Ecosystem — Practice Questions with Answers

Q1.

Which organisms are the primary producers in most ecosystems?

• A Herbivores that consume plants
• B Carnivores that prey on consumers
• C Plants and algae (photosynthesizers)
• D Decomposers breaking down matter

Q2.

The 10% law states that energy transferred from one trophic level to next is approximately:

• A 1%
• B 10%
• C 50%
• D 90%

Q3.

A food chain shows:

• A How organisms within a population reproduce
• B Flow of energy from producers to consumers
• C How water moves through an ecosystem
• D How organisms disperse across a habitat

Q4.

Decomposers in an ecosystem are mainly:

• A Herbivores
• B Carnivores
• C Bacteria and fungi
• D Large animals

Q5.

Biodiversity refers to the:

• A Total number of individual trees growing in a forest
• B Variety of living organisms on Earth (genes, species, ecosystems)
• C Number of officially listed endangered species in a region
• D Total percentage of land area covered by forest canopy

Q6.

The carbon cycle includes which processes?

• A Mainly the process of photosynthesis occurring in green plants
• B Mainly the process of cellular respiration in living organisms
• C Photosynthesis, respiration, decomposition, and combustion
• D Mainly the slow fossilization of buried organic remains over geologic time

Q7.

Ozone layer in the stratosphere protects Earth from:

• A Visible light
• B Harmful UV radiation
• C Radio waves
• D Infrared radiation

Q8.

Eutrophication is caused by:

• A Excess dissolved carbon dioxide gradually entering a freshwater body
• B Excess nutrients (N, P) causing algal blooms, depleting oxygen
• C Oil spills slowly contaminating the surface layer of a water body
• D Heavy metal pollution draining in from nearby industrial runoff sites

Q9.

The term used for the place where an organism lives is:

• A Niche
• B Habitat
• C Biome
• D Ecosystem

Q10.

Food web is:

• A A single, simplified linear food chain within one ecosystem
• B Multiple interconnected food chains in an ecosystem
• C A pyramid diagram showing energy loss at each successive level
• D Mainly the decomposer organisms living within a habitat

Q11.

Mutualism is a relationship where:

• A One benefits, one is harmed
• B Both organisms benefit
• C One benefits, other is unaffected
• D Neither benefits

Q12.

Primary succession starts on:

• A Abandoned farmland
• B Bare rock with no soil
• C Disturbed forest
• D Sandy beach with some soil

Q13.

Which gas is depleting the ozone layer?

• A Carbon dioxide (CO2)
• B CFCs (chlorofluorocarbons)
• C Oxygen (O2) gas
• D Methane (CH4) gas

Q14.

Keystone species are species whose:

• A Possess the single largest overall biomass within the ecosystem
• B Removal causes disproportionately large effects on the ecosystem
• C Maintain the single largest population size in the community
• D Occupy the single smallest geographic range in the habitat

Q15.

The competitive exclusion principle states:

• A Two species generally tend to coexist stably regardless of their resource needs in most cases
• B Two species occupying exactly the same ecological niche cannot coexist -- one will be excluded
• C Competition between species generally tends to increase overall biodiversity in most ecosystems
• D Predators are generally understood to substantially reduce their prey species populations over time

Q16.

Biomagnification refers to:

• A Organisms gradually getting physically larger at higher trophic levels over generations
• B Increasing concentration of toxins at each higher trophic level
• C Increasing biodiversity observed gradually with rising altitude in mountain ecosystems
• D Greater available energy concentrated specifically at the top of the energy pyramid

Q17.

The nitrogen cycle includes denitrification, which converts:

• A Converts atmospheric N2 gas into ammonia (NH3) directly
• B Converts ammonia (NH3) into nitrate (NO3-) ions
• C NO3- back to N2 gas (by bacteria in anaerobic conditions)
• D Converts organic nitrogen compounds into ammonia (NH3)

Q18.

r-selected species (r-strategists) are characterized by:

• A Slow reproduction and production of few offspring accompanied by extensive parental care
• B Rapid reproduction, many small offspring, little parental care, boom-bust population cycles
• C Consistently long individual life spans extending over many years
• D Stable population sizes maintained right at the environment's carrying capacity

Q19.

Ecological succession reaching a stable, self-sustaining community is called:

• A Pioneer stage
• B Intermediate stage
• C Climax community
• D Seral stage

Q20.

The energy available at each trophic level can be represented as a:

• A A symmetrical bell-shaped curve plotted across all the trophic levels present
• B Pyramid of energy (decreasing from producers to top consumers)
• C A perfect circle connecting all of the trophic levels together in sequence
• D A flat, unchanging line plotted consistently across all trophic levels present

Q21.

