Biosphere: Ecology and Ecosystem, Flow of Energy in the Ecosystem, Food Chain/Cycle, Natural Cycles

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Ecology and Ecosystem

  • Ecology is the study of interactions between the organisms and their environment. The two components, organisms and environment are not distinct. For a particular organism, other organisms can constitute a part of its environments. Similarly, environment can also be modified and influenced by organisms. Thus, organisms and environment are interacting parts of a system.

  • The word ecosystem is a short form of ecological system. The term was first used by A.G. Tansley in 1935. An ecosystem can be defined as a system of regularly interacting and interdependent components forming a unified whole. For example, a lake or pond is an ecosystem when it is considered in its totality and not just a water body. In that sense, pond is a representative of small ecosystem and biosphere is considered as the largest ecosystem. The concept revolves around two aspects.

    • Firstly, its studies interaction among the various components and subcomponents.

    • Secondly, flow of energy among various components of ecosystem which is the essential determinants of how a biological community function.

Flow of Energy in an Ecosystem

Flow of Energy in an Ecosystem

Flow of Energy in an Ecosystem

Therefore, for studying the functional aspects of an ecosystem, we must study it in terms of the followings:

Flow of Energy in the Ecosystem

A continuous interaction goes on within an ecosystem. This interaction between components and sub-components involves the flow of energy and cycling of mineral nutrients. In this process transfer of energy takes place from one level to another. This is known as trophic level. Therefore, trophic level is the level or the stage at which food energy passes from one group to another. In the biosphere, there are broadly two groups of living organisms, autotrophs and heterotrophs. On the basis of food habits, these heterotrophs are further sub-divided into three categories. They are herbivores, carnivores, and omnivores. Herbivores are plant eating animals, carnivores are flesh eating animals, and omnivores are both plant and animal eating organisms.

Food Chain/Cycle

Food chain can be defined as a sequence of transfer of energy from organisms in one trophic level to those in another trophic level. Plants form the basis of food for large number of herbivores. These herbivores are used as food substances for carnivores. Besides, there are omnivores who feed on plants as well as animal flesh. The solar energy absorbed by the soil is reflected in the form of plants and animals. These organisms have a limited cycle and die after some time. Once these organisms die, another group of organisms start their functioning as they feed on dead material. They help in decomposing the dead bodies of plants and animals on releasing the energy which is again absorbed by the soil to enrich its production of plants. Thus, the cycle completes.

Food Chain/Cycle

Food Chain/Cycle

Food Chain/Cycle

  • The food chains are not always so simple and isolated sequences. Several inter-connected and overlapping food chains present complicated patterns. Such patterns are called food web.

  • Solar energy is the source for all the plants for preparation of their food. The energy which is stored by the plants is known as trophic level I. It becomes the source of energy for the herbivores. Transfer of energy from trophic level I to trophic level II takes place when the plant eating animals consume these plants. Again, this chemical energy through foods consumed by herbivores gets stored at trophic level II and becomes source of energy for the carnivores at trophic level III. Carnivores are flesh eating animals and depend upon other animals for food.

Image of Energy Pyramids In Different Food Chains

Image of Energy Pyramids in Different Food Chains

Image of Energy Pyramids In Different Food Chains

These animals require a lot of energy for building their tissues. They receive their energy from trophic level II through food consumption. A part of the chemical energy from this level III of the food chain is transferred to omnivores at trophic level IV. Therefore, omnivores are at the top level of the food chain which receives their energy from all the three levels. So, in a food chain the members at the successive higher levels becomes smaller in number. When the numbers at successive levels are plotted, they assume the shape of a pyramid, hence it is called food pyramid or pyramid of numbers.

Energy Pyramids In Different Food - Chains

Energy Pyramids in Different Food - Chains

Energy Pyramids In Different Food - Chains

Natural / Bio-Geochemical Cycles

Biogeochemical cycles are the movement and circulation of soluble inorganic substances or nutrients derived from soil and atmospheric phases of inorganic substances through organic phase of various biotic components. Similarly, a return circulation and movement of organic substances takes place in favour of inorganic objects such as soil and atmosphere. Thus, these two systems are supplementary to each other and complete the cycle. The study of biogeochemical cycles can be approached on two scales e.g., cycling of all elements together or cycling of individual elements, such as hydrological cycle, carbon cycle, nitrogen cycle, phosphorous cycle, oxygen cycle, sulphur cycle etc. Besides these cycles, sediment cycles and mineral cycles are also included in the broader biogeochemical cycles. These natural or biogeochemical cycles functions in a balanced manner which stabilizes biosphere and sustains the life processes on the earth.

The Hydrological Cycle

This cycle helps in exchange of water between air, land, sea, living plants and animals. Solar energy is used to drive the hydrological cycle. Massive evaporation of water from the oceans, cloud formation and rainfall give us the supply and reserves of fresh water.

At sub-zero temperature, rainwater freezes into snow and in presence of strong wind forms hail. Water as rain, snow and hail is precipitated on land and water surfaces. On land surface water seeps into the soil and is stored as ground water. The natural water level or water table exists below the ground. The water table is supported by the underlying clay and rock strata. Ground water moves up through capillary action and reaches soil surfaces where it is drawn by plant roots.

The Nitrogen Cycle

Nitrogen and its compounds are essential for life processes in the biosphere. There is continuous exchange of nitrogen within the ecosystem operating the nitrogen cycle. Proteins produced by plants and animals in their metabolic processes are organic compounds of nitrogen. The major load of nitrogenous organic residue in soil originates from death and decay of plants and excreta of animals. These organic residues in soil are taken up by various soil micro-organisms who break down soil nitrate into nitrogen by denitrification process while others transform nitrogen into soluble nitrogen compounds.

The Carbon Cycle

The atmosphere is the minor reservoir of carbon. Hydrosphere is the major reservoir which contains approximately 50 times more as that of atmosphere. It is stored as bicarbonate mineral deposit on the ocean floor. The later regulates the carbon dioxide level in the atmosphere. The cycle operates in the form of carbon dioxide exchanging among the atmosphere, biosphere and the oceans.

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