Passive Transport
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
Types of Membranes:
1. Permeable: allows all (or most) things to
cross
2. Selectively (semi-permeable) membrane:
allows some things to cross but not others
(ie. water can cross but solutes like salt
and sugar can NOT)
3. Impermeable membrane: does NOT allow
anything to cross
Diffusion & Osmosis
DIFFUSION
• The NET movement of particles from an area
of high concentration of particles to an area of
low concentration of particles.
Q: What is a concentration gradient??
Dynamic Equilibrium
• At dynamic equilibrium there is no NET
(overall) 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 dynamic equilibrium particles are still moving,
its just that overall, they will remain “mixed” unless acted
upon by another force. (So no “net” movement overall).
Diffusion occurs because particles
move DOWN a concentration gradient.
From high to low.
Q: How large would the concentration gradient be at
Dynamic Equilibrium?
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
• Is special type of diffusion. The diffusion of
WATER across a semi permeable membrane.
What is the difference between
diffusion and osmosis?
• Diffusion is the NET movement of particles
across a semi-permeable membrane from an
area of high concentration to an area of low
concentration.
• Osmosis is the NET movement of water
across a semi-permeable membrane from an
area of high water concentration to an area
of low water concentration.
Bozeman Podcast
• Cell transport
What is Facilitated Diffusion?
• Facilitated diffusion (or facilitated transport) is
a process of diffusion, a form of passive transport
facilitated by transport proteins.
Facilitated Diffusion
• The two types of proteins involved in facilitated diffusion
are:
– 1) Channel Proteins (or ion channels)
– 2) Carrier Proteins
What molecules can pass easily
across the cell membrane?
SOLUTIONS
1. Hypertonic
2. Hypotonic
3. Isotonic
Solute = The substance that dissolves to form a solution
Solvent = A substance, usually a liquid, in which other
substances are dissolved
HYPERTONIC
•
solutions are those in which more solute is present.
– concentration of dissolved substances is higher outside
the cell than inside.
(Water will move OUT OF THE CELL)
HYPOTONIC
•
solutions are those with less solute present.
– concentration of dissolved substances is lower
outside the cell than inside.
(Water will move INTO THE CELL)
ISOTONIC
•
solutions have equal (iso-) concentrations of
dissolved substances. Solute concentrations are the
same outside the cell and inside.
(Equal amounts of water movement in and out of the cell,
with a net flow of zero).
Animal cell in different solutions
isotonic
hypotonic
hypertonic
Plant cell in different solutions
isotonic
hypotonic
hypertonic
Turgor pressure
• The pressure exerted by the cytoplasm (and
water in the cell) against the non-living cell wall
of plant cells.