Ecosystem Revision Notes For NEET


        Ecosystem can be defined as an interactive system, where biotic and abiotic components interacts with each other (via energy exchange and flow of nutrients) as well as with their surrounding environment. The term ‘Ecosystem’ was coined by Sir AG Tansley (1935).

        Natural ecosystem are capable of operating and maintaining themselves without any major interference by human, e.g. terrestrial and aquatic ecosystem.

        Artificial ecosystem are maintained and manipulated by human for different purposes, e.g. cropland, cities, etc.

        Biotic component of an ecosystem consists of producers, consumers, decomposers and detritivores.

        Autotrophic (producer) fix light energy to manufacture complex organic food from simple inorganic substances, e.g. green plants.

        Producers derive their food directly or indirectly from the producers or the green plants.

        Decomposers feeds upon dead bodies of animals and plants and organic wastes of living organism.

        Decomposition is the process of breaking down of complex organic matter into inorganic substances. Fragmentation, leaching, catabolism, humification and mineralisation are different steps, which are involved in decomposition. It is largely an oxygen requiring process. Many factors influence the decomposition process such as chemical nature of detritus, soil pH, temperature, etc.

        Food chain is the transfer of energy from the producers, through a series of organism, i.e. herbivore to carnivore to decomposers with repeated eating. A simple food chain consists of three steps as follows

Producers → herbivore → carnivore

        Each level or step in a food chain where transfer of energy takes place is called trophic level. The amount of energy decreases at each successive trophic level.

        Food web is a network of cross connecting food chains involving producers, consumers, and decomposers. The complexity of food web can vary greatly and we can express this complexity by a measure called the connectance of the food web.

        Productivity is the rate of biomass production per unit are over a time period. It is expressed in kcal/m²/yr.

        Primary productivity is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It has two aspects gross primary productivity and net primary productivity.

        Secondary productivity is the rate of energy storage at consumer’s level. Net productivity is the rate of storage of organic matter not used by the heterotrophs or consumers.

        Ten percent law was given by Lindeman. According to this law only 10% of the energy is transferred to each trophic level from the lower trophic level. The number of trophic levels in the food chain is restricted due to this law.

        Nutrient cycles are the movement of nutrients elements through the various components of an ecosystem. Atmosphere is the reservoir for gaseous nutrient cycle and soil and rocks are the major reservoir for sedimentary cycles.

        Atmosphere is the reservoir for gaseous type of nutrient cycle (e.g. nitrogen and carbon cycle).

        Earth’s crust is the reservoir of sedimentary cycle (e.g. sulphur and phosphorous cycle).

        Human activities have influenced the carbon cycle by significantly increasing the rate of release of CO₂ into the atmosphere.

        The nitrogen cycle depends upon different kinds of bacteria known as the nitrifiers, de-nitrifiers and the nitrogen fixers.

        The natural reservoir of phosphorus is rock, which contains phosphorus in phosphates form. The waste products and the dead organism are decomposed by phosphate solubilising bacteria releasing phosphorus.

        Ecological pyramids are the diagrammatic illustration of connection between different trophic levels in terms of energy, biomass and number of an organism. The base of each pyramid represents the producer, while the apex represents tertiary or top consumer.

        Pyramid of number shows relationship between the number of producer and consumers. Pyramid of biomass shows relationship between the biomass of producer and consumers. Pyramid of energy shows the flow of energy from producer to consumers.

        Ecological succession is a sequential, gradual and predictable change in the species composition of an area over a period of time. Primary succession occur in an area which has been bare from the beginning. Secondary succession occur in an area, which has been renuded recently.

        Xerosere originate on bare rock surfaces. The sequence of xerosere as follows, Crustose lichen stage → Foliose lichen stage → Moss stage → Annual grass stage → Perennial grass stage → Shrub stage → Forest stage.

        Hydrosere occurs on pond/lake or water body. The sequence of hydrosere are as follows, Plankton stage → Submerged stage → Floating stage → Reed swamp stage → Marsh meadow stage → Woodland stage → Climax forest.

        Ecosystem services these are follows

        The products of ecosystem processes are termed as ecosystem services.

        Forests are the major sources of ecological services. These are useful in following ways

            Purification of air and water

          Mitigating droughts and floods

            Cycling nutrients

            Generating fertile soils

            Providing wildlife habitat

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