National 5

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National 5

• Energy in Ecosystems

Mr G Davidson
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Food Chains

• All organisms require energy.
• This energy comes, initially, from the sun.
• It is trapped by green plants by photosynthesis.
• This energy is then passed from organism to
  organism along the food chain.

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Food Chains

• Food chains always begin with the producer (green
  plant).
• The producer is eaten by animals which are
  herbivores.
• These are called primary consumers.
• This animal is then eaten by the next animal in
  the food chain and this is called the secondary
  consumer.

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Food Chains

• Each time an organism is eaten, energy passes
  along the food chain.
• The arrows indicate the direction of the energy
  flow.
• This passing of energy is represented by arrows,
  e.g.

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Food Chains

• Energy is being passed from the grass to the
  rabbit to the fox.
• As energy is passed along the food chain, about
  90 of it is lost.
• Therefore, the next organism only gains about 10
  of the energy of the previous organism.

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Food Chains

• The lost energy is lost as
• Heat
• Movement
• Undigested materials.
• Food chains are not as simple as they first
  appear because they usually involve other
  organisms.

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Food Webs
A combination of a number of food chains leads to
the formation of a food web.
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Pyramid of Numbers

• Food chains give us the feeding relationships
  between the different organisms, but they dont
  provide any information about numbers.
• As we move along a food chain the numbers should
  start high and decrease.
• If we take our food chain and look at the
  numbers, the grass should be the most numerous.

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Pyramid of Numbers
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Pyramid of Numbers

• Each level of the pyramid represents the total
  population of this organism.
• As we travel up the pyramid, these numbers
  decrease as energy is lost.
• There are, however, exceptions to the true
  pyramid shape and these pyramids are said to be
  irregular.

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Irregular Pyramids of Numbers
Fleas
Fox
Rabbit
Grass
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Irregular Pyramids of Numbers
Sparrow hawk
Blue tit
Greenfly
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Pyramid of Biomass

• Due to the irregular pyramids of numbers, they
  are not always the best way to represent feeding
  relationships.
• Instead, we use something called a pyramid of
  biomass.
• In this way, each level is represented by the
  total mass of the organisms.

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Pyramid of Biomass
Fox 4kg
Rabbit 40kg
Grass 400kg
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Pyramid of Energy

• The most reliable way of showing feeding
  relationships is to use a pyramid of energy.
• It is measured as kilojoules per square metre per
  year (kJ/m2/year).
• Since energy is lost at each stage, the pyramid
  formed must be true.

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Pyramid of Energy
Seal 60kJ
Squid 600kJ
Zooplankton 6 000kJ
Phytoplankton 60 000kJ
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Nutrient Cycles

• All organisms are made of chemical elements.
• These elements come from the environment.
• There is a limited supply of these elements and
  so they need to be recycled.
• Nitrogen is one such element.

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Nutrient Cycles

• Organisms require nitrogen to make proteins.
• They cannot use the nitrogen directly from the
  air.
• Plants get their nitrogen from the soil in the
  form of nitrates.
• Animals get their nitrogen from eating plant or
  animal protein.

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Nutrient Cycles

• Nitrogen is an element which is recycled.
• It is very much dependent on bacteria converting
  compounds into other compounds.
• There are different types of bacteria involved in
  the nitrogen cycle.

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Nitrogen Cycle
Nitrates in the Soil
Denitrification
Nitrogen fixating bacteria in plant roots
Converted to Nitrates
Plants
Nitrogen (in air)
Nitrification
Decomposer Bacteria
Converted to Nitrites
Animals
Decomposer Bacteria
Nitrogen in ammonium compounds
Death (products are turned to ammonium
compounds)
Nitrification
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Nitrogen Cycle

• Decomposer bacteria are responsible for breaking
  down dead plants and animals into ammonium
  compounds.
• Nitrifying bacteria are responsible for the
  process of nitrification, which is the conversion
  of ammonium compounds into nitrites and then
  nitrates.

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Nitrogen Cycle

• Denitrifying bacteria are responsible for
  breaking down nitrates and releasing nitrogen
  back into the atmosphere.
• Nitrogen-fixing bacteria are responsible for
  converting atmospheric nitrogen back into
  nitrates.

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Nitrogen Cycle

• There are other bacteria which live in plant root
  nodules of legumes, which also convert nitrogen
  to nitrates.
• Legumes grow well in soil that is nitrogen
  deficient.
• Many modern day fertilisers contain nitrates to
  allow the crops to produce higher yields.

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Competition in Ecosystems

• All organisms require basic resources to stay
  alive.
• If these resources are in short supply then
  competition will occur.
• There are two types of competition
• Interspecific Competition
• Intraspecific Competition

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Interspecific Competition

• Interspecific competition happens when members of
  a different species are competing for similar
  resources.
• This type of competition is generally not as
  fierce because they are not competing for the
  exact same resources, but it may result in one
  species having to move away from the ecosystem.

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Intraspecific Competition

• Intraspecific competition occurs between members
  of the same species.
• This type of competition is usually very fierce
  as the organisms will be competing for the same
  resources.
• Intraspecific competition also helps to regulate
  the size of a population by weeding out the
  weaker members by natural selection.