Structure of Ecosystems

An Ecosystem is a dynamic, stable system characterised by the interaction of plants and animals with each other and with the non-living components of the environment

The components of an ecosystem are categorised as either biotic and abiotic


Biotic means the living environment, components include:

  • Vegetation (living and decomposing)
  • Mammals, insects, birds and microorganisms

Biomass is the mass of material in the bodies of animals and plants (total mass of living matter)


Abiotic means the non-living, chemical and physical components of the ecosystem and includes:

  • Climate- in particular the seasonal pattern of temperature and precipitation
  • Soil characteristics
  • Underlying parent rock
  • Relief of the land
  • Drainage characteristics

Ecosystems are open systems because energy and living matter can both enter and leave the system:

  • Inputs - Energy from the sun, which drives photosynthesis-enabling the plants to grow, water transported into the ecosystem from precipitation and animals that arrive from elsewhere
  • Outputs - nutrients are transferred out of the system by: animals can physically move out, water can leave through evapotranspiration, groundwater flow and throughflow
  • Flows - nutrients can be transferred from one store to another e.g. capillary uptake
  • Stores- stores of nutrients: vegetation, plant litter and soils

Energy Flows and nutrient cycling

Energy flows arethe flow of energy through a food chain

  • Energy flows flow through an ecosystem from one stage to another.
  • Through photosynthesis plants are able to capture light energy from the sun to make carbohydrates from carbon dioxide and water to grow and increase their biomass
  • Within all ecosystems, nutrients are required for plant growth and are recycled from one store to another

e.g. leaves fall from tree-> when they decompose nutrients are returned to the soil

Trophic levels, food chains and webs

Energy transfer within an ecosystem, represented by a pyramid diagram


  • At each trophic level, some energy is available as food for the next level
  • Each level decreases in size, 90% of energy lost through life processes-respiration, movement and excretion
  • Only 10% available as food, number of living organisms decreases as trophic levels increase
  • Producers/autotrophs - first layer, produce their own food through photosynthesis(green plants)
  • Primary consumers -eat the producers(herbivores)
  • Secondary consumers - consume the herbivores(carnivores)
  • Tertiary consumers - top predators that eat secondary consumers
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