Invasive species cause problems because:

• A They are characterized mainly by their unusually large physical body size compared to natives
• B They disrupt native ecosystems, outcompete native species, or prey on them without natural controls
• C They are sometimes thought to function mainly as apex predators within their new environment
• D They are sometimes thought to mainly require greater access to direct sunlight than natives

Q22.

The term for organisms that occupy the same trophic level is:

• A Niche equivalents
• B Trophic equals
• C Guild (functional group)
• D Biome type

Q23.

Which of these best describes the concept of carrying capacity (K)?

• A The maximum possible growth rate achievable by a population
• B Maximum population size an environment can sustainably support
• C The minimum population size needed for long-term viability
• D The combined total biomass of every species in an area

Q24.

Primary productivity measures:

• A The total combined biomass of all animal consumers present in an ecosystem
• B Rate at which producers convert light energy to chemical energy (organic matter)
• C The total number of distinct species present within an entire ecosystem
• D The overall rate at which decomposers break down organic matter present

Q25.

Parasitism differs from predation in that in parasitism:

• A The host organism is understood to usually be killed by the parasite
• B The parasite lives in or on host, harming it without immediately killing it
• C Both interacting species are understood to mutually benefit from the relationship
• D The parasite is understood to usually be physically larger than its host

Q26.

Commensalism is a relationship where:

• A Both interacting species derive clear benefit from the relationship
• B One benefits, the other is neither helped nor harmed
• C One species benefits while the other species is actively harmed
• D Neither of the two interacting species derives any benefit

Q27.

A biome is defined primarily by:

• A Primarily defined by the total number of species present
• B Climate (temperature and precipitation patterns)
• C Primarily defined by altitude above sea level alone
• D Primarily defined by soil composition and type alone

Q28.

Which process in the nitrogen cycle makes N2 available to plants?

• A Denitrification converting nitrate back into atmospheric nitrogen gas
• B Nitrogen fixation (converting N2 to NH3 by bacteria)
• C Nitrification converting ammonia into nitrite and then nitrate
• D Ammonification converting organic nitrogen into ammonia

Q29.

The concept of ecological stoichiometry examines:

• A The genetic structure and allele frequencies present within a population, a description of population genetics rather than elemental nutrient ratios
• B The balance of chemical elements (C, N, P) within and between organisms and their environment, affecting food webs and nutrient cycling
• C Mainly the cycling of carbon between the atmosphere and living organisms, ignoring nitrogen and phosphorus ratios that actually define this concept
• D Mainly the dynamics of dissolved oxygen within aquatic ecosystems, a narrower topic unrelated to the elemental balance this term describes

Q30.

Net primary productivity (NPP) equals:

• A The total combined photosynthetic output across an entire ecosystem without subtracting any respiratory losses
• B Gross primary productivity (GPP) minus autotroph respiration (Ra) -- energy available to consumers
• C Mainly the total biomass produced by animal consumers each year excluding any contribution from producers
• D Mainly the total organic matter generated by decomposer organisms excluding any net production from autotrophs

Q31.

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

Q32.

Global warming potential (GWP) of methane is approximately _____ times that of CO2 over 100 years:

• A 2 times
• B 12 times
• C 28-36 times
• D 100 times

Q33.

Nutrient spiraling in streams refers to:

• 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

Q34.

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

Q35.

IPCC defines climate sensitivity as:

• 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 CO2 doubling
• B Equilibrium global surface temperature increase due to a doubling of atmospheric CO2 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

Q36.

Apparent competition occurs when:

• 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

Q37.

The green world hypothesis (Hairston, Smith, Slobodkin) proposes:

• A Plants are sometimes thought to dominate ecosystems mainly because sunlight is universally abundant everywhere in general practice
• B The world is green because herbivores are kept in check by their predators (top-down control), not by plant food supply
• C Every trophic level in an ecosystem is sometimes thought to be limited primarily by available food supply alone as frequently described
• D Producer biomass is sometimes thought to consistently outcompete consumer biomass in nearly any ecosystem in most textbook accounts

Q38.

Mycorrhizal networks in forests:

• 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

Q39.

Ecosystem engineers modify their environment by:

• 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

Q40.

The biological pump in the ocean moves carbon by:

• 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 CO2 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

Q41.

REDD+ (Reducing Emissions from Deforestation and Degradation) is a mechanism for:

• A Establishing new forest plantations specifically within urban city environments mainly during normal conditions as generally observed
• B Providing financial incentives for developing countries to reduce forest carbon emissions and sustainably manage forests
• C Funding the construction of new fossil-fuel power generation plants in rural regions broadly in typical laboratory settings
• D Monitoring and recording deforestation rates while offering little real financial incentive under usual circumstances

Q42.

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

Q43.

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