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Ecosystem


  • The portion of the earth which sustains life is called biosphere. Biosphere is very huge and cannot be studied as a single entity. It is divided into many distinct functional units called ecosystem.

ecosystem

Components of an ecosystem

  • They are broadly grouped into:- (a) Abiotic and (b) Biotic components.

Abiotic components (Non-living)

  • Physical factors: Sun light, temperature, rainfall, humidity and pressure. They sustain and limit the growth of organisms in an ecosystem.
  • Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulphur, water, rock, soil and other minerals.
  • Organic compounds: Carbohydrates, proteins, lipids and humic substances. They are the building blocks of living systems and therefore, make a link between the biotic and abiotic components.

Biotic components

  • Producers: The green plants manufacture food for the entire ecosystem through the process of photosynthesis.
  • Green plants are called autotrophs, as they absorb water and nutrients from the soil, carbon dioxide from the air, and capture solar energy for this process.
  • Consumers: They are called heterotrophs and they consume food synthesized by the autographs. Based on food preferences they can be grouped into three broad Categories. Herbivores (e.g. cow, deer and rabbit etc.) feed directly on plants, carnivores are animals which eat other animals (eg. lion, cat, dog etc.) and omnivores organisms feeding upon plants and animals e.g. human, pigs and sparrow.
  • Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed and the dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in recycling of nutrients. They are also called detrivores or detritus feeders.

Functions of ecosystem

  • Energy flow through food chain
  • Nutrient cycling (biogeochemical cycles)
  • Ecological succession or ecosystem development
  • Homeostasis (or cybernetic) or feedback control mechanisms
  • Ponds, lakes, meadows, marshlands, grasslands, deserts and forests are examples of natural ecosystem. Many of you have seen an aquarium; a garden or a lawn etc. in your neighbourhood. These are manmade ecosystem.

Types of Ecosystem

  • Ecosystems are classified as follows: Natural ecosystems, manmade ecosystems
  • Natural ecosystems-Totally dependent on solar radiation e.g. forests, grasslands, oceans, lakes, rivers and deserts. They provide food, fuel, fodder and medicines. Ecosystems dependent on solar radiation and energy subsidies (alternative sources)such as wind, rain and tides. e.g tropical rain forests, tidal estuaries and coral reefs.
  • Manmade ecosystems-Dependent on solar energy-e.g. agricultural fields and aquaculture ponds. Dependent on fossil fuel e.g. urban and industrial ecosystems.

ECOSYSTEM FUNCTION–ENERGY FLOW THROUGH ECOSYSTEM

  • Functional processes an ecosystem are energy flow, food chains, nutrient cycles, ecosystem development and homeostasis.

Food Chain

  • Transfer of food energy from green plants (producers) through a series of organisms with repeated eating and being eaten is called a food chain. e.g. Grasses ® Grasshopper ® Frog ® Snake ® Hawk/Eagle
  • During this process of transfer of energy some energy is lost into the system as heat energy and is not available to the next trophic level. Therefore, the number of steps is limited in a chain to 4 or 5.

Food web

  • Trophic levels in an ecosystem are not linear rather they are interconnected and make a food web. Thus food web is a network interconnected food chains existing in an ecosystem.
  • One animal may be a member of several different food chains. Food webs are more realistic models of energy flow through an ecosystem.

Ecological pyramid

  • Ecological pyramids are the graphic representations of trophic levels in an ecosystem.
  • They are pyramidal in shape and they are of three types: The producers make the base of the pyramid and the subsequent tiers of the pyramid represent herbivore, carnivore and top carnivore levels.

BIOGEOCHEMICAL CYCLES

  • The nutrients move from the non-living to the living and back to the non-living component of the ecosystem in a more or less circular manner. These nutrient cycles are known as biogeochemical cycles. (Bio = living, geo = rock chemical = element).
  • There are more than 40 elements required for the various life processes by plants and animals. The entire earth or biosphere is a closed system i.e. nutrients are neither imported nor exported from the biosphere.
  • The main components of all the biogeochemical cycles are:- a) the reservoir pool that contains the major bulk of the nutrients soil or atmosphere. b) cycling pool which are the living organisms (producers, consumers and decomposers), soil, water and air in which it stays temporarily.
  • Carbon cycle-The source of all carbon is carbon dioxide present in the atmosphere. It is highly soluble in water; therefore, oceans also contain large quantities of dissolved carbon dioxide.
  • Nitrogen cycle-Nitrogen is an essential component of protein and required by all living organisms including human beings. Our atmosphere contains nearly 79% of nitrogen but it cannot be used directly by the majority of living organisms. Broadly like carbon dioxide, nitrogen also cycles from gaseous phase to solid phase then back to gaseous phase through the activity of a wide variety of organisms. Cycling of nitrogen is vitally important for all living organisms.
  • Water Cycle-Water is essential for life. No organism can survive without water. Precipitation (rain, snow, slush dew etc.) is the only source of water on the earth. Water received from the atmosphere on the earth returns back to the atmosphere as water vapour resulting from direct evaporation and through evapotranspiration the continuous movement of water in the biosphere is called water cycle (hydrological cycle).

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