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