Ecosystem MCQs

Biogeochemical cycling ensures the continuous flow of nutrients. Read the following statements regarding nutrient cycles:

I. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycling.
II. Nutrient cycles are of two types: gaseous and sedimentary.
III. The reservoir for the gaseous nutrient cycle (e.g., nitrogen, carbon) exists in the atmosphere.
IV. The reservoir for the sedimentary nutrient cycle (e.g., sulfur, phosphorus) is located in the Earth's crust.

Environmental factors exert significant control over nutrient release rates. Analyze these statements regarding the reservoir function:

I. The function of the reservoir is to meet the deficit which occurs due to an imbalance in the rate of influx and efflux of nutrients.
II. Environmental factors like soil, moisture, pH, and temperature regulate the rate of release of nutrients into the atmosphere.
III. The standing state of nutrients is the amount of living organic matter present in an ecosystem at any given time.
IV. Nutrients are constantly lost from the ecosystem altogether and must be replenished by cosmic dust.

Carbon is a critical structural element of organic molecules. Study these carbon reservoir statistics:

I. Carbon constitutes 49 per cent of the dry weight of organisms, second only to water.
II. About 71 per cent of the global carbon is found dissolved in the oceans.
III. This massive oceanic reservoir regulates the amount of carbon dioxide in the atmosphere.
IV. The atmosphere contains about 25 per cent of the total global carbon.

The dynamic pathways of the Carbon Cycle involve fixation and release. Analyze the following statements:

I. According to estimates, 4 × 10¹³ kg of carbon is fixed annually in the biosphere through photosynthesis.
II. A substantial amount of carbon returns to the atmosphere as CO₂ through respiratory activities of producers and consumers.
III. Decomposers also contribute substantially to the CO₂ pool by processing waste materials and dead organic matter.
IV. Burning of wood, forest fires, combustion of organic matter, and fossil fuels represent additional sources of CO₂ release.

Human interventions are rapidly altering the carbon balance. Which of the following statements regarding human impacts on the carbon cycle are correct?

I. Rapid deforestation has significantly increased the rate of carbon dioxide release into the atmosphere.
II. Massive burning of fossil fuels for energy and transport has significantly increased atmospheric CO₂.
III. Human activities have enhanced the greenhouse effect, leading to global warming.
IV. High atmospheric CO₂ has caused an increase in the rate of carbon fixation in sedimentary rocks by 50%.

Phosphorus is a constituent of vital biological macromolecules and structures. Read these biological facts about phosphorus:

I. Phosphorus is a major constituent of nucleic acids, proteins, and cellular membranes.
II. Phosphorus is required for cellular energy transfer systems (like ATP).
III. Many animals of aquatic ecosystems need large quantities of phosphorus to make their shells, bones, and teeth.
IV. Phosphorus forms the structural backbone of cellulose fibers in plant cell walls.

The phosphorus cycle is sedimentary and differs from gaseous cycles. Consider these pathways:

I. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
II. When rocks weather, minute amounts of phosphates dissolve in soil solution and are absorbed by the roots of plants.
III. Herbivores and other animals obtain phosphorus by eating plants.
IV. The waste products and dead organisms are decomposed by phosphate-solubilizing bacteria, releasing phosphorus.

Gaseous cycles and sedimentary cycles show key differences in transport mechanisms. Compare the Carbon and Phosphorus cycles:

I. Atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs.
II. Gaseous exchanges of phosphorus between organisms and the environment are negligible.
III. Phosphorus cycle has a major gaseous phase that operates in tropical rain forests.
IV. Dissolved organic phosphorus in the oceans is the main reservoir for terrestrial plants.

Ecosystem services represent the benefits humans derive from healthy ecosystems. Study the work of Robert Costanza and his colleagues:

I. Robert Costanza and his colleagues put price tags on nature's life-support services.
II. Researchers have put an average price tag of US $33 trillion a year on global ecosystem services.
III. This US $33 trillion valuation is nearly twice the value of the global gross national product (GNP), which is about US $18 trillion.
IV. Most of these ecosystem service valuations are officially incorporated into global economic policies.

The breakdown of Costanza's US $33 trillion ecosystem services provides insights into resource priority. Read these percentages:

I. Soil formation accounts for nearly 50 per cent of the total cost of ecosystem services.
II. Recreation and nutrient cycling together account for less than 10 per cent of the total cost.
III. The cost of climate regulation and habitat for wildlife are about 6 per cent each.
IV. Soil formation accounts for only 10 per cent, while nutrient cycling accounts for 50 per cent.