Page 1 - Lesson note-Ecosytem

CHAPTER- 14

ECOSYSTEM

Ecosystem is the functional unit of nature where living organisms interact among themselves

and also with the surroundings physical environment.

Ecosystem- Structure and Functions

Ecosystem : There are two basic categories of ecosystem , namely the terrestrial and the

aquatic.

Terrestrial ecosystem – forest, grassland , desert etc.

Aquatic ecosystem – ponds, lake, river estuary etc.

The biotic and abiotic factors of ecosystem work in integrated manner for flow of energy

within the components of ecosystem. Interaction of biotic and abiotic components results in

a physical structure that is characteristic for each type of ecosystem. The vertical distribution
of different species occupying different levels is called stratification.For example, trees

occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses

occupy the bottom layers.

The components of ecosystem that are seen as functional unit are

(i) Productivity

(ii) Decomposition

(iii) Energy flow

(iv) Nutrient cycling.

· Productivity- Primary production is defined as the amount of biomass or organic matter
produced per unit area over a time period by plants during photosynthesis. It is expressed in

terms of weight (g –2 ) or energy (kcal m–2 ).The rate of biomass production is called

productivity. It is expressed in terms of g –2 yr –1 or (kcal m–2 ) yr –1. It can be divided into
gross primary productivity (GPP) and net primary productivity (NPP). GPP of an ecosystem is

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