Download Diffusion Rate and Water Potential

Diffusion and Osmosis
Transport- Passive or Active
• Passive transport-the movement of materials
across a cell membrane without the expenditure of
cell energy
• Active transport-the use of cell energy to move
materials across a cell membrane (against
concentration gradient)
PASSIVE TRANSPORT
• From high to low
concentration
• Does not require
energy from the cell
– Diffusion
– Osmosis
– Facilitated diffusion
ACTIVE TRANSPORT
• From low to high
concentration
• Requires energy from the
cell
– Active transport proteins
– Endocytosis
– Exocytosis
Diffusion & Osmosis
DIFFUSION
• The NET movement of particles from an area
of high concentration to an area of low
concentration
Q: What is a concentration gradient??
What is a concentration gradient?
• Concentration Gradient the
difference in concentration of
solutes in a given space
• Diffusion happens when
substances move “down” a
concentration gradient (from
high to low) until the
concentration of the two areas
becomes equal.
• http://www.biologycorner.com/bio1/diffusion.html
Dynamic Equilibrium
• At dynamic equilibrium there is no
NET movement of particles.
• DYNAMIC implies movement
• EQUILIBRIUM implies a balance
– No longer a concentration gradient
– Particles move equally in all directions
Dynamic Equilibrium
NOTE: At D.E. particles are still moving, its just that
overall, they will remain “mixed” unless acted upon by
another force. (So no “net” movement overall).
Diffusion
Diffusion will always be from an area of
HIGH concentration to an area of
___________
LOW
____________
concentration.
DYNAMIC
It will continue until _______________
EQUILIBRIUM is reached.
_______________
Diffusion
OSMOSIS
• The diffusion of WATER across a
semipermeable membrane.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBooktransp.html
Osmosis Demos
• http://www.biologycorner.com/bio1/diffusion.html
#
• http://www.emc.maricopa.edu/faculty/farabee/BI
OBK/BioBooktransp.html
What is the difference between
diffusion and osmosis?
• Diffusion is the NET movement of particles
from an area of high concentration to an
area of low concentration!”
• Osmosis is just a “special case of diffusion”.
It is the diffusion of water across a
selectively permeable membrane.
• Sometimes we refer to this movement as being from an area
of HIGH water potential to an area of LOW water potential.
But What is
“WATER POTENTIAL”??
• Water potential is the measure of the ability of
water to move (always from high to low) . It is the
free energy of water in a system.
• Think of osmosis as the net movement of water
(remember water is also just a particle) down its concentration gradient.
Diffusion occurs because particles
move DOWN a concentration gradient.
From high to low.
Q: How large would the concentration gradient be at
Dynamic Equilibrium?
What is the cause of diffusion?
• Diffusion happens because of the random kinetic
energy (energy of motion) of particles and the
existence of a concentration gradient.
• All matter is made of particles and those particles
are constantly in motion.
What determines how fast
diffusion occurs?
• WHAT AFFECTS THE RATE OF DIFFUSION
IN CELLS??
1. Temperature
2. Charge
3. Diameter (Size) of particle
4. Concentration gradient (difference in concentration)
5. Surface Area of membrane
Can We Control Diffusion?
• Diffusion is a physical process.
• It happens in both living and non-living systems.
• We can’t control it because it is a natural process.
• The cell sometimes needs to use energy to reverse
the natural process of diffusion Q: What is this
called??
Q: What type of cell transport is
this?
Inside Cell
Outside Cell