Gas exchange in plants and animals.

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Gas exchange in plants and animals.  
By the end of this lecture you should be able
to Define diffusion and discuss the major
physical factors controlling the rate of
diffusion.  Discuss the limitations to diffusion
imposed by variation in the surface area to
volume ratio of structures.  Describes the basic
structures involved in gas exchange in animals.
Concepts and terms gills, lungs, cutaneous,
tracheal system.
Derive an equation that describes the flux of
gases into and out of leaves. Concepts and
terms Ficks Law, Ohms Law analogy,
resistance, conductance Describe a basic tradeoff
in evolution of gas exchange capacity for plants
and animals. Concepts and terms water use
efficiency   Assigned Readings Campbell et al.
884-890 (gas exchange in animals 749-751
(control of transpiration in plants)
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Diffusion the net movement of substances to
regions of lower concentration as the result of
random and spontaneous motions. It tends to
distribute substances uniformly resulting in
equilibrium in closed systems. Temperature,
pressure, gas concentrations and the intrinsic
capacity of the molecule influence the rate of
diffusion
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Composition of dry air Oxygen 20.95 Carbon
dioxide 0.03 Nitrogen 78.09 Argon 0.93
minor constituents are not included.
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The diffusion constant for oxygen (20oC)
in air 11 water 34 x 10-6 muscle 14 x
10-6 chitin 1 x 10-6 cm2 atm-1 min-1
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Limitations imposed by the surface area of three
dimensional structures contributed to the
evolution of respiratory surfaces.
FO2 VO2 r2 / 6 K FO2 is O2 at the surface VO2
is the rate of O2 consumption (0.001
ml/g/min). K is the diffusion constant (11x10-6
cm2/atm/min).
A sphere works in water if its less than R 0.1
cm.
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Respiratory surfaces Gills body surface
turned out rarely used in air Lungs body
surface turned in ventilated or
diffusion Cutaneous amphibians Tracheae
insects combine circulation and gas
exchange Stomata modified epidermal cells
(guard cells) of plants
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The tracheal system of a flea. Wigglesworth 1972
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Lice abdominal spiracles
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Close up of a spiracle
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Respiratory surface area varies in proportion to
metabolic activity. The numbers indicate the
ratio of gill surface area to body weight. Do
you see a relationship between body shape and
these values? What does it mean? From
Schmidt-Nielsen
Mackerel 2551
Sea bass 1111
Flounder 268
Goosefish 51
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From Evans and Loreto
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Photosynthesis and transpiration are diffusion
processes.
From Nobel 1999
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Tradescantia epidermis stomata consist of two
guard cells and the pore they create. Plants
regulate diffusion through this pore by changing
the shape of the guard cells.
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Diffusion coefficients (in air at 1 atm) DCO2
1.42 x 10-5 m2 s-1 (10oC) 1.60 x 10-5 m2 s-1
(30oC) DO2 1.95 x 10-5 m2 s-1
(20oC) Dwv 2.27 x 10-5 m2 s-1 (10oC) 2.57 x
10-5 m2 s-1 (30oC)
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Ficks First Law of Diffusion Jj Dj dcj /
dx
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Ohms Law I (current) V (voltage) / R
(resistance) Ohms Law Analogy JCO2 (CO2out
CO2in) / SR JH2O (H2Oin H2Oout) / SR
Ficks Law Jj (Dj n ast) / dst Dcj note
resistance 1 / conductance
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but there is more than one resistor in the
pathway.
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The rate of water loss is about 100X the rate of
CO2 uptake. Why?
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Terrestrial life for animals is a continual
conflict between the need for oxygen and the need
to reduce water loss. for plants, its the
balance between uptake of carbon dioxide and the
conservation of water. How have plants and
animals found the proper balance?