How Big is It?
•
http://www.cellsalive.com/howbig_js.htm
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The Plasma Membrane Gateway to the Cell
Allows molecules to move in and out of the
2 cel
What needs to get into and
out of the cell?
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CO2 and Oxygen
Blood cells take Oxygen and nutrients to every
cell in the body and CO2 is removed
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Wastes, Carbon dioxide and
Urea pass out of cells
through membrane
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Cells are limited to size due to its
Volume to Surface area Ratio
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Photograph of a Cell
Membrane
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Cell Membrane
The cell
membrane is
flexible and
allows a
unicellular
organism to
move
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Homeostasis
• Balanced internal condition of
cells
• Also called equilibrium
• Maintained by plasma membrane
controlling what enters & leaves
the cell
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Functions of Plasma
Membrane
 Protective barrier
 Regulate transport in & out of cell
(selectively permeable)
 Allow cell recognition
 Provide anchoring sites for filaments
of cytoskeleton
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Structure of the Cell
Membrane
copyright cmassengale
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Structure of the membrane is
Made up of phospholipids,
Proteins and cholesterol
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FLUID MOSAIC MODEL
FLUID- because individual phospholipids and
proteins can move side-to-side within the
layer, like it’s a liquid.
MOSAIC- because of the pattern produced by
the scattered protein molecules when the
membrane is viewed from above
http://www.dnatube.com/video/360/Fluid-Mosaic-Model
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Cell Membrane
Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses15
Cell Membrane
The cell membrane is
made of 2 layers of
phospholipids called the
lipid bilayer
Hydrophobic
molecules pass
easily; hydrophilic
DO NOT
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Semipermeable or
selectively permeable
Membrane
Small molecules and larger hydrophobic
molecules move through easily.
e.g. O2, CO2, H2O
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Semipermeable Membrane
Ions, hydrophilic molecules larger than
water, and large molecules such as proteins
do not move through the membrane on their
own.
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http://www.bing.com/videos/search?q=Cell+Membrane+animation&go=Submit&qs=n&form=Q
BVR&pq=cell+membrane+animation&sc=8-23&sp=1&sk=#view=detail&mid=7FC1F9FD1D31B1EAB2057FC1F9FD1D31B1EAB205
Types of Transport
Across Cell
Membranes
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Passive Transport
Simple Diffusion
 Doesn’t require energy
 Moves high to low
concentration
 Example: Oxygen or
water diffusing into a
cell and carbon dioxide
diffusing out.
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Simple Diffusion
• Requires NO
energy
• Molecules
move from
area of HIGH
to LOW
concentration
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DIFFUSION
Diffusion is a
PASSIVE process
which means no
energy is used to
make the
molecules move,
they have a
natural KINETIC
ENERGY
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Diffusion through a
Membrane
Cell membrane
Solute moves DOWN concentration gradient (HIGH to LOW)
Solute= anything that is dissolved (in water)
Diffusion of Liquids
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Passive Transport
Facilitated diffusion
Doesn’t require energy
Uses transport
proteins to move high to
low concentration
Examples: Glucose or
amino acids moving from
blood into a cell.
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Active Transport
Requires energy or
ATP
Moves materials from
LOW to HIGH
concentration
AGAINST
concentration gradient
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Carrier Proteins
• Other carrier
proteins
change shape
to move
materials
across the cell
membrane
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Endocytosis – Phagocytosis
Used to engulf large particles such as
food, bacteria, etc. into vesicles
Called “Cell Eating”
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Phagocytosis
- Capture
of a Yeast
Cell (yellow)
by
Membrane
Extensions
of an
Immune
System Cell
(blue)
copyright cmassengale
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Moving the “Big Stuff”
Exocytosis
- moving
things
out.
Molecules are moved out of the cell by vesicles that fuse
with the plasma membrane.
This is how many hormones are secreted
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Exocytosis
The opposite of endocytosis is exocytosis. Large
molecules that are manufactured in the cell are
released through the cell membrane.
Inside Cell
Cell environment
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Three Forms of Transport Across the Membrane
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Osmosis
• Diffusion of water
across a
membrane
• Moves from HIGH
to Low
Diffusion across a membrane
Semipermeable
membrane
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Diffusion of H2O Across A
Membrane
High H2O potential
Low solute concentration
Low H2O potential
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High solute concentration
Aquaporins
• Water Channels
• Protein pores used during
OSMOSIS
copyright cmassengale
WATER
MOLECULES
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Cell in Isotonic Solution
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
NO NET
MOVEMENT
What is the direction of water movement?
equilibrium
The cell is at _______________.
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Cell in Hypotonic Solution
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
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Cell in Hypertonic Solution
15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
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Isotonic Solution
NO NET
MOVEMENT OF
H2O (equal amounts
entering & leaving)
Hypotonic
Solution
CYTOLYSIScell busts
Hypertonic
Solution
PLASMOLYSIS
- shriveling of
cell
Cytolysis & Plasmolysis
Cytolysis
Plasmolysis
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Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic
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hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic
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