Courtesy: www.conchsoc.org/habitats/freshwater-habitats.php There are four main constituents of the living environment that form the freshwater ecosystem, they are as follows. Elements and Compounds of the ecosystem that are absorbed by organisms that are required as a food source or for respiration. Many of these compounds are required by plants and passed along the food chain. Plants which are autotrophic by nature, meaning that they synthesize food by harnessing energy from inorganic compounds (plants do so by photosynthesis and the sun); this is done via photosynthesis. These plants (and some bacteria) are the primary producers, as they produce (and introduce) new energy into the ecosystem. Consumers, which are the organisms that feed on other organisms as a source of food. These may be primary consumers who feed from the plant material or secondary consumers who feed on the primary consumers. Decomposers attain their energy by breaking down dead organic material (detritus), and during this reaction, release critical elements and compounds which in turn are required by plants.