(i) Ecosystem or Ecological system : The complex interactions, interrelationships and interdependencies between living organisms form an ecosystem or ecological system. No living organism, plant, animal, micro-organism or human can live in complete isolation. They all depend upon their immediate physical surrounding or habitat for their survival. In the process, they interact with other living organisms and are interdependent on each other. These interrelationships create an ecosystem. (ii) Flora and Fauna : The plant life of a region is termed as flora and the animal life is termed as fauna. Example, Mangifera indica or mango tree is a natural flora, and tiger, the national animal of India is example of fauna.