Understanding the structure of an ecosystem is essential for B. Pharm students studying pharmacognosy, medicinal plant ecology, and environmental impacts on drug discovery. This concise set of Structure of an ecosystem MCQs With Answer focuses on ecosystem structure, trophic levels, biotic and abiotic components, food chains and food webs, energy flow, productivity, and decomposer roles. MCQs cover producers, consumers, nutrient cycling, ecological pyramids, succession, and how habitat structure influences secondary metabolite production in medicinal plants. Each question is tailored to reinforce conceptual understanding and exam readiness. Use these MCQs to prepare effectively for practicals and university exams. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary definition of “structure of an ecosystem”?
- The spatial and functional arrangement of biotic and abiotic components
- The number of species present only
- The chemical composition of soil exclusively
- A record of historical climate data
Correct Answer: The spatial and functional arrangement of biotic and abiotic components
Q2. Which components are included in the biotic part of an ecosystem?
- Producers, consumers, and decomposers
- Soil minerals and water
- Temperature and light
- Atmospheric gases only
Correct Answer: Producers, consumers, and decomposers
Q3. Which of the following best describes an autotroph?
- An organism that synthesizes organic compounds from inorganic sources
- An organism that consumes other organisms for energy
- A microorganism that decomposes dead matter only
- An animal that scavenges carcasses
Correct Answer: An organism that synthesizes organic compounds from inorganic sources
Q4. Which group forms the base of most terrestrial food chains?
- Green plants (producers)
- Herbivores
- Detritivores
- Top carnivores
Correct Answer: Green plants (producers)
Q5. The 10% law in ecology refers to:
- The average energy transfer efficiency between trophic levels
- The amount of water retained by soil
- The proportion of species that are endemic
- The fraction of sunlight reaching the soil surface
Correct Answer: The average energy transfer efficiency between trophic levels
Q6. Which term defines the total chemical energy produced by photosynthesis in a given area and time?
- Gross primary productivity (GPP)
- Net primary productivity (NPP)
- Secondary productivity
- Ecological efficiency
Correct Answer: Gross primary productivity (GPP)
Q7. Net primary productivity (NPP) equals:
- GPP minus plant respiration
- Primary productivity plus secondary productivity
- Only the energy consumed by herbivores
- Energy lost as heat from the ecosystem
Correct Answer: GPP minus plant respiration
Q8. Which of these organisms is classified as a decomposer?
- Fungi
- Rabbit
- Eagle
- Algae
Correct Answer: Fungi
Q9. A food web differs from a food chain because it:
- Shows interlinked feeding relationships among many species
- Only includes herbivores
- Shows a single linear energy flow
- Excludes decomposers
Correct Answer: Shows interlinked feeding relationships among many species
Q10. Which pyramid type can be inverted in aquatic ecosystems?
- Pyramid of biomass
- Pyramid of energy
- Pyramid of numbers in all terrestrial systems
- Pyramid of productivity always
Correct Answer: Pyramid of biomass
Q11. Primary productivity in aquatic systems is most often limited by:
- Nutrient availability (e.g., nitrogen or phosphorus)
- Number of predators
- Soil pH
- Altitude
Correct Answer: Nutrient availability (e.g., nitrogen or phosphorus)
Q12. Which cycle involves nitrogen fixation by bacteria?
- Nitrogen cycle
- Carbon cycle
- Phosphorus cycle
- Hydrological cycle
Correct Answer: Nitrogen cycle
Q13. Biomagnification most commonly affects which type of substances?
- Persistent, fat-soluble pollutants
- Water-soluble vitamins
- Inorganic salts
- Short-lived gases
Correct Answer: Persistent, fat-soluble pollutants
Q14. Which of the following is an example of a detritivore?
- Earthworm
- Deer
- Wolf
- Phytoplankton
Correct Answer: Earthworm
Q15. Succession that begins on bare rock after a volcanic eruption is called:
- Primary succession
- Secondary succession
- Retrogressive succession
- Climax succession
Correct Answer: Primary succession
Q16. A keystone species is best defined as:
- A species with a disproportionate effect on community structure
- The most abundant species numerically
- A species found only at the edge of ecosystems
- A species that competes with all others
Correct Answer: A species with a disproportionate effect on community structure
Q17. Which is an abiotic factor influencing ecosystem structure?
