Correct Option
The correct option is Energy flow is unidirectional and dissipates as heat at each transfer..
Explanation
The flow of energy in an ecosystem is governed by the laws of thermodynamics. Unlike nutrients, which circulate through biogeochemical cycles, energy enters the ecosystem from an external source (the Sun) and moves through trophic levels in a linear, non-cyclic manner.
Statement-wise Analysis
- Energy flow is unidirectional and dissipates as heat at each transfer. is Correct. Energy flow is unidirectional. Solar energy is captured by producers and converted into chemical energy. As this energy is transferred to successive trophic levels (herbivores, carnivores), a significant portion is dissipated as heat due to respiration and metabolic activities (in accordance with the Second Law of Thermodynamics). This dissipated heat cannot be recaptured by producers for photosynthesis, preventing the recycling of energy.
- All energy is stored permanently as humus. is Incorrect. While humus represents a reservoir of organic matter and nutrients, it does not store energy permanently. Decomposers eventually break down humus, releasing the stored chemical energy as heat during respiration.
- Energy is conserved strictly among decomposers. is Incorrect. Energy is not conserved strictly among decomposers. Decomposers (bacteria and fungi) also perform cellular respiration, converting the chemical energy from dead organic matter into heat, which is lost to the environment.
- Energy is trapped permanently in biomass. is Incorrect. Energy is not trapped permanently in biomass. Biomass is either consumed by the next trophic level or decomposed after death. In both processes, energy transformation occurs, leading to inevitable heat loss.
Key Takeaway
Energy flows through an ecosystem (unidirectional), whereas nutrients cycle (cyclic). The inability of ecosystems to reuse heat energy for photosynthesis makes energy recycling impossible.