Methods of Transport Across Membranes
1
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Active Transport
AS Biology. Foundation. Cell membranes and
Transport
Solution Review
2
 Solutions are made of solute and a solvent
 Solvent - the liquid into which the solute is
poured and dissolved. We will use water as our
solvent today.
 Solute - substance that is dissolved or put into
the solvent. Salt and sucrose are solutes.
AS Biology. Foundation. Cell membranes and
Transport
Diffusion-movement of molecules down a
concentration gradient
1.Passive transport
= no energy used
3
2. Molecules move
from high
concentration to
low concentration
http://www.youtube.com/watch?v=VY0
mZUDvbH4
AS Biology. Foundation. Cell membranes and
Transport
Osmosis- movement of water down a concentration
gradient
1.Passive transport
=no energy used
4
2. Water moves from
high concentration to
low concentration
due to solute
concentration
http://leukophobia.files.wordpress.com
/2008/01/gummi-bear.jpg
http://www.youtube.com/watch?v=w3_
8FSrqc-I
AS Biology. Foundation. Cell membranes and
Transport
5
 Hypotonic Solution - solution has a lower
concentration of solute outside of cell than inside cell.
 Hypertonic Solution - solution has a higher
concentration of solute outside the cell than inside cell.
 Isotonic Solution - both solutions have same
concentrations of solute.
*Predict what will happen to an animal and plant
cell when put into each solution.
AS Biology. Foundation. Cell membranes and
Transport
Examples of Osmosis
isotonic
hypotonic
http://www.biologycorner.com/resources/beakers_solutions_ABC.p
ng
hypertonic
Plant and Animal Cells put into
various solutions
AS Biology. Foundation. Cell membranes and
Transport
7
Facilitated Diffusion
 No use of energy
 It requires protein molecules to transport molecules across
the membrane
 Proteins are specific to the molecules they transport
 The molecules move from an area of high concentration to
an area of low concentration.
-SUGAR and charged molecules pass across the cell
membrane by this method of transport
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__
how_facilitated_diffusion_works.html
Carrier Proteins Carry
Molecules Across the
Membrane
 Good Example - transport of Glucose into the
cell
Affects on the Rate of Diffusion
 Temperature
 Medium in which diffusion takes place
 Size of solute concentration
http://www.austincc.edu/biocr/1406/labm/ex5/images/Diffusion_animated.gif
“Yellow food coloring diffusing through water. The glass on the left
contains hot water, while the glass on the right contains cold water.
The food coloring was added to the cold water slightly before the
coloring was added to the hot water, yet after a few seconds it has
diffused more thoroughly through the hot water. The frames are
roughly 1 second apart (so the animation is roughly 2x real-time).”
Active Transport
11
Active transport
-requires energy – ATP is used directly or indirectly
to fuel active transport
-moves substances from low to high concentration
-requires the use of carrier proteins
Active Transport
12
1. Protein pump
-an active transport mechanism
-ATP energy is used to change the conformation of the
carrier protein
- large ions (Na+ or K+) are carried across the membrane
that are traveling from low to high concentration
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/an
imation__how_the_sodium_potassium_pump_works.h
tml
13
Bulk Transport- Active
14
2. Endocytosis occurs when the plasma membrane
envelops food particles and liquids.
 Phagocytosis (particles)
 Pinocytosis (liquids)
3. Exocytosis occurs when material is discharged
from the cell.
-vesicles in the cytoplasm fuse with the cell membrane and
release their contents to the exterior of the cell
15
Endocytosis (white blood cell takes in bacteria to destroy it
https://www.youtube.com/watch?v=0TvTyj5FAaQ
Exocytosis-
let big bulk
16 items out of the cell
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sit
es/dl/free/0072437316/120068/bio02.swf::Endocytosis
%20and%20Exocytosis