Ecosystem MCQs

Robert Costanza and his team calculated the economic value of various ecosystem services. Analyze the percentage distribution:

I. Soil formation accounts for about 50 per cent of the total ecosystem services cost.
II. Recreation and nutrient cycling each account for about 10 per cent of the total cost.
III. Climate regulation and habitat for wildlife account for about 6 per cent each.
IV. The total average cost of these services is estimated to be US $33 trillion per year.

Energy transfers are limited by thermodynamic inefficiencies. Study these energy dynamics:

I. Only 10 per cent of the energy is transferred from a lower trophic level to the next higher level.
II. Energy flow is strictly unidirectional, moving from solar input to producers and then to consumers.
III. Because of the 10% law, the number of trophic levels in a Grazing Food Chain (GFC) is restricted, rarely exceeding 4 to 5.
IV. Top carnivores receive the maximum concentration of energy in an ecosystem.

Standing crop is an important community parameter. Identify the correct statements regarding its measurement:

I. Each trophic level has a certain mass of living material at a particular time, called the standing crop.
II. It is measured as the mass of living organisms (biomass) or the number in a unit area.
III. Biomass of a species is expressed in terms of either fresh or dry weight.
IV. Measurement of biomass in terms of fresh weight is more accurate than dry weight.

Stratification represents a key structural attribute of terrestrial ecosystems. Analyze these statements:

I. Vertical distribution of different species occupying different levels is called stratification.
II. In a forest ecosystem, trees occupy the top vertical strata, shrubs occupy the second layer, and herbs or grasses occupy the bottom layers.
III. Tropical rainforests exhibit the least pronounced vertical stratification.
IV. Stratification allows different species to share light and space resources efficiently.

Ponds are excellent systems to study basic ecosystem dynamics. Which of the following functional components is or are active in a pond?

I. Productivity: autotrophic plants convert inorganic materials into organic molecules.
II. Decomposition: fungi and bacteria break down dead organic matter.
III. Energy flow: unidirectional transfer of chemical energy from autotrophs to zooplankton and small fish.
IV. Nutrient cycling: release of inorganic nutrients from sediment back to the water and plants.

Decomposers perform vital saprotrophic recycling. Read these statements:

I. Decomposers are heterotrophic organisms, mainly fungi and bacteria.
II. They meet their energy and nutrient requirements by degrading dead organic matter or detritus.
III. Decomposers secrete digestive enzymes extracellularly to convert dead organic material into simple soluble inorganic substances.
IV. Detritivores like earthworms are also categorized as microbial decomposers.

Carbon cycles globally through both biotic and abiotic pathways. Analyze these statements:

I. Carbon is fixed in the biosphere through the process of photosynthesis.
II. A major amount of fixed carbon returns to the atmosphere as CO₂ through respiration of plants and animals.
III. Burning of fossil fuels, wood, and forest fires are additional sources of CO₂ release.
IV. Volcanic activity does not release any carbon compounds into the atmosphere.

Secondary productivity is defined by energy capture at consumer levels. Study these statements:

I. Secondary productivity is the rate of formation of new organic matter by consumers.
II. It is the rate at which primary consumers assimilate food energy into their own biomass.
III. Secondary productivity is always greater than Gross Primary Productivity (GPP) because consumers are more active.
IV. Herbivores represent the primary level of secondary productivity.

Decomposition rate is sensitive to physical and chemical parameters. Read these statements:

I. Decomposition is highly accelerated under warm and moist conditions.
II. Decomposition is extremely slow under low temperature and anaerobiosis.
III. Detritus rich in lignin and chitin decomposes very rapidly.
IV. Detritus rich in nitrogen and water-soluble substances decomposes quickly.

Ecological pyramids are heavily simplified and abstract. Identify their specific limitations:

I. They assume a simple food chain, which almost never exists in nature.
II. They do not accommodate a complex food web.
III. They do not take into account that the same species can belong to multiple trophic levels.
IV. Saprophytes (decomposers) are completely ignored and excluded from these pyramids.