Transport Across Membranes Flashcards
2 main categories of transport across membranes:
1) Passive Transport
2) Active Transport
Passive Transport
The diffusion of a substance across a membrane with NO energy investment
Types of passive transport
1) Diffusion
2) Osmosis
3) Facilitated diffusion
Diffusion
Transport of a solute down a concentration gradient
–> Solute goes from areas of high conc. to low conc.
In diffusion, all molecules move___________ but as a population move ___________
RANDOMLY, but as a population diffusion becomes DIRECTIONAL
Each substances diffuses down…
ITS OWN gradient
–> Unaffected by the gradient of others
Equilibrium
Molecules are still moving but concentrations remain constant
Osmosis
The diffusion of free water across a selectively permeable membrane
Osmosis is helpful when…
solute cannot diffuse through a membrane
–> H2O will then move through the membrane to attempt to dilute the more concentrated side
Tonicity
The ability of a surrounding solution to cause a cell to gain or lose water
–> Depends largely on concentration of solutes that cannot cross the membrane
Isotonic
Concentrations are ~ equal on either side of membrane
= NO NET MOVEMENT of water across membrane
Hypertonic
A solution that has > conc. of solute than other solution across a membrane
= Water moves INTO hypertonic solution
Hypotonic
A solution that has < conc. of solute than another solution across a membrane
= Water moves OUT OF hypotonic solution
Most animals have their cells in a ______________ extracellular fluid
ISOTONIC: to maintain a stable cell volume
Osmotic Pressure
The tendency for a solution to take up water when separated from pure water by a selectively permeable membrane
Animal Cell in Hypotonic Solution
= LYSED
–> Too much water entering cell causes it to swell and then burst
Animal Cell in Isotonic Solution
= NORMAL
–> Maintains proper cell volume
Animal Cell in Hypertonic Solution
= SHRIVELED
–> Too much water leaves cell causing it to shrink in on itself
Plant Cell in Hypotonic Solution
= TURGID (ideal condition) – Very firm
–> More water entering cell creates turgor pressure that pushes up against cell wall
–> Keeps plants “perky”
Plant Cell in Isotonic Solution
= FLACCID (limp)
–> Not enough water to produce the turgor pressure needed
Plant Cell in Hypertonic Solution
= PLASMOLYZED
–> Cell inside shrinks but cell wall maintains shape (too much water leaving cell)
Facilitated Diffusion
Diffusion aided by transport proteins (“to make faster”)