CELLULAR TRANSPORT
The Fluid Mosaic Model
The cell membrane is also called the
plasma membrane and is made of a
phospholipid bilayer.
The phospholipids have a
hydrophillic (water attracting) head
And two hydrophobic (water
repelling) tails.
Phospholipid
The phospholipid has a hydrophilic
(water loving) head and two
hydrophobic (water
fearing) tails.
Quiz
1) Please draw a rough sketch of a cell membrane with 20
phospholipids, 2 integral proteins and 2 peripheral proteins.
2) What does “HYDROPHOBIC”
mean?
3) What does “HYDROPHILIC “ mean?
Proteins called integral proteins go all the way through the bilayer
While peripheral proteins are only on the outside or inside of the
membrane.
Quiz
4) What is an integral protein?
5) What is a peripheral protein?
Integral proteins are also called channel proteins.
Large molecules use integral proteins
to help move across cell membranes
The plasma membrane helps a cell to maintain homeostasis, or a
relatively stable internal environment.
It does this by being semi-permeable (it lets certain molecules inside of
the cell, while keeping others out).
Quiz
6) The ability of a molecule to move across the membrane depends on what two things?
7) How does the semi-permeability of the cell membrane help it
maintain homeostasis?
Diffusion
But what determines the
direction of the traffic across the membrane?
Most solutes (or particles dissolved in
a solution) naturally want to spread
out from each other.
Diffusion
So particles want to move from areas of high concentration to areas of low concentration.
This is known as diffusion. Ex:
When you spray perfume, the perfume particles will spread out in the room.
If you drop food coloring into water, the
color will spread out.
Diffusion
The particles will keep spreading out until the concentration is the same throughout the solution.
Once the concentration is the same everywhere, the particles have
reached what we call equilibrium.
Diffusion: The movement of
molecules from an area of high
concentration to an area of low
concentration.
Diffusion
This process of diffusion is how some molecules move into and out of the cell.
Since diffusion occurs naturally, the
cell does not need to use energy and
this is called PASSIVE transport.
Quiz
8) Please define diffusion.
9) Why is diffusion a passive
process?
Osmosis
Osmosis is the diffusion of water
across a semi-permeable membrane.
It is also driven by the concentration
of particles.
Some particles cannot move across the membrane, so water moves
instead to even out the
concentration.
A solution that has a high
concentration of particles is said to be HYPERtonic
A solution that has low concentration
of particles is said to be HYPOtonic.
Solute
We refer to the molecules in the as SOLUTE.
Solute is measured in Moles (M).
A solution that is 0.8M has more solute than a solution that is 0.4M.
In this case the 0.4M solution is
Hypotonic. The 0.8M solution is
Hypertonic.
Water will move from the hypotonic solution to the hypertonic solution, until the ratio of water to particles is the same on both sides.
The solution is then said to be
ISOtonic (it has reached equilibrium).
Quiz
10) Please define “OSMOSIS.”
11) Of the 3 solutions, which is
Hypotonic and which is Hypertonic:
0.6M, 0.2M, and 1.0M
12) If a cell that has 0.2M salt is put into a beaker of water that has 0.8 M salt. Which way will the water move:
into the cell, out of the cell, or into
and out of the cell the same amount.
Facilitated Diffusion
Non-lipid materials cannot diffuse across the membrane as easily as lipid molecules.
