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Ecosystem of Class 12

What is Ecosystem?

(Gr. eco = environment, system = interacting and independent complex) is an integrated system resulting from interactions of living and non-living factors of the environment. It is also called as ecological system. Ecosystem can be recognised as self-regulating and self-sustaining unit of landscape.The environment influences vital processes and distribution of flora, fauna (vegetation) and microbes. The ecosystem comprises of the biotic community and the non biotic environment. It is the basic functional unit asit includes both the organisms and its environment, each influencing the properties of the other and both are necessary for the survival and maintenance of life. Each ecosystem characteristically possesses a well defined abiotic and biotic factors and it has its own potential for adaptation, change and tolerance.

The functioning of any ecosystem involves a series of cycles which includes energy cycles, water cycles and a series of nutrient cycles.The nutrient cycles are directly or indirectly related with the energy cycles and water cycles. Continuation of life supporting systems needs a constant exchange and return of nutrients to the different components of ecosystem and from the components of the ecosystem.

  • A.G. Tansley (1935) coined the term ecosystem and defined it as the whole complex of living organisms living together as a sociological unit and its habitat.
  • Lindeman (1942) defined the ecosystem as a system composed of physical-chemical-biological processes active within a space-time unit of any magnitude.
  • Odum (1963) explained the ecosystem as the basic functional unit of biosphere including both organisms and their non living environment, each interacting with the other and influencing each other’s properties and both necessary for the maintenance and development of the system.
  • Eugene P. odum (1913-2002) widely recognized as the ‘‘Father of ecosystem ecology’’. He received (jointly with his brother Prof. H.T. Odum) the prestigious crawford prize of the Royal Swedish Academy, considered to be the equivalent of the Nobel prize in Ecology.

Other Terms Applied to the Ecosystem

  • Karl Mobius (1877) changed the term from the ecosystem to biocoenosis
  • S. A. Forbes (1887) coined the term microcosm
  • Friederichs (1930) put forward the term holocoen
  • Sukhachev (1944) gave the term geobiocoenosis
  • Thienemann (1939) named the ecosystem as the biosystem

Kinds and Size of Ecosystem

Natural ecosystems operate under natural conditions without any major interference by man. e.g. terrestrial and aquatic ecosystems. Terretrial—Grassland, desert, forest, ecosystems comes under this category. Aquatic—Fresh-water (e.g. Ponds, lakes and streams) and marine (e.g. open sea, coastal and estuarine) ecosystems comes under this category.

Artificial ecosystems are man-made ecosystems or anthropogenic ecosystems. e.g. Croplands, Space-ecosystem etc.Human activities may modify or convert natural ecosystems into man-made ecosystems.For example, natural forests have been cut and the land converted to tree plantations or agricultural systems.Space crafts and aquariums may also be considered as man-made ecosystems.Ecosystems vary greatly in size, such as a small pond or a large forest.

Characteristics of Ecosystem

It is major structural and functional unit of biosphere. The structure of an ecosystem is related to its species diversity, more complex ecosystem has high species diversity.The function of the ecosystem is related to energy flow and material cycling through and within the system.

Relative amount of energy needed to maintain an ecosystem depends on its structure. The more complex the structure,the lesser the energy it needs to maintain itself.Ecosystems mature by passing from less complex to more complex states. Early stages of such succession have an excess of potential energy and a relatively high energy flow per unit biomass.

Mature stages have less energy accumulation and its flow through more diverse components.Both the environment and the energy fixation in any given ecosystem are limited and cannot be exceeded without causing serious undesirable effects.Alterations in the environment represent selective pressures upon the population to that organisms must adjust themselves.Organisms that are unable to adjust to the changed environment must get perished.

Components of Ecosystem

An ecosystem has two basic components

  • Abiotic (non-living) organisms
  • Biotic (living) organisms

Abiotic Components (Physical Factors)

Abiotic components comprise inorganic materials (e.g. carbon, nitrogen, oxygen, CO2, water etc.) and dead organic matter containing proteins, carbohydrates, lipids, humic substances etc. Abiotic substances are present in soil, water and air. The climatic parameters like solar radiation and temperature determine the abiotic conditions with in which the organisms carry out life functions.

