The correct option is 2 and 3 only.
Explanation
The flow of energy in an ecosystem is governed by the laws of thermodynamics. Unlike nutrients, which circulate in cycles (biogeochemical cycles), energy moves through the ecosystem in a unidirectional and non-cyclic manner. This flow occurs through various trophic levels in a food chain.
Statement-wise Analysis:
- Statement 1 is Incorrect: The flow of energy in an ecosystem is unidirectional, not reversible. Energy flows from the sun to producers (autotrophs) and then to consumers (heterotrophs). Energy captured by autotrophs does not revert to the sun, and energy transferred to herbivores does not flow back to autotrophs.
- Statement 2 is Correct: According to the 10% Law (proposed by Lindeman), only about 10% of the energy is transferred from one trophic level to the next higher level. The remaining energy is lost as heat during respiration, used for metabolic activities, or remains trapped in unconsumed biomass. Consequently, the available energy decreases significantly at each successive trophic level.
- Statement 3 is Correct: The energy fixed by autotrophs eventually dissipates into the environment as heat due to metabolic activities and decomposition. This energy is lost to the immediate environment and does not return to the solar input (the sun). Thus, the ecosystem requires a constant supply of solar energy to function.
Key Takeaway:
Energy flow in an ecosystem is always unidirectional and follows the laws of thermodynamics, resulting in a progressive decline in energy at higher trophic levels (Pyramid of Energy).