In this chapter, we can visualise the ecosystem as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem greatly varies in size from a small pond to a large forest or sea. Here we will look at the structure of the ecosystem, in order to appreciate the productivity, transfer of energy, degradation and the energy loss. We will also look at the relationships -cycles, chains, webs – that are created as a result of these energy flows  and their inter-relationship.


Ecosystem-Structure and function
Energy Flow
Ecological Pyramids
Ecological Succession
Ecosystem services

What is an ecosystem?

It is a biological community of interacting organisms and their physical environment. It is also a structural and functional unit of nature comprising abiotic and biotic components. Abiotic components are inorganic materials like air, water and soil. Biotic components are producers, consumers and decomposers.

Important components of an ecosystem:

Productivity, decomposition, energy flow, and nutrient cycling are the four important components of an ecosystem. Productivity: Primary productivity is the rate of capture of solar energy or biomass production of the producers. It is divided into two types: 1.Gross primary productivity (GPP): Rate of capture of solar energy or total production of organic matter 2.Net primary productivity (NPP): Remaining biomass or the energy left after utilisation of producers in an ecosystem. Decomposition: In decomposition, complex organic compounds of detritus are converted to carbon dioxide, water and inorganic nutrients by the decomposers. Decomposition involves three processes, namely fragmentation of detritus, leaching and catabolism. Energy flow:  Energy flow is unidirectional. First, plants capture solar energy. Then food is transferred from the producers to decomposers. Organisms of different trophic levels in nature are connected to each other for food or energy relationship forming a food chain. The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling. Nutrient cycling is of two types: 1. Gaseous: Atmosphere or hydrosphere is the reservoir for the gaseous type of cycle (carbon). 2. Sedimentary: Earth’s crust is the reservoir for sedimentary type of cycle (phosphorus). The biotic community is dynamic and undergoes changes with the passage of time. These changes are sequentially ordered and constitute ecological succession. Succession begins with invasion of a bare lifeless area by pioneers which later pave way for successors and ultimately a stable climax community is formed. The climax community remains stable as long as the environment remains unchanged.