Chapter 14: Ecosystem

An ecosystem can be visualised as functional unit of nature, where living organsism interact among themselves and also with the surrounding physical environment. Ecosystem may small or large, may be terrestrial or aquatic. Forest, grassland and desert are some example of natural terrestrial ecosytem. Pond, lake, wetland, river and estuary are some example of natural aquatic ecosystems. Cropfield and an aquarium may also be considered as man-made ecosytems.

Question 1 : Define Ecosystem , stratification , and functions of ecosystem .
Answer :
Ecosystem: System where biotic and abiotic components interact together to produce various functions .
Stratification: Vertical distribution of different species occupying different levels .
Functions of ecosystem:

  • Productivity
  • Decomposition
  • Energy flow
  • Nutrient cycling.

Question 2 : Write about productivity and its various types ?
Answer : Productivity
: The rate of production is called productivity . Productivity is of two types :

  1. Primary productivity: Amount of biomass produced per unit area in a certain time period by plants through photosynthesis is primary productivity . It depends on following:

    1. Type of plant species.
    2. Photosynthesis capacity of plants .
    3. Nutrient availability .
    4. Availability of light , water ,etc

    GPP(Gross Primary Productivity) : Rate of production of organic matter during photosynthesis
    NPP(Net Primary Productivity) : It is the amount of GPP produced after excluding respiration and other losses.
    NPP = GPP – respiration

  2. Secondary Productivity: Secondary productivity is the rate of formation of new organic matter by the consumers . Ex : milk , meat , egg.


Decomposition is the process that concerns breakdown of complex organic matter by decomposers to inorganic raw materials like carbon dioxide, water and various nutrients. The upper layer of soil is the main site for decomposition processes in the ecosystem. The process of decomposition involves several processes. These processes can be categorised as fragmentation of detritus, leaching and catabolism. After these steps humification or mineralisation occurs. By humification humus formation take place. By mineralisation mineral formation take place.

Decomposition Cycle

Question 3: Explain in detail about Decomposition ?
Answer: Decompostion:
Process of breakdown of the organic matter present in detritus into inorganic substances like CO2, H2O. Detritus : dead decaying remains of plants and animals.
Detritivores: Organism which break large detritus particle into small particle are detritivores . Ex : earthworm , bacteria .
Steps of decomposition:

  1. Fragmentation : Detritivores break large detritus particle into small particles .
  2. Leaching : Water soluble inorganic nutrients go into soil horizon and get precipitated as unavailable salts .
  3. Catabolism : Bacterial and fungal enzymes degrade into inorganic substances .
  4. Humification : is accumulation of dark colored amorphous substance called humus . humus is resistant to microbial action and undergoes decomposition at very slow rate.
  5. Mineralisation : Humus is degraded by various enzyme and microbes release inorganic nutrients by mineralization process .

Fctors affecting decomposition :

  • Moisture availability : Decomposition fast in wet condition .
  • Warm temperature : Decomposition fast in warm temperature .
  • Chemical composition of detritus : decomposition is fast when detritus is rich in nitrogen and sugar and slower when detritus is rich in lignin and chitin .

Question 4: Write about Energy flow , food chain , food web , trophic level?
Answer: Energy flow:
There is a flow of energy through the ecosystem without its return. There is regular supply of energy from outside. Energy is dissipate at every level. Flow of energy is unidirectional.

Energy Flow

Food chain: A chain of organism in which one organism is eaten up by the other organism for flow of energy from one trophic level to another.
Example: Rat —– Snake —– Eagle.
Food web: Various interconnected food chain together form food web.
Trophic level: It is place in food chain where all organism have similar food habits .

Question 5: Write difference between primary and secondary succession ?
The difference between primary and secondary succession is :

Primary succession Secondary succession
Starts where no living organism ever existed takes place in an area that have lost all living organism s that existed there
Primary succession takes more time to complete secondary succession takes less time to complete
Ex : Bare, rock , lava ,etc Ex : Burnt forest , flooded area , cutted forest

Question 6: Write about ecological succession and terms related to it ?
Answer: Ecological succession :
The sequential , gradual and predictable change in a species composition of an area is called ecological succession . Primary and secondary successions are types of ecological successions.
Sere: Entire sequence of communities that successively change in a given area during biotic succession . Sere begins with pioneer community and ends in climax community.
seral stage: Individual transitional communities during succession. It is a stage between pioneer community and climax community .
Pioneer community: species that invade a bare area . It is the first community to colonise an area .
Climax community: It is the final community to develop over an area the area is already covered by late successional community before the arrival of climax community it is near equilibrium with the enviorment

Question 7: Write about Hydrach succession in detail ?
Answer: Hydrarch succession:
takes place in wetter areas and the successional series progress from hydric to the mesic conditions . It consists of following steps:

  • Pioneer species are small phytoplankton's .
  • Pioneer species are replaced by submerged plant stage .
  • Submerged free floating plant stage : floating plant like lemma , azolla begin to appear with the rise in shallowness of the pond .
  • Reed swamp stage : shallowness incresese more , appearance of more plants .
  • Marsh Meadow stage : free water is changed to swampy land, the water plants give way to swampy plants such as sedges and rushes .
  • Scrub stage: herb , shrub appears profusely.
  • Forest stage: It is the climax community which consists of trees.

Hydrach Succassion

Dharmendra Gaur

Dharmendra Gaur (Msc. Zoology) aka DRGP. I love to learn and teach biology. By this blog I want to increase my knowledge and share my knowledge with others. Feel free to ask what ever you want to ask related to biology, I try my best to help you.

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