Trophic interactions

Aquisition of food

  • Maintenence of body structures, functions, growth and reproduction.
  • Food consists of organic molecules - one containing carbon atoms which usually form long chains or rings to which other atoms are joined.
  • Atoms held together by chemical bonds - energy in the bonds is chemical energy, the only type cells can use.
  • Trophic interactions related to way in which an organism obtains organic molecules.
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Food Producers

  • Usually green plants
  • Chloroplasts convert light energy into chemical energy
  • Produce O2
  • Autotrophic
  • Photoautotrophs or chemoautotrophs 
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Food Consumers

  • Predators or parasites
  • Utilise organic compounds for food that have been manufactured by other organisms
  • Heterotrophs
  • Carnivores - kill prey & consume all of it
  • Herbivores - only consume certain parts of vegetation
  • Parasite - close association with host - much smaller , does not kill the host. One host can support many varying viruses, bacteria, some fungi, protozoa, worms, crustaceans and insects.
  • Parasitoids - usually flies or wasps - live within the eggs and larvae and pupae of other insect parasites.
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Dead food consumers

  • Saprophytes
  • Scavengers
  • Detritivores
  • Decomposers
  • Utilise dead body parts and waste materials of organisms.
  • Responsible for recycling nutrients
  • Detritivores reduce larger DOM to smaller particles that can be attacked by decomposers which breakdown organic compounds into their inorganic components which are returned to the substrate or atmosphere to be reused by autotrophs. 
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  • A community is determined by the nature of its producers.
  • It may be considered as a system for the transfer, storage and disspation of energy. 
  • The energy entering a system must be equal to the energy leaving a system
  • AS energy passes through a community, some is always lost in the form of heat.
  • Heat energy cannot be used by organisms - it only affects them via its influence on temperature of either the environment or organism. 
  • The source of energy is solar radiation
  • Some lost by absorption, reflection ect.
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  • Wavelengths 380-710 most effective in PHS - red & blue spectrum - photosynthetically active radiation.
  • Light energy used in chloroplasts - area maximised by thin, flat leaf structure.
  • Total amount of energy that is 'fixed' as chemical energy in PHS is known as 'gross primary productivity'
  • Some used by the plant for maintenence ect.
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Energy availibility

  • NPP - energy potentially availible to consumers. 
  • GPP - R = NPP
  • Energy consumed by 1st trophic level (herbivore) - some respired, some as waste, and some to produce animal tissue.
  • Energy from wastes of dead plants and animals -> detritivores -> decomposers -> energy fixed into PHS and returned to environment as heat. 
  • Energy passes through community in a one way flow. 
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