lab 2 Flashcards
(45 cards)
what is diffusion?
the movement of molecules from regions of high concentration to regions of lower concentration as the result of random molecular drift. it also includes the passive movement down an electrochemoical gradient in single phased systems, as well as to passive trasnfer across membranes that does not involve specific mechansims
what is the major way that solvent and solutes move across a capillary wall and across cell membanes?
diffusion
what is fick’s first law of diffusion?
the rate of transport is equal to the diffusion coefficient times the concentration difference over distance
what is osmosis?
the movement of water from a less concentrated solution when a semipermeable membrane separates the solutions and when the membrane is impermeable to solute
what are two ways to measure the concentration of particles in a solution of interest?
- if you have a stable strong and truly semipermeable membrane you can measure hydrostatic pressure, which opposes the movement of water by osmosis
- look at colligative properties
what is a colligative property?
a property that depends on the number of particles
what is osmotic concentration?
the effective concentration of particles in solution
what is osmolality?
the osmotic coefficient * number of particles which the molecule forms in solution*number of moles/kg of solvent
what is osmolarity?
the osmotic coefficient * number of particles which the molecule forms in solution*number of moles/L of solvent
what does the osmotic coefficient depend upon?
the interaction of particles
what is osmotic pressure?
the force that tends to move water in an osmotic system
osmotic pressure=RT (Concentration inside-concentration outside)
why are erythrocytes considered osmometers?
their membranes are freely permeable
when placed in solutions with an osmotic pressure difference they distort; because they are biconcave disk, they can increase in volume without having to increase their surface area
what are examples of ways to measure osmolality (osmometers)
membrane osmometers
measurement of alterations in vapour pressure
measurements of alterations in freezing point
how does a membrane osmometer work?
it measures the osmotic pressure with reference to a macromolecular species
how does alterations in vapour pressure measure osmolality?
it measures the total effective particle concentration (macromolecules and crystalloid)
how does measuring freezing point measure osmolality?
it measures the total effective particle concentration (macromolecules and crystalloid)
what determines the rate of membrane penetration by a solute?
the sphere of hydration
the nature of the charge
the molecular size
the lipid solubility
how does lipid solubility alter rate of membrane penetration?
increased lipid solubility increases the speed with which they cross the membrane
how does molecular size alter the rate of membrane penetration by the solute?
with lipid soluble compounds, increased size means decreased speed of penetration of the membrane. at >200, permeability is considered negligible
how does the nature of the charge affect the rate of membrane penetration by a solute?
charged molecules are insoluble in lipids. they do not cross membranes
how does the sphere of hydration affect rate of membrane penetration by a solute
charged particles must shed their hydration shell to cross the membrane, even with transport mechanisms
the larger the hydration shell the slower the transport
what is a hydration shell?
charged particles are surrounded by a shell of water molecules that is unique for each element
with organic acids, when are they more likely to cross a membrane?
when they are uncharged. the charged and uncharged species exist in equilibrium. as the uncharged molecules cross the membrane, the equilibrium will reestablish itself on both sides
will higher or lower concentrations of solute cause higher rates of diffusion?
higher
