Biology 2601A/B Lecture Notes - Semipermeable Membrane, Molality, Relative Permittivity

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16 Oct 2011
Organismal Lecture 19
Principles of Osmoregulation: Water Balance 1
Osmoregulation: Balancing water and ions in both the cells and the body to allow physiological
Osmolarity/ Osmolality
The amount of “stuff”/solutes in a solution
1 mol of solutes = 1 Osmole
This measurement is cumulative: 0.2 M of 5 things = 1 Osmole
Osmolality = per kg of solvent
Osmolarity = per Litre of solvent
Water Properties
Highly polar
o Involved in hydrogen bonding
o Has a large dielectric constant (large ratio of the permittivity of a substance to the
permittivity of free space)
o High heat of fusion and vaporisation
o Large thermal capacity (takes lots of energy to heat HO from one temp to another)
o Has cohesion and adhesion (essential to maintain the continuous water column)
Allows proteins to fold, involved in the lipid bilayer
Water Interacts with Other Molecules
Can interact with cations and anions
Water molecules hydrogen bind to the protein; this mean the water is not active (can’t interact
with other components of the protein)
Keeps ions dissociated (the amount of ions dissociated in a water solution is very high
Water in Cells
Regulates pressure
Determines the cell volume in animals
o Cell volume is often the bottom level of regulation of water and ion balance
Determines the cell turgor in plants
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Comparison of Plant and Animal Cells at High and Low Concentrations
Remember that hypoosmotic means that there is more solutes and less water on the inside of
the cells; water will move into cells, causing them to burst
Isosmotic means the same amount of water and solutes in both the cell and environment
Hyperosmotic concentration means there is more solutes and less water outside the cells,
causing water to move of of the cell ; the cell then shrinks
In comparison to this, in plants, the pressure of the vacuole will control the amount of water
flowing in
o Since the vacuole has a rigid cell wall, it will not burst in hypoosmotic conditions
o Plasmolysis: the process of the cell shrinking and moving away from the cell wall
(hyperosmotic situation)
Moving Water: Diffusion
Between the 2 solutions is a perforated barrier with
holes in it
Shows the diffusion of solutes into a low concentrated
Note: the pressure remains the same
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