Ecosystem MCQs

Study the statements below regarding the Detritus Food Chain (DFC) and its interactions with the Grazing Food Chain (GFC):

I. The detritus food chain (DFC) begins with dead organic matter.
II. Decomposers are also known as saprotrophs because they degrade dead organic matter.
III. In a terrestrial ecosystem, a much larger fraction of energy flows through the grazing food chain (GFC) than through the DFC.
IV. Organisms of DFC are completely isolated and can never be prey to GFC animals.

Differentiate between standing crop and standing state in ecological ecosystems:

I. Standing crop is the certain mass of living material at a particular trophic level at a given time.
II. Standing crop is measured only as the number of organisms in a unit area.
III. Standing state is the amount of inorganic nutrients, such as carbon, nitrogen, phosphorus and calcium, present in the soil at any given time.
IV. Standing state is measured in terms of the fresh or dry weight of the living organisms.

Catabolism is one of the important processes of decomposition. Read these statements:

I. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
II. This process is called catabolism.
III. Catabolism operates only after fragmentation and leaching are entirely completed.
IV. Enzymes involved in catabolism are secreted extracellularly by saprotrophic decomposers.

Study the dynamics of Global Net Primary Productivity (NPP) across terrestrial and marine biomes:

I. The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter.
II. Oceans occupy about 70 percent of the Earth's surface but contribute only 55 billion tons to global NPP.
III. The main reason for the low productivity of oceans is the severe limitation of water.
IV. Terrestrial ecosystems contribute approximately 115 billion tons to the annual NPP.

Consider the pioneer community and seral progress of xerarch succession on bare rock:

I. Lichens are the pioneer species on a bare rock.
II. Mosses succeed lichens and are able to hold a tiny amount of soil, helping build up a substrate.
III. Mosses are replaced by bigger plants, which are eventually followed by shrubs and then climax forest trees.
IV. The climax forest stage in xerarch succession remains highly unstable because of severe water scarcity.

Robert Costanza and his colleagues estimated price tags on nature's life-support systems. Identify the correct valuations:

I. The average price tag for global ecosystem services is US $33 trillion a year.
II. Soil formation alone accounts for nearly 50 per cent of this total cost.
III. Recreation and nutrient cycling together account for 20 per cent of the total cost (about 10 per cent each).
IV. Climate regulation and habitat for wildlife account for about 6 per cent each.

Ecological succession involves systematic structural transformations. Consider these principles:

I. The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
II. The entire sequence of communities that successively change in a given area are called seral stages.
III. In the successive seral stages, there is no change in the total biomass of the community.
IV. A change in species composition always occurs parallel to a change in the physical environment.

Ecological pyramids fail to represent the complete complexity of ecosystems. What are their limitations?

I. They do not accommodate a food web.
II. They do not take into account the same species belonging to two or more trophic levels.
III. Saprophytes are placed at the topmost tier above tertiary consumers.
IV. They assume a simple food chain which almost never exists in nature.

Of the solar radiation hitting the earth, only a small fraction drives biological production. Analyze these metrics:

I. Less than 50 per cent of the total incident solar radiation is photosynthetically active radiation (PAR).
II. Plants capture only 2 to 10 per cent of the total incident solar radiation.
III. Plants capture only 2 to 10 per cent of the PAR.
IV. This small captured energy (2 to 10% of PAR) sustains the entire living world.

Consider the positions of primary, secondary, and tertiary consumers in standard food chains:

I. Herbivores belong to the second trophic level.
II. Primary carnivores occupy the third trophic level.
III. Secondary consumers are primary carnivores.
IV. Secondary consumers are always herbivores.