Ecosystem MCQs

Global carbon fixation involves massive biological transfers. Study these carbon dynamics:

I. About 4 × 10¹³ kg of carbon is fixed in the biosphere annually through photosynthesis.
II. Carbon is returned to the atmosphere as CO₂ through the respiratory activities of producers and consumers.
III. Decomposers do not contribute to the atmospheric CO₂ pool.
IV. Volcanic activity and forest fires act as natural sources of carbon release.

Seral progressions of hydrarch succession show specific transitions. Study the late stages:

I. Rooted-floating plants are followed by the reed-swamp stage.
II. The reed-swamp stage is followed by the marsh-meadow stage.
III. The marsh-meadow stage is followed by the scrub stage.
IV. The scrub stage is followed by the climax forest.

Seral communities change systematic traits as succession moves forward. Identify the correct statements:

I. Seral stages show a progressive change in the species of organisms inhabiting the area.
II. There is an increase in the number of species and organisms as succession proceeds.
III. The diversity of species decreases as we move toward the climax community.
IV. The stable climax community is in near-equilibrium with the environment.

Tree-based ecosystems show unique numbers when plotted. Analyze these patterns:

I. The pyramid of numbers in a grassland ecosystem is upright.
II. Nearly 6 million primary producers support only 3 top-carnivores in a grassland ecosystem.
III. In an ecosystem dominated by a single big tree, the pyramid of numbers is always upright.
IV. In a tree ecosystem, one big tree supports many insects, which support fewer small birds, which support even fewer large birds, resulting in a spindle-shaped pyramid of numbers.

Biogeochemical reservoirs differ depending on elements. Review these reservoir types:

I. The reservoir for gaseous nutrient cycles exists in the atmosphere or hydrosphere.
II. The reservoir for sedimentary nutrient cycles is located in the Earth's crust.
III. Nitrogen and carbon cycles are gaseous, whereas sulfur and phosphorus are sedimentary cycles.
IV. The standing state of nutrients remains completely constant and never fluctuates across seasons.

Read the statements below regarding humification and the nature of humus:

I. Humification occurs during decomposition in the soil and leads to the accumulation of a light-colored amorphous substance called humus.
II. Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
III. Being colloidal in nature, humus serves as a reservoir of nutrients.
IV. Humus is further degraded by some microbes, and inorganic nutrients are released by the process of mineralization.

Succession represents a dynamic change in biological communities. Examine these statements about the starting conditions:

I. Primary succession occurs in areas where no soil or organic matter exists from the start.
II. Secondary succession occurs in areas where natural biotic communities have been destroyed but some soil or sediment remains.
III. Lichens are the typical pioneer species in primary succession on bare rock.
IV. Secondary succession is slower than primary succession because the existing soil contains inhibitors.

Primary productivity is divided into gross (GPP) and net (NPP) components. Identify the correct relationships:

I. Gross primary productivity is the rate of production of organic matter during photosynthesis.
II. Net primary productivity is the fraction of organic matter remaining after respiratory losses (R) of plants.
III. NPP = GPP - R.
IV. Secondary productivity is the biomass of producers left over for decomposers.

Hydrarch succession is marked by specific plant species representing different seral stages. Analyze these stages:

I. The pioneer community is made up of microscopic autotrophs called phytoplanktons.
II. Rooted-submerged plants like Vallisneria and Hydrilla occupy the next seral stage.
III. The rooted-submerged stage is followed by rooted-floating plants like lotus, and then free-floating plants like Pistia.
IV. The transition from reed-swamp and marsh-meadow stages eventually results in a stable forest climax.

Compare the phosphorus cycle with gaseous nutrient cycles. Read these comparisons:

I. Phosphorus is an essential component of nucleic acids, biological membranes, and cellular energy systems.
II. Weathering of rocks releases minute amounts of dissolved phosphate ions into the soil solution.
III. Atmospheric inputs of phosphorus through rainfall are much larger than those of carbon.
IV. Gaseous exchanges of phosphorus between organisms and the environment are practically negligible.