Ecosystem energy flow is strictly governed by physical laws. Read these thermodynamic properties:
I. Ecosystems require a constant supply of energy to counteract the universal tendency toward increasing entropy or disorderliness. II. The unidirectional flow of energy from the sun to producers and then to consumers conforms to the First Law of Thermodynamics. III. Energy transfer between trophic levels is 100% efficient, leaving no energy lost as metabolic heat. IV. No energy trapped in an organism remains in it forever; it either flows to consumers or decomposers upon death.
Statements I, II, and IV are correct. Statement III is incorrect because only about 10% of energy is transferred to the next trophic level, with most being lost as heat.
Question 62 of 100
📘 CLASS XII
Detritus is the critical fuel that powers decomposition. Study these composition statements:
I. Dead plant remains such as leaves, bark, and flowers constitute detritus. II. Dead remains of animals, including fecal matter, also constitute detritus. III. Detritus is the key raw material for the process of decomposition. IV. Living organic tissue of primary producers is called detritus.
Statements I, II, and III are correct. Statement IV is incorrect because detritus consists only of dead organic matter and animal wastes, not living tissues.
Question 63 of 100
📘 CLASS XII
Seral stages of hydrarch succession show distinct vegetational structures. Study these transitions:
I. The pioneer species in a water body during hydrarch succession are free-floating plants. II. The correct sequence of initial stages is: Phytoplankton → Rooted-submerged plants → Rooted-floating plants → Free-floating plants. III. The marsh-meadow stage is followed by the scrub stage and finally the forest climax. IV. The ultimate climax community of hydrarch succession is a stagnant bog.
Statements II and III are correct. Statement I is incorrect because phytoplankton are the pioneer species in hydrarch succession. Statement IV is incorrect because the climax community is a mesophytic forest.
Question 64 of 100
📘 CLASS XII
Compare the developmental templates of primary and secondary succession:
I. Newly cooled lava, bare rocks, and newly created ponds are sites of primary succession. II. Abandoned farm lands, burned forests, and flooded lands are sites of secondary succession. III. Primary succession starts where some soil or sediment is already present. IV. Secondary succession is much slower than primary succession because the land is sterile.
Statements I and II are correct. Statement III is incorrect because primary succession starts where neither soil nor previous life exists. Statement IV is incorrect because secondary succession is much faster as soil and organic matter are already present.
Question 65 of 100
📘 CLASS XII
Carbon is a critical block of global biochemistry. Study these carbon reservoir facts:
I. Carbon constitutes 49 per cent of the dry weight of organisms. II. Fossil fuels represent a massive, deep sedimentary reservoir of carbon. III. About 71 per cent of the global carbon is found dissolved in the oceans. IV. The atmospheric reservoir regulates the oceanic carbon pool completely.
Statements I, II and III are correct. Statement IV is incorrect because the oceanic reservoir buffers and regulates atmospheric carbon dioxide, not vice versa.
Question 66 of 100
📘 CLASS XII
The phosphorus cycle shows unique transport and structural properties. Study these pathways:
I. Phosphorus is a sedimentary cycle whose natural reservoir is rock in the form of phosphates. II. Small amounts of phosphates dissolve in soil solution when rocks weather. III. Soil phosphates are absorbed by the roots of plants. IV. Large amounts of phosphorus are added to the terrestrial ecosystem via rainfall inputs.
Statements I, II and III are correct. Statement IV is incorrect because atmospheric and rainfall inputs of phosphorus are negligible due to the absence of a significant gaseous phase.
Question 67 of 100
📘 CLASS XII
Ecosystems can be analyzed through their structure and locations. Identify the correct matches:
I. Forest, grassland, and desert are aquatic ecosystems. II. Pond, lake, wetland, and river are terrestrial ecosystems. III. Crop fields and an aquarium are examples of man-made or anthropogenic ecosystems. IV. Species composition and stratification are the two main structural features of an ecosystem.
Statements III and IV are correct. Statements I and II are incorrect because forests, grasslands and deserts are terrestrial ecosystems, whereas ponds, lakes, wetlands and rivers are aquatic ecosystems.
Question 68 of 100
📘 CLASS XII
Food webs represent natural feeding webs in a community. Read these concepts:
I. Animals like cockroaches and crows are omnivores. II. Omnivores help connect multiple grazing food chains into a complex food web. III. Humans function at a single trophic level (always primary consumer). IV. Food webs represent the realistic, interconnected pathway of energy flow in nature.
Statements I, II and IV are correct. Statement III is incorrect because humans occupy different trophic levels depending on their diet.
Question 69 of 100
📘 CLASS XII
Decomposition rate is heavily regulated by organic and inorganic factors. Study these controls:
I. Decomposition rate is slower if detritus is rich in lignin and chitin. II. Decomposition rate is quicker if detritus is rich in nitrogen and water-soluble sugars. III. Warm and moist environments favor decomposition, while low temperature and anaerobiosis inhibit it. IV. Aerobiosis (presence of oxygen) inhibits decomposition altogether.
Statements I, II and III are correct. Statement IV is incorrect because decomposition is largely an aerobic process and anaerobic conditions inhibit it.
Question 70 of 100
📘 CLASS XII
Marine trophic biomass exhibits a paradox. Study these marine pyramid features:
I. The pyramid of biomass in the sea is generally upright. II. A small standing crop of phytoplankton supports a larger standing crop of zooplankton and fishes. III. Phytoplankton have a very high rate of turnover, allowing them to support higher consumer biomass. IV. The pyramid of energy in the sea is also inverted.
Statements II and III are correct. Statement I is incorrect because the marine biomass pyramid is generally inverted. Statement IV is incorrect because the pyramid of energy is always upright.
