# cell membrane

``` All organisms are made of cells
 Cells are mostly liquid. Surrounding the cells is also
liquid.
*
 The cell membrane separates the cell from the liquid it
is bathed in.
 a) It allows only certain particles to enters and leave
the cell. Therefore the cell membrane is considered
Selectively Permeable
____________________
b) The cell membrane is made up of two parts:
protein channels
___________________________
lipid bilayer
____________________________
 All particles of matter--atoms or molecules are
constantly in motion.
 In liquids, the molecules randomly move.*
 In organisms, molecules are dissolved in liquids =
solutions
 Liquid mixture of 2 or
more substances.
 The substance with the
greater volume = solvent
 The substance with the
smaller volume = solute
 Concentration =
mass of solute/
volume of solution
 Concentration is similar to
density.
 Calculate the
concentration in
grams/liter for:
B) 100 grams of glucose in
2000 liters of water.
.05 grams/liter
C) 300 grams of fructose
 A) 100 grams of sucrose
in 200 liters of water.
 Set up:
100grams/200 liters =
.5g/liter
in 1200 liters of water
.25 grams/liter
D) 300 grams of dextrose
in 100 liters of water
3 grams/liter
 Particles within an organism must continuously enter
and exit the cell through the cell membrane using one
of four processes:
• Diffusion
• Osmosis
• Facilitated diffusion
• Active transport
 The movement of a substance (liquid or gas) from
areas of high concentration to areas of low
concentration.
 The motion is random --eventually all particles spread
out evenly throughout the solution = equilibrium.
 Food coloring + water
 Once equilibrium is reached, the movement of
particles continues, but it is equal in all directions.
 Solution remains in equilibrium.
 Particles remain equally spaced out.*
 The cell membrane allows many types of particles
(ions, atoms, molecules) to move in and out of the cell
by diffusion.
 But some types of molecules are not able to cross the
membrane.
 What determines whether a particle can cross the cell
membrane?
Complete Worksheet to find out!
 Design an experiment to
test the effect of the size of
a particle on its ability to
 Small particles diffuse __________
faster than large particles
across a cell membrane
•Only substances that can permeate the cell membrane
can diffuse across it.
•Diffusion occurs from areas of high concentration of
solute particles to areas of low concentration.
•The movement of particles is always taking place.
The cell expends NO ENERGY on the process of diffusion
•Diffusion
•Osmosis
•Facilitated diffusion
•Active transport
 Diffusion of water through a selectively permeable
membrane. Water diffuses from where there is less
concentration of a solute (pure water) to an area of
more concentration of a solute (water + other
substance).

 Osmosis results in equilibrium when the
concentration of the solutions is equal on both sides of
the membrane. A solution in equilibrium is also
referred to as isotonic.
 When solutions on both sides of the cell membrane do
not have equal concentration they are described as
hypotonic or hypertonic.
 Hypotonic = lower concentration of solute
 Hypertonic = higher concentration of solute
Overall Direction of Water flow
At your table: Draw a picture illustrating #1 and #2 below
and answer the questions! Use arrows to show the
movement of water.
1. What happens if blood cells are placed in a hypertonic
solution? (saltwater)*
2. What happens if blood cells are placed in a hypotonic
solution?
(distilled water)*
 Under normal bodily conditions, blood is the liquid that
surround the cells.
 Blood has the same concentration of solutes as those
inside the cell. This means that blood and cytoplasm are
isotonic
______________________
to each other.
At your table: Draw a picture illustrating #1 ,#2 and #3
below and answer the questions! Use arrows to show
the movement of water.
1) What happens if plant cells are placed in a hypertonic
solution (example: salt water)?
2) What happens if plant cells are placed in a hypotonic
solution (example: distilled water)?
3) What happens if plant cells are placed in an isotonic
solution (example: water with minerals)?
 A plant cell is filled with proteins, sugars, salts.
  The cytoplasm of plant cells is more concentrated
than fresh water
  The plant cell is hypertonic relative to freshwater
 Since freshwater is used to water plants (not blood),
the plant cells fill up with water.
 Diffusion
 Osmosis*
 Why doesn’t a plant cell burst (like a blood cell) when
placed in freshwater? (Hint: What is a MAJOR
difference between plant and animal cells?)
Cell Wall is RIGID
 In one-celled organisms the cell does not burst when
in a hypotonic solution.
 One-celled organisms have mini-pumps called
contractile vacuoles. As water enters, it is pumped out
of the cell.
*
 Because osmosis is a special type of diffusion
The cell expends NO ENERGY on osmosis
Now: Complete Worksheet on OSMOSIS
•Diffusion
•Osmosis
•Facilitated diffusion
•Active transport
 Movement of specific molecules through protein
channels in the cell membrane
 The protein channels are specific to a type of particle.
Example: glucose moves through a protein channel
that is specific to glucose.
 The movement of particles is two ways but always from
areas of high concentration (hypertonic) to areas of
low concentration (hypotonic).
 Cells use facilitated diffusion for substances such as
salt, sugars and starches*.
The cell expends no energy on facilitated diffusion.
•Diffusion
•Osmosis
•Facilitated diffusion
•Active transport
 Active Transport: Movement of material across the
cell membrane in the OPPOSITE direction of
diffusion.
 Because the flow of solute is from an area of LESS
concentration to an area of MORE concentration the
solute must be pumped by the cell*.
The cell EXPENDS ENERGY (found in molecules of
ATP) on Active Transport
 You will be assigned an article on a topic with a group
of students. Read and discuss the article with your
group and present the information to the class…as a
poster, as a play, as a song, etc.
 Topics



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Facilitated diffusion, insulin and diabetes
Diffusion of oxygen into our lungs and emphysema
Diffusion and alcohol
Pregnancy and diffusion of nutrients between mother
and fetus.
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