Chap 4 Pt 2 Flashcards
Membrane Transport
; Process of obtaining (stuff enters) and eliminating substances (stuff exits) across the plasma membrane
Passive Process
Does not require energy
Depend on substances moving down concentration gradient
Two types: diffusion and osmosis
Active Processes
Require energy
Two types: active transport and vesicular transport
Diffusion
Net movement of a substance from area of greater concentration to area of lesser concentration
Diffusion, why?
Why? Molecules and ions in constant motion
–kinetic energy
Passive Processes: Rate of Diffusion Influenced By
“Steepness” of concentration gradient
Measure of the difference in concentration between two areas
Steeper gradient (biggest difference) faster diffusion
Temperature
Reflects kinetic energy or random movement
More movement with higher temperature faster diffusion
Passive Process: Simple Diffusion 1
Molecules pass between phospholipids
Small and nonpolar solutes
Simple Diffusion 2
O2 and CO2, fatty acids, ethanol, urea
Not regulated by plasma membrane!!!!
Simple Diffusion 3
Movement dependent on concentration gradient
Continues to move as long as gradient exists
Facilitated Diffusion
Transport process for small charged or polar solutes
**Requires assistance from plasma membrane proteins
Facilitated Diffusion
Two types
Channel-mediated diffusion
Carrier-mediated diffusion
Channel-mediated diffusion 1
Movement of small ions through protein channels
Channel mediated diffusion 2
**Channels specific for each ion
Leak channels
Continuously open
Gate Channel
Usually closed
Opens in response to stimulus for fraction of second
Carrier - mediated diffusion 1
Small polar molecules assisted across membrane by carrier protein
Carrier - mediated diffusion 2
Binding of substance causing change in carrier protein shape
Carrier - mediated diffusion 3
Releases substances on other side of membrane
Osmosis
Movement of water (solvent), not solutes
Osmosis 2
Passive movement of water through selectively permeable membrane
Osmosis 3
Membrane allows passage of water
Membrane prevents passage of most solutes
Water moves from greater concentration of water to lower concentration of water
Water moves from lower concentration of solutes to higher concentration of solutes
2 types of soluble (1) permeable
solutes
Pass through bilayer
small and nonpolar solutes (oxygen, carbon dioxide, urea
2 types of soluble (2) Nonpermeable
solutes
Don’t pass through bilayer
charged, polar, or large solutes (ions, glucose, proteins)
2 ways water crosses membrane (1)
A small portion slips between molecules of phospholipid bilayer
2 ways water crosses membrane (2)
Moves through special protein water channels—aquaporins
