Download Movement of Materials Through the Plasma Membrane

CELL MEMBRANES
GUIDING QUESTION: HOW
DOES A CELL MEMBRANE
HELP A CELL STAY ALIVE?
Homeostasis- A stable internal condition inside of
a living organism.
-Homeo= same
-Stasis= not moving
CELL MEMBRANE
A phospholipid is a lipid
with a phosphate “head” and
two fatty acid “tails”.
 The head is attracted to
water



= Hydrophilic
The tail is not attracted to
water

= Hydrophobic
CELL MEMBRANE THOUGHT
EXPERIMENT

1st Experiment
CELL MEMBRANE THOUGHT
EXPERIMENT

2nd Experiment
CELL MEMBRANE THOUGHT
EXPERIMENT

3rd Experiment
A phospholipid bilayer forms the basic unit of the cell membrane.
QUESTION # 1

Where in this diagram of a cell membrane would you
expect to find the FEWEST water molecules?
A
B
C
The fatty acid “tails” of
the phospholipids are
hydrophobic. They
would repel any water
molecules that came into
that area of the
membrane.
SELECTIVE PERMEABILITY

Cell membranes are said to be selectively permeable
membranes, meaning that they allow some, but not all,
materials to simply pass through them.
http://www.johnkyrk.com/cellmembrane.html
http://www.youtube.com/watch?v=Rl5EmU
QdkuI
QUESTION # 2
Which of the following is NOT an accurate analogy
for a cell membrane?
A.
a window screen
B.
the US – Mexico border
C.
the Kansas – Colorado border
D.
a university admissions department
QUESTION #3
WHICH OF THE FOLLOWING COULD NOT
PASS THROUGH A CELL MEMBRANE
WITHOUT THE HELP OF A PROTEIN?
A. Sugar
 B. Oxygen (O2)
 C. Carbohydrates
 D. Water

MEMBRANE COMPOSITION
Proteins embedded in the bilayer help the cell
transport materials in and out.
 Carbohydrate chains (cell surface markers) attached to
some membrane proteins help the cell communicate
with other cells.

Structure of the Cell
Membrane
QUESTION # 4: WHAT TYPE OF
MEMBRANE MOLECULES ARE
RESPONSIBLE FOR CELL-TO-CELL
COMMUNICATION?
A. lipids
B. proteins
C. phospholipids
D. carbohydrates
Carbohydrate chains act
like “ID tags.” Different cell
types have different kinds
of carbohydrate chains on
their surfaces.
CELL MEMBRANE ANALOGY

The cell membrane is similar to the walls that
surround a house.
BOTH HELP PROTECT THE INSIDE FROM THE
OUTSIDE.
inside
outside
A HOUSE NEEDS A WAY OF RECEIVING
FUEL AND POWER FROM THE OUTSIDE.
SUPPLY LINES PASS THROUGH THE
WALLS OF THE HOUSE TO BRING IN
THESE MATERIALS.
A CELL RECEIVES
FUEL AND POWER FROM THE
OUTSIDE THROUGH PROTEIN CHANNELS IN THE
MEMBRANE.
PEOPLE IN A HOUSE ALSO NEED TO
COMMUNICATE WITH THE OUTSIDE.
CARBOHYDRATES IN THE MEMBRANE ALLOW
THE CELL TO COMMUNICATE WITH OTHER
CELLS.
SENSING THE OUTSIDE
ENVIRONMENT
People in a house need to know when deliveries or friends arrive.
RECEPTOR PROTEINS

