Cell Transport – Part 1. Cell Membrane Structure and Permeability
Use the animations listed, your observations, class notes, your book (and don’t forget to think) to answer
the following questions.
THE CELL MEMBRANE
1. Go to http://www.wisc-online.com/objects/construction-of-the-cell-membrane/
Work through the animation creating a picture of the cell membrane below. Be sure to include
integral and peripheral proteins, cholesterol, and phospholipids
a. Use your completed drawing of the cell membrane. Label the region that is hydrophobic and
the regions that are hydrophilic. What are these two regions of the phospholipid bilayer
called?
b. What do pore proteins allow to enter/exit the cell?
c. What role do glycoproteins play in the cell membrane?
FLUID MOSAIC MODEL (Be sure to know WHY this model is called a fluid mosaic model).
Go to: http://www.susanahalpine.com/anim/Life/memb.htm and view the animation
a. What do you notice about the proteins that are imbedded in the phospholipid bilayer?
(Hint: think about their relative positions to each other).
b. Using knowledge gained from your notes and the last two websites, draw a cross section of a cell
membrane. Include at least two trans-membrane proteins and at least one glycoprotein.
1
PASSIVE AND ACTIVE TRANSPORT
Go to the website: http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html
Read the intro:
a. What is the difference between passive and active transport? (include both the energy
requirement and the direction of movement)
b. Click on the animation, then start with diffusion: What type of molecules can move directly
through the phospholipid bilayer.
c. What is equilibrium?
d. What happens to the movement of molecules when they reach equilibrium?
Click on Options in the lower left corner of the animation window to return to the menu.
Select: Facilitated Diffusion: Channel Proteins
Watch the entire animation (be sure to read the opening information first)
a. How does facilitated diffusion differ from regular diffusion?
b. How are facilitated diffusion and regular diffusion the same?
Read the conclusion and then take the quiz. Write the entire correct answer below each question.
a. This channel protein is also:
b. If a cell transports a number of these ions across the membrane, which direction of transport
would require energy from the cell?
c. Which of the following is NOT true about the carrier molecules involved in facilitated diffusion?
2
How stuff moves through the cell membrane.
Go to http://www.teachersdomain.org/asset/tdc02_int_membraneweb/
After clicking on each type of molecule and viewing how they move, list how the following molecules
enter/exit the cell membrane. If needed, indicate what type of membrane protein allows the molecule to
enter/exit the cell.
Water
Oxygen
Carbon Dioxide
Glucose
Sodium/Potassium Ions
Cell Transport Part II - Osmosis
Review:
a.
Diffusion is the movement of molecules from a _______________ to ______________
concentration. This movement is due to the random movement of molecules in a fluid such as water or
air.
Website 1. Go to :
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
Watch the animation and read the bottom. Use the information to answer the following questions
a. Which two molecules can easily cross directly through the plasma membrane?
b. What molecule are we moving when osmosis occurs?
c.
Is this a passive or active process? How do we know?
d. Why do water molecules move? (meaning: what is the goal? What point are they trying to
reach?)
3
Website 2. Go to http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf (“Cell
biology animations”) and select “osmosis” under “cell transport”.
a. In the basic animation, describe the movement of the water molecules across the membrane.
Consider the volume of fluid on each side.
b.
Now click on “Add salt” and observe what happens.
After salt (in reality there would be many Na+ and Cl- ions) is added, how do the water
molecules move across the membrane? Is there an overall direction of movement (where do most
of the molecules end up?)
Go to
http://www.abpischools.org.uk/page/modules/homeostasis_kidneys/kidneys4.cfm?coSiteNavigation_allTopic=1
The first animation shows a simulated cell. The “bag” tied around the end of the glass pipette is made of a
material that is semi-permeable (like our cell membrane). The red dots represent a solute like sugar water.
Watch the animation and what happens to the bag.
a. Which side of the bag is hypertonic?
b. Which direction does water move?
Scroll down to “osmosis in red blood cells” The animation shows three conditions for the red blood
cell. Define what each of these conditions means below in terms of where the solute concentrations
is greater:
c. Cell is in a hypertonic solution (in the cell or the solution around it?)
d.
e.
4
Comparing solutions:
f.
Draw dots to represent solute concentration in the cell and the extracellular fluid, and arrows to
indicate the direction of water movement for isotonic conditions.
g. In what direction will water have a net movement? Use an arrow on your drawing to show this.
h. What will happen to the shape of the cell?
i.
Draw dots to represent solute concentration in the cell and the extracellular fluid, and arrows to
indicate the direction of water movement for hypertonic conditions (cell is placed in a
hypertonic solution).
j.
In what direction will water have a net movement? Use an arrow on your drawing to show this.
k. What will happen to the shape of the cell?
5
l.
Draw dots to represent solute concentration in the cell and the extracellular fluid, and arrows to
indicate the direction of water movement for hypotonic conditions.
m. In what direction will water have a net movement? Use an arrow on your drawing to show this.
n. What will happen to the shape of the cell?
o. Animal cells are intended to function under reasonably isotonic conditions. This is very
important when making solutions that will be given intravenously! What might happen to an
animal cell in a very hypotonic solution, like pure water? Explain your answer.
Plant cells work differently. Now go to http://www.kscience.co.uk/animations/turgor.htm
Watch the animation loop to understand what happens with plant cells
p. Plant cells depend on being in hypotonic solutions to build turgor pressure, which helps them to
stand up. What is turgor pressure?
q. What structure in a plant cell allows it to take in a great deal of water without diluting materials in
the cytoplasm too much?
r.
What structure keeps a plant cell from exploding due to being in a hypotonic solution?
6
Go to http://www.kscience.co.uk/animations/plasmolysis.htm and observe what happens to a cell if it
loses turgor pressure.
s. Plasmolysis occurs if a plant cell is put in a hypertonic solution. Explain what happens in
plasmolysis and draw a series of pictures to illustrate it happening.
Cell Transport Part III – Active Transport
Go to http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11203
At the bottom of the apparently empty box, Click on the “Next” button to view the “Active
Transport” animations until you see a screen that tells you that you have completed the activity.
Cells often need to move materials against the concentration gradient (from low concentration to
high), or to move materials that will not pass through the membrane easily because they are too
large, carry a charge, etc.
a. What makes this process active? (What molecule is needed to supply energy?)
b. How is active transport different from facilitated diffusion? (List two things!)
Watch endocytosis. This is also an active transport process, but we don’t see any ATP being spent.
ATP definitely is being used to make this happen (chemical bonds are being broken and reformed
in several steps in the process.
c. What happens in phagocytosis?
7
d. How is pinocytosis different from phagocytosis?
f.
One last thinking question: Are plant cells likely to use endocytosis? Explain your answer.
Congratulations! You are finished! Think about what you have learned. Be prepared to discuss the
different means of moving materials across a cell’s membrane. Know which processes are active and
which are passive. Think about what kinds of materials rely on each type of transport.
8