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All organisms and their cells respond to
external conditions to maintain a stable
internal condition. They are maintaining
Homeostasis.
To understand how this works we need
to first discuss the Plasma Membrane.
Polar heads
love water
(Hydrophilic)
Non-polar tails
fearwater
(Hydrophobic)
Membrane
movement
animation
II. Movement of Substances
Into and Out of Cells
2 types of transport across membranes:
• Passive- tranport that does not require any
energy. (moves from high to low
concentration)
• Active- transport that requires energy.
(moves from low to high concentration)
Passive Transport
•
•
•
Cell doesn’t use energy
Molecules spread out from an area of high
concentration to an area of low concentration.
(HighLow)
Weeee!!
!
3 types of Passive transport
1.
2.
3.
Diffusion
Facilitated Diffusion-diffusion with
the help of transport proteins
Osmosis-diffusion of water
high
low
A. Passive Transport:
Simple Diffusion
Animation
1. Diffusion: random movement of
molecules down a concentration
gradient, from high to low
concentrations
(High to Low)
•
Diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)-Note:
molecules will still move around
but stay spread out.
http://bio.winona.edu/berg/Free.htm
A. Passive Transport:
2.Facilitated diffusion:
diffusion of specific particles
through transport proteins
found in the membrane
a.Transport Proteins are
specific – they “select”
only certain molecules
to cross the membrane
b.Transports larger or
charged molecules
A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport From aHigh Concentration
High
• Channel Proteins
animations
Cell Membrane
Low Concentration
Through a  Protein Transport Channel
Go to
Section:
Protein
channel
Low
A. Passive Transport:
Osmosis
animation
3.Osmosis: diffusion of
water through a
selectively permeable
membrane
Water moves from
high to low
concentrations
•Water moves freely
through pores.
•Solute (green) is too
large to move across.
A solution is a mixture of solutes (things being dissolved) and a solvent (things
doing the dissolving). Water is typically the solvent. (i.e. sugar cube in water, the
sugar is the solute)
Use new vocab to make Koolaid
Koolaid powder
sugar
Solutes = ___________________________& __________
Water
Solvent = ____________
solution
Koolaid drink = ______________
http://www.makash.ac.il/h_school/hst/hstsb/chem/luach/dissolve.jpg
Water Balance in a Cell
A Simple rule to remember is:
SALT SUCKS
Salt is a solute, when it is concentrated inside
or outside the cell, it will draw the water in
its direction.
Types of Solutions
1. Hypertonic: solution with a greater concentration
of dissolved particles than its surroundings.
2. Hypotonic: solution with a lower concentration of
dissolved particles than its surroundings.
3. Isotonic: solution concentration is equal to its
surroundings.
Hypertonic
1. Cells placed in a hypertonic solution
(environment like salt water) will shrink or
shrivel.
Remember – Salt sucks!
•
Hypertonic Solution
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Hypertonic: The solution has a higher concentration
of solutes and a lower concentration of water than
inside the cell. (High solute; Low water)
shrinks
Result: Water moves from inside the cell into the
solution: Cell shrinks (Plasmolysis)! This is why you
get thirsty after eating something salty.
Hypotonic
Cells placed in a hypotonic solution
(environment like fresh water) will swell
and could burst.
Think hypo - hippo
•
Hypotonic Solution
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than
inside the cell. (Low solute; High water)
Result: Water moves from the solution to inside the
cell): Cell Swells and bursts open (cytolysis)!
Isotonic
Cells placed in an isotonic solution
(environment) will remain the same size.
ISO = Equal or same
•
Isotonic Solution
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Isotonic: The concentration of solutes in the solution
is equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and
the cell remains same size! (Dynamic Equilibrium)
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
VACUOLES store WATER
OSMOTIC PRESSURE
________________________________________ =
Pressure exerted by the movement of water
during osmosis
How Organisms Deal
with Osmotic Pressure
•
Paramecium
(protist) removing
excess water
video
•Bacteria and plants have cell walls that prevent them
from over-expanding. In plants the pressure exerted on
the cell wall is called turgor pressure.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
Grocery stores spray water on
their veggies to “plump them
up”
http://www.painetworks.com/photos/gt/gt0461.JPG
SO WHAT?
