In This Lesson:
Cell Membranes
and Cell
Transport
(Lesson 3 of 5)
Today is Monday,
October 12th, 2015
Pre-Class:
Today is our first look at the cell. First, choose one of the
following to answer in your notes:
1. What do the terms diffusion, osmosis, or passive/active
transport mean to you?
2. Have you ever had Aquafina or Dasani water? Why is it different
from Poland Spring, for example? Do you know the name of the
process?
Also, take a worksheet from the Turn-In Box and get a paper
towel for your pair.
Today’s
• Cell membrane [Part 1]
– Form
• Brief aside on blood type
• Cell transport [Part 2]
– Function
• Doodling on whiteboards
– Yes, you will be making pictures.
• Where is this in my book?
– Academic: P. 182-189
– Honors: P. 79 and following…
http://www.greatscopes.com/objectives.jpg
By the end of this lesson…
• You should be able to describe the
structure and function of the cell
membrane.
• You should be able to identify the direction
and energy-intensive movement of
particles or water.
But First, a Word About Size…
• Ye Olde BioScale
• What It Looks Like
• Scale of the Universe
Osmosis and Diffusion
Pre-Class
• What did you come up with?
– We will talk about the details of these
processes today and later in the week.
• One other thing…
– When you hear me mention an organic
molecule today, raise your hand.
• Keep your ears open!
The Cell Membrane
• Like the “shell” of the cell.
• Also called the plasma membrane.
• Double layer of phospholipids called a
bilayer.
• Separates the cell’s
cytoplasm from the
extra-cellular matrix.
• ECM
• Which one is outside,
which is inside?
http://api.ning.com/files/bjQpqLaT64H6U9Rm1cTtQzE8e7iMnMN*e7NCiUPA*ly2QfxrMD-yIx3-4bZ494uPFWMBd4jtn3cnGophzG2Rj1i*8RZJLtZh/et2.jpg
Permeability
• Some things are “impermeable:”
– Raincoats, balloons, brick walls.
• Some things are “permeable:”
– Air, water.
• Some things are “semi-permeable:”
– Nets, gates, cell membranes.
• Semi-permeability is sometimes called selective
permeability.
The Phospholipid Bilayer
• Most plant and animal cells
have a double-layered cell
membrane called a
phospholipid bilayer.
– The phospholipid bilayer acts
as its own gate.
Polar ----------->
Non-Polar
• Because the cell is in and
made of water, a polar
substance, the non-polar
Polar ----------->
tails stay on the inside of the
layer.
– This polar/non-polar deal
makes the phospholipid
amphipathic.
http://textbookofbacteriology.net/themicrobialworld/phospholipid_bilayer.jpg
Phospholipids?
Fatty Acid
Chains
http://bioweb.wku.edu/courses/biol115/wyatt/biochem/lipid/P-lipid.gif
Glycerol
Molecule
• Fun fact: A phospholipid
is actually just like a
triglyceride molecule…
• …but it’s usually
unsaturated…
• …missing a fatty acid
chain (diglyceride)…
• …and with a phosphate
group.
P
What It Looks Like
http://micro.magnet.fsu.edu/cells/plasmamembrane/images/plasmamembranefigure1.jpg
Modeling the Cell Membrane
• Time for a class bonding experience.
– The Classroom Cell!
• So to summarize, you are a phospholipid.
Polar (your
• You have a polar [hydrophilic] “head”
Non-Polar
upper body) and a non-polar [hydrophobic]
“tail” (your legs).
Non-Polar
• The desks are like the imaginary Polar
dividing line
between polar and non-polar.
http://textbookofbacteriology.net/themicrobialworld/phospholipid_bilayer.jpg
http://farm1.static.flickr.com/76/174946884_64a0b8b304.jpg
Now for the Proteins
• Membrane proteins are embedded in some
places in the cell membrane. They might
have one of many jobs:
–
–
–
–
Marker Proteins
Receptor Proteins
Enzymes
Transport Proteins
http://library.thinkquest.org/C004535/media/cell_membrane.gif
And we return to the model…
• More “Classroom Cell!”
Embedded
Protein!
There’s more…
• Attached to some proteins are
carbohydrates (remember them?) that help
in cell-cell recognition.
And we return to the model one
last time…
• More “Classroom Cell!”
Okay, one last thing…
• Cell membranes are fluid.
– What does this mean?
• The cell’s phospholipids and
embedded proteins flow around the
membrane and are in motion.
– Called the Fluid Mosaic Model.
• A certain lipid (actually, a steroid)
can slow down or stop this fluidity.
– Do you know what it is?
http://www.herdaily.com/blogimg/health/c----.bmp
Fluid Mosaic Model
• Remember, it moves!
