Cell Membrane
Movement of Substances Into
and Out of the Cell
Created by Mr. Woodbury & Mrs. Beddes
Modified by Mrs. Slater
Cell Membrane Structure

Cells are surrounded by a thin, flexible, selectively
permeable membrane.
Selective Permeability
 Allows
only certain substances to pass
through
Fluid Mosaic Model
 The
membrane is
fluid because it is
not rigid or fixed
 The membrane is
like a wall
like a mosaic with
 Fluid in the verbthe different parts
sense…
http://www.youtub
put together
e.com/watch?v=S
pPXewlgmcw
 The parts shuffle,
move and flex
 Different
parts
have different
shapes and
functions
Phospholipids
 A phospholipid
is
made of a 1 polar,
hydrophilic head
and 2 non-polar
hydrophobic tails
 Classified
as a
lipid
 The main part of
membranes
5
Cell Membrane Structure

Phospholipid bilayer

Arranged with hydrophilic head on outside and hydrophobic tails
on inside
Definitions
 Hydrophilic
head
≈ water
 -philic ≈ loving
 Polar regions of a molecule that are
attracted to water
 Hydro-
 Hydrophobic
tails
≈ water
 -phobic ≈ afraid or hating
 Nonpolar regions of a molecule that avoid
water or prefer other hydrophobic parts
 fatty acid tails
 Hydro-
Cell Membrane Structure

Proteins

Enzyme activity, cell-to-cell recognition, cell signaling, transport
Cell Membrane Structure

Cholesterol

Helps to stabilize membrane
10
Selectively Permeable
Cell Membrane Drawing
 Draw
and label the parts of a cell
membrane include phospholipids,
proteins, and cholesterol
 Draw and label the hydrophobic regions
& the hydrophilic regions
 Describe/explain each part of the cell
 What
do phospholipids, proteins, and
cholesterol do?
 What does hydrophobic & hydrophilic mean?
11
Membranes in organelles
 You
will be given one of the following
organelles to draw.
 Since these are all made of membranes,
you must draw a large portion of the
membrane as the phospholipid bilayer
 If
it has an outer layer that is made of a
membrane, you must draw that as a
phospholipid bilayer
12
13
Cell Membrane Processes
 Cell
Transport
14
Cell Membrane Illustration
 We
will add in the different parts and
processes of the cell membrane to this
drawing as we go.
 First section: the phospholipid bilayer.
 Two
layers of phospholipids
 Hydrophilic heads pointing out and in
 Hydrophobic tails pointing towards each
other.
15
16
Methods of Transport
 Transport
of materials in and out of the
cell falls into two categories
 Passive
transport
 Active transport
 Which
one sounds like it requires
energy?
 http://www.youtube.com/watch?v=j5Qway
4LAkk&feature=related
17
Membrane Proteins
18
Passive Transport
 Does
not require energy from the cell
 Type 1: Diffusion
 Movement
of particles from an area of high
concentration to an area of low
concentration
 Stuff goes from where it is to where it isn’t
 Happens because of random movement of
particles
 Examples: Oxygen, carbon dioxide, some
water, and lipid-soluble substances (nonpolar molecules)
19
O2
CO2
20
Diffusion… High to Low
 To
determine which direction material will
go, you must know the
amounts/ratios/percentages of materials
in the different areas.
 Water coloring example
 Coloring
first went to bottom (high
concentration)
 Then slowly diffused through water (low
concentration)
 High to low = passive transport
21
A Special Condition
 Equilibrium
 Number
of molecules moving in one direction
is equal to the number moving in the other
direction
 The random motion and collisions are still
happening
 The net movement in all directions equals
out.
22
Passive Transport, cont.
 Type
2: Facilitated diffusion
 Transport
proteins allow the diffusion of
certain substances
 Channels, tunnels, sometimes with gates
 Gates may open & close due to changes in
conditions.
 Examples: Water, ions and sugars
23
Facilitated Diffusion
24
O2
CO2
25
Passive Transport, cont.
 Type
3: Osmosis: Passive transport of
water across a membrane
 Hypertonic

