Plasma Membrane &
Cellular Transport
http://www.i-sup2008.org/images/venue_transport.jpg
Cell Transport
A cell has to move food and wastes into and out
of the cell. Materials must move through the
plasma membrane which maintains
homeostasis in the cell.
food
food
waste
waste
waste
waste
food
food
Cell Transport
The Plasma Membrane surrounds the cell. How
does it work?
Plasma Membrane
Boundary between the cell and its environment
1. Allows nutrients into the cell
2. Removes wastes and excess materials
3. Maintains homeostasis: a stable internal
environment
Plasma Membrane
How does it work?
1. Semi-permeable: only allows some
molecules in the cell, keeps others out
http://media3.washingtonpost.com/wpdyn/content/photo/2006/10/15/PH2006101500491.jpg
Plasma Membrane
2. Fluid Mosaic Model: membrane is flexible,
made of many pieces working together
http://www.youtube.com/watch?v=Qqsf_UJcfBc
Plasma Membrane
3. Phospholipid Bilayer: membrane is 2 layers,
made of phosphates and fats (lipids) with
proteins mixed in
Plasma Membrane Parts
Phosphate heads – hydrophilic (like water), outside
and inside membrane
Fatty Acid Tails – hydrophobic (fear water), inside
membrane, like OREO cream
Cholesterol – prevents fats from sticking together,
stabilize membrane
Transport proteins – move molecules into and out
of cell
Identification proteins – outside cell, “nametag”
Support proteins – inside cell for framework,
“skeleton”
Membrane Model Lab
Purpose: What are the parts of a plasma membrane?
Arrange your membrane parts to look like this section
of membrane. On your paper towel, label the inside
and outside of the cell.
Marshmallows = phosphates
Gummy Worms / Twizzlers= proteins
Toothpicks = fatty acid chains
Candy Corn= cholesterol
#3
#1
Inside cell
#2 Outside cell
Membrane Model Lab
1. Draw model in your notes. Label proteins,
lipids, phosphates, cholesterol, outside and
inside of cell, hydrophobic portion.
2. What type of protein is each of the
numbered arrows? How is each used?
3. Why are the marshmallows not attached to
each other?
4. Where would cholesterol be found in the
membrane? Why?
Model a membrane
1. Using bubble solution, show a flexible
membrane. Why is this important?
2. Form an opening in the membrane with a
circle of string, pop the inside. This is how a
channel protein works. Move it around in
the membrane. (Membrane is fluid)
3. What happens when a “wand” is pushed
through the membrane?
Passive Transport
NO ENERGY required, moves molecules from
high concentration to low concentration
1. Osmosis
movement of water across a membrane
http://schools.moe.edu.sg/chijsjc/Biology/Diffusion&osmosis/osmosis.gif
Passive Transport – no energy required
2. Diffusion
molecules move from an area of high
concentration to low concentration
http://iweb.tntech.edu/mcaprio/diffusion-animated.gif
Passive Transport – no energy required
3. Facilitated Diffusion
movement of molecules from high
concentration to low concentration with help of
membrane transport proteins
Low concentration
High concentration
http://www.biology.arizona.edu/CELL_BIO/problem_sets/membranes/graphics/CHANNEL.GIF
Passive Transport
Active Transport
Requires energy
Moves molecules against concentration gradient
Moves from area of low concentration to high
concentration
Examples:
gated channels, sodium/potassium pumps,
endocytosis, exocytosis
Active Transport
Endocytosis and Exocytosis
http://media-2.web.britannica.com/eb-media/38/8038-004-A29C9C02.jpg
Active Transport
Example: Paramecium uses contractile vacuole
to regulate water content
http://www.cartage.org.lb/en/themes/sciences/BotanicalSciences/MajorDivisions/KingdomPr
otista/Protists/paramecium.gif
Active Transport
Modeling Diffusion Lab
1. Make simulated agar cells in 3x3cm, 2x2cm, and
1x1cm cubes.
2. Immerse the cells in a “food” solution of sodium
hydroxide (NaOH) for 10 minutes.
3. Pour off NaOH solution, rinse cells.
4. Cut cells in half. Measure from outside in and
record distance NaOH penetrated into cell.
Cell Side Size (cm)
Distance
Penetrated (cm)
Distance Not
Penetrated (cm)
Diffusion Lab Questions
1. Which cell is most efficient in moving
materials throughout its entire structure?
2. What are the limitations to cell size?
3. How does the surface area relate to the
volume of each cell?
Surface area = 6 x (side)2
Volume = length x width x height (cm3)
Gummy Bear Lab
Day
Length
(mm)
Width (mm)
Depth
(mm)
Volume
(mm3)
Mass
(grams)
1
2
3
Day 1: Measure L,W,D of bear. Place in a plastic cup and
mass the bear and cup. Record in table. Fill ½ full with
distilled water. Initial your cup. Place on tray. Write
hypothesis of what will happen to bear overnight.
Day 2: Pour out water. Measure volume. Mass bear and
cup. Record. Fill ½ full with salt water. Write
hypothesis of what will happen to bear overnight.
Day 3: Pour out water. Measure mass of bear and cup.
Write statement of what happened to bear from day 1
to day 3.
Solutions
Isotonic solution – equal concentrations of
solute (salt) inside and outside cell
http://www.biologycorner.com/resources/isotonic.gif
Solutions
Hypotonic solution – less solute in solution, more
solute in cell, WATER FOLLOWS SALT, cells swell
http://www.biologycorner.com/resources/hypotonic.gif
Solutions
Hypertonic solution – more solute in solution,
less solute in cell, WATER FOLLOWS SALT, cells
shrink
http://www.biologycorner.com/resources/hypertonic.gif
Osmosis in blood cells
http://aryatiabdul.files.wordpress.com/2008/07/osmosis2.gif
Solutions – how transport affects
animals and plants
http://kentsimmons.uwinnipeg.ca/cm1504/Image130.gif
Transport in Plants
Healthy
plant cells
are crisp
due to
TURGOR
PRESSURE
Wilted plant
cells are
flaccid due to
lack of water
Transport, again
Draw this in your notes
Over time, water level changes to make water
concentrations equal on both sides of tube
TIME
Diffusion of water across a semi-permeable membrane = osmosis