Transcript Concentration gradient

Cellular Transport
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The plasma membrane is responsible for
helping to maintain homeostasis in the
cell because it controls what enters and
exits the cell.
The membrane is made of a doublelayered sheet called a phospholipid
bilayer.
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The head of a phospholipid is polar and is
called hydrophilic (water-loving). It points to
the cytoplasm and external environment.
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The two tails are nonpolar point toward
each other in the center of the
membrane and are called hydrophobic
(water-fearing).
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Embedded in the phospholipids layers
are membrane proteins and cholesterol
molecules.
Some membrane proteins help certain
molecules pass across the cell
membrane, while others serve as means
of communication between cells.
Proteins Are Critical to
Membrane Function
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The cell membrane has a liquid quality to
it. This along with the scattered proteins
causes it to sometimes be referred to as
a “fluid mosaic”.
Cholesterol molecules help strengthen
the cell membrane and help to keep its
fluid property.
Passive Transport = NO Energy
Required
Passive transport is the passage of
particles/molecules across the plasma
membrane without the use of energy.
This is movement with the concentration
gradient from high to low. Simple
diffusion, facilitated diffusion, and
osmosis are the 3 types of passive
transport.
* Floating with the tide- no energy required
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Concentration gradient
Concentration gradient means there is a
difference in concentration of a substance
across a space or a membrane.
Equilibrium is the opposite of a gradient.
 The concentration is equal on both sides.
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1. DIFFUSION
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Diffusion is the net
movement of particles
from an area of high
concentration to low
concentration. Small
molecules like Oxygen
and hydrogen use
simple diffusion to get
into the cell. This
means they travel
directly across the
phospolipids.
Diffusion through a
Membrane
Cell membrane
Solute moves DOWN concentration gradient (HIGH to
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LOW)
2. OSMOSIS
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Osmosis is the diffusion of water
molecules across a selectively permeable
membrane.
Osmosis is powered by the unequal
distribution of particles called a
concentration gradient. The difference in
concentration causes water to move
across the membrane.
3 TYPES OF SOLUTIONS
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There are 3 different types of solutions
that the cell comes in contact with.
Hypertonic, hypotonic, and isotonic
solutions all affect the cell differently.
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A. Isotonic solutions
have the same
concentration of solute
as the solution on the
inside of the cell. The
water concentration is
equal inside and outside
the cell. The water will
move in and out of the
cell at an equal rate. This
causes no change in
shape of the cell.
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B. Hypotonic
solutions have a lower
concentration of solute
than the solution
inside the cell. This
means the water
concentration is
greater OUTSIDE the
cell. This causes water
to move into the cell
and the cell will swell.
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Hypo = Gonna Blow
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Hypotonic solutions cause plants to
stand up and become rigid and stiff. The
central vacuole fills up and presses
against the cell wall causing turgor
pressure. They do not burst because of
the cell wall.
Animal cells will rupture and die if in
hypotonic solutions too long. Rupture of
the cell is called cytolysis.
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C. Hypertonic solutions have a higher
concentration of solute than the solution
inside the cell. Therefore, the water
concentration is greater INSIDE the cell.
This causes water to move out of the cell
and the cell to shrink. Shrinking of the
cells is called plasmolysis.
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Hypertonic solutions
cause plants to wilt.
Both hypertonic and
hypotonic solutions
can kill cells.
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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Osmosis in Red Blood Cells
Isotonic
Hypotonic
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Hypertonic
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hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic
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Passive transport also uses membrane
proteins to move particles in and out of
the cell. Channel proteins and carrier
proteins are used for transport.
Channel proteins are hollow and particles
move through them with the
concentration gradient.
3. FACILITATED DIFFUSION
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Facilitated
diffusion uses
carrier proteins
that opens and
closes to either
side of the cell
membrane.
These also move
with the
concentration
ACTIVE TRANSPORT=USES
ENERGY
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Active transport is the passage of
particles across the membrane against
the concentration gradient, from low to
high. This type of transport requires
energy.
There are 3 examples of active transport.
Sodium-potassium pump, endocytosis,
and exocytosis.
* swimming against the tide = energy
required
Three Forms of Transport Across the Membrane
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Active transport is
done by carrier
proteins. They bind
with a substance
outside the cell and
then energy causes
the protein to release
the substance inside
the cell against the
concentration
gradient.
1. Sodium-Potassium Pump
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Inside the cell there are a large number
of negatively charged proteins and other
organic compounds that cannot escape
from the cell. A large number of + ions
like to collect around them. These ions
cause water to draw into the cell which
unless checked can cause the cell to
burst. The Sodium-Potassium (Na+-K+)
pump is a mechanism to prevent this.
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The pump transports 3 Na+ ions out of
the cell and in exchange takes 2 K+ ions
into the cell. This automatically activates
when the cell begins to swell.
Sodium-Potassium Pump
3 Na+ pumped in for every 2 K+ pumped out;
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travels through
the transport protein35
2. Endocytosis- uses vesicles to move material
into the cell
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When a cell needs to take IN large
particles it uses the process of
endocytosis. The cell surrounds and
encloses the material in a portion of its
membrane. This forms a vesicle that
floats in the cytoplasm like a bubble.
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Materials INTO cell = En
3. Exocytosis- uses vesicles to move materials
out of the cell.
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When a cell is ready to release the
materials as waste the “bubble” attaches
itself to the plasma membrane. It then
opens to the outside of the cell and
releases its contents. This is called
exocytosis.
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Materials EXIT the cell = EX