Ecosystem Structure and Function Practice Questions
20 free Ecosystem Structure and Function practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following are the four basic components that function as a unit in an ecosystem?
- A Productivity, Decomposition, Energy flow, and Nutrient cycling
- B Stratification, Identification, Productivity, and Energy flow
- C Fragmentation, Leaching, Catabolism, and Humification
- D Evaporation, Transpiration, Precipitation, and Condensation
Correct answer: Productivity, Decomposition, Energy flow, and Nutrient cycling
According to NCERT, the four fundamental aspects of an ecosystem are productivity, decomposition, energy flow, and nutrient cycling. These components integrate to allow the ecosystem to function as a self-sustaining unit.
Vertical distribution of different species occupying different levels in a biotic community is known as:
- A Zonation
- B Stratification
- C Succession
- D Eutrophication
Correct answer: Stratification
Stratification refers to the vertical layering of a community. For example, in a forest, trees occupy the top strata, shrubs the second, and herbs/grasses the bottom layers.
The rate of biomass production per unit area over a time period by plants during photosynthesis is called:
- A Net Primary Productivity
- B Secondary Productivity
- C Gross Primary Productivity
- D Net Community Productivity
Correct answer: Gross Primary Productivity
Gross Primary Productivity (GPP) is the total rate at which organic matter is created by producers. A considerable amount of GPP is utilized by plants in respiration before it becomes available to consumers.
What is the relationship between Net Primary Productivity (NPP) and Gross Primary Productivity (GPP)?
- A NPP = GPP + Respiration (R)
- B NPP = GPP - Respiration (R)
- C GPP = NPP - Respiration (R)
- D NPP = GPP / Respiration (R)
Correct answer: NPP = GPP - Respiration (R)
Net Primary Productivity is the weight of organic matter stored by producers after accounting for respiratory losses. It represents the actual biomass available for consumption by heterotrophs.
The rate of formation of new organic matter by consumers is defined as:
- A Net Primary Productivity
- B Secondary Productivity
- C Gross Primary Productivity
- D Standing Crop
Correct answer: Secondary Productivity
Secondary productivity refers to the rate of resynthesis of organic matter by consumers (herbivores and carnivores). It depends on the amount of food energy assimilated from the previous trophic level.
Which of the following ecosystems generally has the lowest net primary productivity?
- A Tropical rain forest
- B Coral reef
- C Deep sea / Ocean
- D Estuary
Correct answer: Deep sea / Ocean
Despite occupying about 70 percent of the Earth's surface, the productivity of oceans is only about 55 billion tons. This is relatively low compared to terrestrial ecosystems due to light limitation and nutrient scarcity in deep waters.
The process of breaking down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients is called:
- A Humification
- B Mineralization
- C Decomposition
- D Catabolism
Correct answer: Decomposition
Decomposition is the metabolic process where detritivores and decomposers break down detritus. It involves several steps including fragmentation, leaching, catabolism, humification, and mineralization.
During decomposition, the process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts is called:
- A Fragmentation
- B Catabolism
- C Leaching of soluble nutrients
- D Mineralization
Correct answer: Leaching of soluble nutrients
Leaching is a specific step in decomposition where water moves through the detritus and carries dissolved nutrients into the lower soil layers. These nutrients often become chemically unavailable to plants in the short term.
Which of the following factors favors a faster rate of decomposition?
- A Detritus rich in lignin and chitin
- B Anaerobic conditions
- C Low temperature
- D Warm and moist environment
Correct answer: Warm and moist environment
Decomposition is largely an oxygen-requiring process. High temperature and soil moisture are the most important climatic factors that increase the metabolic activity of decomposers, thereby speeding up the process.
In a terrestrial ecosystem, what percentage of the energy in the sunlight is typically captured by green plants (PAR)?
- A 100%
- B 50%
- C 2-10%
- D 20-30%
Correct answer: 2-10%
Plants capture only 2-10 percent of the Photosynthetically Active Radiation (PAR). This small amount of energy sustains the entire living world through various food chains and webs.
In an aquatic ecosystem, which food chain is the major conduit for energy flow?
