Impala ecosystem

Natural ecosystem. Image credit

ZIMSEC O Level Combined Science Notes: Natural Ecosystems

  • In a natural ecosystem there is close interaction between the plants and animals
  • The green plants are the producers
  • The animals are the consumers
  • There are several levels of consumers
  • Primary consumers-these eat plants directly
  • They are also known as herbivores
  • Secondary and tertiary consumers eat other animals
  • The relationship and links between these producers is shown by a food chain
  • Each food chain relies on energy from the sun
  • Each link level is also known as a trophic level
  • Trophic level-is a feeding level in the food chain
  • Energy is transferred from one trophic level to another as each level is used by another level
  • As organisms die they are broken down by decomposers
  • The nutrients trapped in the living organisms are released back into the soil for use by plants
  • Decomposers such as bacteria are not typically included in the food chain diagrams
  • There are many different food chains around us
  • There are links between food chains
  • These links join food chains to form food webs
  • A food web is made up of plants and animals which are closely linked by their feeding relationships
  • For example there may be four consumers feeding on the same type of plant each consumer with its own chain
  • The more organisms are in a food web the more stable it is
  • This is because if one organism dies out, there are other organisms that can carry out a similar role in the food web
  • While energy is transferred from one trophic level to another in a food chain there is a limit to the number of consumers in a food chain because energy is lost at each level
  • At each trophic level the organism uses some of the energy for itself
  • More energy is lost to the environment as heat
  • Some energy may also be lost as sweat, excretion or feces
  • There is only one source of energy input in the cycle i.e the sun
  • There is one way flow of energy along and out of the food chain
  • Because energy is lost at each trophic level the number of organisms at each level is restricted
  • As a result there are usually not more than four levels of consumers in a food chain
  • The amount of organisms decrease as one goes up the food chain to the upper trophic levels
  • The amount of living material is known as a biomass
  • The relationship between organisms can be shown in a pyramid of biomass
  • When organisms in a food chain die they are processed by decomposers
  • Some of the energy that is trapped in their bodies is used by the decomposers
  • Decomposers include fungi and bacteria
  • These decomposers recycle components or nutrients in the soil
  • Two mineral elements that are part of all living organisms are nitrogen and carbon
  • All organic components contain carbon in the form of organic components
  • I is the main essential element in carbohydrates, fats and proteins
  • Nitrogen is essential for protein manufacture and growth in plants and animals
  • These two elements are constantly being recycled in the ecosystem

To access more topics go to the Combined Science Notes page.

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