These proteins let a cell sense its surroundings so
that it can change and maintain homeostasis.
BACKGROUND INFORMATION
Most cells exist in liquid, making it easy
for materials to move into and out of the
cell.
Every cell membrane is selectively
permeable, meaning that some
substances but not others can cross
them.
Particles have a tendency to move from a
region where they are more numerous to
a region where they are less numerous.
A CONCENTRATION GRADIENT
IS…
…a
difference in the number of
particles of a substance in two
neighboring regions.
Particles tend to move down their
concentration gradients (higher to
lower concentration).
PARTICLES OF A SUBSTANCE TEND TO GO
FROM AREAS OF HIGHER
CONCENTRATION TO AREAS OF LOWER
CONCENTRATION.
A.
B.
True
False
It's not simply a case of movement in one
direction. Particles move in both directions, but
because one side has more particles to start
with, they are more likely to move in one
direction than the other. When both sides have
the same number of particles, they are just as
likely to move one way as the other way, so
there will be no change in amounts - both sides
will stay equal.
DIFFUSION IS…
…the
process by which particles
of a substance move from areas
of higher concentration to areas
of lower concentration.
…the driving force behind the
movement of materials across
the plasma membrane.
A.
B.
C.
A barrier separates two different substances.
The barrier is removed, and the substances move down
their concentration gradients.
Equilibrium is reached.
OSMOSIS IS…
…the
diffusion of
water molecules
through a selectively
permeable membrane
from an area of
greater concentration
of water to an area of
lesser concentration of
water.
BASED ON THE CONCEPT OF OSMOSIS, WHAT
WOULD YOU EXPECT TO HAPPEN IN THIS
SETUP?
A.
B.
C.
D.
No movement of water will occur.
Water will move in both directions equally.
The net movement of water will be from side B to side
A.
The net movement of water will be from side A to side
B.
OSMOSIS TERMINOLOGY
When comparing two solutions…
 …solutions with higher concentrations of
solute are hypertonic
(hyper means "above").
 …solutions
with lower concentrations of
solute are hypotonic
(hypo means “below”).
 …solutions
in which the concentrations
are equal are isotonic
(isos means “equal”).
WHICH OF THE FOLLOWING
CORRECTLY LABELS THIS SETUP?
A.
B.
C.
D.
left: isotonic / right: isotonic
left: isotonic / right: hypertonic
left: hypertonic / right: hypotonic
left: hypotonic / right: hypertonic
IMAGINE THAT THE MEMBRANE SHOWN
BELOW IS IMPERMEABLE TO THE SOLUTE
MOLECULES BUT PERMEABLE TO WATER.
WHICH WAY WILL WATER FLOW?
A.
B.
left to right
right to left
NORMALLY, IN THE PROCESS OF OSMOSIS,
THE NET FLOW OF WATER MOLECULES INTO
OR OUT OF THE CELL DEPENDS UPON
DIFFERENCES IN THE
A.
B.
C.
D.
rate of movement of molecules inside the cell
concentration of water molecules inside and outside
the cell
rate of molecular motion on either side of the cell
membrane
concentration of enzymes on either side of the cell
membrane
FACILITATED DIFFUSION
Diffusion of a substance
through a transport
protein embedded in a
membrane.
In facilitated diffusion,
solute particles pass
through a channel in a
transport protein.
Facilitated Diffusion
Transport
Protein
Higher Concentration of
Molecules
Outside Cell
Lower Concentration of
Molecules
Inside Cell
PASSIVE TRANSPORT
Diffusion, osmosis, and
facilitated diffusion are
all forms of passive
transport across the
plasma membrane
because energy is not
required for them to
happen.
Like riding a bike down
a hill, no energy is
needed.
ACTIVE TRANSPORT
…involves
a substance
being forced through a
transport protein in the
plasma membrane
against the concentration
gradient (from lower to
higher concentration).
Like riding a bike up a
hill, an energy boost is
required.
Active Transport
Lower Concentration
of Molecules
Transport
Protein
Outside Cell
Molecule
to be
carried
ENERGY
Higher Concentration
of Molecules
Inside Cell
Active Transport
Outside Cell
Molecule is
transported
to the other
side of the
membrane
Inside Cell
WHICH OF THE FOLLOWING TYPES OF
TRANSPORT ACROSS MEMBRANES WAS
COMPARED TO RIDING A BIKE UP A HILL?
A.
B.
C.
D.
diffusion
osmosis
active transport
facilitated diffusion
Like an enzyme, a transport protein
recognizes a specific solute,
molecule or ion. During active
transport, the protein uses energy,
usually moving the solute in a
direction from lesser concentration
to greater concentration.
ENDOCYTOSIS AND
EXOCYTOSIS
…the
processes of
taking material into
(endocytosis) or out
of (exocytosis) the
cell by means of
pockets of the cell
membrane.
WHAT PROCESS IS SHOWN
HERE?
A.
B.
C.
D.
osmosis
exocytosis
endocytosis
facilitated diffusion
INTERACTIVE VISUALS OF TRANSPORT
ACROSS A MEMBRANE
OSMOSIS DEMO
Procedure: The water surrounding an
Elodea leaf will be replaced with salt
water.
Before the demo, write a paragraph
describing what you expect to observe.
After you have observed osmosis, write a
paragraph describing what you observed
and what caused it to happen.
Correctly use the words equilibrium,
hypertonic, hypotonic, and isotonic in your
description.