diffusion of water - osmosis
● water diffuses through the partially permeable membrane through tiny spaces in the
phospholipid bilayer and specialised channel proteins called porins
osmosis
● the movement of water molecules from a more dilute solution to a more concentrated
solution through a partially permeable membrane
○ osmosis will continue until the solutions either side of the membrane are
isotonic
water potential and osmotic pressure
● water potential is a measure of the tendency of water to pass from one place to
another
● water potential (Ψ) is measured in Pascals (Pa) or kilopascals (kPa)
● pure water has the highest water potential as the molecules have the greatest
freedom to move
○ pure water has a water potential of zero
● therefore more concentrated solutions (molecules have less freedom to move) have
more negative numbers
diffusion (passive)
● higher concentration to lower concentration
● small, non-polar particles can diffuse through the phospholipid diagram (e.g.,
oxygen)
● some polar molecules (like carbon dioxide) are able to pass through due to their
small size
○ typically polar molecules will not diffuse through the phospholipid bilayer
facilitated diffusion (still passive)
● larger, polar particles cannot pass through the phospholipids
● the hydrophobic tails of the bilayer provide a barrier to hydrophilic molecules
● therefore proteins are needed
● water diffuses through the partially permeable membrane through tiny spaces in the
phospholipid bilayer and specialised channel proteins called porins
osmosis
● the movement of water molecules from a more dilute solution to a more concentrated
solution through a partially permeable membrane
○ osmosis will continue until the solutions either side of the membrane are
isotonic
water potential and osmotic pressure
● water potential is a measure of the tendency of water to pass from one place to
another
● water potential (Ψ) is measured in Pascals (Pa) or kilopascals (kPa)
● pure water has the highest water potential as the molecules have the greatest
freedom to move
○ pure water has a water potential of zero
● therefore more concentrated solutions (molecules have less freedom to move) have
more negative numbers
diffusion (passive)
● higher concentration to lower concentration
● small, non-polar particles can diffuse through the phospholipid diagram (e.g.,
oxygen)
● some polar molecules (like carbon dioxide) are able to pass through due to their
small size
○ typically polar molecules will not diffuse through the phospholipid bilayer
facilitated diffusion (still passive)
● larger, polar particles cannot pass through the phospholipids
● the hydrophobic tails of the bilayer provide a barrier to hydrophilic molecules
● therefore proteins are needed
