Overview of Passive
Transport
Remember, cells need to constantly
move molecules across the plasma
(cell) membrane to maintain
homeostasis.
The plasma membrane is selectively
permeable – only certain items can
cross without energy.
Passive Transport
• Movement of materials WITHOUT energy !
• Molecules are constantly in motion
• Move from high concentration to low concentration
until equilibrium.
• Equilibrium is where molecules are balanced equally
inside and outside of cell.
• 3 Types of PASSIVE transport
• Diffusion
• Facilitated Diffusion
• Osmosis
Passive Transport moves..
• Small molecules
• Uncharged molecules (do not have a + or -)
• H2O
• Gases like O2 and CO2
Passive Transport is like….
riding a bike down a hill, no energy input
from you is needed.
Diffusion
• Type of PASSIVE transport (no energy)
• Movement of molecules across the membrane
down the concentration gradient.
• High to a low concentration.
• “Spreading Out” of molecules
• Always trying to reach “equilibrium”
(molecules evenly spread out)
Rate of diffusion is driven by kinetic energy
~The more KE, the faster the rate of
diffusion
~Temperature
~Motion: High Conc. = More Collisions
Facilitated Diffusion
• Type of diffusion of specific particles
• Still does NOT require energy, but is FACILITATED
by a Transport Protein
• Moves from High-Low concentration
• Used to move larger molecules, or rapid water
movement across membrane