Energetics of Marine Ecosystems

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Energetics of Marine Ecosystems

• Photosynthesis and chemosynthesis as means of
  energy capture
• Productivity and energy flow along food chains

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Explain that photosynthesis captures the energy
of sunlight and makes the energy available to the
food chain

• Green plants, including phytoplankton in aquatic
  food chains, capture light energy and use this to
  synthesize organic substances, including
  carbohydrates, in the process of photosynthesis.
• In this way, energy is made available to higher
  trophic levels in food chains and food webs.
• Energy, in the form of organic substances, passes
  to the primary consumers, such as herbivorous
  zooplankton.

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How do plants make energy food?

• Plants use the energy from the sun
• to make ATP energy
• to make sugars
• glucose, sucrose, cellulose, starch, more

Photosynthesis Song
sun
ATP
sugar
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Building plants from sunlight air
sun

• Photosynthesis
• 2 separate processes
• ENERGY building reactions
• collect sun energy
• use it to make ATP
• SUGAR building reactions
• take the ATP energy
• collect CO2 from air H2O from ground
• use all to build sugars

ATP

sugars
carbon dioxide CO2
sugars C6H12O6
water H2O

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Using light air to grow plants

• Photosynthesis
• using suns energy to make ATP
• using CO2 water to make sugar
• in chloroplasts
• allows plants to grow
• makes a waste product
• oxygen (O2)

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What do plants need to grow?

• The factory for making energy sugars
• chloroplast
• Fuels
• sunlight
• carbon dioxide
• water
• The Helpers
• enzymes

sun
ATP
enzymes
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Photosynthesis
sun
ENERGYbuilding reactions
ATP
ADP
SUGARbuilding reactions
used immediatelyto synthesize sugars
sugar
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How are they connected?
Respiration
Photosynthesis
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Energy cycle
Photosynthesis
plants
CO2
O2
animals, plants
Cellular Respiration
ATP
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Another view
capturelight energy
Photosynthesis
synthesis
producers, autotrophs
CO2
O2
organicmoleculesfood
waste
waste
waste
consumers, heterotrophs
digestion
Cellular Respiration
ATP
releasechemical energy
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In other words
Take it from me!

• All of the solid material of every plant was
  built out of thin air
• All of the solid material of every animal was
  built from plant material

sun
Then all the cats, dogs, mice, people
elephantsare really strands of air woven
together by sunlight!
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Photosynthesis Overview

• Energy for all life on Earth ultimately comes
  from photosynthesis.
• 6CO2 12H2O C6H12O6 6H2O 6O2
  
• Oxygenic photosynthesis is carried out by
• cyanobacteria, 7 groups of algae, all land plants
  

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Electromagnetic Spectrum
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Pigments

• Pigments molecules that absorb visible light
• Each pigment has a characteristic absorption
  spectrum, the range and efficiency of photons it
  is capable of absorbing.

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Pigments

• chlorophyll a primary pigment in plants and
  cyanobacteria
• -absorbs violet-blue and red light
• chlorophyll b secondary pigment absorbing light
  wavelengths that chlorophyll a does not absorb

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Pigments

• A graph of percent of light absorbed at each
  wavelength is a compounds absorption spectrum.
• Action spectrum
• Oxygen production and therefore photosynthetic
  activity is measured for plants under each
  specific wavelength when plotted on a graph,
  this gives an action spectrum for a compound.
• The action spectrum for chlorophyll resembles its
  absorption spectrum, thus indicating that
  chlorophyll contributes to photosynthesis.

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Pigments

• accessory pigments secondary pigments absorbing
  light wavelengths other than those absorbed by
  chlorophyll a
• increase the range of light wavelengths that can
  be used in photosynthesis
• include chlorophyll b, carotenoids,
  phycobiloproteins
• carotenoids also act as antioxidants

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How to Measure

• Secchi Disk

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Autotrophs

• Autotrophs (self-nourishing) are called primary
  producers.
• Photoautotrophs fix energy from the sun and
  store it in complex organic compounds
• ( green plants, algae, some bacteria)

light
simple inorganic compounds
complex organic compounds
photoautotrophs
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• Chemoautotrophs (chemosynthesizers) are bacteria
• oxidize reduced inorganic substances
• (typically sulfur and ammonia compounds) and
  produce complex organic compounds

oxygen
reduced inorganic compounds
complex organic compounds
chemoautotrophs
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Chemosynthesis near hydrothermal vents
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Heterotrophs

• Heterotrophs (other-nourishing) cannot produce
  their own food directly from sunlight inorganic
  compounds. They require energy previously stored
  in complex molecules.

heat
simple inorganic compounds
complex organic compounds
heterotrophs
(this may include several steps, with several
different types of organisms)
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The Laws of Thermodynamics

• Energy flow is a one-directional process.
• Sun ? heat (longer wavelengths)

FIRST LAW of THERMODYNAMICS Energy can be
converted from one form to another, but cannot be
created or destroyed.
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• SECOND LAW of THERMODYNAMICS
• Transformations of energy always result in some
  loss or dissipation of energy
• or
• In energy exchanges in a closed system, the
  potential energy of the final state will be less
  than that of the initial state
• or
• Entropy tends to increase (entropy amount of
  unavailable energy in a system)
• or
• Systems will tend to go from ordered states to
  disordered states (to maintain order, energy must
  be added to the system, to compensate for the
  loss of energy)

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Examples

• Internal combustion engines in cars are 25
  efficient in converting chemical energy to
  kinetic energy the rest is not used or is lost
  as heat.

