Food chains + webs

• Producers

  Make their own organic moleculres
• Consumers


  Heterotrophs, get organic molecules by eating other organisms
• Food Chain

  A linear sequence of organisms through which nutrients and energy pass as one organism eats another

  Each organism occupies a different trophic level, defined by how many energy transfers separate it from the basic input of the chain.
• Food webs

  Consists of many interconnected food chains - are a more realistic representation of consumption relationship in ecosystems.

  Arrows point from an organism that is eaten to the organism that eats it. Some species can eat organisms from more than one trophic level
• Energy transfer

  Energy is transferred from each trophic level to the other

  Eats another and gets energy-rich molecules from its prey's body

  Inefficient --> Energy is stored as biomass --> only 10% of the energy is available to the next
• Food chain levels

  Base of food chain - primary producer, autotrophs, are most photosynthetic organisms - plants, algae, cyanobacteria

  2nd level - Primary consumers, eat primary producers - herbivores, plant eaters, can be algae/bacteria eaters

  3rd level - Secondary consumers, eat primary consumers - meat eaters - carnivores

  4th level - Tertiary consumers eat secondary consumers - carnivore eating carnivore - eagles, big fish

  5th level - quaternary consumers eats tertiary consumers

  Top of food chain - Apex consumer/predator
• Reasons for efficiency

  1. A significant amount of energy is dissipated as heat as organisms carry out cellular respiration and go about their daily lives
  2. Some organic molecules an organism eats cannot be digested and leave the body as faeces rather than being useful
  3. Not all organisms get eaten, some die without being eaten
• Decomposers

  Fungi and bacteria are the key decomposers in many ecosystems - they use chemical energy in dead matter and want to fuel their metabolic processes.

  Other decomposers are detritivores - detritus/debris eaters - multicellular animals such as earthworms, crabs and vultures

  They also fragment dead matter --> more available for bacterial or fungal decomposers
• Importance of decomposers

  Critical for keeping ecosystems healthy, when they break down waste it releases nutrients that can be recycled and used as building blocks by primary producers
• Autotroph

  "auto" - self

  "troph" - feeding

  an organism that produces its own nutrients through photosynthesis (a plant) or chemosynthesis (bacteria)
• Heterotroph

  "Hetero" - different

  "troph" - feeding

  an organism that cannot produce its own food and has to eat another organism for food (animals)
• Scavenger

  An organism that feeds on dead organisms