Diffusion/Osmosis
Osmosis Diffusion Intro - YouTube
Diffusion:
• Movement of molecules across a cell
membrane
• Diffusion requires NO ENERGY
• Molecules move from HIGH to LOW
concentration.
• Let’s see!
• Let’s see MORE!
Facilitated Diffusion
• Many cell membranes have special channels
(carrier proteins) that allow molecules to cross it.
• These channels help or facilitate diffusion to
happen.
• This is known as facilitated diffusion.
• Like regular diffusion, will ONLY occur if there is
a higher concentration of molecules on one side
of the membrane.
• Let’s see!
Osmosis
• Osmosis:
• Movement of WATER from an area of
more water (H) to an area of less water
(L)
• Water moves OPPOSITE of all other
molecules (i.e. solutes)!
How does osmosis work?
• Across a SEMI-PERMEABLE membrane
• Only certain molecules, like water, can move
freely across the membrane
• Water molecules move from HIGH to LOW
• They want to BALANCE OUT a solution
• Therefore, water moves OPPOSITE of other
molecules
• Let’s See!
Example of Osmosis #1
• Condition #1: More Water outside of cell
• Inside cell = 98% Water, 2% salt
• Outside cell = 100% Water, 0% salt
Water moves into cell,
salt moves out to balance
CELL SWELLS or
BURSTS!
Example of Osmosis #2
• Condition #2: More water inside of cell
• Inside cell: 98% Water, 2% Salt
• Outside cell: 95% Water, 5% Salt
Water moves out of cell,
salt moves in to balance
CELL SHRIVELS!
Osmotic Pressure
• Cells behave differently when placed in
different solutions!
• This is due to OSMOSIS!
• Most cells are ~ 98% water!
• Three types of osmotic pressure:
• Hypotonic
• Hypertonic
• Isotonic
Hypotonic Condition
• Cell is placed in 100% water
• Solution outside of cell has MORE water, less of
other materials (i.e., salt)
• Therefore, solution is below strength (hypo)
100%
98%
Water ENTERS cell
CELL
SWELLS!
• Red Blood Cells in Hypotonic Solution YouTube
Hypertonic Condition
• Cell is placed in 95% water
• Solution outside of cell has LESS water, more of
other materials (i.e., salt)
• Therefore, solution is above strength (hyper)
95%
98%
Water LEAVES cell
CELL
SHRINKS!
• Red Blood Cells in a Hypertonic Solution YouTube
Isotonic Condition
• Cell is placed in 98% water
• Solution outside of cell has SAME water, same
amount of other materials (i.e., salt)
• Therefore, solution is equal strength (iso)
98%
98%
Water moves equally;
Equilibrium exists
CELL
STAYS
THE SAME!
• Red Blood Cells in an Isotonic Environment
- YouTube
Review of Osmosis
Isotonic, Hypertonic, Hypertonic Animation
You Tube Onion Cell Osmosis
Active Transport
• Sometimes, materials will move across the cell
membrane AGAINST a concentration gradient.
• LOW
HIGH
• This is Active Transport.
• THIS REQUIRES ENERGY!!! Just like pulling
something uphill!
• Cells get this energy from ATP (Adenosine
Triphosphate)