Transport mechanisms are described as four types:
1)Passive transport
2)Faciliated transport
3)Active transport
4)Bulk transport
PASSIVE TRANSPORT OR DIFFUSSION:
§Simple diffusion :-
molecules are passing
through membrane on their concentration gradient from higher to lower
concentration due to their own kinetic energy.
§It does not require any metabolic energy.
§[solution = solute particle in less amount + solvent in
higher amount], when the solute
particles arranged uniformly then solution is called homogenous solution.
§For eg : cells are having
higher amount of k+ ions instead of
environment , so cells draw k+ ions from environment.
§Membrane of kidney cells , epithelial cells, red blood
cells and muscles cells are impermeable to substance unless their transport is
facilitated .All membranes are
permeable for o2 , co2 , and water .
Diffusion down concentration
gradient:
Simple diffusion :In a concentration solution , a substance separated by
its dilution , so the solute molecule move from higher to lower concentration
until equilibrium is reached , it a physical phenomenon and its does not
depends on cellular energy.
Empirical term of
diffusion can be explained by the first law of fick:
dm/dt= - DA [dc/dx]
dm/dt= flow of matter in
per moles
dc/dx =
concentration gradient
D = diffusion gradient. [cm2 s-1]
Diffusion down the electrical
gradient: In a solution the
solutes are dissociates into ions and having charge. Cell are also having
charge particles inside and outside the media, cell membrane maintain their
potential difference, this difference is measured by MICROELECTRODE. Its range from 50mV to 100mV. The ions which involved to form potential
gradient are k+ and Na+ ions .
Each individual
substance will diffuse independently of others as per gradient of its own
concentration, diffusion pressure, or partial pressure.
OSMOSIS: Diffusion of water from semi permeable membrane that
occurs under the influence or osmotically active solution.
^= RTc c= molar concentration
R= constant
T= temperature
^= osmotic pressure