NCERT Class 12 Environment & Ecology — Chapter 2: Ecosystem

The correct Answer is

Energy flow - unidirectional movement through trophic levels

Explanation

Ecosystems exhibit several functional attributes, including productivity, decomposition, energy flow, and nutrient cycling. These processes describe how energy and matter move within an ecosystem, sustaining its structure and function.

Statement-wise Analysis

1. Statement

   Productivity - mineral return to soil

   : Productivity - mineral return to soil
   Incorrect. Productivity refers to the rate of biomass production or the rate at which energy is accumulated by producers. Mineral return to the soil is primarily a function of decomposition, where decomposers break down organic matter, releasing inorganic nutrients back into the soil.
2. Statement

   Decomposition - energy capture from sun

   : Decomposition - energy capture from sun
   Incorrect. Decomposition is the process by which decomposers break down dead organic matter into simpler inorganic substances. Energy capture from the sun is the primary function of photosynthesis, carried out by producers (autotrophs), which is a component of ecosystem productivity.
3. Statement

   Energy flow - unidirectional movement through trophic levels

   : Energy flow - unidirectional movement through trophic levels
   Correct. Energy flow in an ecosystem is indeed unidirectional. It moves from producers to primary consumers, then to secondary consumers, and so on, with a significant loss of energy at each successive trophic level, primarily as heat. Energy is not recycled within the ecosystem.
4. Statement

   Nutrient cycling - irreversible loss of elements

   : Nutrient cycling - irreversible loss of elements
   Incorrect. Nutrient cycling (biogeochemical cycles) involves the movement of nutrient elements (like carbon, nitrogen, phosphorus) through various components of an ecosystem (biotic and abiotic). This process is largely cyclical, meaning nutrients are reused and recycled within the ecosystem, not irreversibly lost. While some loss can occur, the defining characteristic is cycling and reuse.

Key Takeaway

Energy flow in an ecosystem is unidirectional, moving progressively through trophic levels with energy loss at each transfer.