How do decomposers meet their energy and nutrient requirements?

The correct answer is Option (2) → By degrading dead organic matter

Decomposers are heterotrophs: they cannot make their own food. They are mainly fungi and bacteria, and they form the detritus food chain. They secrete digestive enzymes onto dead plant and animal matter (detritus), break it down into simple inorganic substances and absorb what they need. So they get their energy and nutrients by degrading dead organic matter. They are also called saprotrophs.

Option (1) By consuming live organisms — Incorrect. Feeding on living organisms is the way of consumers such as herbivores and of parasites. Decomposers work on dead matter.

Option (2) By degrading dead organic matter — Correct. Decomposers break down dead organic matter (detritus) and absorb the simple substances released.

Option (3) By photosynthesis — Incorrect. Photosynthesis is the way of producers (autotrophs) such as green plants. Decomposers are heterotrophs and cannot photosynthesise.

Option (4) By hunting prey — Incorrect. Hunting prey is the way of predators, which are carnivorous consumers. Decomposers do not catch living animals.

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. These are also known as saprotrophs (sapro: to decompose). Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them.”