• This is why it is dangerous to drink sea water-it’s
also a myth that drinking sea water will cause
you to go insane, but people marooned at sea
will speed up dehydration (and death) by
drinking sea water.
• This is also why “salting fields” was a common
tactic during war, it would kill the crops in the
field, thus causing food shortages
Molecules
need to
move
across
membranes
in cells
PROBLEM for CELLS?
Diffusion only moves molecules
from high concentration to low
concentration.
What if cell needs to move a
AGAINST the
molecule _________
CONCENTRATION
GRADIENT?
_______________
(LOWER  HIGHER)
Cell example:
Want to put MORE glucose
into mitochondria when there is
already glucose in there
Image from: http://www.biologyclass.net/mitochondria.jpg
CELL EXAMPLE:
DIFFUSION automatically moves oxygen
from HIGHER concentration (in lungs)
to a LOWER concentration (in blood)
CO2 automatically moves
from where there is a
HIGHER concentration
(in blood) to where there
is a lower concentration
(in lungs)
http://www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.html
Video from: http://www.southtexascollege.edu/tdehne/BC_ShockwaveAnimations/08SWF-MembraneStructureAndFunct/08-02-MembraneStructure.swf
PROBLEM for
Cells?
Cell membranes
are
SELECTIVELY
PERMEABLE
See a movie
What if a cell needs to
LARGE or ______
POLAR
move _____
molecules
that can’t get
through the
membrane?
http://www.d.umn.edu/~sdowning/Membranes/membraneImages/jpegimages/diffusionmedium.jpg
PROBLEM for CELLS?
Diffusion happens very slowly
What if cell needs to move
FAST
molecules really _______?
(can’t wait for it to diffuse)
Cell example:
Movement of
Na + & K+ ions
required to send
nerve signals
http://www.steve.gb.com/images/science/neuron.png
WAY to
Cells need a ____
HELP molecules across
____
cell membranes that
can’t go across by
_______
themselves
___________
Cells use energy to transport materials that cannot
diffuse across a membrane.
• Passive transport requires no energy from the
cell.
• Active transport is powered by chemical energy
(ATP).
• Active transport occurs through transport
protein pumps.
• Cells use active transport to maintain
homeostasis.
A cell can import and export large materials or large amounts of
material in vesicles during the processes of endocytosis and
exocytosis.
• Cells use energy to transport material in vesicles.
• Endocytosis is the process of taking
material into the cell.
• Phagocytosis is a type of endocytosis.
A cell can import and export large materials or large amounts of
material in vesicles during the processes of endocytosis and
exocytosis.
• Cells use energy to transport material in vesicles.
• Exocytosis is the process of expelling
material from the cell.
Kidspiration by: Riedell
•
Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
This is
gonna
be hard
work!!
high
low
Protein
Pump
Endocytosis
Exocytosis
Active Transport
•cell uses energy
•actively moves molecules to where they are
needed
•Movement from an area of low concentration
to an area of high concentration
•(Low  High)
•Three Types:
Types of Active Transport
1. Protein Pumps transport proteins that
require energy to do
work
•Example: Sodium /
Potassium Pumps
are important in nerve
responses.
Sodium
Potassium Pumps
(Active Transport
using proteins)
Protein changes
shape to move
molecules: this
requires energy!
Types of Active Transport
• 2. Endocytosis: taking
bulky material into a cell
• Uses energy
• Cell membrane in-folds
around food particle
• “cell eating”
• forms food vacuole &
digests food
• This is how white blood
cells eat bacteria!
Types of Active Transport
3. Exocytosis: Forces
material out of cell in bulk
• membrane surrounding the
material fuses with cell
membrane
• Cell changes shape –
requires energy
• EX: Hormones or
wastes released from
cell
Endocytosis &
Exocytosis
animations
• Animations of Active Transport & Passive
Transport
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