PRODUCTIVITY AND ENERGY FLOW Source: http//web3.ibo.org/

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PRODUCTIVITY AND ENERGY FLOW Source
http//web3.ibo.org/
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ENERGY ENTERS THE ECOSYSTEM AS SUNLIGHT

• Only 2 of the light energy falling on a tree is
  captured and turned into chemical energy by
  PHOTOSYNTHESIS
• The rest is reflected, or just warms up the tree
  as it is absorbed

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Gross productivity is a measure of total energy
captured

• It is measured in joules (J)
• It is the energy captured or assimilated by an
  organism
• for a plant, it is the sunlight actually fixed
  by the leaves during photosynthesis

Energy is stored in leaf as sugars and starches,
which later are used to form flowers, fruits,
seeds,etc.
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Net productivity

• Plants have to use some of the energy they
  capture to keep themselves growing
• they move water and stored chemicals around
• they make hormones and enzymes to control their
  metabolism
• they make flowers, fruits, new leaves and stems
• the energy left over after they have used what
  they need is called the net productivity
• the energy used by the plant for essential tasks
  is called respiration energy, and eventually it
  is released to the environment as heat

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So how are gross and net productivity related ?

• Net productivity Gross productivity -
  Respiration Energy
• or using symbols
• NP GP - R
• This equation applies to animals too, but more on
  that later..
• The productivity of a plant is called
• PRIMARY PRODUCTIVITY
• because plants are the first or primary organisms
  in the food web

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So what about animal productivity?

• Animals must eat other organisms to obtain
  energy, unlike plants which photosynthesize
• Animals may eat plants or animals or both
• Not all the energy in food is absorbed
  (assimilated) into an animals body
• Unassimilated food is ejected as faeces or
  droppings
• So gross productivity food assimilated
• or gross productivity food eaten - energy in
  faeces

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What about net productivity for an animal
(secondary consumer)?

• Gross secondary productivity
• Energy eaten - energy in faeces
• As well as keeping themselves alive, animals must
  use energy to move and keep warm - plants need
  rather less energy- but in the end it, as in
  plants, it all turns to heat
• Net secondary productivity (NSP )
• food eaten - faeces - respiration energy
• so NSP GSP- R (just like plants)

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Net and gross productivity in the food web

• In a food web diagram, you can usually assume
  that
• the energy input into an organism represents the
  GP
• the energy output from that organism to the next
  trophic level represents the NP
• the difference between GP and NP R (respiration
  energy ) and/or loss to decomposers

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Now check what you have understood!
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• Complete this energy flow diagram
• label GPP, NPP and R for the primary producer
• add arrows to show missing energy pathways (3 in
  total)
• fill in the blank box to explain why some
  sunlight is not fixed by plant

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• Draw your own energy flow diagram, rather like
  the one on the previous slide to show energy
  flows through one of the animals named in your
  food web. You should include the following
  labels
• energy lost in faeces
• food ingested
• respiration loss, R
• GSP, NSP
• arrows showing energy moving to carnivores and
  decomposers