Some important abiotic components are :

  • Light : Light is essential for life. The quality, intensity and duration of light can influence the different aspects of life.Green plants require light for photosynthesis i.e., to prepare food in green leaves. Light affects the colouration and eye structure of some animals.
  • Air : Air contains several gases whose approximate percentages are; nitrogen (78.2%), oxygen (21.00%), carbon dioxide (0.03%), argon (0.94%) and others are variable.
  • During inspiration O2 is taken in and during expiration CO2 is given out.
  • Burning of coal, wood and other fossil fuels, emissions of factories are responsible for increasing the percentage of CO2 in the atmosphere. If only this goes on, our atmosphere will be filled with CO2 and life would not be possible. But it does not happen. Green plants use this CO2 during photosynthesis to prepare their food and release O2. Thus, plants maintain a balance of O2 and CO2 of the air. Plants are very useful for all living organisms and there is a close inter-relationship between plants and animals.
  • Along with O2 and CO2, nitrogen also plays an important role. The atmospheric nitrogen is converted into nitrites by electric discharges and soil bacteria. Plants use these nitrites to build vegetable proteins and when animals feed on these plant and their products, the vegetable proteins change to animal proteins which take part in the formation of tissue and growth of animals.
  • Water : It is another important factor of life, used extensively for different metabolic processes and provides a medium foraquatic life (both flora and fauna). The viscosity of water helps planktonic organisms to float, transparency allows light to pass to a certain depth. Water as solvent contains many essential minerals and gases for aquatic life. The more or less uniform salinity of sea water (3.5%) allows free movement of marine animals. Animals and plants require proper amount of water in their bodies to perform normal physiological activities.
  • Temperature : It is one of the most important environmental factors which affect the metabolic rate and an optimum temperatureis needed for normal growth and development of flora and fauna e.g., sea urchin becomes very large in warmer waters. Temperature also acts as a limiting factor for the distribution of cold blooded animals.
  • Inorganic and organic components : These are essential factors which are present as nutrients. Some elements are required in large quantities and called as macronutrients e.g., calcium, which is needed for molluscs and vertebrates; plants need large quantity of magnesium for the formation of chlorophyll. There are some elements which are needed in very small quantity hence called as micronutrients; e.g., iron, chlorine, zinc, boron, cobalt, molybdenum, etc.
  • Soil : It provides surface for growing and anchorage for plants as well as provides water and dissolved nutrients to the plants.It supports many lives such as earthworms (live in blows). Chemical composition of the soil determines the presence or absence of a particular species of plants or animals. The earthworm prefers soil rich in humus, which is a dark coloured organic substance, formed by the decomposition of plants, dung and dead animals. Land snails are generally found on soil rich in calcium because calcium takes part in the formation of shell.

Biotic Component (Biological Factors)

Biotic components of the ecosystem are the living organisms (flora and fauna). When different types of living entities are present together, they constitute the community or biotic population. These biotic population forms relation with the abiotic factors forming a system termed as ecosystem.

  • Autotrophs : They are also called producers as they are capable for synthesizing their own food (through photosynthesis) and change the solar energy (light energy) to chemical energy, which is contained within the organic molecules that make up their tissues. A small contribution is also made by chemosynthetic bacteria. For example, the major primary producers of aquatic ecosystems are algae, phytoplankton of water bodies. The terrestrial ecosystem has primary producers as the plants(angiosperms and conifers which constitute forests and grasslands).
  • Heterotrophs : Organisms which are directly dependent upon the products of autotrophs as a whole or partially to obtain their source of energy or they also depend upon other organisms for their food. They are collectively called as consumers or phagotrophs (phago = to eat).
  • Primary consumer: A consumer which derives nutrition by eating plants is called Primary consumer or herbivore e.g. grazing cattle.
  • Secondary consumer: An animal that devours the flesh of herbivore or other animals is called Secondary consumer or carnivore. e.g. Tiger, Lion etc.
  • Decomposers or Microconsumers: It constitute a very important components of pond ecosystem. A variety of bacteria and fungi are especially abundant in the mud water and the bottom of the ponds. Their principal function is to decompose the excreta of animals and dead bodies of plants and animals and thereby releasing the locked inorganic substances back into the pond ecosystem. As these feed on dead bodies, they are also known as saprotrophs (sapro = to decompose) or reducers.


