·         The interaction between the living organism and the non-living environment is called ecosystem.


·         Interaction of biotic and abiotic components results in a physical structure that is characteristic of each type of ecosystem.

·         Identification and description of plant and animal species of an ecosystem gives its species composition.

·         Vertical distribution of different species occupying different levels is called stratification.

·         The components of the ecosystem are seen to function as a unit:

o    Productivity.

o    Decomposition.

o    Energy flow and

o    Nutrient cycle.

·         Description of pond as an ecosystem:

o    The abiotic components include all dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond.

o    The solar input, cycle of temperature, day length, regulates the rater of function of the entire pond.

o    The producer (autotrophic) includes phytoplankton, some algae and the floating, submerged and marginal plants found in edge of pond.

o     The consumers are represented by zooplankton, free swimming and bottom dwelling animals.

o    The decomposers are the fungi, bacteria especially abundant at the bottom of the pond.

·         Basic events (in terms of function) in an ecosystem:

o    Conversion of inorganic into organic material (photosynthesis) by producers.

o    Consumption of the autotrophs by heterotrophs.

o    Decomposition and mineralization of the dead organic matter to release them back for reuse by the autotrophs.

o    There is unidirectional flow of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.




·         Primary productivity:

o    The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.

o    It is expressed in terms of weight (g-2) or energy (kcal m-2)

o    The rate of biomass production is called productivity.

·         Gross primary productivity: (GPP) is the rate of production of organic matter during photosynthesis.

·         Net primary productivity:

o    A considerable amount of energy is utilized by plants in respiration.

o    Gross primary productivity minus respiration losses (R) is the net primary productivity.

o    GPP – R = NPP.

·         Net primary productivity is the available biomass for the consumption to heterotrophs (herbivore and decomposers.

·         Secondary productivity: is defined as the rate of formation of new organic matter by the consumer.


·         Earthworm is said to be ‘friends’ of farmer:

o    Breakdown the complex organic matter.

o    Loosening of the soil helps in aeration and entry of root.

·         The decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients, called decomposition.

·         Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute the detritus.

·         The process of decomposition completed in following steps:

o    Fragmentation  :  Break  down  of  detritus  into  smaller  particles  by  detritivore  (earthworm).

o    Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

o    Catabolism  :  Bacterial  and  fungal  enzymes  degrade  detritus  into  simple  inorganic  substances.

o    Humification: Accumulation of dark coloured amorphous substances called humus.

Importance of humus:

o    Highly resistance to microbial action.

o    Undergo decomposition at an extremely slow rate.

o    Being colloidal in nature, it serves as reservoir for nutrients.

o    Mineralization: The  humus  is  further  degraded  by  some  microbes  and  release of  inorganic nutrients  occur.

Factor affects rate of decomposition:

·         Decomposition is largely an oxygen-requiring process.

·         Detritus rich in chitin and lignin has slow rate of decomposition.

·         Detritus rich in nitrogen and water-soluble substance like sugar has faster decomposition.

·         Temperature and soil moisture are most important climatic factor that regulate decomposition

·         Warm and moist environment favor decomposition.

·         Low temperaturedryness and anerobiosis inhibit decomposition.


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