The correct option is 2 and 3 only.
Explanation
Ecosystems function through the flow of energy and the cycling of nutrients. While nutrients circulate within the ecosystem, energy flow is unidirectional and governed by the laws of thermodynamics. Food chains represent the transfer of energy and organic matter from one trophic level to another.
Statement-wise Analysis:
- Statement 1 is Incorrect.
Energy flow in an ecosystem is unidirectional and non-cyclic. Energy enters the ecosystem from the sun (in the case of the grazing food chain) and is transferred between trophic levels. At each transfer, a significant portion of energy is dissipated as heat due to respiration and metabolic activities (Second Law of Thermodynamics). Once dissipated as heat, this energy cannot be reused by the ecosystem and is lost to the environment. Unlike nutrients, energy does not remain in the ecosystem indefinitely. - Statement 2 is Correct.
The Detritus Food Chain (DFC) begins with dead organic matter (detritus). When organisms die, their biomass becomes the primary energy source for decomposers and detritivores (such as fungi, bacteria, and earthworms), thereby initiating the detritus pathway. - Statement 3 is Correct.
The Grazing Food Chain (GFC) and the Detritus Food Chain (DFC) are not isolated; they are interconnected at various levels. For instance:- Organisms from the GFC die and become detritus, fueling the DFC.
- Certain organisms (e.g., cockroaches, crows, or humans) are omnivores and feed on prey from both food chains.
- Predators in the GFC (e.g., birds) often feed on detritivores (e.g., earthworms) from the DFC.
Key Takeaway:
Energy flow in an ecosystem is unidirectional and eventually lost as heat, whereas nutrient movement is cyclic. The grazing and detritus food chains are functionally linked, ensuring the continuous flow of matter and energy through the ecosystem.