Solution with a higher solute concentration

Water leaves the cell to dilute the external solution
 Isotonic

Solution with an equal solute concentration

No net movement of water (water enters and leaves the
cell at the same rate = equilibrium)
 Hypotonic

Solution with a lower solute concentration

Water enters the cell to dilute the internal solution
26
Transport Across a Membrane
 Video
footage:
http://www.linkpublishing.com/videotransport.htm
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How cells behave...
Tonicity Flip Diagram
 Fold
a piece of paper in half hot dog-style
 Fold in thirds. Label & draw 1 for each
section:

Hypertonic Solution



Isotonic Solution



Inside of the cell: 10% NaCl & 90% water
Outside of the cell (the environment):
15% NaCl & 85% water
Inside of the cell: 10% NaCl & 90% water
Outside of the cell (the environment):
10% NaCl & 90% water
Hypotonic Solution


Inside of the cell: 6% NaCl & 94% water
Outside of the cell (the environment):
3% NaCl & 97% water
29
Flip Diagram – Hypertonic
 "HYPER"
means more than.
 The concentration of solute (salt)
outside the cell is greater than that of the
solution outside the cell, so water will
move out of the cell. Plant cells lose
water and start to wilt. Animal cells will
shrink / shrivel. In both cases, the cell
may die. Overall, the cell size will
decrease.
30
Flip Diagram – Isotonic
 "ISO"
means equal to.
 If the concentration of solute (salt) is equal
on both sides of the cell membrane, the water
will move into the cell, but it won't change
the overall amount of water on either side.
Humans need isotonic solutions to be at
equilibrium which occurs when equal
amounts of water are entering and exiting
the cell. Overall, the cell size will not
change.
31
Flip Diagram – Hypotonic
 "HYPO"
means less than.
 The concentration of solute (salt) inside the
cell is greater than that of the solution
outside the cell, so water will move inside of
the cell. The cell will _____________ water
and grow ____________. In plant cells, the
central vacuoles will fill and the plant
becomes stiff and rigid. In animal cells, the
cell may be in danger of ________________.
Overall, the cell size will ___________.
32
Active Transport

Requires energy from the cell
Movement of particles from an area of
low concentration to an area of high
concentration
 Goes “uphill”
 Type 1: Pumps
 Particle binds to a transport protein
 Protein changes shape which requires
energy
 Releases particle inside the cell
 Protein returns to original shape

The
SodiumPotassium
Pump
34
O2
CO2
35
Active Transport, cont.
 Movement
of large particles, using
membrane movement/reconfiguration
 Type 2: Endocytosis
 “Inside
+ cell + process”
 Cell surrounds and takes in material from its
environment
 Often used for nutrients or foreign invaders
 Type
3: Exocytosis
 “Outside
+ cell + process”
 Reverse process of endocytosis
 Used to expel wastes and secrete
substances produced by the cell
Endocytosis
Exocytosis
Endocytosis & Exocytosis
 http://www.youtube.com/watch?v=1w10R
9lv7eQ
38
O2
CO2
39
Basic types of transport
40
A Summary
41
Membrane Transport
Animation
 And
once again, so you understand what
she’s talking about…
 http://www.youtube.com/watch?v=j5Qw
ay4LAkk&feature=related
42
Vocab Terms
Passive
Transport
Active
Transport
Diffusion
Equilibrium
Facilitated
Diffusion
Osmosis
Hypertonic
Isotonic
Hypotonic
Endocytosis
Exocytosis
43
For the lab
 Compare
the internal environment of the
egg/cell to the liquid it is soaking in.
Interior of cell = water + solutes (stuff)
 Exterior of cell = corn syrup or pure water
 Which exterior liquid has a higher
percentage of water?
 Which exterior liquid has a higher
percentage of stuff?
 Which one was hypertonic?
 Which one was hypotonic?
 Is your mystery solution hyper-, hypo-, or
isotonic?
