CELL TRANSPORT
Homeostasis
Membrane permeability
Equilibrium
Transport
Homeostasis:
Maintaining a Balance
Organisms must
adjust to changes
in their
environment.
If not…DEATH!
What Maintains Homeostasis?
The PLASMA
MEMBRANE maintains
the proper
concentrations of
materials by
controlling the
passage.
Characteristics of
the Cell Membrane
Selectively Permeable
aka Semipermeable
1.Water, oxygen, nitrogen,
carbon dioxide and other small
nonpolar molecules can diffuse
directly
2.Allows some things in and
others not
Plasma Membrane-Structure
1. Phospholipid Bilayer2. 2 fatty acids and
1 phosphate group
attached to a glycerol
3. Polar Heads (water
soluble)
4. Non Polar -Fatty acid
chain (not water soluble)
REVIEW NOTES FROM
THE CELL!
The cell membrane
also has proteins
floating in it that do
many things. Some
are gates to let
substances in and
out.
Protein in membrane
Plasma Membrane Function-Proteins
• The cell membrane's function,
in general, revolves around
membrane proteins.
1. Receptor proteins which
allow cells to communicate
2. Transport or channel
proteins regulate what enters or leaves the cell
3. Marker proteins which identify the cell
Cellular Transport
NO ENERGY REQUIRED
• Diffusion (passive)
• Facilitated Diffusion (passive)
• Osmosis-Diffusion of Water (passive)
ENERGY REQUIRED
• Active Transport
Diffusion
 Diffusion - the
process by which
molecules spread from
areas of high
concentration,
to areas of low concentration.
 Passive Transport-requires no
energy
• Concentration gradient - a difference
between concentrations in a space.
• C. When the molecules are even
throughout a space - it is called
Dynamic EQUILIBRIUM
About this diagram: this represents a cell in a solution. The cell will not let
the red particles pass through the membrane. The green molecules can
pass through, as can water molecules. The arrows show the direction of
particle movement. The green particles are moving in to the cell where
their concentration is lower, and water is moving out of the cell because its
concentration is higher inside
diffusion
osmosis
Osmosis
A. Osmosis - the
diffusion of water
molecules through a
selectively permeable
membrane. Passive
Transport
Ex.Water will move in the direction
where there is a high concentration
of solute (and hence a lower
concentration of water).
Isotonic Solution
• Concentration
of solute in cell
and solution is
equal
• No net
movement into
or out of cell
Hypotonic Solution
 There are less solute
(salt) molecules in the
solution.
 Water will move into
the cell.
 Cell will swell
 Cell could burst
 Plant cells have vacuoles
to collect extra water
Hypertonic Solution
A.There are more solute
(salt) molecules in
solution, which causes
the water to leave the
cell
B.Plants wilt and animal
cell shrink-Plasmolysis.
In both cases, the cell
may die.
Crenated red blood
cells in hypertonic salt
solution
X 1000
Notice that the cells
have shrunk.
Red blood cells in
isotonic solution
X 1000
Note that all the cells
appear normal.
Red blood cells in
hypotonic solution
X 1000
Note that the pinkish
cells have swollen
(the little dip in the
middle of a normal
rbc is not visible and
one side bows out).
Facilitated Diffusion
(Transport Proteins, passive)
• Moves substances down
the concentration
gradient without using
cell’s energy
• Use of carrier proteins
located in membrane
Animations of cell processes:
Diffusion & Osmosis:
http://www.biologycorner.com/bio1/diffusion.html#
Osmosis Examples
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Hypotonic, Hypertonic, Isotonic Interactive Quiz
http://www2.nl.edu/jste/osmosis.htm#Osmosis
Active Transport
Move particles from a region of
lesser concentration to a region of
greater concentration. Move against
the concentration gradient. Must
use energy (ATP)
Sodium-Potassium Pump
Sodium/Potassium pump:
3 Na+ out of cell
2 K + into cell
Here the energy of a
phosphate (shown in red)
is used to exchange
sodium atoms for
potassium atoms.
Endocytosis and Exocytosis
Cells can also move things in and out by using pieces of
membrane. Look at the animations on the link to view these
processes:
Endocytosis:
pinocytosis – cellular drinking
phagocytosis – cellular eating
Exocytosis:
- can involve getting rid of waste, or can involve
secreting cell products (such as hormones or other important
compounds)
Active Transport
Exocytosis
Exocytosis- substances inside a vesicle are
released from a cell as the vesicle fuses with
the cell membrane
• Requires Energy
Endocytosis
Substances are moved into a cell
by a vesicle that pinches off
from the cell membrane
Phagocytosis-cell “eating” engulfs
food
Pinocytosis- cell “drinking”
Requires energy
ATP