In a natural ecosystem, the grazing food chain (GFC) and the detritus food chain (DFC) are interconnected to form a food web because:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → some of the organisms of the DFC are prey to the GFC animals
The grazing food chain (GFC) starts with living green plants (producers). The detritus food chain (DFC) starts with dead organic matter and is made up of decomposers, mainly fungi and bacteria. The two are linked because some organisms of the DFC are eaten by GFC animals; omnivores such as crows add more links. These links make a food web.
Option (1) some of the organisms of the DFC are prey to the GFC animals — Correct. Energy passes from one chain to the other through this link between the chains.
Option (2) the DFC, like the GFC, begins with living green plants — Incorrect. The DFC begins with dead organic matter (detritus), not with living green plants. Only the GFC starts with producers.
Option (3) the GFC is the major conduit for energy flow in every ecosystem — Incorrect. The GFC is the major channel of energy flow only in aquatic ecosystems. On land, more energy flows through the DFC. Either way, this does not explain why the chains are linked.
Option (4) the decomposers of the DFC feed on the living producers of the GFC — Incorrect. Decomposers feed on dead and waste matter, breaking it down into simple inorganic materials. They do not feed on living producers.
NCERT Extract:
Energy Flow – “… The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. … In an aquatic ecosystem, GFC is the major conduit for energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC. Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of DFC are prey to the GFC animals, and in a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores. These natural interconnection of food chains make it a food web.”