Fig. : A scheme of the structure of a unit of typical ecosystem

Function of Ecosystem

The functions of the ecosystem are:

  1. It regulates basic ecological processes, supports living systems and ensures stability.
  2. It is also responsible for nutrient cycling between biotic and abiotic components.
  3. It maintains the balance between the different trophic levels in the ecosystem.
  4. It cycles minerals through the biosphere.
  5. Abiotic components help in the synthesis of organic components that involve energy exchange.

The functional units of the ecosystem or the functional components that work together in the ecosystem are therefore:

  • Productivity – It expresses the production rate of biomass.
  • Energy Flow – It is the process by which energy flows from one trophic level to another. Energy captured from the sun that flows from producers to consumers and then to decomposers and finally back to the environment.
  • Decomposition – This is the process of breaking down dead organic material. Topsoil is the main site for decomposition.
  • Nutrient cycling – In an ecosystem, nutrients are consumed and recycled back in different forms for use by different organisms.

Types of ecosystem

An ecosystem can be small as an oasis in the desert or as large as an ocean, covering thousands of kilometers. There are two types of ecosystems:

  1. Terrestrial Ecosystem
  2. Aquatic Ecosystem

Terrestrial Ecosystem

Terrestrial ecosystems are exclusively land-based ecosystems. Different types of terrestrial ecosystems are distributed in different geological zones. They are as follows:

  1. Forest Ecosystem: A forest ecosystem consists of several plants, especially trees, animals, and microorganisms, that live in coordination with the abiotic factors of the environment. Forests help maintain the Earth's temperature and are a significant carbon store.
  2. Grassland Ecosystem: In this ecosystem, the vegetation is dominated by grasses and herbs. Temperate grasslands and tropical or savanna grasslands are examples of grassland ecosystems.
  3. Tundra Ecosystem: These ecosystems lack trees and are found in cold weather or rainfall, where it is scarce. These are covered with snow for the year. A tundra-type ecosystem is located in the Arctic or on mountaintops.
  4. Desert Ecosystem: Deserts are found all over the world. They are areas with little rainfall and rare vegetation. The days are hot, and the nights are cold.

Aquatic Ecosystem

Aquatic ecosystems are present in a body of water. These can be further divided into two types, namely:

  1. Freshwater ecosystem: A freshwater ecosystem is an aquatic ecosystem that includes lakes, ponds, rivers, streams, and wetlands. Unlike the marine ecosystem, these have no salt content.
  2. Marine ecosystem: The marine ecosystem includes seas and oceans. These have a more substantial salt content and greater biological diversity than the freshwater ecosystem.

Frequently Asked Question (FAQs)

Q1. What is the importance of the ecosystem in our day-to-day life?

Ans. It provides a habitat for wild animals and plants. It promotes various food webs and food chains. It promotes lives and controls essential ecological processes. It is involved in the recycling of nutrients between biotic and abiotic components.

Q2. What are the functional components of an ecosystem?

Ans. The functional components of the ecosystem:

  1. Abiotic factors- Abiotic factors refer to all the non-living things present in the atmosphere.
  2. Biotic factors- Biotic factors relate to all the living things in the ecosystem, including:
  3. Consumers
  4. Producers
  5. Decomposers

Q3. How can we protect the ecosystem?

Ans. Following are the steps to protect the ecosystem:

  1. Reduce, reuse, and recycle. Cut down on what you throw away.
  2. Volunteer. Volunteer for cleanups in your community.
  3. Educate
  4. Conserve water
  5. Choose sustainably
  6. Shop wisely
  7. Use long-lasting light bulbs
  8. Plant a tree

Q4. Which is the largest ecosystem in the world?

Ans. The largest existing ecosystem on our planet is the World Ocean. It cover over 71% of the Earth's surface, it's a source of livelihood for over 3 billion people.

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