- Temperature
- Herbivore population
- Pathogen diversity
- Plant species richness
Correct Answer: Temperature
Q18. Which statement about ecological niche is correct?
- It is the role and position of a species within an ecosystem
- It is the physical place where an organism lives only
- It refers to the total number of individuals in a species
- It describes only reproductive behavior
Correct Answer: It is the role and position of a species within an ecosystem
Q19. Which process releases CO2 back into the atmosphere from ecosystems?
- Respiration
- Photosynthesis
- Denitrification only
- Transpiration
Correct Answer: Respiration
Q20. Which is a measure commonly used for primary productivity?
- g C m⁻² yr⁻¹ (grams of carbon per square meter per year)
- kg protein per person
- L per minute
- ppm of oxygen in soil
Correct Answer: g C m⁻² yr⁻¹ (grams of carbon per square meter per year)
Q21. The detritus food chain primarily begins with:
- Dead organic matter
- Green plants
- Herbivore feces only
- Abiotic mineral inputs
Correct Answer: Dead organic matter
Q22. Which of the following increases ecosystem stability?
- Higher biodiversity
- Lower species richness
- Monoculture plantations exclusively
- Narrow trophic interactions
Correct Answer: Higher biodiversity
Q23. In ecological terms, carrying capacity refers to:
- Maximum population size an environment can sustain
- Minimum viable population
- Maximum number of species in a community
- Rate of species immigration
Correct Answer: Maximum population size an environment can sustain
Q24. Which process converts atmospheric nitrogen into biologically usable forms?
- Nitrogen fixation
- Nitrification only
- Denitrification
- Ammonification exclusively
Correct Answer: Nitrogen fixation
Q25. Which habitat feature often increases edge effects?
- Fragmentation of habitat
- Continuous unbroken forest
- Deep ocean zones
- High-altitude meadows only
Correct Answer: Fragmentation of habitat
Q26. Which is a major ecological service provided by ecosystems relevant to pharmacognosy?
- Provisioning of medicinal plants and secondary metabolites
- Regulation of traffic flow
- Manufacture of synthetic drugs
- Urban wastewater treatment only
Correct Answer: Provisioning of medicinal plants and secondary metabolites
Q27. Which factor can increase production of secondary metabolites in medicinal plants?
- Environmental stress such as herbivory or drought
- Zero herbivore pressure always
- High levels of pesticides exclusively
- Complete nutrient saturation
Correct Answer: Environmental stress such as herbivory or drought
Q28. Which organism type performs chemosynthesis?
- Certain bacteria using inorganic chemicals as energy source
- Green plants using sunlight only
- Fungi decomposing wood
- Herbivorous insects
Correct Answer: Certain bacteria using inorganic chemicals as energy source
Q29. Which statement about food chain length is usually true?
- Energy loss limits the number of trophic levels
- Longer chains always increase biomass
- They are not influenced by productivity
- They are fixed for all ecosystems
Correct Answer: Energy loss limits the number of trophic levels
Q30. Eutrophication in aquatic ecosystems is most often caused by excess:
- Nutrients such as nitrogen and phosphorus
- Salinity only
- Heavy metals exclusively
- Oxygen input
Correct Answer: Nutrients such as nitrogen and phosphorus
Q31. Which of the following is characteristic of a climax community?
- Relatively stable and in equilibrium with local environment
- Always dominated by pioneer species
- High rates of colonization only
- Rapid species turnover continuously
Correct Answer: Relatively stable and in equilibrium with local environment
Q32. Which of these describes ecological resilience?
- The ability of an ecosystem to recover after disturbance
- The number of endemic species only
- The total biomass present always
- Rate of primary productivity exclusively
Correct Answer: The ability of an ecosystem to recover after disturbance
Q33. Which factor often controls the rate of decomposition?
