BISC 101 Lecture Notes - Lecture 14: Sockeye Salmon, Osmoregulation, Stenohaline

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BISC 101 – Lecture 14 – Osmoregulation and Excretion: Part I
Osmoregulation And Excretion
In organisms, relative concentration of water and solutes must be maintained
within fairly narrow limits
Osmoregulation: Regulates solute concentrations and balances the gain and lose
of water
oFreshwater animals show adaptations that reduce water uptake and
conserve solutes in order to prevent their body fluids from being too dilute
oDesert animals face very dry and hot environments that can quickly
deplete body water
They must conserve water
oThe success of marine birds and fishes in an ocean depends critically on
conserving water and eliminating excess salts
Excretion: Elimination of nitrogenous waste products during the break down of
amino acids and nucleic acids
Osmoregulation balances the uptake and loss of water and solutes
Osmoregulation is based largely on controlled movement of solutes between
internal fluids and the external environment
Regardless of habitat and type of waste produced, all animals face the same
need to balance water uptake and loss
oWater enters and leaves cells by osmosis
Osmosis: When two solutions separated by a selectively permeable membrane
differ in osmolarity
Osmolarity: Total solute concentration of a solution expressed as molarity
oMolarity: Moles of solute per liter of solution
Unit of measurement of osmolarity is millliosmoles per liter
o1 mOsm/L is equivalent to a total solute concentration of 10-3 M
oThe osmolarity of human blood is about 300 mOsm/L
oSeawater has an osmolarity of about 1000 mOsm/L
The total solute concentration of a solution determines the movement of water
across a selectively permeable membrane
Iso – osmotic: The movement of water is equal in both directions in two solutions
oThe net movement of water will be zero
If two solutions differ in osmolarity, the net flow of water moves from the hypo –
osmotic to the hyper – osmotic solution
Hyper – osmotic Side
oHigher solute concentration
oLower free water concentration
Hypo – osmotic Side
oLower solute concentration
oHigher free water concentration
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