO₂ in for photosynthesis and releasing oxygen and water vapor, aiding in both energy production and transpiration.
50. How does biodiversity enhance ecosystem resilience?
Answer
Diverse ecosystems can better absorb disturbances, maintain function, and recover from environmental stress due to the variety of species fulfilling different roles.