Correct Option
The correct option is 1, 2 and 3 only 1, 2 and 3 only.
Explanation
Ecosystem dynamics rely on the flow of energy through food chains. There are two main types of food chains: the Grazing Food Chain (GFC), which begins with living green plants (producers), and the Detritus Food Chain (DFC), which begins with dead organic matter. The relative importance of these chains varies between aquatic and terrestrial ecosystems.
Statement-wise Analysis
- Pair 1 is Correct: In an aquatic ecosystem, the Grazing Food Chain (GFC) is the major conduit for energy flow. Phytoplankton (producers) are consumed by zooplankton, which are then eaten by small fish. A significant portion of the primary productivity is consumed directly by herbivores in these environments.
- Pair 2 is Correct: In a terrestrial ecosystem, a much larger fraction of energy flows through the Detritus Food Chain (DFC) than through the GFC. Most terrestrial plant biomass (leaves, wood, etc.) is not consumed by herbivores while alive; instead, it dies and decays, entering the detritus pathway.
- Pair 3 is Correct: Omnivores (e.g., cockroaches, crows, humans) occupy multiple trophic levels and can feed on both plant matter and other animals. By consuming organisms from the grazing chain and potentially utilizing resources linked to the detritus chain, they serve as a connection between the two food chains in a food web.
- Pair 4 is Incorrect: Decomposers (mainly fungi and bacteria) feed on dead and decaying organic matter (detritus). They secrete digestive enzymes to break down dead material. The primary consumers of live plant tissue are herbivores, not decomposers.
Key Takeaway
Key Takeaway: The Grazing Food Chain dominates energy flow in aquatic ecosystems, whereas the Detritus Food Chain is the primary energy pathway in terrestrial ecosystems due to the high volume of unconsumed plant biomass.