Ecosystem MCQs

Consider the following statements regarding the structural features and classification of ecosystems:

I. Vertical distribution of different species occupying different levels is called stratification.
II. In a forest ecosystem, shrubs occupy the top vertical strata or layer, while trees occupy the second strata.
III. Crop fields and an aquarium are examples of man-made or anthropogenic ecosystems.
IV. Many ecologists regard the entire biosphere as a local ecosystem.

An aquatic ecosystem like a shallow pond exhibits complex biotic and abiotic interactions. Which of the following statements regarding a pond ecosystem is/are correct?

I. Phytoplankton, some algae, and floating, submerged, and marginal plants represent the autotrophic components.
II. Zooplankton, free-swimming, and bottom-dwelling forms represent the heterotrophic consumers.
III. Decomposers like fungi, bacteria, and flagellates are especially abundant at the bottom of the pond.
IV. The solar input, cycle of temperature, and day-length regulate the rate of function of the entire pond.

To analyze and compare the productivity of different ecosystems, scientists measure biomass and rate of production. Analyze the statements below:

I. Primary production is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
II. Primary productivity is expressed in terms of weight (g m^-2 yr^-1) or energy (kcal m^-2 yr^-1).
III. Productivity is defined as the rate of biomass production.
IV. Biomass of a species is expressed only in terms of fresh weight because fresh weight measurement is more accurate than dry weight.

Net Primary Productivity (NPP) and Gross Primary Productivity (GPP) are related through respiratory losses (R). Identify the correct statements regarding this relationship:

I. Gross Primary Productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis.
II. A considerable amount of GPP is utilized by plants in cellular respiration.
III. Net Primary Productivity (NPP) is the total rate of capture of solar energy.
IV. Net Primary Productivity is the available biomass for the consumption of heterotrophs (herbivores and decomposers).

The biosphere is characterized by wide variations in productivity. Study the statements regarding global Net Primary Productivity:

I. The annual Net Primary Productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter.
II. Despite occupying about 70 percent of the Earth's surface, the productivity of the oceans is only 55 billion tons.
III. Terrestrial ecosystems contribute approximately 115 billion tons to the annual Net Primary Productivity.
IV. Primary productivity is entirely independent of the plant species inhabiting a particular area.

Consumer energy dynamics are crucial to understand food chains. Which of the following statements regarding secondary productivity is/are correct?

I. Secondary productivity is defined as the rate of formation of new organic matter by consumers.
II. Secondary productivity is the rate of assimilation of food energy by consumers.
III. Herbivores act as secondary producers in a grazing food chain.
IV. Secondary productivity is the rate of capture of solar energy by plants.

Decomposition is a vital ecosystem function. Identify the correct statements regarding the raw materials and initial agents of decomposition:

I. Dead plant remains (leaves, bark, flowers) and dead remains of animals (including faecal matter) constitute detritus.
II. Detritus is the raw material for decomposition.
III. Decomposers are autotrophic organisms that meet their energy needs by fixing carbon dioxide.
IV. Earthworms are detritivores that break down detritus into smaller particles and loosen the soil.

Decomposition involves five distinct, highly coordinated processes. Consider the following statements:

I. Fragmentation, leaching, and catabolism are the three initial steps of decomposition that operate sequentially and never simultaneously.
II. Detritivores break down detritus into smaller particles during fragmentation.
III. By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
IV. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances during catabolism.

Humification and mineralization occur during decomposition in the soil. Study the statements below:

I. Humification leads to the accumulation of a dark-coloured amorphous substance called humus.
II. Humus is highly resistant to microbial action and undergoes decomposition at an extremely rapid rate.
III. Being colloidal in nature, humus serves as a reservoir of nutrients.
IV. Mineralization is the process where humus is further degraded by some microbes to release inorganic nutrients.

Decomposition is heavily regulated by chemical and climatic parameters. Read the following statements:

I. Decomposition is largely an oxygen-requiring process.
II. Decomposition rate is quicker if detritus is rich in lignin and chitin.
III. Decomposition rate is quicker if detritus is rich in nitrogen and water-soluble substances like sugars.
IV. Warm and moist environments favour decomposition, whereas low temperature and anaerobiosis inhibit it.