- A Detritus Food Chain (DFC)
- B Grazing Food Chain (GFC)
- C Parasitic Food Chain
- D Saprophytic Food Chain
Correct answer: Grazing Food Chain (GFC)
In aquatic ecosystems, GFC is the major channel for energy flow. In contrast, in terrestrial ecosystems, a much larger fraction of energy flows through the Detritus Food Chain than through the GFC.
According to Lindeman’s 10 percent law, if 1000 J of energy is available at the producer level, how much energy will be available at the secondary consumer level?
- A 100 J
- B 10 J
- C 1 J
- D 0.1 J
Correct answer: 10 J
Only 10 percent of energy is transferred to the next trophic level. If Producers have 1000 J, Primary Consumers (level 2) get 100 J, and Secondary Consumers (level 3) get 10 J.
Each trophic level has a certain mass of living material at a particular time called the:
- A Standing state
- B Standing crop
- C Biomass
- D Net productivity
Correct answer: Standing crop
Standing crop is the total amount of living biomass present in a trophic level at a specific time. It is usually measured as fresh or dry weight, with dry weight being more accurate.
The pyramid of biomass in a sea/ocean ecosystem is generally:
- A Upright
- B Inverted
- C Spindle shaped
- D Urn shaped
Correct answer: Inverted
In oceans, the pyramid of biomass is inverted because the biomass of fishes (consumers) far exceeds the biomass of phytoplankton (producers). This is possible because phytoplankton have very high turnover rates.
Which pyramid can NEVER be inverted in a functional ecosystem?
- A Pyramid of Number
- B Pyramid of Biomass
- C Pyramid of Energy
- D None of the above
Correct answer: Pyramid of Energy
The pyramid of energy is always upright because energy is lost as heat at every trophic level transfer. No ecosystem can transfer more energy to a higher level than it received from the level below.
The amount of nutrients, such as carbon, nitrogen, phosphorus, and calcium, present in the soil at any given time is referred to as:
- A Standing crop
- B Standing state
- C Nutrient pool
- D Mineral reserve
Correct answer: Standing state
Standing state refers to the amount of inorganic nutrients present in the soil/abiotic component of an ecosystem at a given time. It varies in different kinds of ecosystems and also on a seasonal basis.
What is the primary reservoir for the gaseous type of nutrient cycle (e.g., Nitrogen, Carbon)?
- A Earth's crustal rocks and sediments
- B Atmosphere or Hydrosphere
- C Sedimentary rocks and mineral deposits
- D Fossil fuels and organic deposits
Correct answer: Atmosphere or Hydrosphere
For gaseous cycles, the reservoir is located in the atmosphere or the ocean (hydrosphere). For sedimentary cycles (like Phosphorus), the reservoir is located in the Earth's crust.
In the phosphorus cycle, what serves as the natural reservoir of phosphorus?
- A Atmosphere
- B Ocean water
- C Sedimentary rocks
- D Animal bones and tissue
Correct answer: Sedimentary rocks
Phosphorus is a sedimentary cycle. Rocks contain phosphorus in the form of phosphates; when rocks weather, minute amounts of these phosphates dissolve in soil solution and are absorbed by plant roots.
Which of the following is NOT a limitation of ecological pyramids?
- A It does not take into account species belonging to two or more trophic levels simultaneously
- B It assumes a simple food chain and does not accommodate complex food webs
- C Saprophytes are not given any position or place in ecological pyramids
- D It cannot represent the number of individual organisms at each trophic level
Correct answer: It cannot represent the number of individual organisms at each trophic level
Ecological pyramids can indeed show the number of organisms (Pyramid of Numbers). Their limitations include ignoring food webs, saprophytes, and species that occupy multiple trophic levels.
Robert Costanza and his colleagues tried to put price tags on nature’s life-support services. Which service was assigned the highest share of the total cost?
- A Recreation
- B Nutrient cycling
- C Soil formation
- D Climate regulation
Correct answer: Soil formation
Out of the total cost of various ecosystem services, soil formation accounts for about 50 percent. Other services like recreation and nutrient cycling contribute less than 10 percent each.