Download The Plasma Membrane

Plasma Membrane Function
 Maintains balance by controlling
what enters and exits the cell
What characteristic of life is this?
HOMEOSTASIS
 Membrane is selectively permeable
only allows certain molecules
through
Plasma Membrane Structure
Phospholipid Bilayer (2 layers of lipids)
 Polar heads face out because they are
hydrophilic “water loving”
 Nonpolar tails face in because they are
hydrophobic
Fluid Mosaic Model
Plasma Membrane Structure
Fluid Properties:
 Unsaturated
fatty acid tails
 Cholesterol in
animal membranes
Plasma Membrane Structure
Mosaic Properties
 Proteins in the lipid
bilayer
 Integral proteins are
inside the membrane
 Peripheral proteins are
only found on one side of
the membrane
Integral Protein Examples
 Channel – allow materials to
pass through (tunnel)
 Carrier – transport materials
across
 Receptor – transmit
information
 Marker – identify the cell to
other cells
Diffusion of Liquids
9
Diffusion
Solute particles move from HIGH
concentration to LOW concentration
 This always occurs when there is a
concentration gradient
 It will continue until dynamic
equilibrium is reached
Diffusion Demonstration
1. What solution is being put into the
bag? What color is it?
starch & water; cloudy white
2. What solution is in the beaker? What
color is it?
iodine & water; amber
3. Predict what will happen to the bag
and/or beaker color(s).
Diffusion Demonstration
Results
1. What color is the bag?
2. What color is the beaker?
3. Explain what happened.
Iodine molecules were small enough to
fit across the membrane. Starch
molecules were too large. The
solution turned blue when starch &
iodine mixed.
Diffusion review
Movement of particles from HIGH
concentration to LOW concentration
 This is caused by a concentration
gradient
 It will stop when dynamic equilibrium
is reached
Osmosis
 Diffusion of water molecules across a
selectively permeable membrane
 Occurs when the solute particles (dots)
cannot pass through the membrane
Osmotic Solutions
Hypotonic =
lower
concentration
(less dots)
Hypertonic =
higher
concentration
(more dots)
What controls osmosis?
 Unequal
distribution of
particles, called
a concentration
gradient, is one
factor that
controls osmosis.
Before
Osmosis
Selectively
permeable
membrane
After
Osmosis
Water molecule
Sugar molecule
Cells in an isotonic solution
 water molecules move
H2O
H2O
Water
Molecule
Dissolved
Molecule
into and out of the cell
at the same rate, and
cells retain their
normal shape.
Cells in an isotonic solution
 water molecules move
H2O
H2O
Water
Molecule
Dissolved
Molecule
into and out of the cell
at the same rate, and
cells retain their
normal shape.
Cells in an isotonic solution
 A plant cell has its
normal shape and
pressure in an isotonic
solution.
Cells in a hypotonic solution
 hypotonic solution:
dilute solution thus low
solute concentration
 In a hypotonic solution,
water enters a cell by
osmosis, causing the
cell to swell.
H2O
H2O
Water
Molecule
Dissolved
Molecule
Cells in a hypotonic solution
 Plant cells swell beyond
their normal size as
pressure increases.
(plants prefer this –it
makes the leaves firm)
 Turgor Pressure –
water pushing the
plasma membrane
against plant cell
wall
Cells in a hypertonic solution
 hypertonic solution:
concentrated solution,
thus a high solute
concentration
In a hypertonic solution,
water leaves a cell by
osmosis, causing the
cell to shrink
H2O
H2O
Water
Molecule
Dissolved
Molecule
Cells in a hypertonic solution
 Plant cells lose
pressure as the plasma
membrane shrinks away
from the cell wall.
PLASMOLYSIS –
shrinking of cytoplasm
away from cell wall due
to outward water flow
Osmotic Solutions
Isotonic = equal concentration
Direction of Water
Hypotonic solutions = water moves
INTO the cell
Hypertonic solutions = water moves
OUT of the cell
Isotonic solutions = NO net
movement of water
Effects on different cells
Animal Cell
Solution
Plant Cell
burst
Hypotonic
Turgor
pressure
shrivel
Hypertonic
plasmolysis
normal
Isotonic
limp
Passive Transport
 Movement of particles from HIGH
concentration to LOW concentration
 Requires NO energy
 3 types:
1. Diffusion
2. Osmosis
3. Facilitated diffusion
Facilitated Diffusion
 Diffusion of particles across a
membrane using transport proteins
 Uses both channel and carrier proteins
Active Transport
 Movement of particles from LOW
concentration to HIGH concentration
 Requires cell energy
 3 types:
1. Pumps
2. Endocytosis
3. Exocytosis
Active Transport
 Pumps
-use carrier proteins to push/pull
molecules across the membrane
Active Transport
 Endocytosis
- Transport of very large molecules
INTO the cell
- Forms a vacuole
 Exocytosis
- Release of very large molecules
(from a vacuole or vesicle) OUT of
the cell