Here is your Short Speech on Ecosystem !
A classic example of an ecosystem is a small lake or pond the abiotic or non-living parts of a freshwater pond include the water, dissolved oxygen, carbon dioxide, inorganic salts such as phosphates, nitrates and chlorides of sodium, potassium, and calcium, and a multitude of organic compounds such as amino acids, humic acids, etc.
The living part of the freshwater pond can be subdivided according to the functions of the organisms, i.e., what they contribute toward keeping the ecosystem operating as a stable, interacting whole.
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In a freshwater pond there are two types of producers, the larger plants growing along the shore or floating in shallow water, and the microscopic floating plants, most of which are algae, that are distributed throughout the water as deep as light will penetrate.
These tiny plants, collectively referred to as phytoplankton, are usually not visible unless they are present in great abundance and give the water a greenish tinge. Phytoplanktons have more significance as food producers for the freshwater pond ecosystem than are the more readily visible plants.
The macroconsumers or phagotrophs of pond ecosystems include insects and ‘insect larvae, Crustacea, fish and perhaps some freshwater clams. Primary consumers such as zooplankton (animal plankton) found near the surface of water and benthos (bottom forms) is the plant eaters (herbivores) and secondary consumers are the carnivores that eat the primary consumers. There might be some tertiary consumers that eat the carnivores (secondary consumers).
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The ecosystem is completed by saprotrophs or decomposer organisms such as bacteria, flagellate protozoans and fungi, which break down the organic compounds of cells from dead producer and consumer organisms either into small organic molecules, which they utilize themselves, or into inorganic substances that can be used as raw materials by green plants.