Biology Class 12 NCERT Solutions: Chapter 14 Ecosystem Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 7 Describe the components of an ecosystem.


  • An ecosystem is defined as an interacting unit that includes both the biological community as well as the non-living components of an area.
  • The living and the non-living components of an ecosystem interact amongst themselves and function as a unit, which gets evident during the processes of nutrient cycling, energy flow, decomposition, and productivity. There are many ecosystems such as ponds, forests, grasslands, etc.
  • The two components of an ecosystem are:
  1. Biotic component:
  2. It is the living component of an ecosystem that includes biotic factors such as producers, consumers, decomposers, etc. Producers include plants and algae. They contain chlorophyll pigment, which helps them carry out the process of photosynthesis in the presence of light.
  3. Thus, they are also called converters or transducers. Consumers or heterotrophs are organisms that are directly (primary consumers) or indirectly (secondary and tertiary consumers) dependent on producers for their food.
  4. Decomposers include micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals.
  5. Abiotic component:
  6. They are the non-living component of an ecosystem such as light, temperature, water, soil, air, inorganic nutrients, etc.

Q. 8 Define ecological pyramids and describe with examples, pyramids of number and biomass.


  • An ecological pyramid is a graphical representation of various ecological parameters such as the number of individuals present at each trophic level, the amount of energy, or the biomass present at each trophic level.
  • Ecological pyramids represent producers at the base, while the apex represents the top level consumers present in the ecosystem.
  • There are three types of pyramids: Pyramid of numbers, Pyramid of energy, Pyramid of biomass
  1. Pyramid of numbers:
  2. It is a graphical representation of the number of individuals present at each trophic level in a food chain of an ecosystem. The pyramid of numbers can be upright or inverted depending on the number of producers.
  3. For example, in a grassland ecosystem, the pyramid of numbers is upright. In this type of a food chain, the number of producers (plants) is followed by the number of herbivores (mice) , which in turn is followed by the number of secondary consumers (snakes) and tertiary arnivores (eagles) . Hence, the number of individuals at the producer level will be the maximum, while the number of individuals present at top carnivores will be least.
Pyramid of Numbers
  • On the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of a food chain, a single tree (producer) provides food to several fruit eating birds, which in turn support several insect species.
  1. Pyramid of biomass:
  2. A pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem.
  3. It can be upright or inverted. It is upright in grasslands and forest ecosystems as the amount of biomass present at the producer level is higher than at the top carnivore level.
  4. The pyramid of biomass is inverted in a pond ecosystem as the biomass of fishes far exceeds the biomass of zooplankton (upon which they feed) .
Pyramid of Biomass

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