Transcript INTRODUCTION - Penn State York

Energy and Nutrient Relations
Chapter 6
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Energy Sources
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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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Oxygenic Photosynthesis
(There are anoxygenic photosynthetic bacteria!)
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Photosynthetic Pathways
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C3 Photosynthesis
 Used by most plants and algae.
 CO2 + ribulose bisphosphate (RuBP;
5 carbon sugar) = 2x phosphoglyceric acid
(3PGA; 3 carbon acid)
 To fix carbon, plants must open stomata
to let in CO2 .
 Water gradient may allow water to
escape.
http://ntri.tamuk.edu/bio/photo/
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C3 Plant Photorespiration:
“Too much of a good thing.”
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Photosynthetic Pathways
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C4 Photosynthesis
 First CO2 fixed to phosphoenolpyruvate
(3 carbons) to form 4 carbon acid.
 Reduces internal CO2 concentrations.
 Increases rate of CO2 diffusion inward.
 Need fewer stomata open.
 Conserves water
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C4 Photosynthesis
e.g. grasses, corn, sugar cane
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Photosynthetic Pathways
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CAM Photosynthesis
 (Crassulacean Acid Metabolism)
 Limited to succulent plants in arid and
semi-arid environments.
 Carbon fixation takes place at night.
 Reduces water loss.
 Low rates of photosynthesis.
 Extremely high rates of water use
efficiency.
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CAM Photosynthesis
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Energy Limitation
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Liebig’s Law of the Minimum:
 The resource in least supply relative to an
organism’s needs will control growth.
 It is the growth limiting resource.
Limits on the potential rate of energy intake
by plants (hence growth) have been
demonstrated by studying response of
photosynthetic rate (P) to photon flux density
(light intensity or irradiance; I).
The P versus I curve.
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P versus I
curve
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Photon Flux and Photosynthetic
Response Curves
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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 may:
 level off at different maximum P.
 respond differently at lower levels of I.
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Which P vs I curve would favor a sunny as
opposed to shady habitat?
http://www.marietta.edu/~spilatrs/biol103/photolab/sunexpl.gif
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Using Organic Molecules for
Energy and Growth
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Three Feeding Methods of Heterotrophs:
 Herbivores: Feed on plants.
 Carnivores: Feed on animal flesh.
 Detritivores: Feed on non-living organic
matter that becomes colonized by
microbes (detritus)
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Herbivores
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Substantial nutritional chemistry problems.
 Low N:C ratio compared to plants.
 Carbon mostly as cellulose & NO
cellulases of their own.
Must overcome plant physical and chemical
defenses.
 Physical: structures, woody parts, silica
 Chemical: toxins, inhibitors of digestion.
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Detritivores
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Consume food rich in carbon and energy,
but very poor in nitrogen.
 Dead leaves may have half nitrogen
content of living leaves.
Fresh detritus may still have considerable
chemical defenses present.
Microbial colonization of plant derived
detritus increases nutritional value.
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Carnivores
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Consume nutritionally-rich prey.
Carnivore C:N is equivalent to prey C:N.
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Energy Limitation
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Limits on potential rate of energy intake by
animals (hence growth) have been
demonstrated by studying relationships
between feeding rate and food availability.
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Holling described (3) basic functional
responses to food density:
 1. Feeding rate increases linearly as food
density increases - levels off at maximum.
 Consumers require little or no search
and handling time.
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2. Feeding rate rises in proportion to food
density.
 Feeding rate partially limited by
search/handling time.
 3. Feeding rate increases most rapidly at
intermediate densities.
 S-shaped curve.

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http://www.tnstate.edu/ganter/Functional.Response.JPG
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06_22.jpg
Which type
of response?
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06_23.jpg
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Optimal Foraging Theory
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All other things being equal, more abundant
prey yields larger energy return.
What about different prey types and sizes as
well as densities (real world complexity)?
Must consider energy expended during:
 Search for prey
 Handling time
Consumers choose prey that maximize rate
of energy intake per unit of foraging energy
expenditure.
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Optimal Foraging in Bluegill Sunfish
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Optimal Foraging By Plants
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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.
 E.g. shading of some plants causes
increased stem growth (spindly looking).
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06_25.jpg
Which stand of birch trees grows
on infertile (nutrient poor) soil?
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Using Reduced Inorganic Molecules
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1977 - Organisms found living on sea floor.
 Near nutrients discharged from volcanic
activity through oceanic rift.
 Autotrophs depend on chemosynthetic
bacteria that oxidize reduced inorganics.
 Free-living forms.
 Living within tissue of invertebrates.
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