47. Identify the CORRECT statements with respect to functioning of ecosystem.
P. A food chain is a series of organisms, each one feeding on the organism succeeding it Q. Food
web presents a complete picture of the feeding relationships in any given ecosystem R. In
ecosystem, energy flows in unidirectional way, whereas nutrients flow in cyclic fashion S. In
biogeochemical cycles, nutrients do not alternate between organisms and environment
(A) P, Q
(B) P, R
(C) R, S
(D) Q, R
Food chains and food webs form the backbone of ecosystem dynamics, illustrating feeding relationships and energy flow. Understanding these concepts is crucial for exams in environmental biology and ecology. The correct answer to the multiple-choice question is (B) P, R.
Statement P: Food Chain Definition
A food chain represents a linear series of organisms where each feeds on the succeeding one, such as grass → grasshopper → frog → snake. This sequential feeding transfers energy from producers to consumers. Statement P is correct as it accurately defines the basic unit of trophic interactions in ecosystems.
Statement Q: Food Web Role
A food web illustrates interconnected food chains, providing a complete picture of feeding relationships across multiple pathways in an ecosystem. It shows complex interactions, like multiple predators for one prey, unlike simplistic chains. Statement Q is correct, as food webs capture the realistic network of who-eats-whom.
Statement R: Energy and Nutrient Flow
Energy in ecosystems flows unidirectionally from producers through herbivores and carnivores to decomposers, with significant loss at each level (about 90% as heat). Nutrients, however, recycle cyclically between organisms and the environment via processes like decomposition. Statement R is correct, reflecting the fundamental one-way energy path versus nutrient cycling.
Statement S: Biogeochemical Cycles
Biogeochemical cycles involve nutrients alternating between living organisms (biotic) and the non-living environment (abiotic), such as the carbon or nitrogen cycle. Reservoirs like atmosphere, soil, and water facilitate this exchange. Statement S is incorrect, as it wrongly denies this alternation essential for ecosystem sustainability.
Why Option B is Correct
Options (A) P,Q and (D) Q,R include valid statements but miss the full pair. Option (C) R,S pairs a correct flow principle with an incorrect cycle description. Only (B) P,R aligns perfectly with ecosystem principles: food chains as sequences and distinct energy/nutrient flows. This combination tests core ecological knowledge for competitive exams.
