Download S10 Notes L2C8 Cell transport

Sci 10. Ch 8.2
Transport Across Cell Membranes
Materials move across cell membranes in 3 ways
1) passive transport
1. diffusion (and osmosis)
2. facilitated diffusion
2) active transport
3) endocytosis/exocytosis
PASSIVE TRANSPORT: NO ENERGY REQUIRED
Passive transport is the movement of particles from areas of high concentration to low
concentration. (diffusion, osmosis, facilitated diffusion)
DIFFUSION : Particles move randomly with no particular direction or destination but always
move from areas of high concentration to areas of low concentration = ALONG
THE CONCENTRATION GRADIENT (because bang into each other and ricochet).
Water, O2, and CO2 diffuse in and out of cells easily because of their small size.
Concentration gradient: the difference in concentration between the two areas.
Equilibrium: Particles continue to move until they are evenly distributed in the solution
(equal concentration throughout the solution). Once equilibrium is reached the
particles DO NOT STOP MOVING, they continue to move throughout the solution.
Diffusion is faster when particles are warmer, and when concentration gradient is larger.
 Label high concentration, low concentration, equilibrium in following diagram of DIFFUSION
OSMOSIS:
Movement (diffusion) of water molecules across a membrane from areas of high
concentration to low concentration
TONICITY compares the amount of water inside the cell to the amount of water outside the
cell. This lets us predict if water will move in or out of a cell in different solutions.
(dots = solute,
i.e. salt)
Sol’n
Hypotonic Solution:
Cell
Sol’n
Cell
The solution has more water molecules and less solute molecules
than the cell, water will move (into, out of) the cell and the cell will
_________________________________________. The cell is _________tonic to the
solution.
Isotonic Solution:
The solution has same number of water molecules and solute
molecules as the cell. We say the solution is isotonic to the cell. The
solutions are in ________________________ = no net movement of water or
solute molecules. The cell is _________tonic to the solution.
Hypertonic:
The solution has less water molecules and more solute molecules
than the cell . We say the solution is hypertonic to cell. Because of
osmosis, water will move (into, out of) the cell and the cell will
_________________________________________. The cell is ___________tonic to the
solution.
 Draw large arrows indicating the movement of water molecules in each of the diagrams above.
FACILITATED DIFFUSION: Passive transport of molecules that cannot diffuse across the
membrane on their own because they are too large (i.e. glucose) to diffuse through the
membrane, or because they are charged (ions like Na+ or K+) and are repelled by the cell
membrane’s hydrophobic tails.
• In facilitated diffusion molecules still move down
the concentration gradient (from areas of high
concentration to low concentration) so NO ENERGY
IS REQUIRED.
• Transport proteins help move the molecules
across.
• There are 2 types of proteins: carrier and
channel proteins
Carrier proteins move large molecules like glucose that are too big to diffuse through the cell
membrane. Carrier proteins recognize specific molecules, bond to them, and then carry them across
the cell membrane.
Channel proteins form water filled pores that allow charged particles (ions) to move in and out
of cell, i.e. Na+ , K+ .
Assignment: Answer the following questions
1) How does the particle model of matter help to explain the process of diffusion?
2) A student has two beakers, each containing one litre of water. She dissolves 10 g
sugar in beaker A, and 50 g sugar in beaker B. She then removes 500 mL of the
solution from beaker A and places it inside a bag made of dialysis tubing (a manmade semipermeable membrane). She immerses the bag in 500 mL of the solution
from beaker B.
(a) Which solution has the higher solute
concentration? Is this solution hyper-,
hypo, or iso-tonic to the dialysis tubing
bag?
(b) Will osmosis occur? If so, in which
direction?
3) A raisin was left overnight in a dish of apple juice. The next day the raisin was
swollen.
(a) Was the apple juice hypertonic, hypotonic, or isotonic relative to the inside of
the raisin? Explain.
(b) Illustrate what happened to the raisin using circles () to represent water
molecules, triangles () to represent sugar molecules, and arrows () to
show the direction of molecule movement.
4. Imagine that you have been given two solutions of unknown concentrations and a piece of dialysis
tubing. Devise a way to experimentally determine which solution has the higher solute
concentration.
5. Some organisms live in shallow ponds that dry up after a few weeks of hot, dry weather. This
means that the concentration of solutes in the water will change. How will this affect the cells of
organisms living in the ponds?
 Osmosis Lab: Potato Sailors
ACTIVE TRANSPORT: REQUIRES ENERGY (ATP)
In ACTIVE TRANSPORT molecules move AGAINST the concentration gradient– from areas of low
concentration to high concentration. Molecules do not move this way
naturally so active transport REQUIRES ENERGY (ATP).
Active transport is used to maintain specific
internal environments in the cell and uses
specialized transport proteins and protein
pumps found in the membrane. A good example
of active transport is in nerve cell transmissions.
