75 free MCQs on Ecosystem, each with its own worked answer and explanation. Ecosystems, food chains, energy flow, nutrient cycles, biodiversity, and conservation.
75 practice questions on Ecosystem, sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Ecosystem notes.
Energy pyramid showing a simple food chain (producer to herbivore to carnivore) with energy decreasing roughly tenfold at each trophic level.
Easy - 25 questions
Q1.
An upright pyramid of numbers is typically seen in a ___ ecosystem:
Although oceans cover about 70 percent of Earth, their contribution to the annual net primary productivity of the biosphere is comparatively small because:
A Light and nutrients often limit open-ocean producers
B Oceans have no producers
C Decomposition does not occur in water
D Respiration is completely absent in all marine plants
A study finds the grazing food chain removes only a small fraction of net production while most energy flows through dead matter. This indicates that in that ecosystem:
A Producers are absent
B Energy is flowing upward through the chain without any loss
C Biomagnification is occurring
D The detritus food chain is the major pathway of energy flow
During succession, the early pioneer and seral communities are gradually replaced until a stable climax forms. Compared with pioneer stages, the climax community usually shows:
A Greater species diversity and higher total biomass
B Lower species diversity and much less total biomass
If the energy entering the producer level of a pond is 1000 units, applying the ten percent law, the energy reaching the secondary consumers would be about:
The dilution effect in host-pathogen dynamics means:
A Greater species diversity is usually associated with higher overall disease transmission, the reverse of what the dilution effect actually predicts in real ecosystems
B Greater biodiversity dilutes pathogen transmission risk by including non-competent hosts (reducing pathogen to effective host contact)
C Pathogens become physically diluted when mixed into a larger body of water, a literal chemical dilution rather than any host-community ecological effect
D A larger number of available hosts usually results directly in less disease overall, regardless of whether those additional hosts are competent disease reservoirs
A The circular, rotating water currents that form naturally within flowing streams, a hydrological pattern unrelated to nutrient cycling between organisms and water
B Downstream transport and cycling of nutrients -- nutrients spiral through biotic and abiotic forms while being transported downstream
C The cycling of phosphorus specifically, occurring independently of any other nutrient, excluding nitrogen, carbon, and other nutrients that also spiral downstream
D The natural meandering and lateral movement of a river channel over time, a geomorphological process distinct from nutrient transport and uptake
The Janzen-Connell hypothesis explains tropical tree diversity via:
A Exclusion of weaker competitor tree species through sustained direct resource competition, a resource-competition explanation rather than one involving natural enemies
B Species-specific seed predators and pathogens causing high mortality near parent trees, preventing any one species from dominating
C Differences in the amount of sunlight reaching the forest understorey alone, excluding any role for host-specific seed predators or pathogens
D Gradual gradients in soil nutrient availability across the forest floor, excluding any role for natural enemies near the parent tree
A The measured rate at which global sea levels rise per degree of atmospheric warming, a sea-level metric rather than the equilibrium temperature response to CO<sub>2</sub> doubling
B Equilibrium global surface temperature increase due to a doubling of atmospheric CO<sub>2</sub> concentration (currently estimated 2.5-4 degrees C)
C The minimum global temperature threshold required to begin melting polar ice caps, a melting-point threshold rather than an equilibrium temperature response metric
D The total annual rate of carbon dioxide emissions released worldwide each year, an emissions rate rather than a measure of equilibrium temperature response
A Two species directly competing with one another for exactly the same limited resource, a direct resource-competition scenario rather than one mediated indirectly through a shared predator
B Two prey species are negatively affected by a shared predator -- increasing one prey species benefits the predator, which then preys more on the other
C Two species happening to occupy precisely the same ecological niche in a habitat, a niche-overlap scenario distinct from the shared-predator mechanism this term actually describes
D Multiple parasite species competing directly with one another for the same host, a parasite-on-parasite competition scenario rather than a predator-mediated prey interaction
A They actively compete against host tree roots for water and mineral nutrients in soil, a competitive relationship rather than the mutualistic exchange that actually occurs
B Connect roots of different trees, enabling carbon and nutrient transfer between trees (symbiotic network, sometimes called wood wide web)
C They function mainly to absorb water from the soil, with little other ecological role, ignoring their well-documented role in inter-tree carbon and nutrient transfer
D They form symbiotic associations mainly with young seedling trees, not mature ones, excluding the well-documented associations they form with largely mature canopy trees
A By consuming prey organisms more efficiently than other species in the same habitat, a predation-based description rather than one involving physical habitat modification
B Physically creating, modifying, or maintaining habitat (altering abiotic conditions) for other organisms (e.g., beavers, earthworms, elephants)
C By simply possessing the single largest body biomass within their ecosystem, a biomass-based description unrelated to physically altering habitat structure
D By breaking down and decomposing dead organic matter faster than other decomposers, a decomposition-based description unrelated to physically modifying habitat structure
A Through large-scale physical mixing of ocean water layers by wind and currents alone, a purely physical process unrelated to photosynthetic carbon fixation by phytoplankton
B Photosynthesis in surface waters fixing CO<sub>2</sub> into organic matter, which sinks as particles or via organisms to depth, sequestering carbon
C Through volcanic activity releasing carbon dioxide from vents on the ocean floor, a geological carbon source rather than the biologically driven sequestration process
D Through the long-distance seasonal migration patterns of whales across ocean basins, a description of animal migration unrelated to sinking organic particulate carbon
The phosphorus cycle is particularly important because:
A Phosphorus happens to be the single most abundant chemical element found in Earth's crust, when in fact silicon and oxygen far exceed phosphorus in overall crustal abundance by comparison
B Phosphorus has no atmospheric gaseous phase -- it cycles slowly from geological rocks through soil, water, and organisms, making it often the limiting nutrient in aquatic ecosystems
C Phosphorus is generated directly as a byproduct of the photosynthesis reaction in plants, when in reality phosphorus is obtained by plants from weathered rock and soil, not from photosynthesis
D Phosphorus is understood to be an essential nutrient required only within animal tissue, when in fact phosphorus is equally essential for plant growth, not just for animal tissue alone
The paradox of the plankton (Hutchinson) refers to:
A Plankton organisms are simply too microscopically small to be observed without magnification, an observational limitation unrelated to the competitive coexistence puzzle this paradox describes
B Multiple phytoplankton species coexisting in seemingly homogeneous water, violating competitive exclusion principle -- explained by fluctuating environments and multiple limiting resources
C The remarkable way in which plankton populations are able to adapt to chemical pollution over time, a pollution-adaptation description unrelated to the niche-overlap puzzle this paradox actually addresses
D The disproportionately large amount of atmospheric oxygen that plankton are responsible for producing, an oxygen-production fact that has no bearing on the species-coexistence puzzle this paradox addresses