Passive Membrane Transport Flashcards
Solvent
is what dissolves
Solute
is what gets dissolved
Concentration
amount of solute per volume of solvent
Concentration gradient
Difference in concentration of a chemical from one area to another
concentration gradient info
– More Na+ and O2 in interstitial fluid than cytosol
– More K+ and CO2 in cytosol than interstitial fluid
electrical gradient
Difference in electrical charge from one area to another
electrical gradient info
– Inner surface of plasma membrane is more negatively charged
– Outer surface of plasma membrane is more positively charged
– Charge difference across plasma membrane termed membrane potential
electrochemical gradient
Combined influence of concentration and electrical gradients on a
particular ion
electrochemical gradient directions
– Substances tend to move down concentration gradient to reach equilibrium
– Positively charged substances tend to move to negatively charged areas
– Negatively charged substances tend to move to positively charged areas
passive transport
– Do not require energy (ATP)
– Substances move DOWN/ALONG concentration gradient (high to low)
– Naturally move from where there is more of a substance to where there is less
active transport
– Require energy (ATP)
– Substances move UP/AGAINST concentration gradient (low to high)
– Move from where there is less of a substance to where there is more
Diffusion
Movement of substances from
regions of higher concentration to
regions of lower concentration
(down their concentration gradient)
* Particles continue to move until
equilibrium is reached
Factors influencing diffusion rate
– Steepness of concentration gradient
▪ The greater the difference in concentration between the two sides, the
higher the rate of diffusion
– Temperature
▪ The higher the temperature, the faster the rate of diffusion
– Mass of diffusing substance
▪ The larger the mass of the diffusing particle, the slower its diffusion rate
– Surface area
▪ The larger the membrane surface area for diffusion, the faster the
diffusion rate
– Diffusion distance
▪ The greater the distance over which diffusion must occur, the longer it
takes
simple diffusion
*Movement of solutes from regions of
higher concentration to regions of
lower concentration without a
protein transporter
* Small, non-polar solutes
– Includes: oxygen, carbon dioxide,
nitrogen, fatty-acids, steroids, fat-soluble
vitamins (A,D,E,K), water, ethanol, urea
*Movement dependent on
concentration gradient alone
– Continues to move as long as
gradient exists
facilitated diffusion
- Movement of solutes from regions of higher concentration to
regions of lower concentration with a protein transporter - Two types:
– Channel-Mediated diffusion
– Carriers-Mediated diffusion
Channel-Mediated Diffusion
– Channels specific for one ion type
– Most numerous: K+ or Cl–
– Fewer channels: Na+ or Ca+
Leak channel
continuously open
gated channel
– Usually closed
– Open in response to a stimulus for
fraction of second
types of gated channel
▪ Ligand-gated: open in response to a ligand binding to the receptor
▪ Voltage-gated: open in response to a change in the electrical gradient
▪ Mechanically-gated: open in response to mechanical stimulation (vibration, touch, pressure, tissue stretch)
Carrier-Mediated Diffusion
Movement of small, polar
molecules through a carrier protein
- Binding of substance causes change in carrier protein shape
- Releases substance on other side of membrane
Osmosis
Osmosis is diffusion of a solvent
– In living systems, the solvent is water
– Osmosis is movement of water from an area of higher water concentration toan area of lower water concentration
How osmosis works
Plasma membrane is selectively permeable, and allows water to pass through, but prevents some solutes
– Osmosis moves WATER from an area of lower solute concentration to an area of higher solute concentration
Methods of osmosis
Water passes through plasma membrane in two ways
– By moving between neighboring phospholipid molecules via simple diffusion
– By moving through aquaporins- integral proteins that function as water channels
Hydrostatic pressure
force exerted by water onto the surface of its container
– The higher the water concentration, the greater the hydrostaticpressure
– Produces water movement