Food Chains

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Food Chains

Each stage in a food chain is called a trophic level, and the arrows represent the flow of
energy and matter through the food chain.

  • Food chains always start with photosynthetic producers (plants, algae, plankton and photosynthetic bacteria) because, uniquely, producers are able to  extract both energy and matter from the abiotic environment.
  • All other living organisms get both their energy and matter by eating other organisms. All living organisms need energy and matter from their environment.
  • Matter is needed to make new cells (growth) and to create new organisms (reproduction), while energy is needed to drive all the chemical and physical processes of life, such as biosynthesis, active transport and movement.

Deep water ecosystems have few producers (since there is little light), so the main food source for consumers is detritus washed down from rivers.

The top of a food chain is often not a top consumer, but rather scavengers or parasites feeding on them.

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Matter and Energy

Organisms need both matter and energy from their environment.


  • Matter (chemicals) is measured in kilograms and comes in three different states (solid, liquid and gas).
  • It cannot be created, destroyed or used up.
  • The Earth is a closed system with respect to matter, in other words the total amount of matter on the Earth is constant.
  • The matter of a living organism is called its biomass.
  •  Matter (and especially the biochemicals found in living organisms) can contain stored chemical energy.


  • Energy is measured in joules and comes in many different forms (such as heat, light, chemical, potential, kinetic, etc.).
  • These forms can be inter-converted, but energy can never be created, destroyed or used up.
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Matter and Energy 2

  • If we talk about energy being“lost”, we usually mean as heat, which is radiated out into space.
  •  The Earth is an open system with respect to energy, in other words energy can enter and leave the Earth.
  •  Energy is constantly arriving on Earth from the sun, and is constantly leaving the earth as heat, but the total amount of energy on the earth remains roughly constant.
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