4.2 - Diffusion Flashcards
what are the 3 important concepts to understand about particle movement
- all particles are constantly in motion due to kinetic energy they posses
- this motion is random, no set pattern for movement
- particles are constantly bouncing off one another as well as off other objects
what is the definition of diffusion
the net movement of molecules or ions from one region where they are more highly concentrated to one where their concentration is lower until evenly distributed
what molecules can diffuse through the CSM
- small, non-polar molecules
- such as oxygen and carbon dioxide
what type of process is facilitated diffusion
passive
describe facilitated diffusion
- passive process
- relies on the kinetic energy of diffusing molecules
- occurs down a concentration gradient but occurs only at certain points in the CSM where there are special protein molecules
- happens via 2 mechanisms: protein channels and carrier proteins
describe protein channels
- water-filled hydrophilic channels spread across the membrane
- allow specific water-soluble ions to pass through
- the channels are selective, each opens in the presence of a specific ion (if not present = closed)
- therefore it has control over entry/exit of ions
- ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it up to the other side
describe carrier proteins
- when a molecule such as glucose that is specific to the protein present, it binds with the protein
- this causes it to change shape in such a way that the molecule is released to the inside of the membrane
- No external energy is needed for this
- the molecules diffuse using only their kinetic energy
what 6 factors determine the rate of diffusion
- the concentration gradient
- the surface area
- Temperature
- the length of the diffusion path
- the type of molecule or ion diffusing
- the number of proteins
how does the concentration gradient affect the rate of diffusion
steeper the gradient = the faster the rate of diffusion
how does the surface area affect the rate of diffusion
- greater the surface area = the faster the rate of diffusion
- because: more molecules or ions can pass at any one time
how does the Temp affect the rate of diffusion
-higher temp = molecules have more kinetic energy
- molecules move faster = diffusion takes place faster
- NB: if too high = proteins denature
how does the length of the diffusion path affect the rate of diffusion
- thinner exchange surfaces increase speed of diffusion
how does the type of molecule/ion diffusing affect the rate of diffusion
- large molecules: need more energy to move = so diffuse slower
- Non-polar molecules: diffuse easier than polar molecules because they are soluble in the non-polar phospholipid tails
Which direction does diffusion happen
- the net movement will be from high —> low (until particles are evenly distributed
What is the concentration gradient
- the path from an area of higher concentration to an area of lower concentration
- for diffusion: particles diffuse DOWN the concentration gradient
Give examples of molecules that can easily diffuse through membranes + why
- carbon and oxygen
—> small: so passes through the spaces between the phospholipids
—> non-polar: makes them soluble in lipids, so they can dissolve in the hydrophobic bilayer
What is it known as when molecules diffuse directly through a cell membrane
Simple diffusion
What types of molecules would need to diffuse via facilitated diffusion (via carrier proteins and protein channels)
- larger molecules (e.g. amino acids/glucose) - they diffuse extremely slowly through phospholipid bilayer because they’re so big —> therefore need facilitated diffusion to speed it up
- charge molecules (e.g. ions and polar molecules) - diffuse very slowly because they’re water soluble and the centre of the bilayer is hydrophobic —> therefore need facilitated diffusion to speed it up
Is facilitated diffusion a passive process
Yes
Which molecules do carrier proteins help move during facilitated diffusion, how is it done
large molecules
1) a large molecule attaches to a carrier protein in the membrane
2) then, the protein changes shape
3) this releases the molecule on the opposite side of the membrane
What molecules do channel proteins help move during facilitated diffusion, how is this done
- channel proteins form pores in the membrane for charged molecules
- they can diffuse through these pores (down a concentration gradient)
Are carrier proteins/protein channels specific
- yes
- different carrier proteins facilitate the diffusion of different molecules
- different channel proteins facilitate the diffusion of different charged particles
What 3 factors does the rate of simple diffusion depend on
- the concentration gradient
- the thickness of the exchange surface
- the surface area
How does the concentration gradient affect the rate of simple diffusion
- the higher the gradient = the faster
because: - As diffusion takes place, the difference in concentration between the 2 sides of the membrane decreases until it reaches an equilibrium
- this means that diffusion slows down over time
How does the thickness of the exchange surface affect the rate of simple diffusion
- the thinner the exchange surface = the shorter the distance the particles need to travel = the faster the rate of diffusion
How does the surface area affect the rate of simple diffusion
- the larger the surface area (e.g. of the CSM) = the faster the rate of diffusion
- larger SA means that more particles can be exchanged in the same amount of time — increasing the rate of diffusion
Give an example of one adaptation for improving the rate of simple diffusion in the small inetstine
- some cells (e.g. epithelial cells in small intestine) have microvilli
- these are projection formed by the CSM folding up on itself
- the microvilli give the cell a larger surface area
What 2 factors does the rate of facilitated diffusion rely on
- the concentration gradient
- the number of channel or carrier proteins
How does the concentration gradient affect the rate of facilitated diffusion
- the higher the concentration gradient = the faster the rate of facilitated diffusion
- As equilibrium is reached, the rate of facilitated diffusion will level off
How does the number of channel or carrier proteins affect the rate of facilitated diffusion
- once all proteins in a membrane are in use, facilitated diffusion can’t happen any faster
- even if you increase the concentration gradient
- therefore: the greater the number of channel or carrier proteins in the cell membrane = the faster the rate of facilitated diffusion
Give an example of one adaptation for improving the rate of facilitated diffusion in kidney cells
- some kidney cells are adapted to have lots of aquaporins
- aquaporins are special channel proteins that allow the facilitated diffusion of water through cell membranes
- the aquaporins allow the cells to reabsorb a lot of water that would otherwise be excreted by the body
