Download Cellular Transport - St. John the Baptist Diocesan High School

Diffusion, Osmosis, and Active Transport
The Cell Membrane
 Recall that the cell membrane is the structure found in
both plant and animal cells that controls the
movement of materials both into and out of the cell
Functions of the Cell Membrane
Separates the contents of the cell
from the outside environment
2. Serves as a barrier for which
substances can enter and exit a
cell
3. Recognizes chemical signals
(messages) which will trigger the
cell to react in a particular way
1.
Selective Permeability
 The cell membrane is
considered selectively
permeable, which means that
some molecules can pass
through, and some molecules
cannot
 It maintains balance both inside
and outside the cell
Selective Permeability
Structure of the Membrane
 Fluid Mosaic Model- a model of the cell membrane
 The membrane is a double lipid layer (bilayer) with large
proteins embedded in it
Structure of the Cell Membrane
 Made up of a double layer of “phospholipids”
 A phospholipid is made of two parts:
 Phosphate head- hydrophilic, or “water-loving”
 Lipid Tails- hydrophobic, or “water-fearing” (think oil,
a substance that does not dissolve in water)
Structure of the Cell Membrane
 The “water-loving” phosphate heads face the outside
environment and the inside of the cell
 The “water-fearing” lipid tails face each other on the
inside of the membrane
Structure of the Cell Membrane
 Proteins are embedded within the membrane because
most molecules cannot easily pass through the “waterfearing” lipid tails
 A protein channel enables molecules to pass through
without interacting with the lipids
Passage of Materials through Cell
Membranes
 In addition to receiving information, cells need a way
to move molecules and other substances through their
membranes
 Some molecules, such as water, pass freely. This is
called passive transport.
 Others that do not pass freely must be carried through
channels. This is called active transport
Diffusion
 Movement of molecules from an area of HIGH
concentration to an area of LOW concentration
 Form of passive transport because NO ENERGY is
required!
Diffusion
Animation
Facilitated Diffusion
 Movement of molecules down their concentration
gradient with the help of transport proteins embedded
within the cell membrane
 No energy is required!
 Animation
Osmosis
 The diffusion of water through a membrane
 Water molecules move from an area of high concentration
to low concentration
 NO ENERGY is required
Hypotonic Solution
 When the inside of a cell has a
much higher salt (solute)
concentration than the outside of a
cell
 Water will diffuse into the cell to
“dilute” the inside contents
 Result = Cell Swells and sometimes
bursts (lyses)
 Video Demo
Hypertonic Solution
 When the outside of a cell has
a much higher salt (solute)
concentration than the inside
of a cell
 Water will diffuse out of the
cell to “dilute” it’s
surroundings
 Result = Cell Shrivels
(shrinks)
 Video Demo (Start at 3:10)
Isotonic Solution
 When the solute
concentration outside the cell
is equal to the solute
concentration inside the cell
 No net movement of water
occurs!
 Video Demo (Start at 4:25)
Summary
Name that solution!
Isotonic
Hypertonic
Hypotonic
Active Transport
 Movement of molecules through a
cell membrane from an area of
LOW concentration to an area of
HIGH concentration
 Always requires ENERGY (ATP)!
 Often uses a protein “pump”
embedded within the membrane to
move molecules
Types of Active Transport
 Endocytosis- cells take in
large particles by engulfing
them- cell membrane
pinches in to form a vesicle
 Exocytosis- cells get rid of
particles by enclosing them
in a vesicle (a membrane)
and fusing that membrane
with the cell membrane
Passive vs. Active Transport
Passive Transport
Active Transport
 Does not require energy
 Requires Energy
 Diffusion, Osmosis
 Protein pumps, endocytosis,
 Water, Oxygen, Carbon
exocytosis
 Large and charged particles!
 Like riding a bike uphill!
dioxde
 Like riding a bike downhill!