Homeostasis and Cell Transport
http://www2.nursingspectrum.com/articles/article.cfm?aid=11971
http://ailil.deviantart.com/art/Osmosis-Jones-Strikes-Back-3678440
Section 1 Vocabulary Pretest
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Passive Transport
Diffusion
Concentration gradient
Equilibrium
Osmosis
Hypotonic
Hypertonic
Isotonic
Contractile vacuole
Turgor pressure
Plasmolysis
Cytolysis
Facilitated diffusion
Carrier protein
Ion channel
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B.
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D.
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F.
G.
H.
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J.
K.
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M.
N.
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Movement of water from high to low concentration
Movement of molecules from high to low conc.
Organelles that remove water from cells
Pressure exerted by water molecules on cell walls
Proteins that help move molecules through cells
State where molecules are evenly spaced
Difference in the concentration of molecules over
a distance
Bursting of a cell
Shrinking of a cell
Assisted diffusion of molecules
Proteins that move ions through a membrane
Solution with a low concentration of solute
outside a cell
Solution with a high concentration of solute
outside a cell
Solution with an equal concentration of solute
inside and outside a cell
Moving substances without using energy
Answer Key
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Passive Transport
Diffusion
Concentration gradient
Equilibrium
Osmosis
Hypotonic
Hypertonic
Isotonic
Contractile vacuole
Turgor pressure
Plasmolysis
Cytolysis
Facilitated diffusion
Carrier protein
Ion channel
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Types of Transport
 Cells move molecules using different types of passive
and active transport
 These differ from each other by whether or not cells
must use energy.
 Passive= no energy
 Active = use energy
Passive Transport
 Passive transport —movement of substances
through a membrane that requires NO ENERGY
 Types:
 Diffusion —movement of molecules from high to low
concentration
 Osmosis —movement of WATER from high to low
concentration
 Facilitated Diffusion —assisted diffusion of large or
insoluble molecules through a cell membrane.
 Ion Channel Diffusion —movement of ions from high
to low concentration.
Diffusion
 Simplest type of passive transport
 Moves molecules from high to low concentration
 They have kinetic energy and are in constant motion.
 They will spread out simply because they “bump” into each other.
 They move away from areas where they are too crowded
 This is called moving down a “concentration gradient”
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Concentration gradient is the difference in concentration of molecules
across a distance
 Diffusion can happen in a gas, liquid or solid
 It can happen in a living or nonliving system
 It is how most molecules pass into and out of cell membranes.
 It continues until equilibrium is reached
 Equilibrium —the concentration of molecules is the same throughout
the space they occupy
How Diffusion
Works
Animation
Note: Even at equilibrium the random movement
of molecules continues but we no longer see a
net movement of molecules in one direction
 Cell membranes are semi-permeable:
some molecules can pass through and
some cannot.
 Depends on size and chemical nature
of the molecule
 Passing unassisted through the
membrane is called simple diffusion
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Example: CO2 and O2 dissolve in lipids
and can pass directly through the
phospholipid bilayer
Example: Molecules like NH3 and some
hormones that can’t dissolve in lipids but
are small enough can pass through the
Channel Protein Pores in the membrane
http://www2.estrellamountain.edu/faculty/farabee/biobk/biobooktransp.html
Osmosis
 Osmosis is the diffusion of WATER from high to low
concentration.
 Direction of osmosis (water movement) depends on
the relative concentration of solutes inside and
outside the cell
 Review:
 Solute —substance dissolved in water (Ex: sugar, salt)
 Solvent —water
Pay attention!! This gets
confusing!!
 Hypotonic Solution —a
solution outside the cell that
has a lower concentration of
solute molecules than the
concentration inside the
cell. Ex: (less salt outside the
cell)
 This means that there is a
higher concentration of
solvent outside the cell. Ex
(more water outside the cell)
 So water will move into the
cell by osmosis.
“Hypo” means less
http://www.biologycorner.com/bio1/diffusion.html
 Hypertonic Solution —a
solution outside the cell
that has a higher
concentration of solute
molecules than the
concentration inside the
cell. Ex: (more salt outside
the cell).
