Energy and Nutrient Relations

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Energy and Nutrient Relations

• Chapter 7

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Energy Sources

• Organisms can be classified by trophic levels.
• Autotrophs use inorganic sources of carbon and
  energy.
• Photosynthetic Use CO2 as carbon source, and
  sunlight as energy.
• Chemosynthetic Use inorganic molecules as source
  of carbon and energy.
• Heterotrophs use organic molecules as sources of
  carbon and energy.

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Solar - Powered Biosphere

• Light propagates through space as a wave.
• Photon Particle of light bears energy.
• Infrared (IR) Long-wavelength, low energy.
• Interacts with matter, increasing motion.
• Ultraviolet (UV) Short wavelength, high energy.
• Can destroy biological machinery.
• Photosynthetically Active Radiation (PAR)
• Between two extremes.

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Photosynthetically Active Radiation
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Solar - Powered Biosphere

• PAR
• Quantified as photon flux density.
• Number of photons striking square meter surface
  each second.
• Chlorophyll absorbs light as photons.
• Landscapes, water, and organisms can all change
  the amount and quality of light reaching an area.

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Photosynthetic Pathways

• C3 Photosynthesis
• Used by most plants and algae.
• CO2 ribulose bisphosphate (5 carbon sugar)
  phosphoglyceric acid (3 carbon acid)
• To fix carbon, plants must open stomata to let in
  CO2 .
• Water gradient may allow water to escape.

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C3 Photosynthesis
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Photosynthetic Pathways

• C4 Photosynthesis
• Reduce internal CO2 concentrations.
• Increases rate of CO2 diffusion inward.
• Need fewer stomata open.
• Conserving water
• Acids produced during carbon fixation diffuse to
  specialized cells surrounding bundle sheath.

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C4 Photosynthesis
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Photosynthetic Pathways

• CAM Photosynthesis
• (Crassulacean Acid Metabolism)
• Limited to succulent plants in arid and semi-arid
  environments.
• Carbon fixation takes place at night.
• Reduced water loss.
• Low rates of photosynthesis.
• Extremely high rates of water use efficiency.

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CAM Photosynthesis
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Using Organic Molecules

• Three Feeding Methods of Heterotrophs
• Herbivores Feed on plants.
• Carnivores Feed on animal flesh.
• Detritivores Feed on non-living organic matter.

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Chemical Composition and Nutrient Requirements

• Five elements make up 93-97 of biomass of
  plants, animals, fungi and bacteria
• Carbon
• Oxygen
• Hydrogen
• Nitrogen
• Phosphorus

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Essential Plant Nutrients

• Potassium
• Calcium
• Magnesium
• Sulfur
• Chlorine
• Iron

• Manganese
• Boron
• Zinc
• Copper
• Molybdenum

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Herbivores

• Substantial nutritional chemistry problems.
• Low nitrogen concentrations.
• Must overcome plant physical and chemical
  defenses.
• Physical
• Cellulose lignin silica
• Chemical
• Toxins
• Digestion Reducing Compounds

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Detritivores

• Consume food rich in carbon and energy, but poor
  in nitrogen.
• Dead leaves may have half nitrogen content of
  living leaves.
• Fresh detritus may still have considerable
  chemical defenses present.

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Carnivores

• Consume nutritionally-rich prey.
• Cannot choose prey at will.
• Prey Defenses
• Aposomatic Coloring - Warning colors.
• Mullerian mimicry Comimicry among several
  species of noxious organisms.
• Batesian mimicry Harmless species mimic noxious
  species.

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Carnivores

• Predators are usually selection agents for
  refined prey defense.
• Usually eliminate more conspicuous members of a
  population (less adaptive).
• Must catch and subdue prey - size selection.
• Predator and prey species are engaged in a
  co-evolutionary race.

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Using Inorganic Molecules

• 1977 - Organisms found living on sea floor.
• Near nutrients discharged from volcanic activity
  through oceanic rift.
• Autotrophs depend on chemosynthetic bacteria.
• Free-living forms.
• Living within tissue of invertebrates.

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Energy Limitation

• Limits on potential rate of energy intake by
  animals have been demonstrated by studying
  relationship between feeding rate and food
  availability.
• Limits on potential rate of energy intake by
  plants have been demonstrated by studying
  response of photosynthetic rate to photon flux
  density.

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Photon Flux and Photosynthetic Response Curves

• Rate of photosynthesis increases linearly with
  photon flux density at low light intensities,
  rises more slowly with intermediate light
  intensities, and tends to level off at high light
  intensities.
• Response curves for different species generally
  level off at different maximum photosynthesis
  rates.

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Food Density and Animal Functional Response

• Holling described (3) basic functional responses
• 1. Feeding rate increases linearly as food
  density increases - levels off at maximum.
• Consumers require little or no search and
  handling time.
• 2. Feeding rate rises in proportion to food
  density.
• Feeding rate partially limited by search/handling
  time.

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Food Density and Animal Functional Response

• 3. Feeding rate increases most rapidly at
  intermediate densities
• (S-shaped).

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Optimal Foraging Theory

• Assures if energy supplies are limited, organisms
  cannot simultaneously maximize all life
  functions.
• Must compromise between competing demands for
  resources.
• Principle of Allocation

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Optimal Foraging Theory

• All other things being equal,more abundant prey
  yields larger energy return. Must consider energy
  expended during
• Search for prey
• Handling time
• Tend to maximize rate of energy intake.

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Optimal Foraging in Bluegill Sunfish
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Optimal Foraging By Plants

• Limited supplies of energy for allocation to
  leaves, stems and roots.
• Bloom suggested plants adjust allocation in such
  a manner that all resources are equally limited.
• Appear to allocate growth in a manner that
  increases rate of acquisition of resources in
  shortest supply.

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