The Cell
Membrane
BE ABLE TO:
•Identify the parts and its
structure
•Importance in eukaryotic cells
•Describe its functions
• The plasma membrane of an animal cell
Glycoprotein
Carbohydrate
(of
glycoprotein)
Fibers of the
extracellular
matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments
of the
cytoskeleton
Proteins
CYTOPLASM
• Membranes are selectively permeable
• Membranes can hold enzymes that function in
metabolism and many chemical reactions
• Membrane parts play a role in cellular
communication
• Membrane is a phospholipid bilayer w/
embedded proteins
– Some proteins form cell junctions• Connections between cells
– Most transport special substances
across the membrane
Importance in Eukaryotes:
•Membranes organize the chemical reactions making up
metabolism
•Create “compartments” w/in organelles to isolate one
reaction from another


Cytoplasm
2 MAJOR CATEGORIES OF
CELLULAR TRANSPORT
Passive
&
Active
Passive transport – the movement of
substances without the cell using energy
or doing work; by diffusion across a
membrane
-Move from areas of high
concentration to areas of
lower concentration
-Move “with” the
concentration gradient
Molecule
of dye
Membrane
EQUILIBRIUM
-3 types of Passive
Transport:
– Simple diffusion
– Osmosis
– Facilitated diffusion
EQUILIBRIUM
Osmosis is the passive transport
of water
• In osmosis, water
travels from an
area of lower
solute
concentration to an
area of higher
solute
concentration
Hypotonic
solution
Hypertonic
solution
Selectively
permeable
membrane
Solute
molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water
molecule
Selectively
permeable
membrane
Solute molecule with
cluster of water molecules
NET FLOW OF WATER
What controls osmosis?
• Unequal
distribution of
particles, called
a concentration
gradient, is one
factor that
controls
osmosis.
Before
Osmosis
After
Osmosis
Water molecule
Sugar molecule
Selectively
permeable
membrane
Knowing the tonicity of a
solution allows you to
predict what will happen to
cells and organisms in
certain environments.
Tonicity is the relative
concentrations of two areas;
a means of comparing [ ]’s.
Terms used to compare two areas
of concentration
Hypotonic
Hypertonic
Isotonic
Osmosis in action
10% solute
5% solute
Cells in an isotonic solution
• Most cells are subject to osmosis
because they are surrounded by
water solutions.
H2O
H2O
Water Molecule
Dissolved Molecule
• In an isotonic solution, the
concentration of dissolved
substances in the solution is the
same as the concentration of
dissolved substances inside the
cell.
• In an isotonic solution, water
molecules move into and out of
the cell at the same rate, and cells
retain their normal shape.
Cells in a hypotonic solution
• In a hypotonic
solution, water
enters a cell by
osmosis, causing the
cell to swell.
H2O
H2O
Water Molecule
Dissolved Molecule
Cells in a hypertonic solution
• In a hypertonic
solution, water leaves
a cell by osmosis,
causing the cell to
shrink.
H2O
H2O
Water Molecule
Dissolved Molecule
Draw in your notebook and label Hypotonic, Hypertonic,
Isotonic
A
B
C
The control of water balance (osmoregulation) is
essential for organisms
ANIMAL
CELL
(3) Shriveled =
crenulated
(1) Normal
(2) Bursting =
Lysing
PLANT
CELL
Plasma
membra
ne
(6) Shriveled =
plasmolyzed
(5) Full =
Turgid
(4) Flaccid
ISOTONIC
SOLUTION
HYPOTONIC
SOLUTION
HYPERTONIC
SOLUTION
ANIMAL CELLS --- red blood cells
Plant Cells in an isotonic solution
Cell wall
• A plant cell
has its
normal shape
and pressure
in an isotonic
solution.
• “flaccid”
state
vacuole
membrane
Plant Cells in a hypotonic solution
• Plant cells swell
beyond their normal
size as pressure
increases.
• Increasing “turgor
pressure” on cell walls
• Will become “turgid”
What has happened to the vacuole?
Notice the arrangement of the
organelles compared to the isotonic?
Plasmolysis
Anim.
Plant Cells in a hypertonic solution
• Plant cells lose
pressure as the
plasma membrane
shrinks away from
the cell wall.
• Plasmolysed
What has happened to the
membrane of the cell? Why?
What happened to the vacuole?
Why?
Empty space
Cell membrane
Elodea in isotonic pond water
Elodea with 10% salt solution added
Elodea in 10% NaCl
solution demonstrates
that water has moved
_______
_ the cells.
(out of / into) ?
HYPOTONIC
ISOTONIC
HYPERTONIC
SOLUTION
SOLUTION
SOLUTION
Passive Transport in Action
Facilitated Diffusion
• Diffusion with “help”
• Some substances can diffuse through
special protein ports
• No energy required
• High [ ] to Low[ ]
• Example: glucose enters by Fac. Diff.
Transport(carrier) proteins facilitate(help)
diffusion across membranes
• Small nonpolar molecules diffuse easily through
the phospholipid bilayer; CO2 and O2
• Many other kinds of molecules must pass through
specialized protein pores by facilitated diffusion
Solute
molecule
Carrier protein-
specialized
Transport
protein
ACTIVE TRANSPORT
Active transport –
when cells must use energy to move
substances across the membrane
• Moves large or polar molecules or ions.
• Transport proteins can move solutes across a
membrane against a concentration gradient;
–
–
–
–
low to high
Must use active transport
Proteins act as “pumps”
Requires cell to do work
• uses energy in the form of ATP
• Active
transport
moving two
different
solutes
across a
membrane
Example of Active
Transport
FLUID
OUTSIDE
CELL
Phosphorylated
transport protein
Transport
protein
First
solute
1
First solute,
inside cell,
binds to protein
2
ATP transfers
phosphate to
protein
3
Protein releases
solute outside
cell
5
Phosphate
detaches from
protein
6
Protein releases
second solute
into cell
Second
solute
4
Second solute
binds to protein
PARAMECIUM
Problem: Lives in Fresh Water
Hypertonic to environment
Water constantly diffuses
into cytoplasm
Single cell – no cell wall
Can burst –lyse!
How to get rid of excess?
Pump it out!
Use a Contractile vacuole!
Requires energy – ACTIVE!
BULK TRANSPORT –LARGE MOLECULES,
FOOD, AND OTHER SUBSTANCES ARE
PACKAGED IN MEMBRANE-BOUND SACS
CALLED A VESICLE AND MOVED ACROSS
THE MEMBRANE.
TYPES OF BULK TRANSPORT:
•ENDOCYTOSIS,
•PINOCYTOSIS,
•PHAGOCYTOSIS
•EXOCYTOSIS
Bulk transport of large molecules
• To move large molecules or particles through a
membrane
– a vesicle may fuse with the membrane and expel its
contents (exocytosis)
FLUID OUTSIDE CELL
CYTOPLASM
– or the membrane may fold inward, trapping
material from the outside (endocytosis)
• Types of Endocytosis
Pseudopod of
amoeba
Food being
ingested
Liquid
droplets of
water or
oil/fat being
taken in
Plasma
membrane
Material bound to
receptor proteins
PIT
Cytoplasm
Cell “eating”
Cell “drinking”
PHAGOCYTOSIS
PINOCYTOSIS
Macrophage White Blood Cell
– cell “eater”
Old Red Blood Cells