Challenge Question
• We know that carbohydrates are attached
to proteins in the cell membrane so that
other cells can identify them.
• What do you think might happen if a cell
lost its carbohydrate receptors in your
body?
Blood Type
• For a look at how important these small
signal molecules are, we’ll look at blood
type.
– Anyone know their blood type in here?
• We’re going to keep blood type simple for
today, so let’s assume there are only four
total blood types:
– A, B, O, and AB.
Blood Type
• Each red blood cell (except O) has a specific
kind of receptor on it (in this case called an
antigen).
http://lomalindahealth.org/health-library/graphics/images/en/19450.jpg
White Blood Cells
• You also have white blood cells (leukocytes)
– they’re like angry policemen in your
blood vessels.
Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor  Receptor 
Receptor 
Receptor 
Receptor 
Receptor 
Receptor  Receptor 
http://www.journaldunet.com/science/biologie/dossiers/07/immunite/lymphocyte.jpg
Blood Type
• The wrong type of blood cell receptors
causes agglutination (clumping) .
– Example: My dad has Type A blood. If you give
him Type B blood, the white blood cells will
treat it as an invader.
– Type O blood has no antigens so anyone can
receive it.
• More on blood when we get to the Genetics unit.
Micro Assignment
• Tear a small piece of paper out of your
notebook, write your name on it, and
answer this question:
– Which organic molecules play a role in the cell
membrane? What roles do they play?
Molecular Transport [Part 2]
Question:
You have a sealed container holding
one liter of pure oxygen (O2). You set
the container on a table and leave it
alone. After one week, are the
oxygen molecules moving? Why or
why not?
http://www.electronichealing.co.uk/resources/Image/oxygen_drops.jpg
Molecular Movement
• Molecules are always in motion.
– Gas, liquid, and solid.
• Molecules only stop moving at absolute
zero.
• So, even after a week (or two or three), the
oxygen molecules would still be bouncing
around.
Predictive Doodling
• Today we’re going to do something I’m
calling “Predictive Doodling.”
• It’s like the Challenge Questions we do on
the whiteboards, only you’ll be drawing
instead of writing.
• I’ll give you the “before,” you give me the
“after.”
Before
• Your whiteboard is a square container of water.
• The dots are dissolved solutes.
• What happens next? Talk to your partner – then
draw it.
Diffusion Analogy
• Imagine for a second that at the beginning
of class I jammed all of you into the corner
of the room.
• Then, I just said, “Okay, relax,” and let you
do what you wanted.
– Would all of you stay put or would you spread
out?
Note Organizer
• Use this Cell Transport worksheet in place
of your notebook for now…
Now let’s take a look at
what the science says…
• Diffusion is the passive “spreading out” of
particles of a substance until the particles
are spread out equally.
–
–
–
–
“Passive” meaning “no energy required.”
Diffusion is a form of passive transport.
Heat generally makes diffusion go faster.
Let’s try a little demo or two…
Diffusion Demos
• Diffusion in Water
• Diffusion in Air
Diffusion
http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion.gif
Concentration Gradient
• Concentration refers to the amount of a substance
in a certain area.
• Particles diffuse down their concentration gradient.
– What does that mean?
• In passive transport, particles always go from an
area of high concentration to an area of low
concentration.
• Fun Fact: Passive transport occurs in part to satisfy
the second law of thermodynamics, AKA entropy.
Concentration Gradient
High
Warning:
Steep
Grade
Low
Concentration Gradient
High
Concentration
In Passive Transport, particles
move from areas of high
concentration to areas of low
concentration.
Low
Concentration
Predictive Doodling Again
• The line in the middle is permeable to
water, but not to solute. What happens
next?
Osmosis
• Osmosis is basically the same thing as diffusion,
only with water molecules and some form of a
barrier.
– Osmosis is another form of passive transport.
• Just like in diffusion, in osmosis, water moves
from areas of high water concentration to low
water concentration.
• Or, water moves from areas of low solute
concentration to areas of high solute
concentration.
Osmosis
• Which drink has more liquid in it?
Drink A
Drink B
Osmosis in a U-Tube
Side A
Side B
Which side has more water on it?
http://www.biologycorner.com/resources/osmosis.jpg
Osmosis in Carrots
• Remember when I put the carrots in these
beakers?
– They were roughly equal carrots at the time.
• For the carrot in the salt water, there is
more solute outside the carrot than inside
the carrot.
– Which way does the water go?
– What kind of change can we expect to find in
the carrots?
Tonicity
• Hypertonic solution
– Relatively more solute than surroundings.
• Water flows TOWARD a hypertonic solution.
• Hypotonic solution
– Relatively less solute than surroundings.
• Water flows AWAY FROM a hypotonic solution.
