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| Biosphere |
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| Earth is the only planet on which life exists. It consists of three components Lithosphere (Land), Hydrosphere (Water) and Atmosphere (Air). Life originated and evolved because of this unique combination of the three components and was ideal and favourable for life. The life supporting zone of the earth where atmosphere, hydrosphere and lithosphere meet, interact and make life possible, is known as biosphere. |
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| The lithosphere, hydrosphere and atmosphere are non-living components of the environment and are known as abiotic. The biotic or living components include plants, animals and microbes living on the earth. A constant interaction between the abiotic and biotic components of the biosphere results in the transfer of food and energy, which makes it a dynamic but stable system. The biosphere is the biggest biological system. It consists of smaller functional units known as ecosystems or ecological systems. |
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| An ecosystem is a self sustaining structural and functional unit of the biosphere. The ecosystem may be large or small. In the biosphere several ecosystems exist. Usually there is exchange of material and energy between adjoining ecosystems. Ecosystems can be natural or artificial. Natural ecosystems may be terrestrial as well as aquatic. Land ecosystems include forests, grasslands, deserts and hillsides. Aquatic ecosystem includes ponds, rivers, lakes, seacoasts and oceans. Artificial ecosystems that are man made are croplands, gardens, parks, kitchen gardens and aquariums. |
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| As mentioned earlier, an ecosystem consists of two major components, |
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 Abiotic and |
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 Biotic |
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| Abiotic components are of three kinds |
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 Inorganic substances |
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| These are various chemical substances found in the ecosystem like carbon, nitrogen, sulphur, phosphorous, oxygen and compounds like carbon dioxide, water etc. A vital balance among these components in the environment should be maintained and nature plays an important role in doing this |
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| Example: |
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| Carbon cycle, water cycle, nitrogen cycle etc. |
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 Organic substances |
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| These are various chemical substances found in the ecosystem but they are organic in nature. They form the greater part of the living organism and form a link between the abiotic compounds and the biotic compounds. |
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| Example: |
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| Proteins, carbohydrates, lipids (fats) humic substances, etc. |
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| Climatic factors |
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| These are of two types: |
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 Atmosphere, which means sunlight, temperature, wind, humidity etc. |
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 Edaphic, which means the physical and chemical properties of the soil, it's water and air content etc. |
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| These factors affect the distribution, number, metabolism and behaviour of the organism. |
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| An ecosystem consists of a number of organisms which co-exist and come into regular contact with each other. Some of these organisms may have a special relationship which may profoundly influence its distribution and abundance. |
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| In a given ecosystem three types of biotic components may be found which are grouped according to their modes of nutrition. |
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 Producers |
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| These are autotropic organisms (mainly green plants) so called because they are capable of synthesising organic food. They contain a special pigment called chlorophyll that absorbs solar energy and converts it into chemical energy during photosynthesis. The end product of photosynthesis is glucose, which is stored in the plant in the form of starch. This group forms the source of food for many organisms. |
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 Consumers |
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| These are heterotropic organisms (mainly animals). They are not capable of synthesising organic food and so feed on other organisms (may be plants or animals) to meet their food requirement. They may be further classified as follows: |
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| Animals that stalk their prey are called predators and those that line and grow on other organisms and adapt them as their habitat are known as parasites. |
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| Decomposers |
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| There are saprophytic organisms (mainly bacteria and fungi) that live on dead animals and plants. In terrestrial ecosystem, bacteria act on animal tissue and fungi on plants but there may be exceptions also. This group of organisms plays a vital role in releasing back the biotic components into the environment. By digesting the dead tissue through enzyme secretion, the basic elements of protoplasm are released into the environment, to be made available for reuse by the producers to be built into organic compounds again. So it can be seen that matter circulates in nature: though it constantly changes its form, there is no overall loss or gain. |
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| Here is a diagrammatic representation showing the interdependence of producers and consumers in an ecosystem. |
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| Interdependence of producers and consumers in an ecosystem |
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