Movement Across Cell
Membranes
Passive and Active Transport
Movement Across Membranes
There
are several ways substances can
move across the plasma membrane.
Diffusion
Osmosis
Transport
by proteins
Endocytosis and Exocytosis
Diffusion
Diffusion
is the movement of particles from an
area of their
Only
small, uncharged molecules can diffuse
across the plasma membrane
Examples
of substances that move across the
plasma membrane by diffusion?
Diffusion
Osmosis
Osmosis
is the movement of water molecules from
an area of their higher concentration to an area of
their lower concentration across a membrane.
This
can also be described as the movement of water
from a dilute solution to a concentrated solution
across a membrane.
Osmosis
Tonicity
Tonicity is a relative term
Hypertonic solution: Membrane
bound object is in a solution that
has a
of solute than the object
Hypotonic solution: Membrane
bound object is in a solution that
has a
of solute than the object
Isotonic solution: Membrane
bound object and solution have the
of solute.
*Label the boxes with arrows
showing the overall direction
of water flow
Other molecules
Small
and uncharged
molecules like O2, CO2, and
H2O
They
are not the only things
the cell needs to move. How
might these move through
the membrane?
Method 1: Proteins for Transport
Membrane
transport
There
proteins (integral proteins) can be used to
are two ways they do this job.
Method 1: Proteins for Transport
Facilitated
diffusion
Channel
or carrier proteins provide a pathway for substances
to move down their concentration gradient (from high
concentration to low concentration)
Active
Carrier
Transport
proteins (also called pumps) use energy from ATP
to move substances up their concentration gradient (from low
concentration to high)
Facilitated Diffusion
Facilitated Diffusion
Molecules
are moving
(diffusion)
But
they are being facilitated in that movement by an
integral membrane protein.
They
move through a
Diffusion,
Osmosis, and Facilitated Diffusion are all
examples of Passive Transport across membranes
Active Transport
Active
transport is called “active” because it is
something the cell is actively and intentionally doing,
and it’s using energy to do it.
It
is defined as using the energy from ATP to move
substances
(from low concentration to high concentration)
Active Transport
Active Transport: Sodium-Potassium Pump
as an example
*Mark on the dia
gram where the
areas of high
concentrations of
Na+ and K+ are.
Sodium Potassium Pump
Method 2: Endocytosis and Exocytosis
These
processes use vesicles (little sacs formed by parts of the
membranes) to transport substances in and out of the cell.
Endocytosis:
Transport of large molecules
by the
“engulfing” action of the cell membrane & the formation of a
membrane bound vesicle
Exocytosis:
- vesicles formed within the cell fuse
with the cell membrane, emptying their contents into the
extracellular environment
Membrane Fluidity
One
result of the plasma membrane’s fluidity is that
parts of it can pinch off to form vesicles, and vesicles
can travel to another part of the cell and join the
membrane there.
In
this way vesicles are used to transport materials
around the cell, especially from the rER to the Golgi,
and from the Golgi to the plasma membrane
This
is how some products exit and enter the cell
Vesicles, exocytosis and endocytosis
Review:
Make
a flow chart to display the methods of moving substances
across membranes you’ve learned.
Use
the diagram on the next slide to organize the information.
You’ll need to add textboxes as you go.
Flowchart
Active
Transport
Transport in
membranes
Passive
Transport