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Ecosystem Structure and Function


     Biogeography reveals that living organisms (plants and animals) are found practically everywhere on this earth. The living components interact among themselves as well as with their physical environment like soil, air and water.

Ecosystem - Definition

     An ecosystem can be defined as 'a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment, both interacting and exchanging materials between them'.

Components of an Ecosystem

     These include the non-living, physico - chemical factors such as air, water, soil and the basic elements and compounds of the environment.

Ecosystem - Structure and Function

     The characteristic structure of an ecosystem is obtained by the systematic physical organisation of the abiotic and biotic components of that particular ecosystem.

Primary and Secondary Productivity

     'The amount of organic matter or biomass produced by an individual organism, population, community or ecosystem during a given period of time is called productivity'.

Ten Percent Law

     Lindemann (1942) put forth ten percent law for the transfer of energy from one trophic level to the next.

Energy Flow

     Energy is the capacity to do work. Solar energy is transformed into chemical energy by the process of photosynthesis, and is stored in plant tissue and then transformed into mechanical and heat forms during metabolic activities.

Laws Governing Energy Transformations

     The storage and expenditure of energy in an ecosystem is in accordance with the laws of thermodynamics (basic laws of thermodynamics).

Food Chain and Food Webs

     Food chain is a series of groups of organisms called trophic levels, in which, there is repeated eating and eaten by so as to transfer food energy.

Characteristics of a Food Chain

     There is repeated eating in which each group eats the smaller one and is eaten by the larger one. Thus, it involves a nutritive interaction between the biotic components of an ecosystem.

Types of Food Chains

     Grazing food chain is generally seen in ecosystems such as grassland, pond or lake where a substantial part of the net primary production is grazed on by herbivores (cattle and rodents). Usually upto 50% of the NPP is grazed on by these animals in their respective ecosystems and the remaining 50% goes to the decomposer organisms as dead organic matter. Thus, in these ecosystems, the food chain is herbivore based.

Characteristics of Grazing Food Chain

     These are directly dependent upon solar radiations as the primary source of energy and the producers (green plants) synthesize their plant biomass by the process of photosynthesis. Producers form the first trophic level.

Characteristics of Detritus Food Chain

     Primary source of energy is dead organic matter called 'detritus' which are fallen leaves, plant parts or dead animal bodies.

Significance of Food Chains

     Understanding the feeding relationships and the interaction between organisms in any ecosystem.

Biological Magnification

     Certain harmful substances, usually ones not found in nature but introduced by man, may get into plants and/or animals. These poisonous substances may not be broken down in the body or excreted easily, efficiently and quickly. Instead, they accumulate in the tissues, and as the living organism eats more, the concentration of these substances increases and they pass from one trophic level to the next.

Food Web

     In nature, food chain relationships are not isolated. They are very complex, as one organism may form the food source of many organisms. Thus, instead of a simple linear food chain, there is a web like structure formed by these interlinked food chains. Such interconnected matrix of food chains is called 'food web'.

Pyramid of Numbers

     Pyramid of numbers is the graphic representation of number of individuals per unit area of various trophic levels stepwise with producers forming the base and top carnivores the tip.

Pyramid of Biomass

     Pyramid of biomass is the graphic representation of biomass present per unit area of different trophic levels, with producers at the base and top carnivores at the tip.

Pyramid of Energy

     Pyramid of energy is a graphic representation of the amount of energy trapped per unit time and area in different trophic level of a food chain with producers forming the base and the top carnivores at the tip.

Biogeochemical Cycles

     Earth is the source of matter for all living organisms, as they require several (about 40) elements for their growth and life processes.

Types of Biogeochemical Cycles

     In gaseous cycles, the elements have a main reservoir in the gaseous phase, and the reservoir pool is the atmosphere or water. The biogenetic materials involved in circulation pass through a gaseous phase before completing the cycle.

Carbon Cycle

     Carbon is found as graphite and diamond in nature. It also occurs as carbon dioxide in the atmosphere.

Nitrogen Cycle

     Nitrogen is an important structural component of many necessary compounds, particularly proteins. Atmosphere is the reservoir of free gaseous nitrogen and nitrogen compounds are found in bodies of organisms and in the soil.

Oxygen Cycle

     Oxygen is another essential element for living organisms. It is present in large quantities (20.95% v/v) in the atmosphere and is also seen in bound state in water and as oxides and carbonates in rocks.

Water Cycle or Hydrological Cycle

     Water is an indispensable commodity of life. Water determines the distribution, structure and function of organisms in the ecosystem.

Phosphorus Cycle

     Phosphorus is an essential nutrient to biological systems. Its requirement is mainly seen in nucleic acids, cell membrane, bones and teeth.

Sulphur Cycle

     Sulphur is an important component of most proteins, few vitamins and enzymes.

Major Ecosystems (Biomes)

     Biome is a large, regional or sub continental biosystem characterized by a major vegetation type or other distinct landscape characters such as tropical deciduous forest, tundra biome, etc.

Terrestrial Biomes

     Mainly on the basis of latitude and amount and periodicity of rainfall, terrestrial biomes are classified into several types - tundra, taiga, deciduous forests, tropical rain forests, chapparal, savannah, grassland and desert.

The Tundra Biome (Rus:Tundra - Arctic hill)

     The word 'tundra' means 'North of the timber line'. Tundra biomes lie north of timberline or 60o N latitude between the Arctic ocean and the Coniferous forests. It covers about 8 x 106 area (8 million km2) extending across North America, Europe and Asia.

The Taiga Biome

     Taiga are the 'northern coniferous forests' which are also referred as 'North Woods', very common in Siberia.

The Deciduous Forests

     Also referred as "Temperate deciduous forests" are found in temperate regions of North central Europe, Eastern Asia and Eastern United States. In southern hemisphere in Australia and New Zealand.

The Chaparral Biome

     Also referred as 'Mediterranean scrub forest' extends along mediterranean, pacific coast of North America, South Africa, South and Western Australia and Chile.

The Savannah Biome

     Also referred as 'tropical grasslands', primarily located in equatorial and sub - tropical regions of the globe (especially South America, Central Africa and Australia).

Forest Biomes in India

     Major forest biomes found in India are: Tropical evergreen forests / Tropical rain forests.

Tropical Rain Forests

     Tropical rain forests grow in regions with plenty of moisture and heat. They are also referred as 'evergreen forests'.

Tropical Deciduous Forests

     In India, tropical deciduous forests occur in the northern and southern parts.


     These ecosystems are either barren or with scanty vegetation consisting of mainly thorny bushes. Deserts are classified as warm (hot) and cold (temperate) deserts.

Altitudinal Biomes

     Variations in climatic conditions are observed not only in places on different latitudes but also with altitude. The various types of biomes can also be noted with varying altitudes as seen in the slopes of high Himalayan mountains in Asia, Andes in South America and the Rockies in North America.


     The biotic and abiotic components form an interacting system called 'ecosystem'. Producers, consumers and decomposers are the various trophic levels, which are linked by their food relationship forming a 'food chain'.

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