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Energy flow
heat

• Simplistically
• This pattern of energy flow among different
  organisms is the TROPHIC STRUCTURE of an
  ecosystem.

Producers
Consumers
Decomposers
heat
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Foodchains
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Problems

• Too simplistic
• No detritivores
• Chains too long

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• Rarely are things as simple as grass, rabbit,
  hawk, or indeed any simple linear sequence of
  organisms.
• More typically, there are multiple interactions,
  so that we end up with a FOOD WEB.

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Energy transfers among trophic levels

• How much energy is passed from one trophic level
  to the next?
• How efficient are such transfers?

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• Biomass-the dry mass of organic material in the
  organism(s).
• (the mass of water is not usually included, since
  water content is variable and contains no usable
  energy)
• Standing crop-the amount of biomass present at
  any point in time.

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Primary productivity

• Primary productivity is the rate of energy
  capture by producers.
• the amount of new biomass of producers, per
  unit time and space

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• Gross primary production (GPP)
• total amount of energy captured
• Net primary production (NPP)
• GPP - respiration
• Net primary production is thus the amount of
  energy stored by the producers and potentially
  available to consumers and decomposers.

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• Secondary productivity is the rate of production
  of new biomass by consumers, i.e., the rate at
  which consumers convert organic material into new
  biomass of consumers.
• Note that secondary production simply involves
  the repackaging of energy previously captured by
  producers-no additional energy is introduced into
  the food chain.
• And, since there are multiple levels of consumers
  and no new energy is being captured and
  introduced into the system, the modifiers gross
  and net are not very appropriate and are not
  usually used.

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Ecological pyramids

• The standing crop, productivity, number of
  organisms, etc. of an ecosystem can be
  conveniently depicted using pyramids, where the
  size of each compartment represents the amount of
  the item in each trophic level of a food chain.
• Note that the complexities of the interactions in
  a food web are not shown in a pyramid but,
  pyramids are often useful conceptual
  devices--they give one a sense of the overall
  form of the trophic structure of an ecosystem.

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Pyramid of energy

• A pyramid of energy depicts the energy flow, or
  productivity, of each trophic level.
• Due to the Laws of Thermodynamics, each higher
  level must be smaller than lower levels, due to
  loss of some energy as heat (via respiration)
  within each level.

Energy flow in
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Pyramid of numbers

• A pyramid of numbers indicates the number of
  individuals in each trophic level.
• Since the size of individuals may vary widely and
  may not indicate the productivity of that
  individual, pyramids of numbers say little or
  nothing about the amount of energy moving through
  the ecosystem.

of carnivores
of herbivores
of producers
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Pyramid of standing crop

• A pyramid of standing crop indicates how much
  biomass is present in each trophic level at any
  one time.
• As for pyramids of numbers, a pyramid of standing
  crop may not well reflect the flow of energy
  through the system, due to different sizes and
  growth rates of organisms.

biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)
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Pyramid of yearly biomass production

• If the biomass produced by a trophic level is
  summed over a year (or the appropriate complete
  cycle period), then the pyramid of total biomass
  produced must resemble the pyramid of energy
  flow, since biomass can be equated to energy.

Yearly biomass production (or energy flow) of
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• Note that pyramids of energy and yearly biomass
  production can never be inverted, since this
  would violate the laws of thermodynamics.
• Pyramids of standing crop and numbers can be
  inverted, since the amount of organisms at any
  one time does not indicate the amount of energy
  flowing through the system.
• E.g., consider the amount of food you eat in a
  year compared to the amount on hand in your
  pantry.

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Explain that chemosynthesis captures the chemical
energy of dissolved minerals and that
chemosynthetic bacteria at hydrothermal vents
make energy available to the food chain

• There is no light for photosynthesis in the deep
  ocean.
• Some species of bacteria are able to derive
  energy from the oxidation of inorganic
  substances, such as hydrogen sulphide, and use
  this energy to synthesize organic compounds.
• This process is called chemosynthesis.

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Explain that chemosynthesis captures the chemical
energy of dissolved minerals and that
chemosynthetic bacteria at hydrothermal vents
make energy available to the food chain

• Fluid emerging from hydrothermal vents is rich in
  hydrogen sulphide and other gases.
• Chemosynthetic bacteria oxidize hydrogen sulphide
  and are able to fix carbon dioxide to form
  organic substances. These organic substances
  provide a food source for all other animals in
  the hydrothermal vent ecosystem.
• note that these chemosynthetic bacteria form
  symbiotic relationships with tube worms and giant
  clams.

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Vent Food Web
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Explain the meaning of the term productivity and
how productivity may influence the food chain.

