TRANSPORT IN CELLS
Cell Membrane
• Once believed to be a covering like a balloon.
• “Gate keeper” allows materials in and out
while maintaining the integrity of the cell.
• Actually composed of many different
molecules
Phospholipids
Main structural component of cell membrane
Proteins
Proteins embedded in membrane aid in the
transport of large molecules and energy.
Carbohydrates
Function to help cells recognize other cells, hold
proteins in place and provide energy for repair
Fluid Mosaic Model
All the molecules of the cell membrane are in
constant motion.
What benefit does the motion serve?
http://www.dnatube.com/video/360/Fluid-MosaicModel
Cell Size is related to transport. If the surface area to
volume increases to much then materials will not be
able to move in or out fast enough.
A small cell is a more efficient cell.
PASSIVE TRANSPORT
MOVEMENT OF MOLECULES INTO OR OUT OF A
CELL WITHOUT THE CELL USING ANY ENERGY
MOLECULES MOVE DUE TO THEIR OWN KINETIC
ENERGY AS LONG AS THERE IS A
CONCENTRATION GRADIENT PRESENT
DIFFUSION
Movement of any molecule
from an area of greater concentration
to an area of lesser concentration
down a concentration gradient
toward equilibrium.
Important Points…
• All states of matter can diffuse.
– solids, liquids, gases
• Diffusion can take place across a membrane
– O2 and CO2 diffuse across cell membrane
• Factors that affect rate of diffusion
– Heat: warm materials diffuse faster
– Motion: stirring or shaking increases diffusion
– Surface area: greater surface area faster diffusion
– Volume: smaller space faster diffusion
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chap
ter2/animation__how_diffusion_works.html
FACILITATED DIFFUSION
Transport of molecules across a membrane with the
help of cell membrane proteins.
Since the molecules are still moving down a
concentration gradient, no energy is required.
WHAT MOLECULES NEED HELP?
Polar molecules and ions are diffused across by
channel proteins. WHY?
Because they are polar and dissolve in water and can’t
get past the hydrophobic ends of the membrane.
Large molecules like amino acids and glucose are
diffused across with the help of carrier proteins.
OSMOSIS
Very similar to diffusion with two exceptions:
MOVEMENT OF WATER
ACROSS A SEMI-PERMEABLE MEMBRANE
From an area of greater concentration
Down a concentration gradient
Toward equilibrium
MERMAID
The direction the water moves,
into or out of the cell…
depends upon how much material, or,
solute is dissolved in the water!
OK, here’s where it can get confusing!
Solutions are named based upon the amount of
dissolved solute not the amount of water…
even though it’s the water that’s moving!
HYPOTONIC: LOW SOLUTE CONCENTRATION
outside cell membrane
HIGH WATER CONCENTRATION
outside cell membrane
WATER MOVES INTO THE CELL
CAUSING IT TO SWELL, THIS IS
CALLED CYTOLYSIS, IF THE
WATER CANNOT BE
CONTROLLED THE CELL WILL
RUPTURE.
FLOWER
ISOTONIC: SOLUTE CONCENTRATION IS
EQUAL
TO WATER CONCENTRATION
INSIDE AND OUTSIDE OF CELL
WATER MOVES INTO
AND OUT OF CELL
EQUALLY, NET VOLUME IS
MAINTAINED= HOMEOSTASIS
HYPERTONIC: HIGH SOLUTE CONCENTRATION
outside cell membrane
LOW WATER CONCENTRATION
outside cell membrane
WATER MOVES OUT OF THE CELL
CAUSING IT TO SHRIVEL UP, THIS
IS CALLED PLASMOLYSIS
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chap
ter2/animation__how_osmosis_works.html
OSMOSIS PRACTICE
Environment= 75% water
Cell = 25% water
Water moves__________
Environment= 40% solute
Cell = 60% solute
Water moves__________
Environment= 30% solute
Cell = 30% solute
Water moves__________
Environment is 10% water
Cell = 90% water
Water moves__________