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STRUCTURE AND FUNCTION OF ECOSYSTEM Presented by: HALAI DAXA D. M.Sc. (Environmental) Sem-1 Paper 102/c unit 2

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WHAT IS AN ECOSYSTEM ? The term ecosystem was first proposed by A.G.Tansley in1935. He defined it as “ the system resulting from the integration of all the living and non- living factors of environment ”. Ecosystem is most preferred, where ‘eco’ implies the environment , and ‘system’ implies an interacting , inter-dependent complex. Thus any unit that includes all the organisms i.e. the communities in a given area, interact with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity and material cycle within the system, known as an ecological system or ecosystem.

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An ecosystem is a biological environment consisting of all the organisms living in a particular area , as well as all the nonliving, physical components of the environment with which the organisms interact, such as air, soil, water and sunlight. The structure and function are the major aspects of an ecosystem.

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STRUCTURE OF AN ECOSYSTEM the composition of biological community including species, numbers, biomass, life history and distribution in space, etc. the quantity and distribution of non living materials like nutrients, water etc. the conditions of existence such as temperature, light etc. The structure of an ecosystem is characterized by the organization of abiotic and biotic components.

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a without bios life = abiotic without life abiotic components. Climatic factors Inorganic substances Organic substances sunlight precipitation humidity wind carbon cycle nitrogen cycle Water cycle etc Lipids proteins carbohydrates

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a without bios life = biotic with life biotic components. Producers Consumers Decomposers plants Fungi bacteria Herbivores Carnivores Omnivores

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Climatic factors These include factors like sunlight ,precipitation , humidity , wind action etc. abiotic components.

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Inorganic substance These include elements such as carbon, nitrogen, oxygen etc, used in synthesis of complex substances and involved in various material cycle. Examples carbon cycle ,nitrogen cycle , oxygen cycle , … etc.

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The Carbon Cycle

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CO 2 is taken up by plants during photosynthesis CO 2 is released by organisms during respiration and decomposition; fires, volcanoes CO 2 is also released by autos and industries carbon, present in all organic molecules, moves through the food chain as one organism eats another. Carbon (C) enters the biosphere during photosynthesis: CO 2 + H 2 O C 6 H 12 O 6 + O 2 + H 2 O Carbon is returned to the biosphere in cellular respiration: O 2 +H 2 O + C 6 H 12 O 6 CO 2 +H 2 O + energy

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The Nitrogen Cycle

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78% of the volume of trophosphere Most complex cycle N2 gas can’t be used ‘as is’ – it must be ‘fixed’ so that organisms can use it Steps to the cycle: Nitrogen Fixation Assimilation Ammonificatio Nitrification Denitrification Nitrogen Fixation Atmospheric nitrogen must be processed, or "fixed“ to be used by plants. Some fixation occurs in lightning strikes, but most fixation is done by free-living or symbiotic bacteria.

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Assimilation Plants get nitrogen from the soil, by absorption of their roots in the form of either nitrate ions or ammonium ions. Ammonification When a plant or animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or fungi in some cases, convert the organic nitrogen within the remains back into ammonium (NH 4 + ), a process called ammonification or mineralization. Nitrification The conversion of ammonium to nitrate is performed primarily by soil-living bacteria and other nitrifying bacteria. the oxidation of ammonium(NH 4 + ) – by bacteria Nitrosomonas species the nitrites – BY Nitrobacter

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Denitrification Denitrification is the reduction of nitrates back into the largely inert nitrogen gas (N 2 ), completing the nitrogen cycle. is performed by bacterial species such as Pseudomonas and Clostridium in anaerobic conditions They use the nitrate as an electron acceptor in the place of oxygen during respiration. NO 3 -  NO 2 -  N 2 O  N 2

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Organic substances These includes lipids, proteins, carbohydrates. Which are formed by biotic components and that are linked with biotic components. They have a strong influence on structure behavior and inter relationship of various organisms in an ecosystem.

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biotic components. They are generally chlorophyll bearing autotrophic (self + feeding.)organisms which prepare organic compounds from inorganic raw materials . Eg . green plants and some photosynthetic bacteria. Producers

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Consumers They are also called heterotopyhs which means those who feed on others . Herbivores Organisms that eat plants are called primary consumers Primary consumers are herbivores – the only eat plant material

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Carnivores These are the animals which feeds on herbivores .

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Omnivores They consume both plants and animals .

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Decomposers Decomposers are organisms that degrade or decompose dead or organic material in simpler molecules. Fungi and bacteria are decomposers

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FUNCTION OF AN ECOSYSTEM Ecosystem have some functional attributes which keep the component parts running together. For example – green leaves prepare food & roots absorb nutrients from the soil. Herbivores feed on part of the plant production, and in turn serve as food for carnivores. Decomposers carry out the function of braking down complex organic materials into simple inorganic product which can be used by the producers. All these functions in an ecosystem occur through delicately balanced and controlled processes. Thus, this cycle goes on and on, leading to efficient continuous functioning of the ecosystem.

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Food chain, food web and trophic structure Energy flow Cycling of nutrients (biogeochemical cycles) Primary and secondary production Ecosystem development and regulation

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Food Chains “Transfer of food energy through a series of different organisms in the ecosystem is called food chain” Food chain in simple term is a linked feeding series. A single food chain should have at least three links to be complete. PLANTS HERBIVORE CARNIVORE Grass  grasshoppers  Frog  Snake  Hawk (Grassland ecosystem) Phytoplanktons  water fleas  small fish  Carnivorous fish (Pond ecosystem) Lichens  reindeer  Man (Arctic tundra)

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Two major types of food chains: 1 . Grazing food chain It starts with green plants (primary producers) and culminates in carnivores. Phytoplanktons  water fleas  small fish  Carnivorous fish (Pond ecosystem) 2. Detritus food chain: It starts with dead organic matter which the detritivores and decomposers consume. Thus grazing food chain derives its energy basically from plant energy while in the detritus food chain it is obtained primarily from plant biomass, secondarily from microbial biomass and tertiarily from carnivores.

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Food Web Thus food web is a network of food chains where different types of organisms are connected at different trophic levels, so that there are a number of options of eating and being eaten at each trophic levels.

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Decomposer Bacteria , fungi Nutrients Plants grass Grasshopper Bird Hawk Snake Frog Mouse Green plants grass Nutrients

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Thank you

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