membranes and transport Flashcards
control systems
- ## method to control the internal environment of cells
diffusion
causes natural movement of molecules to the point with the lowest concentration
selective permeability
- limit what can enter and leave a cell (small water soluble molecules have trouble passing)
- large polar molecules can not
- tiny charged ions can not breach nonpolar lipid bilayer
active transport
control movement of material but at the expense of cellular energy
solute
particles dissolved in solution
tonicity
measure of the concentration of solutes
solvent
fluid where molecules are dissolved or suspended typically
osmosis
net diffusion of water across a membrane toward a higher solute concentration (special case of diffusion)
hypertonic solution
has a higher solute concentration
hypotonic solution
has a lower solute concentration
osmotic pressure
- force needed to stop osmotic flow across a permeable membrane
- happens in cells with cell wall
- if membrane not strong may burst
- if strong enough, it will reach its equilibrium
isotonic
when the solutions have the same osmotic concentration
diffusion in the blood
- o2 diffuses across thin membrane in lung into blood stream
- high conc. of co2 diffuses into lung space
- o2 diffuses into cells with low conc. when in thin blood capillaries
- waste molecules diffuse from blood to kidney to be excreted
benefit of diffusion
remove waste from body
cost of diffusion
diffusion can remove necessary nutrients
factors of affecting rates of diffusion
- size and energy of particles
- large particles diffuse slower in medium
pressure
gradient can counter act concentration gradient
plasma membrane structure
- phospholipid bilayer
- Cholesterol - within bilayer, strengthen membrane
- integrated proteins - play many roles
- cell surface markers - glycoproteins
