Food Chains and Food Webs

• The sun is the principal source of energy input to biological systems.
• Energy flow is not a cycle; it starts from the sun and then that energy is harnessed by plants which are eaten by animals which are eaten by other animals.
• At each step of the food chain, energy is lost to the environment.
• Food chain: a chart showing the flow of energy (food) from one organism to the next beginning with a producer, for example:

  tree → caterpillar → song bird → hawk
• Food web: showing the transfer of energy from one organism to the next, beginning with a producer
• Energy is transferred between organisms in a food chain by ingestion
• Producer: an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
• Consumer: an organism that gets its energy by feeding on other organisms
• Herbivore: an animal that gets its energy by eating plants
• Carnivore: an animal that gets its energy by eating other animals
• Decomposer: an organism that gets its energy from dead or waste organic matter (i.e. a saprotroph)
• Ecosystem: a unit containing all of the organisms and their environment, interacting together, in a given area e.g. decomposing log or a lake
• Trophic level: position of an organism in a food chain, food web or pyramid of biomass, numbers or energy

  • Primary consumer: eat vegetables
  • Secondary consumer: eat meat/drink milk
  • Tertiary consumer: eat a predatory fish, salmon
• Food chains usually have fewer than five trophic levels, because energy transfer is inefficient
• Humans eating plants is more efficient than eating animals because:

  • Only need 2 vegetables per meal, but to have meat we must feed animals lots of plants in order to get far less meat.
  • While raising an animal, plants lose energy to environment, then animal loses energy to environment and doesn't use all the plant material so it is very inefficient.
• Pyramid of numbers:

  • Shows number of each organism in a food chain
  • When moving up pyramid, number of individuals’ decreases

  
• Pyramid of biomass:

  • Pyramid which shows the biomass
  • (number of individuals × their individual mass)