Ecosystem MCQs

Solar radiation is the primary energy input of the biosphere. Analyze these statements regarding incident solar radiation:

I. Of the incident solar radiation, less than 50% is photosynthetically active radiation (PAR).
II. Plants capture only 2-10% of the total incident solar radiation.
III. Plants capture only 2-10% of the PAR, and this small amount of energy sustains the entire living world.
IV. Except for deep-sea hydrothermal ecosystems, the Sun is the only source of energy for all ecosystems on Earth.

Ecosystems are governed by the fundamental laws of physics. Consider the thermodynamic behavior of ecosystems:

I. The unidirectional flow of energy from the Sun to producers and then to consumers is in keeping with the First Law of Thermodynamics.
II. Ecosystems are exempt from the Second Law of Thermodynamics because energy flow is highly efficient.
III. Ecosystems need a constant supply of energy to synthesize molecules and counteract the universal tendency toward increasing disorderliness.
IV. Energy trapped by a producer remains in it forever after its death, preventing its dispersion.

Compare the dynamics of the Grazing Food Chain (GFC) and Detritus Food Chain (DFC):

I. The GFC begins with autotrophic producers, whereas the DFC begins with dead organic matter.
II. In an aquatic ecosystem, GFC is the major conduit for energy flow.
III. In a terrestrial ecosystem, a much larger fraction of energy flows through the DFC than through the GFC.
IV. DFC is completely isolated and can never be connected with GFC at any level.

Food webs represent the true complexity of community interactions. Read the following statements:

I. Decomposers are also known as saprotrophs, which secrete digestive enzymes to break down detritus into simple inorganic materials that they absorb.
II. Cockroaches and crows are omnivores that help interconnect food chains into a food web.
III. Saprophytes are given a prominent place at the base of ecological pyramids.
IV. Food webs exist in nature because simple food chains almost never exist in isolation.

Trophic levels are defined by feeding relationships. Study these statements:

I. Producers belong to the first trophic level, herbivores to the second, and carnivores to the third.
II. Herbivores are primary consumers, and the carnivores that feed on them are secondary consumers.
III. Trophic level represents a specific species as such and not a functional level.
IV. A given species can occupy more than one trophic level simultaneously in the same ecosystem.

Standing crop and energy transfer limits are crucial metrics of food chains. Consider the following statements:

I. Each trophic level has a certain mass of living material at a particular time called the standing crop.
II. Standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.
III. Measurement of biomass in terms of dry weight is more accurate than fresh weight because fresh weight contains fluctuating water content.
IV. The transfer of energy follows the 10 per cent law, meaning only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.

Ecological pyramids map community structures. Analyze the rules of ecological pyramids:

I. The base of each ecological pyramid represents the producers or the first trophic level.
II. The apex of each ecological pyramid represents the tertiary or top-level consumer.
III. Ecological pyramids can express nutritional relationships in terms of number, biomass, or energy.
IV. Decomposers are placed at the very base of standard ecological pyramids to show their functional importance.

Quantitative studies of grasslands show fascinating ecological dynamics. Look at the data-based statements regarding the pyramid of numbers in a grassland ecosystem:

I. In a grassland ecosystem, the pyramid of numbers is upright.
II. Nearly 6 million primary producers are required to support only 3 top carnivores.
III. The number of primary consumers is greater than the number of primary producers in a grassland.
IV. The number of secondary consumers is smaller than the number of tertiary consumers.

The pyramid of biomass in aquatic environments presents unique features. Read the statements below:

I. The pyramid of biomass in the sea is generally inverted.
II. In the sea, a small standing crop of phytoplankton supports a larger standing crop of zooplankton.
III. The biomass of fishes far exceeds that of phytoplankton.
IV. The inverted pyramid of biomass in the sea violates the 10% law of energy transfer.

The pyramid of energy occupies a unique status among ecological pyramids. Analyze the statements regarding this pyramid:

I. The pyramid of energy is always upright and can never be inverted.
II. When energy flows from one trophic level to the next, some energy is always lost as metabolic heat.
III. Primary producers convert only about 1% of the sunlight available to them into net primary productivity.
IV. In some highly productive deep-sea benthic ecosystems, the pyramid of energy becomes inverted.