Food Chain

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The transfer of food energy from green plants (producers) through a series of organisms with repeated eating and being eaten links is called a food chain. For example, Grasses → Grasshopper → Frog → Snake → Hawk/Eagle.
Each step in the food chain is called the trophic level.
A food chain starts with producers and ends with top carnivores.
The trophic level of an organism is the position it occupies in a food chain.
Types of Food Chains: 1) Grazing food chain and 2) Detritus food chain

The consumers who start the food chain, utilizing the plant or plant part as their food, constitute the grazing food chain.
For example, in a terrestrial ecosystem, the grass is eaten by a caterpillar, which is eaten by a lizard, and the lizard is eaten by a snake.
In Aquatic ecosystem phytoplankton (primary producers) are eaten by zooplanktons which are eaten by fishes and fishes are eaten by pelicans.

This type of food chain starts from the organic matter of dead and decaying animals and plant bodies from the grazing food chain.
Dead organic matter or detritus-feeding organisms are called detrivores or decomposers.
The detrivores are eaten by predators.
In an aquatic ecosystem, the grazing food chain 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 grazing food chain.

Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called catabolism.
Humification and mineralization occur during decomposition in the soil.
Humification leads to accumulation of a dark-coloured amorphous (formless) substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
Being colloidal in nature, humus serves as a reservoir of nutrients.
The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.
Warm and moist environments favor decomposition, whereas low temperature and anaerobiosis inhibit decomposition, resulting in a buildup of organic materials (soils become acidic, like in taiga).

Multiple interlinked food chains make a food web.
The food Web represents all the possible paths of energy flow in an ecosystem.
If any of the intermediate food chains is removed, the succeeding links of the chain will be affected largely.
The food web provides more than one alternative for food to most of the organisms in an ecosystem and therefore increases their chance of survival.

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