 This means that there is a
higher concentration of
solvent inside the cell. Ex:
(more water inside the cell)
 So water will move out of
the cell by osmosis.
“Hyper” means more
http://www.biologycorner.com/bio1/diffusion.html
 Isotonic Solution —
concentrations of solute
are equal both inside
and outside the cell.
 Water will move in both
directions in even
amounts.
http://www.biologycorner.com/bio1/diffusion.html
 Some cells control osmosis to some degree
 Three methods:
 Contractile Vacuole —structures found in certain cells
(usually cells of freshwater organisms that constantly
have water moving in) that pump excess water out. Ex.
Paramecium
 Solute Pumps —pump out solutes so that water is less
likely to move in.
 Cell Walls —support the cell so when water moves in the
cell does not burst. Creates “turgor pressure” which
keeps plants upright. “Plasmolysis” is the shrinking of
the cells cytoplasm creating a loss of turgor pressure.
Result: plant wilts
Contractile Vacuole
http://evervision2.ispace.in.th/contractile-vacuoles-are.html
Solute Pump
Turgor Pressure and Plasmolysis
http://botany.thismia.com/2010/02/24/plasmolysis/
http://www.classhelp.info/Biology/AUnit4Cells.htm
http://www.uic.edu/classes/bios/bios100/lecturesf04a
m/lect09.htm
 Cytolysis —bursting of a cell due to osmosis.
Hypotonic
Isotonic
Hypertonic
Identify the pictures as a cell in an isotonic solution, hypertonic solution
and hypotonic solution
Facilitated Diffusion
 Assisted diffusion of large or insoluble molecules
through a cell membrane.
 Carrier Proteins help the molecules to move from high to
low concentration.
 Glucose is transported to cells in this way.
http://www.ncbi.nlm.nih.gov/books/N
BK9847/
Ion Channel Diffusion
 Several ions are vital to cells but cannot pass through
the cell membrane because they are not soluble in
lipids. They are:
 Sodium (Na+)
 Potassium (K+ )
 Calcium (Ca2+ )
 Chlorine (Cl-)
 They require specific ion channels to pass through
membranes
http://tantalusprime.blogspot.com/2008_02_01_archive.html
Many ion channels have gates that close or open in response
to three stimuli:
1. stretching of cell membrane
2. electrical signals
3. chemical signals
Section 2 Vocabulary Pretest
 Active Transport
 Sodium-potassium Pump
 Endocytosis
 Vesicle
 Pinocytosis
 Phagocytosis
 Phagocyte
 Exocytosis
A. Releasing large molecules from a cell
B. The movement of molecules from
low to high concentration using
energy
C. Taking large molecules into a cell
D. Organelles that form from the cell
membrane and transports molecules
within the cell
E. Carrier protein the transports
sodium ions out of a cell and potassium
ions into a cell
F. Type of endocytosis that takes in liquids
G. Type of endocytosis that takes in solids
H. White blood cell
Answer Key
 Active Transport
 Sodium-potassium Pump
 Endocytosis
 Vesicle
 Pinocytosis
 Phagocytosis
 Phagocyte
 Exocytosis
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Active Transport
 Active Transport —movement of substances through
a cell membrane that REQUIRES ENERGY.
 Molecules move from low to high concentration
( “up” their concentration gradient).
 The Carrier Proteins involved require energy from ATP
and are called Cell Membrane Pumps.
 Example: Sodium-potassium pump
Importance of the Sodium-potassium pump
 The sodium-potassium pump is important in animals
to maintain the normal function of many cells
including nerve cells.
 The exchange of three sodium ions for two potassium
ions creates an electrical gradient. The outside of
the cell becomes positively charged and the inside
becomes negatively charged.
 This helps nerve cells to conduct electrical impulses
Endocytosis
 Movement of VERY LARGE PARTICLES into a cell.
The cell membrane pinches off to trap the particle
inside a vesicle which can then transport the
particle throughout the cell.
Two types of endocytosis:
Phagocytosis—movement of large particles
or whole cells
Pinocytosis—movement of fluids
Exocytosis
 Movement of VERY LARGE PARTICLES out of a cell. Vesicles
bring particles to the cell membrane to be released.