CLEP Biology Ecosystems and Energy Flow 5 — Questions and Answers
Question 1: Which ecological concept explains why most food chains rarely exceed 4–5 trophic levels?
- The principle of competitive exclusion
- Energy loss at each trophic transfer limits available energy (Correct answer)
- Predators become too large to find enough prey beyond 5 levels
- Nutrient cycling becomes inefficient beyond 4 trophic levels
Correct answer: Energy loss at each trophic transfer limits available energy
Because only about 10% of energy passes from one trophic level to the next, energy available to high-order consumers becomes too small to support viable populations beyond 4–5 levels.
Question 2: In the hydrological (water) cycle, which process returns the greatest volume of water vapor to the atmosphere from terrestrial ecosystems?
- Sublimation from glaciers and snowpack
- Evaporation from soil surfaces alone
- Transpiration by plants combined with evaporation (evapotranspiration) (Correct answer)
- Combustion of organic matter releasing water vapor
Correct answer: Transpiration by plants combined with evaporation (evapotranspiration)
Evapotranspiration, the combined loss through soil evaporation and plant transpiration, accounts for the majority of water returning to the atmosphere over land.
Question 3: Which statement accurately describes the relationship between biodiversity and ecosystem stability?
- High biodiversity always decreases ecosystem stability due to more competition
- Ecosystems with greater species richness tend to be more resistant to disturbance (Correct answer)
- Stability depends only on abiotic factors, not species diversity
- Low-diversity ecosystems recover more quickly because fewer species compete for resources
Correct answer: Ecosystems with greater species richness tend to be more resistant to disturbance
Greater species richness provides functional redundancy — if one species is lost, others can fill similar ecological roles, maintaining ecosystem function.
Question 4: Secondary productivity in an ecosystem refers to the rate at which:
- Decomposers break down detritus into inorganic nutrients
- Consumers convert ingested food energy into new consumer biomass (Correct answer)
- Plants fix solar energy through photosynthesis after the first year
- The second trophic level produces oxygen as a byproduct
Correct answer: Consumers convert ingested food energy into new consumer biomass
Secondary productivity measures the rate at which heterotrophic consumers build new biomass from assimilated energy, after subtracting their own respiration losses.
Question 5: Which abiotic factor most strongly determines the distribution and type of terrestrial biome found at a given location?
- Soil pH and mineral content
- Annual temperature and precipitation (Correct answer)
- Atmospheric CO₂ concentration
- Wind speed and direction
Correct answer: Annual temperature and precipitation
Annual patterns of temperature and precipitation are the primary abiotic drivers that determine whether a location supports tundra, grassland, forest, desert, or another biome type.
Question 6: In a freshwater stream, leaf litter that falls from riparian (streamside) trees serves primarily as:
- A source of allochthonous carbon fueling the detrital food web (Correct answer)
- Habitat structure for large fish predators
- A source of autochthonous energy for stream algae
- A physical barrier that increases water oxygenation
Correct answer: A source of allochthonous carbon fueling the detrital food web
Leaf litter is allochthonous (externally derived) organic carbon that fuels shredder invertebrates and decomposers forming the base of many stream food webs.
Question 7: During ecological succession following a volcanic eruption on bare rock, which of the following sequences is correct?
- Shrubs → lichens → mosses → grasses → forest
- Lichens → mosses → grasses/shrubs → forest (Correct answer)
- Grasses → lichens → mosses → pioneer trees → climax forest
- Mosses → lichens → pioneer trees → grasses → climax forest
Correct answer: Lichens → mosses → grasses/shrubs → forest
Primary succession on bare rock begins with pioneer lichens that weather rock, followed by mosses, then herbaceous plants and shrubs, eventually leading to climax forest.
CLEP Biology Ecosystems and Energy Flow 5
Which ecological concept explains why most food chains rarely exceed 4–5 trophic levels?