Name:
Transport Across A Cell Membrane
I. Cell Membrane
1. Play animation to review parts of cell membrane: http://www.susanahalpine.com/anim/Life/memb.htm
List main parts:
Phospholipid bilayer, integral membrane proteins, peripheral membrane proteins, oligosaccharides, cholesterol
molecules,
2. http://www.aber.ac.uk/gwydd-cym/cellbiol/transport/index.htm Fill in the blanks below:
The lipid bilayer is more permeable to non-polar molecules than
to polar molecules and ions. The size of a molecule also affects
permeability – the lipid bilayer is more permeable to small
molecules than to large molecules.
II. Passive Transport
http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html
Click on Passive Transport and answer the following questions:
1. Define Passive Transport:
The movement of molecules across the cell that doesn’t require the use of energy (ATP)
2. Hit next and go through the slides to give a brief description of each of the following types of diffusion:
Main components of cell membrane
Job/description
Integral proteins
Act as channels to transport substances across the membrane
Fluid lipid Bilayer
Houses the proteins and limits what goes in and out of the cell
3. Types of
Diffusion
Simple Diffusion
Definition/Description
The movement of molecules from an area of high concentration to an area of low
concentration, along the Concentration gradient (the relative density of one chemical
substance versus another)
Determinants of diffusion:
Steepness of concentration gradient, temperature, charge, diameter of diffusing molecules
When does diffusion “end?” when equilibrium has been reached
Animation of diffusion http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf
Facilitated Diffusion Is the passive transport of molecules down a concentration gradient with the aid of special
transport proteins; once the molecule enters the protein channel, the protein undergoes a
conformational change (shape change) so that the molecule can pass
Osmosis
The passage of water across a membrane from an area of high concentration to an area of
low concentration; diffusion of water
For animation: http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf
4. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/bloodcells.gif
Pictures of Red
Blood Cells
Identify what
type of solution
each is placed,
what happened
and why
Hypotonic solution (distilled
water), osmosis of water
from [hi] to [low] inside cell,
plasmolysis
Isotonic solution (equal conc),
no net movement
Hypertonic solution (salty),
osomosis of water out of cell
from [hi] inside to [low]
outside
III. Active Transport
http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html
1. Define Active Transport
Is the pumping of molecules against their concentration gradient (lowhigh) with the use of energy (ATP)
2. Why is it necessary?
Living cells often require the uptake of molecules that are scarce in their environment, cells must use ATP to
transport these materials against their concentration gradients.
3. Types of Active
Transport
Ion Pumps
Cotransport
Endocytosis
(Transport of large
molecules)
ENDO = INSIDE
Exocyotosis (EXO = Exit,
outside)
Definition/Description
Aka electrogenic pumps are special proteins which actively transport ions resulting
in an ionic and voltage gradient, ex. Pumping out of H+ ions
For animation:
http://www.stolaf.edu/people/giannini/flashanimat/transport/atpase.swf
The coupled passage of two materials across a membrane
Define:
Is the import of materials to the cell by infoldings of the plasma membrane
Phagocytosis: cell eating, pseudopods surround the food item and fuse together
forming a vesicle to take the food into the cell
For animation:
http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/phagocitosis.swf
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/phagocyt.html
Pinocytosis: cell drinking, vesicles of fluid are formed in the cell membrane without
the formation of pseudopods
For animation:
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html
Receptor Mediated Endocytosis:
Special coated pits in the cell membrane are lined with receptor proteins that bind
with specific materials, once the receptors are filled, the coated pit forms a vesicle
to transport the materials
For animation: http://www.susanahalpine.com/anim/Life/endo.htm
Scroll down to “Movement of large molecules across cell membrane http://www.aber.ac.uk/gwydd-cym/cellbiol/transport/index.htm
A protein-containing vesicle moves towards the cell membrane where the
vesicle’s membrane docks with the cell membrane. The two membranes merge,
releasing proteins from the vesicle into the extracellular fluid. Proteins are
released from cells in response to messages which are normally extracellular.
nsulin is secreted by cells in the pancreas, using exocytosis, to release the
hormone into the blood.
4. Three different transporters systems are involved in active transport. Use all the websites provide to describe
each and to observe the animations.
Different
Use - http://www.uic.edu/classes/bios/bios100/lectures/diffusion.htm
Transporter
systems
Uniport
A carrier protein that only transports one molecule across a membrane
For animation: http://www.stolaf.edu/people/giannini/flashanimat/transport/caryprot.swf
Symport
A carrier protein that carries two molecules in the same direction
For Animation: http://www.stolaf.edu/people/giannini/flashanimat/transport/symport2.swf
Antiport
A carrier protein that carries two molecules in the opposite direction
For animation: http://www.stolaf.edu/people/giannini/flashanimat/transport/antiport.swf
5.
http://www.mhhe.com/biosci/esp/2001_g
bio/folder_structure/ce/m3/s5/
Identify and describe what is occurring in
the picture using the website above.
Active transport using a protein to pump
molecules against their concentration
gradient…may be used to pump two
different substances in opposite
directions, ex. Sodium potassium pump
(important in nerve and muscle cells)
Active Transport in Paramecium
http://www.answers.com/topic/vacuole
http://ebiomedia.com/gall/classics/Paramecium/paramecium3.html (scroll down to 3rd and 4th picture)
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/contractilevac.gif
Slide 4 - http://bioweb.usc.edu/courses/2003-spring/documents/bisc221-watts_lec9.pdf
Paramecium Contractile Vacuole: http://www.stolaf.edu/people/giannini/movies/paramecium/para%20cont.mov
6. What is a contractile vacuole?
A membrane-bound organelle found in certain protists that pumps fluid in a cyclical manner from within the
cell to the outside by alternately filling and then contracting to release its contents at various points on the
surface of the cell. It functions in maintaining osmotic equilibrium
7. Why does a paramecium living in freshwater need it?
The paramecium is in a hypotonic environment, so the freshwater will keep diffusing in by osmosis and unless it is
pumped out, the cell will burst
IV. Summarize the differences between passive and active transport.
Use of ATP
With or against
concentration
gradient
Different types
Passive Transport
No
With
Active Transport
Yes
Against
Simple,
facilitated,
osmosis
Endocytosis
(pinocytosis,
phagocytosis),
exocystosis, ion
pumps,
cotransport