- Temperature and moisture
- Color of foliage only
- Presence of top predators exclusively
- Latitude only
Correct Answer: Temperature and moisture
Q34. Which of the following is NOT a trophic level?
- Abiotic nutrient pool
- Primary producers
- Secondary consumers
- Tertiary consumers
Correct Answer: Abiotic nutrient pool
Q35. Which term describes organisms that feed on both plants and animals?
- Omnivores
- Detritivores
- Autotrophs
- Saprobes
Correct Answer: Omnivores
Q36. Which process converts organic nitrogen back to ammonium?
- Ammonification
- Nitrification
- Denitrification
- Nitrogen fixation
Correct Answer: Ammonification
Q37. Which of the following best explains energy flow in ecosystems?
- Energy flows in one direction from producers to consumers and decomposers
- Energy cycles indefinitely between trophic levels
- Energy is created within consumers
- Energy always increases at higher trophic levels
Correct Answer: Energy flows in one direction from producers to consumers and decomposers
Q38. Which metric compares ecosystem productivity after accounting for respiration?
- Net primary productivity (NPP)
- Gross primary productivity (GPP)
- Gross secondary productivity
- Biomagnification index
Correct Answer: Net primary productivity (NPP)
Q39. Which human activity typically reduces ecosystem structural complexity?
- Deforestation
- Conservation area establishment
- Rewilding efforts
- Agroforestry practices
Correct Answer: Deforestation
Q40. Which of the following is a consequence of reduced biodiversity for ecosystems?
- Lower resilience to disturbances
- Guaranteed increase in productivity
- Higher trophic efficiency always
- Reduced nutrient limitation always
Correct Answer: Lower resilience to disturbances
Q41. What is the primary role of saprotrophs in ecosystems?
- Breakdown of complex organic matter into simpler substances
- Photosynthesis to produce sugars
- Predation on herbivores
- Fixation of atmospheric carbon
Correct Answer: Breakdown of complex organic matter into simpler substances
Q42. Which biome typically has the highest net primary productivity per unit area?
- Tropical rainforest
- Boreal forest
- Desert
- Tundra
Correct Answer: Tropical rainforest
Q43. In aquatic ecosystems, primary producers are mainly:
- Phytoplankton
- Zooplankton
- Fish
- Macroalgae only
Correct Answer: Phytoplankton
Q44. Which process removes phosphorus from ecosystems on geological timescales?
- Sedimentation into rocks
- Atmospheric fixation
- Denitrification
- Volatilization to air
Correct Answer: Sedimentation into rocks
Q45. Which is an indicator of oligotrophic lake conditions?
- Low nutrient concentrations and high oxygen levels
- High algal blooms and low oxygen
- High turbidity and high phosphorus
- Excessive plant growth always
Correct Answer: Low nutrient concentrations and high oxygen levels
Q46. Which term describes a transitional zone between two ecosystems?
- Ecotone
- Biotope
- Ecospecies
- Biome core
Correct Answer: Ecotone
Q47. Which is the best description of ecological productivity relevant to drug resource management?
- Rate of biomass generation affecting availability of plant-derived compounds
- Number of medicinal compounds discovered per year
- Market value of herbal drugs exclusively
- Rate of pharmaceutical manufacturing only
Correct Answer: Rate of biomass generation affecting availability of plant-derived compounds
Q48. Which process contributes to methane production in wetlands?
- Anaerobic decomposition by methanogenic microbes
- Photosynthesis by emergent plants
- High oxygen supply from flowing water
- Denitrification producing oxygen
Correct Answer: Anaerobic decomposition by methanogenic microbes
Q49. Which factor is a limiting nutrient in many freshwater systems affecting ecosystem structure?
- Phosphorus
- Silicon only
- Sodium exclusively
- Iron always
Correct Answer: Phosphorus
Q50. Which concept links ecosystem structure to potential drug discovery from plants?
- Habitat influences stress and secondary metabolite profiles in medicinal plants
- Only genetic engineering determines metabolite production
- Urban soils always increase medicinal compounds
- Pharmaceutical synthesis replaces ecological considerations
Correct Answer: Habitat influences stress and secondary metabolite profiles in medicinal plants
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