• Productivity the rate of production of biomass.
• In almost all ecosystems, green plants are the
  primary producers and we usually refer to primary
  production in relation to plants.
• Productivity is often measured in terms of energy
  capture per unit area (or per unit volume in the
  case of aquatic ecosystems) per year.
• Since consumers depend directly or indirectly on
  the energy captured by primary producers, the
  productivity of an ecosystem affects all trophic
  levels. When conditions are favorable for
  photosynthesis, the productivity of the ecosystem
  tends to be relatively high, such as in tropical
  rain forests, algal beds and reefs.

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Calculate and explain the energy losses along
food chains due to respiration and wastage

• Of the total energy reaching the Earth from the
  Sun, only a very small percentage is captured and
  used for the synthesis of organic substances by
  primary producers.
• Light energy is reflected by surfaces, or may
  pass straight through a producer without being
  absorbed. Energy loss also occurs thorough
  inefficiencies of photosynthesis.
• Candidates may be asked, for example, to
  calculate the percentage of incident light energy
  which appears as energy of newly synthesized
  organic substances.

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• The total energy captured by primary producers is
  referred to as the gross primary production
  (GPP). Some of the organic substances will be
  used by the producers as substrates for
  respiration. This represents a loss of energy.
  The remaining organic substances, referred to as
  the net primary production (NPP), represent an
  energy source which can be transferred to higher
  trophic levels. We can represent this in the form
  of an equation

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Calculate and explain the energy losses along
food chains due to respiration and wastage

• NPP GPP R
• where NPP is the net primary production GPP is
  the gross primary production and R represents
  energy losses through respiration.
• Approximately 10 of the energy available at one
  trophic level is transferred to the next trophic
  level. Reasons for wastage include that facts
  that not all of one organism may be eaten by
  another there are also losses in excretion and
  egestion. Substrates are used for respiration to
  provide energy for movement and consequently
  energy is lost in the form of heat.

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Calculate and account for the efficiency of
energy transfer between trophic levels

• Suppose that the net productivity of plants in a
  food chain is 36 000 kJ per m2 per year and that
  the net production of herbivores is 1 700 kJ per
  m2 per year.

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• The efficiency of transfer of energy from the
  producers to the herbivores is therefore (1 700
  36 000) 100 4.72.
• Energy Flow

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• Energy losses from the energy consumed by the
  herbivore include heat from respiration, losses
  in urine and undigested plant material in feces.
  The energy of production of herbivores represents
  the total energy available to carnivores, the
  next trophic level.

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Represent food chains as pyramids of energy,
numbers and biomass

• Ecological pyramids are a way of representing
  food chains graphically. An ecological pyramid
  has the producers at the base, then a series of
  horizontal bars representing the successive
  trophic levels. In each case, the width of the
  bar is proportional to the numbers, biomass, or
  energy.

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Ecological pyramids

• The standing crop, productivity, number of
  organisms, etc. of an ecosystem can be
  conveniently depicted using pyramids, where the
  size of each compartment represents the amount of
  the item in each trophic level of a food chain.
• Note that the complexities of the interactions in
  a food web are not shown in a pyramid but,
  pyramids are often useful conceptual
  devices--they give one a sense of the overall
  form of the trophic structure of an ecosystem.

61
Pyramid of energy

• A pyramid of energy depicts the energy flow, or
  productivity, of each trophic level.
• Due to the Laws of Thermodynamics, each higher
  level must be smaller than lower levels, due to
  loss of some energy as heat (via respiration)
  within each level.

Energy flow in
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Pyramid of numbers

• A pyramid of numbers indicates the number of
  individuals in each trophic level.
• Since the size of individuals may vary widely and
  may not indicate the productivity of that
  individual, pyramids of numbers say little or
  nothing about the amount of energy moving through
  the ecosystem.

of carnivores
of herbivores
of producers
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Pyramid of standing crop

• A pyramid of standing crop indicates how much
  biomass is present in each trophic level at any
  one time.
• As for pyramids of numbers, a pyramid of standing
  crop may not well reflect the flow of energy
  through the system, due to different sizes and
  growth rates of organisms.

biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)
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Pyramid of yearly biomass production

• If the biomass produced by a trophic level is
  summed over a year (or the appropriate complete
  cycle period), then the pyramid of total biomass
  produced must resemble the pyramid of energy
  flow, since biomass can be equated to energy.

Yearly biomass production (or energy flow) of
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• Note that pyramids of energy and yearly biomass
  production can never be inverted, since this
  would violate the laws of thermodynamics.
• Pyramids of standing crop and numbers can be
  inverted, since the amount of organisms at any
  one time does not indicate the amount of energy
  flowing through the system.
• E.g., consider the amount of food you eat in a
  year compared to the amount on hand in your
  pantry.

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Represent food chains as pyramids of energy,
numbers and biomass

• It is possible to have inverted pyramids of
  numbers and biomass, but pyramids of energy are
• always the right way up because it is
  impossible to have more energy in a higher
  trophic level than
• in a lower trophic level. Figure 3.3 shows a
  typical pyramid of energy.

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Represent food chains as pyramids of energy,
numbers and biomass
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And thats how it all works!