· Plants and photosynthetic and chemosynthetic bacteria (autotrophs) fix sun’s radiant energy to make food from simple inorganic materials. Plants fix only 2-10% of the photosynthetic ally active radiation and this small amount of energy sustain the entire living world. All organisms are depended for their food on producers either directly or indirectly there is unidirectional flow of energy from the sun to producers then to consumers.
· Producers are herbaceous and woody plants in a terrestrial ecosystem. Primary producers in an aquatic ecosystem are various specious like phytoplanktons. Algae and higher plants.
· All animals depend on plants directly or indirectly for their food so they are called consumers or hertrotrops. If they feed on the producers, plants, they are called primary consumers. And if the animals eat other animals then they are called as secondary consumers then tertiary consumers and so on.
· Primary consumers – herbivores for e.g. insects, birds, and mammals in terrestrial ecosystem and mollusks in aquatic ecosystem
· Primary Carnivores or secondary consumers- They fed on herbivores. Secondary carnivores feed on primary carnivores.
· (Producer) (Primary consumer) (Secondary consumer)
· Organisms occupy a specific place in the food chain is that is known as trophic levels. Producers…I trophic level, Herbivores….II trophic level
· .Each trophic level has a certain mass of living material, at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass)or the number n a unit area. The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate.
· Detritus food chain begins with dead organic matter. It includes decomposers which feed on dead and decaying matter or detritus. Decomposer is mainly saprotrophs including fungi and bacteria. Decomposers secrete digestive enzymes that break organic matter into simple inorganic material.
· In an aquatic food chain Grazing food chain is the major source of energy flow. In terrestrial ecosystem a much larger fraction of energy flows through the detritus food chain than through GFC. Detritus food chain may be connected with the GFC 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 interconnections of food chains make it a food web.
· The number of trophic levels in the GFC is not more than 4 or 5.As the transfer of energy follows 10 percent law –only 10 % of the energy is transferred to each trophic level from the lower trophic level. After 4 or 5 trophic levels energy which is left not sufficient to sustain life.