Ecosystem 12 Notes Biology Chapter 14

By going through these CBSE Class 12 Biology Notes Chapter 14 Ecosystem, students can recall all the concepts quickly.

Ecosystem Notes Class 12 Biology Chapter 14

→ An ecosystem is a structural and functional unit of the biosphere which consists of a community of living beings and the physical environment, both of them interacting and exchanging materials between them. In short, the ecosystem is a self-supporting, stable ecological unit that results from an interaction between the biotic community and its abiotic’ environment.

→ The ecosystem has two main components: an abiotic component that includes all plants, animals, and microorganisms, and an abiotic component that includes soil, water, minerals, CO2, and oxygen. It receives energy in the form of sunlight.

→ The biotic component of the ecosystem contains all the living members. These are connected to each Other by food and energy. They are divided into producers (autotrophs) and consumers (herbivores and carnivores) and decomposers.

→ Food is manufactured from inorganic raw materials by autotrophs only so they are called producers. They are mainly photosynthetic plants that contain chlorophyll. Consumers are animals that feed on plants (herbivores) directly, are called primary consumers, and animals that feed on other organisms or their parts are called secondary or tertiary consumers (carnivores).

Microorganisms break the dead organic matter into simple substances which are returned to the environment for reuse, they are called decomposers. Based on the source of nutrition every organism occupies a place in an ecosystem. This place is called a trophic level of the organism.

→ Productivity, decomposition, energy flow, and nutrient cycling are the main functions of an ecosystem. The nutrients are used again and again in a cyclic manner but energy trapped from sunlight is lost as heat.

→ A food chain consists of various trophic levels which include a producer, various levels of consumers, and a decomposer.

→ Food chains are of three kinds viz. predator, parasitic and saprophytic chain. The food chains are interlinked to each other. The various food chains in a community form a food web.

→ Primary productivity is the rate of capture of solar energy or biomass production of the producers. It can be, gross primary productivity (GPP) and net primary productivity (NPP). GPP is the rate of capture of solar energy or total production of organic matter. NPP is the remaining biomass or the energy left after the utilization of producers. Secondary productivity is the rate of assimilation of food energy by the consumers. Decomposition is the breakdown of complex organic compounds of detritus into CO2, water, and inorganic nutrients. It involves three processes: fragmentation of detritus, leaching, and catabolism.

→ Energy flow is unidirectional. The number of materials and energy transferred as food through successive higher trophic levels progressively decreases.

→ The graphic representation of the relationship of food and energy between organisms at different trophic levels is called pyramids. The base of each pyramid represents the producers and the apex represents the tertiary consumer.

The ecological pyramids are of three types:

  1. pyramid of number,
  2. pyramid of biomass and
  3. pyramid of energy.

Mostly the pyramid of number and biomass are upright but sometimes the pyramid of biomass may be of the inverted type, e.g. in a sea. The pyramid of energy is always upright.
Ecosystem 12 Notes Biology 1
The inverted pyramid of biomass. A small standing crop of phytoplankton supports a large standing crop of zooplankton.

→ Biosphere or ecosphere is the part of the earth inhabited by organisms and their living and non-living environment. The earth is a closed system regarding materials. The substances vital for life are limited and must be recycled to sustain life. The earth is an open system regarding energy. It receives energy from the Sun in the form of solar energy, a part of it is trapped by living organisms and the major part is radiated back to outer space. The biosphere consists of the atmosphere, lithosphere, and hydrosphere.

→ The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling or Biogeochemical cycle, bio: living organisms, geo: rocks, air, water.

Nutrient cycles are of two types:

  1. Gaseous cycle: It has carbon, hydrogen, oxygen, and nitrogen as a reservoir and exists in the atmosphere and
  2. Sedimentary cycle: It has phosphorus, sulphur, calcium, potassium etc. as a reservoir and is located in earth’s crust.

The gaseous cycles are more balanced than the sedimentary cycles. The reservoir compensates for the deficit which occurs due to an imbalance in the rate of influx and efflux.

→ Biomes are regional, integrated, natural biotic units, which can be identified by the forum of life of the climax vegetation. Biomes may also include developing and modified communities, within the same climatic region like forest biomes will include young successional forests and open grass-dominated tracts.

The three major biomes are:

  1. forest biome,
  2. grassland biome, and
  3. desert biome.

Each biome has a characteristic array of plants and animal life. Climatic and edaphic factors, latitude, and barriers determine the extent of a biome.

→ Ecotones are the zones present between adjacent biomes, these support some organisms from each adjoining biome and some typical characters of their own.

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