Passive Transport across the Membrane Flashcards
What is Passive Transport?
-Cells moving in & out of a cell without using energy
What is a Concentration Gradient?
-The difference between concentration on the inside of the membrane & the outside of the membrane
What is Diffusion?
-The random motion of molecules & ions dissolved in water that moves from regions of high concentration to low concentration
What is the major to crossing a biological membrane?
-The hydrophobic interior= repels polar molecules but not non-polar molecules
What is the plasma membrane permeable to?
- Limited permeability to Small polar molecules
- Very limited permeability to larger polar molecules & ions
What is Facilitated Diffusion?
-Diffusion mediated by a membrane protein
What are the 2 proteins that aid in Facilitated Diffusion?
- Channel Proteins
- Carrier Proteins
How do Channel proteins allow for Facilitated Diffusion?
-They have a hydrophilic interior that provides an aqueous channel where polar molecules can through when the channel is open
How do Carrier Proteins allow for Facilitated Diffusion?
-They bind specifically to the molecule they assist
Since 2 proteins aid for facilitated diffusion, the Cell Membrane is…
Selectively Permeable
Why can’t Ions move between the cytoplasm of the cell & the extrcellular fluid without help?
-Ions are repelled by non-polar molecules= present in the interior of the plasma membrane
What are Ion Channels?
- They aid in the diffusion of ions bc ion channels posess a hydrated interior= allowing ions to diffuse in either direction depending on the relative concentration across the membrane
- Plays essential role in signaling by the nervous system
What are Gated Channels?
-They are channel proteins that can be opened or closed in response to a stimulus (electrical or chemical)
What are the 3 conditions that determine the net movement of ions?
- Their relative concentration on either side of the membrane
- The voltage difference across the membrane & gated channels
- The stage of the gated channels (open or closed)
What is Membrane potential?
-A voltage difference= electrical potential difference across the membrane
What does changes in the Membrane potential form?
-It forms the basis for transmission signals in the nervous system & other tissues
What do Carrier Proteins help transport?
-Ions & other solutes (sugars, amino acids)
for Carrier Proteins, what is the relationship between concentration & rate of transport?
- Concentration increase=more of the carriers are bound to the transport molecule
- So at high enough concentration, all of the carriers will be occupied= rate of transport will be constant= carriers exhibit saturation
in Simple dffusion, what is the relationship between concetration & rate of transport?
-As concetration increases, transport is linearly increasing
What is an Aqueous Solution?
-The mixture of the ions & molecules (sugars & amino acids) that are dissolved in water
What does water & solutes have in common?
-They both tend to diffuse from regions of high concentration to ones of low concentration
(down their concentration gradients)
What is Osmosis?
-The net diffusion of water across the membrane toward a higher concentration
What determines the Osmotic Concentration?
-The concentration of all solutes in a solution
What is a Hypotonic Solution & what happens to the cell?
- Lower concetrations of solutes
- Water moves into the cell & causes cell to burst= Hydrostatic pressure increases
What is a Hypertonic Solution & what happens to the cell?
- Higher concentrations of solutes
- Water moves out of the cell & causes the cell to shrivel up= Hydrostatic pressure decreases
What is a Isotonic Solution & what happens to the cell?
- Same concentration of solutes inside & outside
- Cells are at a “balanced” state= don’t gain or lose water
What are Aquaporins?
-Specialized channels for water= facilitates water flow in living cells
How many types of Aquaporins have been found in mammals?
-More than 11 types
What are the 2 general classes of Aquaporins?
- Those that are specific to only water
- Those that allow other small hydrophyllic molecules (glycerol & urea) to cross the membrane
What is Hydrostatic Pressure?
-The pressure of the cytoplasm pushing out against cell membrane
What is Osmotic Pressure?
-The force needed to stop osmotic flow
Why won’t the cells of prokaryotes, fungi, plants & many protists burst in a Hypotonic solution?
-They each have cell walls that can withstand high internal pressures without bursting
What are the 3 strategies for having a steady influx when exposed to a Hypotonic solution?
- Extrusion
- Isosmotic regulation
- Turgor
What is Extrusion?
-Some single celled eukaryotes use contractile vacuoles to remove water by collecting it from various parts of the cytoplasm & transporting it the central part of the vacuole near the cells surface
What is Isomotic Regulation?
- Organisms that live in ocean= adjust internal concentration to match the concetration of the sea water
- Terrestial animals= circulate fluid through their bodies that bathes cell in isotonic solution
What is Turgor?
-The Turgor Pressure (internal hydrostatic pressure) presses the plasma membrane against the interior of the cell wall= makes cell ridgid
What are the 3 passive transport processes?
- Simple diffusion
- Facilitated diffusion
- Osmosis
