B.Sc. Zoology                                                                                                                                                  Dept. of Zoology, 
           Part- II                                   RLSY College, Bakhtiyarpur (Patna) 
                                                          Patliputra University, Bihar 
           -------------------------------------------------------------------------------------------------------------------------------------- 
                                      Paper-IIA 
                           Ecology, Animal Behaviors and Biometry 
                  Ecosystem: Definition, structure and function of typical ecosystem 
                                   Mrs. Arusha Modi 
                                   Assistant Professor 
                                           
                                           
           ECOSYSTEM:  DEFINITION,  STRUCTURE  AND  FUNCTION  OF  TYPICAL 
           ECOSYSTEM 
            
           ❖  Definition 
           The simplest definition of an ecosystem is that it is a community or group of living organisms 
           that live in and interact with each other in a specific environment. 
            
           For instance, tropical forests are ecosystems made up of living beings such as trees, plants, 
           animals, insects and micro-organisms that are in constant interaction between themselves and 
           that  are  affected  by  other  physical  (sun,  temperature)  or  chemical  (oxygen  or  nutrients) 
           components. 
            
           ❖  Structure 
           An ecosystem is the basic unit of the field of the scientific study of nature. According to this 
           discipline, an ecosystem is a physically defined environment, made up of two inseparable 
           components: 
            
           The biotope (abiotic): a particular physical environment with specific physical characteristics 
           such as the climate, temperature, humidity, concentration of nutrients or pH. 
           The biocenosis (biotic): a set of living organisms such as animals, plants or micro-organisms, 
           that are in constant interaction and are, therefore, in a situation of interdependence. 
            
           In ecology, the ecosystem structure and dynamics is best described by the term food chain 
           which refers linear sequence of organisms through which nutrients and energy pass from 
           primary producers to higher-level consumers. Depending on their role, we can assign species 
           or groups of species into various trophic (Trophe = nourishment) levels with each organism in 
           a food chain occupying a specific trophic level. 
            
           Energy, water, nitrogen and soil minerals are the essential abiotic components of an ecosystem 
           which  enters  food  chain  primarily  through  producers.  Producers  such  as  photosynthetic 
           organisms (phytoplankton plants and/or) constitute the bottom of the food chain in many 
           ecosystems  and  are  called  Primary  producer.  Primary  producers  are  eaten  by  primary 
           consumers such as herbivores. In this manner, higher-level consumers feed on the subsequent 
           lower tropic levels until it reaches the organisms at the top of the food chain called the apex 
           consumers. 
         B.Sc. Zoology                                                                                                                                                  Dept. of Zoology, 
         Part- II                          RLSY College, Bakhtiyarpur (Patna) 
                                               Patliputra University, Bihar 
         -------------------------------------------------------------------------------------------------------------------------------------- 
                                                  
         However, food chain represents only a simple and isolated relationship and represents only a 
         part of the food or energy flow. In an ecosystem, several such food chains intercalate and forms 
         interconnected networks of feeding relationships that take the form of food webs. Hence, it is 
         a holistic and non-linear graphical representation of primary producers, primary consumers and 
         higher-level consumers which describe ecosystem structure and dynamics and energy in an 
         ecosystem. The food webs can be divided into two general types: A Grazing food web and a 
         Detrital food web. 
          
          
                 B.Sc. Zoology                                                                                                                                                  Dept. of Zoology, 
                 Part- II                                                              RLSY College, Bakhtiyarpur (Patna) 
                                                                                               Patliputra University, Bihar 
                 -------------------------------------------------------------------------------------------------------------------------------------- 
                                                                                                                        
                     ❖  Functions of Ecosystem 
                                  
                     •   The functions of the ecosystem are as follows: 
                          
                     •   It regulates the essential ecological processes, supports life systems and renders the 
                         stability. 
                          
                     •   It is also responsible for the cycling of nutrients between biotic and abiotic components. 
                          
                     •   It maintains a balance among the various trophic levels in the ecosystem. 
                          
                     •   It cycles the minerals through the biosphere. 
                          
                     •   The abiotic components help in the synthesis of organic components that involves the 
                         exchange of energy. 
                          
                          
                  
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