• Isotonic solution
– The same amount of solute as the surroundings.
• No net water change.
Isotonic Solutions
• Water does not experience a net
movement in isotonic solutions.
– There is no concentration gradient.
No concentration gradient
No net movement of water
And now, I present to you…
• …the key to EVERYTHING!!!!!!*
–
*osmosis-related.
• Draw this in your notebook. Make it BIG.
Hypotonic
H2O Flow
Hypertonic
What’s the connection?
Blood hypertonic,
Blood hypotonic,
surroundings
surroundings
hypotonic
hypertonic
Isotonic solutions
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Erythrozyten_und_Osmotischer_Druck.svg/450px-Erythrozyten_und_Osmotischer_Druck.svg.png
Osmosis Videos
• Egg Osmosis
• Onion Osmosis
• Gummi Bear Osmosis
Osmosis in Plant Cells
http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Turgor_pressure_on_plant_cells_diagram.svg/2000pxTurgor_pressure_on_plant_cells_diagram.svg.png
Osmosis in Plant Cells
• As we will soon learn, plant cells are good at
holding water.
• If they’re placed in a hypertonic solution,
however, they lose water and wilt.
– Their cells undergo plasmolysis.
• Place them in a hypotonic solution and they will
swell slightly, like a garden hose with water.
– Their cells become turgid.
– In animal cells, without a cell wall, the cell may burst
in a process called cytolysis.
Osmosis in Kidneys
http://classes.midlandstech.edu/carterp/Courses/bio211/chap25/Slide18.GIF
Osmosis in Kidneys
• The proximal Loop of Henle is the part of
the nephron (kidney component)
responsible for re-absorbing water from
urine.
• With this in mind, would you guess that
desert animals have larger or smaller Loops
of Henle than other animals?
Osmosis in Kidneys
http://www.answersingenesis.org/assets/images/articles/cm/v26/i3/rats.jpg
Osmosis in
Merriam’s
Kangaroo Rats
http://www.bio.davidson.edu/Courses/anphys/1999/Chisholm/nephron1copy.wc2.jpg
One last note…
• If you buy a car for $1000 and sell it for $3000,
how much profit did you make?
• $2000
• If you take two steps forward and three steps
back, how many steps have you moved forward?
• -1
• These are examples of net gains and losses.
• How many steps did you take (total)?
• 5 (but this is not your net steps)
One last note…
• Remember that question we did about
oxygen gas molecules?
• Molecules, especially of liquids and gases,
constantly move or vibrate. They do this
without adding any energy.
• Even after diffusion or osmosis has
stopped, the molecules are still moving.
Equilibrium
• For things like diffusion and osmosis,
eventually the solutes reach a point where
there is no net change in molecule
movement.
– This is equilibrium.
• We call it “dynamic equilibrium” because
the molecules are still moving, but there is
no net change in concentration or
movement.
Equilibrium
• When dynamic equilibrium is reached,
diffusion and osmosis stop.
– Molecular motion continues, though.
Net Water Flow Inward
No Net Water Flow
WATER
WATER
0.50%
Sugar
1.0%
Sugar
WATER
0.75%
Sugar
0.75%
Sugar
WATER
Osmosis Practice Problems
• First, let’s do these as a class.
• Then, log-in to Quia.
• Take the quiz labeled Osmosis Practice
Problems.
– These aren’t easy. That’s why this isn’t graded
and we’ll be taking it a few times.
– I encourage you to work together.
By the way…
• Dasani and Aquafina use a process called
reverse osmosis.
– They make water go from high solute
concentration to low solute concentration –
the opposite direction!
– This is part of their purification process.
– Why do they do this? Because their water is
actually just purified tap water!
Closure [Part 1]
• Find a blank sheet in your notebook for a
nice little concept map of what we’re
doing!
Closure [Part 2]
What’s wrong with this picture?
http://trendliest.files.wordpress.com/2008/09/1b442cec-5d9e-4d51-89ff-7b3e0ab55e9a_450.jpg
Diffusion
and Membranes
• Diffusion occurs across the cell membrane
without much trouble for small molecules.
• For some things, water included due to the
non-polar inner section of the membrane,
diffusion can’t really happen well.
• Some molecules are too large or charged or
polar/non-polar to just fit right through.
– They need help.
Facilitated Diffusion
• When a molecule needs help to diffuse,
(but does NOT need energy), the process is
called facilitated diffusion.
• Basically it just means that a special
channel protein had to let the molecule in
because it couldn’t fit elsewhere.
