Diffusion and Osmosis/
Membrane Transport
Cell Membrane/ Plasma Membrane
Phospholipid Bilayer
Cell Membranes Are Selectively Permeable
Cell Membranes Are Selectively Permeable
Size, Charge and Polarity!!!
Brownian Motion
Random motion of particles suspended in a fluid
https://youtu.be/1jYabtziQZo
https://youtu.be/ernnQJwaKTs
https://youtu.be/R5t-oA796to
Diffusion/ A Form of Passive Transport
Spontaneous movement of molecules
Random movement of atoms or molecules due to their kinetic energy
The net movement of a molecule will be from higher concentration
to lower concentration
Rate is affected by:
o Temperature
o Size of the particle/solute
o Concentration gradient
Diffusion
Membrane Transport Processes
Facilitated Diffusion
Transport protein
allows a polar or
charged substance to
move down its
concentration gradient
across a membrane by
providing a
hydrophilic channel
Active Transport
Requires energy expenditure to move a solute
against its concentration gradient
Osmosis – a special type of diffusion
Movement of water, across a selectively permeable membrane, from a
region of low solute concentration to a region of high solute
concentration
Diffusion of water, across a selectively permeable membrane,
from a region of high free water concentration to a region of low
water concentration
Anything dissolved in water that can NOT cross the semi-
permeable membrane is an osmotically active solute
(OAS)
Flow of H2O
Osmosis
Diffusion vs. Osmosis
Fig 8-4
Movement of H2O depends
on what is dissolved in the
H2O
Osmosis and the RBC
Osmosis and Plant Cells
Osmotic Environments/ Animal and Plant
Cells