Q.Describe the zonation of a lake ecosystem and explain thermal stratification in summer and winter.

An ecosystem is a functional unit of nature where the living community interacts with its non-living environment through energy flow and nutrient cycling.

Explanation:

• The term ecosystem was coined by A. G. Tansley.
• An ECOSYSTEM is a functional unit of nature in which the LIVING organisms (biotic components - producers, consumers and decomposers) interact among themselves and with the NON-LIVING physical environment (abiotic components - soil, water, air, temperature, light).
• The biotic and abiotic components are linked together through a continuous FLOW OF ENERGY (from the sun through food chains) and the CYCLING OF NUTRIENTS (biogeochemical cycles).
• An ecosystem is largely self-regulating and self-sustaining. …

An ecosystem is the basic functional unit of ecology — the biotic community together with its abiotic environment, linked by energy flow and nutrient cycling.

Definition: An ecosystem (a term coined by A.G. Tansley, 1935) is a self-sustaining functional unit of nature comprising all the living organisms (plants, animals, and microbes — the biotic component) of an area, interacting among themselves and with the non-living physical and chemical factors of their surroundings such as soil, water, air, temperature, and light (the abiotic component).

Key features:

• Organisms and environment interact continuously, exchanging energy and matter.
• Energy flows unidirectionally, from producers through consumers to decomposers, ultimately lost as heat.
• Nutrients cycle repeatedly between the biotic and abiotic components (biogeochemical cycles). …