Transcript Active Transport, Diffusion and Osmosis

Active Transport, Diffusion
and Osmosis
Passive Transport by Diffusion
• Diffusion is the movement of molecules
from an area of high concentration to an
area of low concentration.(down the
concentration gradient)
• Diffusion does not refer only to movement
across a membrane.
How Diffusion Works
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__how_diffusion_works
.html
Passive Transport by Osmosis
• Osmosis is the movement of water across
a biological membrane.
• Water molecules move from an area of
low concentration solute (hypotonic) to an
area of high concentration (hypertonic)
• Water moves because the membrane is
impermeable to the solute
Affect of Osmosis
http://www.etomica.org/app/modules/sites/Osmosis_old/Background1.html
Affect of Osmosis
http://en.wikipedia.org/wiki/User:Reo_On/Passive_transport
How Osmosis works
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__how_osmosis_works
.html
Passive transport by Facilitated
Diffusion
• Molecules can enter a cell by diffusion
through a specific channel proteins or
carrier proteins embedded in the
membrane
• This process mediated by a membrane
protein is called facilitated diffusion
• Molecules move down the concentration
gradient
Channel Proteins
• Form highly specific channel through the
cell membrane
• Permit the passage of ions or polar
molecules
• Some channel proteins remain open all
the time, others have gates that can be
opened or closed to allow or prevent the
passage of particles
http://www.biologycorner.com/APbiology/cellular/(notes)cell_membrane.html
Carrier Proteins
• Bind to specific molecules, transport them
across the membrane and release them
• Carrier molecules change shape while
transporting molecules
• Usually transport ions or small polar
molecules but can also transport amino
acids and glucose
• Have a lower rate of diffusion than channel
proteins
Channel and Carrier Proteins
http://www.ncbi.nlm.nih.gov/books/NBK9928/
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__how_facilitated_diffu
sion_works.html
Active Transport
• Active transport is the movement of ions,
molecules or minerals from an area of low
concentration to an area of high
concentration(against the concentration
gradient)
• This requires energy in the form of ATP
Primary Active Transport
• Uses ATP directly to move molecules or
ions from one side of the membrane to the
other
• Ion pumps are carrier proteins that pump
ions against the concentration gradient
• The sodium-potassium pump pumps Na+
out of the cell and K+ ions into the cell
http://saddlebackphysio.blogspot.com/2010/09/membrane-transportjust-passin-through.html
How the Sodium-Potassium pump
works
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__how_the_sodium_po
tassium_pump_works.html
Secondary Active Transport
• As an ion pump functions, a difference in
charge, or electrical potential, builds up
across the membrane
• One side of the membrane gains a more
positive or negative charge compared to
the other side due to the accumulation of
positive or negative ions
Secondary Active Transport
• The combination of concentration gradient
and electrical potential is called an
electrochemical gradient
• This gradient stores potential energy that
can be used by the cell
• This energy is used by another protein to
transport other molecules across a
membrane
Electrochemical Gradient
http://bioap.wikispaces.com/Ch+7+Collaboration+2010
http://www.cetbiology.com/support/biology-photographs.html
Membrane-Assisted Transport
• Macromolecules are too large to cross the
cell membrane through a channel or by
means of a carrier protein
• Cells form vesicles to surround incoming
or outgoing material and move it across
the cell membrane
• Membrane-assisted transport requires
energy
Endocytosis
• The process where a cell engulfs material
by folding the cell membrane around it and
then pinching it off to form a vesicle inside
• There are three methods:
– Pinocytosis
– Phagocytosis
– Receptor-mediated endocytosis
Receptor-mediated Endocytosis
http://www.yellowtang.org/cells.php
Pinocytosis
http://www.yellowtang.org/cells.php
Phagocytosis
http://www.yellowtang.org/cells.php
Exocytosis
• Macromolecules and other large particles
leave a cell by exocytosis
• Vesicles that contain cell products to be
released or waste products to be excreted
fuse with the cell membrane and empty
their contents into the extracellular
environment
http://www.linkpublishing.com/video-transport.htm
Phagocytosis
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__phagocytosis.html