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NEET Biology Ecosystem

Ecosystem PDF Notes, Important Questions and Synopsis



  • Ecosystem is the relationship between a biotic community and an abiotic environment.
  • Stratification is the vertical distribution of different species occupying different levels.
  • Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g–2) or energy (kcal m–2).
  • Productivity is the rate of biomass production and is expressed in terms of dry matter produced or energy captured per unit area of land per unit time.
  • Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.
  • Net primary productivity is the total amount of energy stored in the plant tissues after utilising some energy for their own metabolic activities through respiration.
  • Secondary productivity is defined as the rate of formation of new organic matter by consumers.
  • Decomposition is the process of breakdown of complex organic matter by decomposers to inorganic raw materials like carbon dioxide, water and various nutrients.
  • Dead plant remains such as leaves, bark and flowers and dead remains of animals, including faecal matter, constitute detritus.
  • Humification is the formation of a dark-coloured amorphous substance called humus.

  • Mineralisation refers to the formation of minerals during the process of decomposition in the soil.

  • First law of thermodynamics: Energy is neither created nor destroyed but can be transferred from one component to another or transformed from one state to another.

  • Second law of thermodynamics: Every system when left to itself has the tendency towards disorderliness or entropy.

  • Differences between Food Chain and Food Web

  • Each step in the food chain at which the transfer of food takes place is known as a trophic level.

  • Each trophic level has a certain mass of living material at a particular time called the standing crop.

  • Energy flow in an ecosystem: It is unidirectional and follows the 10% law. According to this law, only 10 percent of energy is transferred from one trophic level to the other; the rest is lost to the atmosphere in the form of heat. 

  • Ecological pyramids are graphic representations of certain specific parameters such as number and biomass of energy of a food chain.

  • The gradual and fairly predictable change in the species composition of a given area is called ecological succession.

  • Difference between Hydrarch Succession and Xerarch Succession

    Hydrarch succession

    Xerarch succession

    • It takes place in wetter areas and the successional series progresses from hydric to mesic conditions.
    • It takes place in dry areas and the successional series progresses from xeric to mesic conditions.


  • The species which invade a bare area is called a pioneer species.

  • The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium etc., present in the soil at any given time is referred to as the standing state.

  • The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling.

    Gaseous Cycle

    Sedimentary Cycle

    • Reservoir – Atmosphere
    • Reservoir – Earth’s crust
    • Nitrogen cycle, carbon cycle
    • Phosphorus cycle, sulphur cycle