Biomass pyramids can show unique shapes across terrestrial and aquatic systems.
I. In most terrestrial ecosystems, the pyramid of biomass is upright because producers have far more mass than herbivores. II. In aquatic ecosystems like the sea, the pyramid of biomass is generally inverted. III. In the sea, a small standing crop of phytoplankton supports a larger standing crop of zooplankton and fishes. IV. The inverted pyramid of biomass in the sea is a stable configuration because phytoplankton have high turnover rates.
All four statements are correct. In terrestrial ecosystems the biomass pyramid is generally upright, whereas in aquatic ecosystems it is inverted because phytoplankton have a very high turnover rate and support a much larger consumer biomass.
Question 92 of 100
📘 CLASS XII
Pyramids of numbers can vary depending on the host-parasite or tree structures.
I. The pyramid of numbers in a grassland ecosystem is upright. II. A single big tree supporting hundreds of herbivorous insects exhibits an inverted base in its pyramid of numbers. III. If hyperparasites feed on parasites of those insects, the pyramid of numbers becomes completely upright again. IV. In a tree-insect-bird chain, the pyramid of numbers is spindle-shaped.
Statements I, II and IV are correct. Statement III is incorrect because addition of parasites and hyperparasites further increases organism numbers at higher trophic levels, making the pyramid more inverted rather than upright.
Question 93 of 100
📘 CLASS XII
Successional sequences lead to a stable climatic endpoint.
I. Hydrarch succession starts in water bodies and progresses from hydric to mesic conditions. II. Xerarch succession starts on dry rock and progresses from xeric to mesic conditions. III. Both hydrarch and xerarch successions converge at a medium moisture status called mesic conditions. IV. The stable climax community for both hydrarch and xerarch successions is a forest.
All four statements are correct. Both hydrarch and xerarch successions ultimately lead to a stable mesic forest climax community.
Question 94 of 100
📘 CLASS XII
Secondary succession is highly influenced by existing environmental factors.
I. Secondary succession occurs on abandoned farm lands, burned forest land, and flooded lands. II. Since some soil or sediment is already present, the rate of secondary succession is much faster than primary succession. III. The pioneer species of secondary succession are always lichens and mosses. IV. The species that invade during secondary succession depend on the condition of the soil, availability of water, and seeds or other propagules.
Statements I, II and IV are correct. Statement III is incorrect because grasses, herbs and weeds usually act as pioneers in secondary succession, whereas lichens and mosses are pioneers in primary succession on bare rock.
Question 95 of 100
📘 CLASS XII
Standing state and standing crop represent distinct structural phases.
I. Standing state represents the inorganic nutrient pool (C, N, P, Ca) present in the soil. II. Standing crop represents the living biomass present at a particular trophic level at a given time. III. Standing state is completely static and never changes with season. IV. Standing crop can be measured as the dry weight of organisms in a unit area.
Statements I, II and IV are correct. Statement III is incorrect because standing state changes seasonally depending on nutrient uptake and environmental conditions.
I. A food web is formed when multiple food chains are interconnected. II. Food webs provide alternative pathways for energy flow, which increases the stability of the ecosystem. III. A species can occupy different trophic levels simultaneously in a food web. IV. In nature, simple linear food chains exist in complete isolation from one another.
Statements I, II and III are correct. Statement IV is incorrect because food chains are interconnected to form food webs.
Question 97 of 100
📘 CLASS XII
Gaseous and sedimentary biogeochemical cycles operate differently.
I. The gaseous nutrient cycle reservoir exists in the atmosphere or hydrosphere. II. The sedimentary nutrient cycle reservoir is located in the Earth's crust. III. Nitrogen and Carbon are sedimentary cycles, while Sulfur and Phosphorus are gaseous cycles. IV. Nutrients are recycled repeatedly within the ecosystem without being permanently lost.
Statements I, II and IV are correct. Statement III is incorrect because nitrogen and carbon are gaseous cycles, whereas sulfur and phosphorus are sedimentary cycles.
Question 98 of 100
📘 CLASS XII
Compare the Grazing Food Chain (GFC) and Detritus Food Chain (DFC).
I. GFC begins with living green plants, whereas DFC begins with dead organic matter. II. GFC is always aquatic, whereas DFC is always terrestrial. III. In an aquatic ecosystem, GFC is the major conduit for energy flow. IV. In a terrestrial ecosystem, a much larger fraction of energy flows through the DFC than through the GFC.
Statements I, III and IV are correct. Statement II is incorrect because both GFC and DFC occur in aquatic as well as terrestrial ecosystems.
Question 99 of 100
📘 CLASS XII
Photosynthetically Active Radiation (PAR) drives primary production.
I. Of the incident solar radiation, less than 50 per cent is photosynthetically active radiation (PAR). II. Plants capture only 2-10 per cent of this PAR. III. This small amount of energy (2-10% of PAR) sustains the entire living world on Earth except deep-sea hydrothermal systems. IV. Plants capture about 50 per cent of total incident solar radiation during photosynthesis.
Statements I, II and III are correct. Statement IV is incorrect because plants capture only 2-10% of PAR, which itself is less than 50% of total incident solar radiation.
Question 100 of 100
📘 CLASS XII
The four major functional components of an ecosystem are highly coordinated.
I. Productivity, Decomposition, Energy flow, and Nutrient cycling are the four basic functional aspects of any ecosystem. II. These four components work in a highly coordinated, integrated manner to make the ecosystem self-sustaining. III. If any one of these four components is completely removed, the ecosystem can still remain fully functional and stable. IV. Energy flow is cyclic, whereas nutrient flow is unidirectional.
Statements I and II are correct. Statement III is incorrect because removal of any major functional component disrupts ecosystem stability. Statement IV is incorrect because energy flow is unidirectional whereas nutrient flow is cyclic.