ENDOCYTOSIS/EXOCYTOSIS
ENDOCYTOSIS and EXOCYTOSIS are used when the cell needs to take in or expel substances that
are too large for passive or active transport.
Endocytosis: Cell membrane forms a pocket around the
substance the cell wants to take in. The membrane closes
off and forms a vesicle which transports the contents inside
the cell to specific parts of the cell.
• 2 types of endocytosis:
1. phagocytosis: takes in large solid particles
2. pinocytosis: takes in small fluid droplets
Exocytosis: In exocytosis the materials that are stored in vesicles and vacuoles are released outside
the cell. The vesicle fuses with the cell membrane and the particles are released outside of the cell.
 Test your cell transport knowledge
http://www.teachersdomain.org/asset/tdc02_int_membraneweb/
ARTIFICIAL SEMI-PERMEABLE MEMBRANES (DIALYSIS MEMBRANES) AT WORK: Reverse
Osmosis, Transdermal Patches, Kidney Dialysis)
A variety of technological and medical applications use diffusion and selective transport
across membranes.  Read pg. 306 or paragraphs below.
WATER PURIFICATION using REVERSE OSMOSIS. Pressure is used to force contaminated water
through an artificial membrane containing very fine pores. The pores are large enough to allow
water to pass through. Larger particles, such as bacteria, salts, and other dissolved molecules, cannot
pass through. The water collected on the other side of the membrane contains far fewer impurities
than before being filtered. Reverse osmosis filtration systems, are commonly used in Canada to
purify drinking water.
Transdermal Patch
TRANSDERMAL PATCHES ALLOW CONTROLLED DELIVERY OF MEDICATIONS: Medications can
be placed in a flat transdermal patch that sticks to the skin. A semi-permeable lining the inner
surface of the patch allows the drugs to diffuse out of the patch at a slow, constant rate. These
medications include nicotine for help in quitting smoking, drugs to prevent motion sickness, pain
reducers and hormones to correct hormone imbalances.
KIDNEY DIALYSIS: Wastes that accumulate in the blood must be eliminated. But valuable
substances, such as proteins, glucose, amino acids, and certain ions, must be retained. The kidneys
filter the blood and regulate its solute and water content. Damaged kidneys do not filter the blood
properly and wastes can build up to toxic, even fatal, levels. Patients with failing kidneys must
receive a kidney transplant, or be treated by filtering their blood through an artificial membrane.
In kidney dialysis, the patient’s blood is pumped
through tubing made from a synthetic, semipermeable membrane. The membrane, called
dialysis tubing, is immersed in a salt solution with a
concentration similar to blood, but which does not
contain wastes. Pores in the tubing allow small
dissolved waste molecules to diffuse out of the blood
while retaining large proteins and blood cells.
Because salts and water are in equilibrium between
the blood and salt solution that bathes the tubing,
there is no loss of salts and water from the blood.
ASSIGNMENT
 Complete the worksheet “ Types of Transport Across Cell Membranes”
 Answer the following questions:
1. What is reverse osmosis, what is it used for and how does it work?
2a) Briefly explain how a dialysis membrane is used in kidney dialysis to filter the blood of patients
with kidney failure.
2b) In kidney dialysis, it is essential for the dialysis tubing to (a) have pores of the right size and (b)
be immersed in a solution with the right solute concentration. Explain how problems with each of
these two conditions might affect the filtering of a patient’s blood.
3. What is a transdermal patch, how does it work and what is it used for?
4. Scientists who study cell membranes often work with membranes from which the proteins have
been removed.
(a) Explain how the function of the protein-free membranes would differ from
regular cell membranes.
(b) How could you use a protein-free membrane to investigate the functions of the
missing proteins?
5. Name the type of transport and cell structures that would most likely be used to move the
following materials into or out of a cell:
a) bacterial cells
b) carbon dioxide
c) water
d) sodium ion
6. A cell is immersed in a solution with the same solute concentration as the fluid filling the cell.
Suddenly, active transport proteins in the cell membrane start working, and the cell begins to shrink.
What did the active transport proteins do? Why did their activity cause the cell volume to change?
7. Cystic fibrosis is caused by a mutation in a gene called the cystic fibrosis transmembrane
conductance regulator (CFTR). CFTR codes for a channel protein. Scinetists conducted an
experiment to identify which ion(s) the CFTR channel protein would transport. The researchers
compared cytoplasmic levels of different ions between normal cells and cystic fibrosis cells.
Interpret the results below and give a possible explanation for them.
Cytoplasmic ion concentration (mmol/dL)
Ions
Normal CFTR
Cystic fibrosis CFTR
Mg2+
0.02
0.02
Na+
0.05
1.55
Cl-
1.2
0.001