2/1/2017
What’s the right size?
• Habitat and ecological
constraints (energetics)
• Phylogenetic constraints
– Mechanics
– Anatomy
– Physiology
Properties of water
Solvent
Polar
Conductivity
compression
H-bonds
– Surface tension
– Heat of fusion
– Heat of vaporization
• Mass – ice vs. water
• 60-90% of animal mass
•
•
•
•
•
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2/1/2017
Solutes in Water
• Molarity, Molality
• Osmolarity, Osmolality
• Seawater – Na:0.469, Cl:0.546, K:0.103, Ca:0.01,
Mg:0.053
– total ~ 1.181
• Hypoosmotic, hyperosmotic, isoosmotic
Osmoregulation and water balance
• Ionic regulators
• Osmoregulators and
conformers
– Hagfish – only isoosmotic
vertebrate
• Osmosis
• Osmotic pressure
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2/1/2017
Osmotic Pressure
• Gas Law:
nRT
P
v
–
–
–
–
–
P – osmotic pressure
n - moles
R – constant
T – temperature
V – volume
• One mole of solute in 1 L water exerts ~ 22.4 atm pressure
Fresh vs. Marine Fishes
• Hypo and
hyperosmotic
• Why are fish more
osmotically exposed
than aquatic birds,
reptiles or mammals?
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2/1/2017
Solutes in Water
• Electrolyte – substance that dissociates
into multiple ions
– NaCl → Na+ Cl– MgCl2 → Na+ 2 Cl• Osmotic coefficient – proportion of solute
ionizing
Solutes in water
• Colligative properties – freezing point depression
(FPD), boiling point increase, vapor pressure
FPD  186
. * Osm
• A solution has a FPD of 2.8 Co, what is its Osm?
– 2.8=1.86 * Osm
– Osm=1.5
• If the solution contains only NaCl, what is the molarity?
– 1.5 / 2 = 0.75
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2/1/2017
Solutes in water
• If that solution contained only MgCL2 , what molarity
was the solution (assume osmotic coefficient of 1.0)?
– molarity=1.5 / 3* Oscoef
– molarity=1.5/3 = 0.5
• Assume MgCL2 has an osmotic coefficient of 0.75,
what molarity was the solution?
– Molarity = 1.5 / 3*0.75
– Molarity = 1.5 / 2.25 = 0.67
Fick’s law of diffusion
• Passive movement of ions
– D – diffusion constant,
related to molecule size,
temperature
– A – area of membrane
– C – concentrations
– X – distance
• Diffusion rate is proportional
to area and concentration
gradient.
J net
C
  DA
x
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2/1/2017
Membrane permeability
• Review plasma membranes
• Not all molecules have
equal permeability
• Metabolic processes
produce some nondiffusible molecules,
increasing cell osmolarity
• Diffusion and osmosis
driven by electrical and
chemical gradients
• Membrane structure and
gradients vary across cell
types
Overton’s Rules
• Low penetrating power
– Polar molecules
– OH- groups
– charged
• High penetrating power
– Lipid soluble
– Smaller
– Uncharged
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2/1/2017
Donnan Equilibrium
• Charged particles with
variable ability to pass will
not distribute evenly.
• Resting potential - charge
difference across membrane
at equilibrium.
Nernst Equation
• Used to determine the
electrical potential of a cell
– C1 and C2 – ion
 RT   C1 
concentrations
E  
 ln 

  C2 
zF
– z – moles of electrons
– R – gas constant
Assume univalent ion, RT/F is constant at 58 mV, z=1:
– T – temperature
– F – Faraday constant
1
C 
E  58 ln 
 C2 
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