Diffusion
- net movement of particles down the concentration gradient
- passive transport: X energy input depends on spontaneous/random movement of
particles
- concentration gradient shows
- rate of diffusion (steeper, higher)
- direction of diffusion
- equilibrium: particles evenly distributed X concentration gradient
- X net movement
- ALWAYS have movement: random in all directions
- site
- simple diffusion: thru lipid layer
- facilitated diffusion: thru channel/carrier proteins
- factors affecting rate of diffusion
concentration steeper, higher rate
gradient1
surface area2 larger, higher rate
distance shorter, higher rate
temperature higher, higher KE, higher rate
particle size smaller, higher rate
particle nature non-polar, higher rate than polar
np: move across membrane thru phospholipid
bilayer directly
p: thru channel/carrier proteins
medium gas, higher rate than liquid
- importance
- life processes
- Gaseous exchange @surface of human lungs
- Absorption of nutrients @human small intestine
- Uptake minerals @from soil to root (root epidermal cells
- cells
- Absorption of oxygen + nutrients into cells
- Excretion/removal of metabolic waste(CO2) out of cells
1
eg. more conc ss
2
eg. longer dialysis tubing
, Osmosis (a kind of diffusion)
- net movement of water molecules down the water potential gradient across a
differentially permeable membrane
- if solute particles X move across the membrane
- then more water molecules move down water potential gradient
- passive transport: X energy input
- in living cells: Xstain cells (kill cells, disintegrate differentially permeable CM)
- observe pigmented cells instead
- site
- facilitated diffusion: thru channel/carrier proteins
- water potential kilopascals (kPa)
- tendency of water molecules to move from one place to another
- ↑ concentration of solution
- ↑ solute particles attract water molecules
- tendency of water molecules to move ↓
- water potential ↓
water potential (potential energy of water) per unit volume relative to pure
water
pure water 0 (kPa)
1% solution -
2% solution --
- equilibrium DOESN’T EXIST: water molecules NEVER evenly distributed
- X net movement
- bc hydrostatic pressure balance force developed by solute potential
gradient
Demonstration of osmosis using dialysis tubing
Dialysis tubing produced by bacteria / chicken crop / pig bladder / fish swim bladder
- differentially permeable cell membrane
- many small pores
- allowing small molecules (water, glucose) to pass thru freely
- but not large ones (disaccharides: eg. sucrose)
Procedures
1. Wet a dialysis tubing of 15cm long by putting it into a beaker of tap water
2. Open up the tubing and tie a knot at one end. Fill the tubing with 20% sucrose
solution using a dropper.
open by rubbing with finger
tie freehand
fully filled without air column > gas pressure > push liquid out
3. Tie the other end of the tubing to a capillary tube with thread.
- net movement of particles down the concentration gradient
- passive transport: X energy input depends on spontaneous/random movement of
particles
- concentration gradient shows
- rate of diffusion (steeper, higher)
- direction of diffusion
- equilibrium: particles evenly distributed X concentration gradient
- X net movement
- ALWAYS have movement: random in all directions
- site
- simple diffusion: thru lipid layer
- facilitated diffusion: thru channel/carrier proteins
- factors affecting rate of diffusion
concentration steeper, higher rate
gradient1
surface area2 larger, higher rate
distance shorter, higher rate
temperature higher, higher KE, higher rate
particle size smaller, higher rate
particle nature non-polar, higher rate than polar
np: move across membrane thru phospholipid
bilayer directly
p: thru channel/carrier proteins
medium gas, higher rate than liquid
- importance
- life processes
- Gaseous exchange @surface of human lungs
- Absorption of nutrients @human small intestine
- Uptake minerals @from soil to root (root epidermal cells
- cells
- Absorption of oxygen + nutrients into cells
- Excretion/removal of metabolic waste(CO2) out of cells
1
eg. more conc ss
2
eg. longer dialysis tubing
, Osmosis (a kind of diffusion)
- net movement of water molecules down the water potential gradient across a
differentially permeable membrane
- if solute particles X move across the membrane
- then more water molecules move down water potential gradient
- passive transport: X energy input
- in living cells: Xstain cells (kill cells, disintegrate differentially permeable CM)
- observe pigmented cells instead
- site
- facilitated diffusion: thru channel/carrier proteins
- water potential kilopascals (kPa)
- tendency of water molecules to move from one place to another
- ↑ concentration of solution
- ↑ solute particles attract water molecules
- tendency of water molecules to move ↓
- water potential ↓
water potential (potential energy of water) per unit volume relative to pure
water
pure water 0 (kPa)
1% solution -
2% solution --
- equilibrium DOESN’T EXIST: water molecules NEVER evenly distributed
- X net movement
- bc hydrostatic pressure balance force developed by solute potential
gradient
Demonstration of osmosis using dialysis tubing
Dialysis tubing produced by bacteria / chicken crop / pig bladder / fish swim bladder
- differentially permeable cell membrane
- many small pores
- allowing small molecules (water, glucose) to pass thru freely
- but not large ones (disaccharides: eg. sucrose)
Procedures
1. Wet a dialysis tubing of 15cm long by putting it into a beaker of tap water
2. Open up the tubing and tie a knot at one end. Fill the tubing with 20% sucrose
solution using a dropper.
open by rubbing with finger
tie freehand
fully filled without air column > gas pressure > push liquid out
3. Tie the other end of the tubing to a capillary tube with thread.