Facilitated Diffusion
http://bbwiki.tamu.edu/images/8/8d/Facilitated_diffusion.jpg
Channel Protein
http://upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Ion_channel.png/350px-Ion_channel.png
Facilitated Diffusion Example
• Nerve cells:
http://www.columbia.edu/cu/psychology/courses/1010/mangels/neuro/neurosignaling/ChannelsPump.gif
Facilitated Diffusion Example
Practice Problems
• Use your computer for the following
activities and quiz in this order:
– Diffusion/Osmosis Battleship [Quia]
• Play till you win
– Osmosis Virtual Lab [Paper]
• More information next slide…
– Osmosis Practice Problems [Quia]
Osmosis Virtual Lab
• Visit this website:
– http://www.glencoe.com/sites/common_assets/science/vi
rtual_labs/LS03/LS03.html
– Found in Biology Links – can be run from my website too
(Osmosis Virtual Lab).
• Use the simulation to run through the various
osmotic scenarios shown on your worksheet.
– Note: If you run this from my website and not from the
Glencoe site, you won’t get the “directions” on the left side
of the screen, but you won’t need ‘em, really.
• Don’t turn in the lab today – it’s a study tool for now.
Osmosis Gizmo
• [Log-in Instructions]
• You’re looking for the Osmosis gizmo
• Also open Quia for the Osmosis Gizmo in a new
tab.
• When finished with the lab, open the Quia
activity called Osmosis Gizmo Lab Cloze.
Active Transport
• In short, active transport is the movement
of a substance up or against its
concentration gradient.
– Substance moves from a low concentration
area to a high concentration area.
• This requires energy!
Concentration Gradient
High
Concentration
Passive Transport
Low
Concentration
Concentration Gradient
Active Transport
Low
Concentration
High
Concentration
ENERGY
NEEDED!
Active Transport
http://www.biology4kids.com/files/art/cell2_active1_240x180.gif
Paths for Active Transport
• Three processes using the membrane:
– Molecular Transport: Pumping stuff in/out using
membrane proteins.
– Endocytosis: Bringing stuff into the cell in cell
membrane packages.
• Phagocytosis: “Cell eating” – bringing in solids (big stuff)
• Pinocytosis: “Cell drinking” – bringing in liquids (small
dissolved stuff)
– Exocytosis: Dumping stuff out of the cell in cell
membrane packages.
• Fun fact: Endo-/exocytosis are sometimes called
vesicular transport.
One Way: Using a Pump
• A pump uses a channel protein in the membrane.
• Called “Molecular Transport” by your book.
http://www.soton.ac.uk/maths/img/research/applied/Scheme_sodium-potassium_pump-en.png
Endocytosis/Exocytosis
http://www.linkpublishing.com/exocytosis5.jpg
Active Transport
• These two main processes of active
transport (pumps or endo/exocytosis) are
important!
• Used in signaling:
– Exocytosis/Endocytosis: Chemical Signaling
• Hormones
– Molecular Transport: Electrical Signaling
• Nervous System
For Example:
Protein Receptors
http://upload.wikimedia.org/wikipedia/commons/2/2f/Second_messenger_pathway.png
How this is used…
Heroin addict
http://www.dr...b.com/images/ha.jpg
http://www.topicsplanet.com/wp-content/uploads/2009/09/10703.jpg
Came up when I Googled
“Beta Blockers”
Video!
• CrashCourse – Membranes and Transport
A “Big-Picture” Example: Neurons
• Whenever a nerve cell transmits an impulse
(called an action potential), cell transport
occurs.
• You won’t need to know this for this class,
but here’s a look at how it works.
– Just in case you were thinking cell transport
isn’t that important.
A “Big-Picture” Example: Neurons
1. Neurons exist in a “resting state” making them negative. To
keep this negative charge, the neuron actively pumps out Na+
ions. It pumps in some K+ ions.
2. The neuron’s Na channels open, allowing Na+ ions to diffuse
into the cell, making the cell more positive.
3. Eventually, changes in voltage potentials cause K channels to
open, allowing K+ to diffuse out of the cell, making the cell
more negative and eventually returning the cell to normal.
4. The neuron’s action potential travels down the axon to the
axon terminal. There, the neuron allows Ca2+ ions to diffuse
into the cell, which releases neurotransmitters by exocytosis
into the synaptic cleft.
5. The process continues in the next neuron (or until a muscle is
reached). The first neuron returns to resting state and the
process repeats.
A “Big-Picture” Example: Neurons
http://4.bp.blogspot.com/_G7_c3nIq9A4/TLkLBPp0CWI/AAAAAAAAACM/E_fRxEwm-H0/s1600/myelinsheaths.gif
Closure
• Part 1: Let’s finish the cell transport
concept map!
• Part 2: TED: Ethan Perlstein - Insights into
Cell Membranes Via Dish Detergent
• Part 3: WhipAround