Is
Selectively
Permeable
Won’t Allow just
anything in or out
Waste Removal
Maintains
Homeostasis
Selective about
what crosses the
membrane
Small particles
diffuse across; Large
have to be “helped”
Balance of water ,glucose, amino
acids, lipids regardless internal
and external cell conditions.
Excess nutrients
and materials
when
concentration is
too high
*Referred to as a phospholipid bilayer (2 layers of
phospholipids) in a fluid mosaic
**Phospholipids  lipids with a phosphate head.
Phosphate
Polar heads
“love” water;
hydrophilic
Non-Polar,
lipid Tails –
“hate” water
and keep
extra water
out of the
cell;
hydrophobic

Cholesterol prevents fatty acid chains of the
phospholipids from sticking together and
collapsing the membrane!
Phospholipid
Cholesterol
Molecule




Carrier proteins will “carry” specific particles,
particularly ions, across membrane
Channel Proteins  allows small things like polar
molecules directly through the membrane
Cholesterol  Stabilizes membrane; prevents fatty
acid chains of phospholipids from sticking together
Carbohydrates  Helps cells identify each other
Channel Proteins
Carbohydrates
Cholesterol
Carrier
Proteins
Transport of Materials Across
The Plasma (Cell) Membrane
2 Kinds:
* Passive (No energy required)
*Active (Energy in the form of ATP is
Required)


Like a hollow tube.
Allows very small molecules diffuse down a
concentration gradient (high concentration to
low concentration)
**Polar molecules and charged ions can not diffuse freely
across the plasma membrane  hydrophobic nature of the
fatty acid tails
**Carrier Proteins “help”
these through the membrane
without using any ATP
** The molecule changes
the shape of protein
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_
diffusion_works.html



Osmosis – water simply diffuses across
the plasma membrane without any help
Simple Diffusion – Small molecules such
as O2 and CO2 will readily diffuse as well
Both depend on Solute Concentration!!
**Goes WITH the concentration gradient – High to low
Plasma
membrane



SOLVENT: A usually liquid substance (such as
water) that is capable of dissolving or dispersing
one or more substances. Water is the universal
solvent
SOLUTE: A substance (such as salt) that dissolves
in a solvent.
SOLUTION: The combination of a solute with a
solvent, when the solute has been evenly dissolved
in the solvent. Such as saline solution for contact
lenses

Solutions In Which Cells are in
(Extra-Cellular Fluid) can be:
Hypertonic
Hypotonic
Isotonic



Solute concentration of a solution is higher
OUTSIDE of the cell than inside cell
Causes water to diffuse OUT of the cell
The sell shrinks



Solute concentration of solution is low thus
MORE H2O!!
Causes water to diffuse INTO the cell
The cell swells


Solute concentration of solution equal to that of
cell
No net movement of water  Dynamic
Equilibrium

Things to remember:

If: It’s hypertonic OUTSIDE of the cell, the CELL
itself is considered to be hypotonic

If: It’s hypotonic OUTSIDE of the cell, the CELL
itself is considered to be hypertonic
 Water would flow from HYPO- to HYPER



Osmosis always moves a solvent in one direction
only, from a less concentrated solution to a more
concentrated solution (Hypo – to Hyper - )
As osmosis proceeds, pressure builds up on the
side of the membrane where volume has increased.
Ultimately, this pressure prevents more water
from and osmosis stops.
THUS, Osmotic Pressure of a solution is the
pressure needed to be applied to the solution in
order to STOP osmosis!!
These are cells are in a hypotonic solution
 The SOLUTION has a low osmotic pressure.
 SOLUTIONS with low
osmotic pressure have a
tendency to LOSE water
 Water enters the cells!!

These are cells in a hypertonic solutions.
 The solution OUTSIDE the cell has a high osmotic
pressure.
 Solutions with a high
osmotic pressure have a
tendency to GAIN water
 The cell itself has a LOW
osmotic pressure

Not enough pressure to stop
water from leaving (osmosis)


The cells shrink!!
The solution and the cell both have equal
osmotic pressures.
 No net movement
of water



Passive Transport
Carrier proteins “help” molecules across



Diffusion and Osmosis Crossword
Answer “Science Organizer” questions about
passive transport. Use terms we’ve used in
class; hypertonic, hypotonic, isotonic, solute,
solvent, diffusion, osmosis, concentration
gradient etc.
Use a separate sheet of paper if you run out of
room!!


In some cases, particles such as ions (charged
particles) move AGAINST the concentration
gradients going from low to high!!!
Requires Transport (carrier) proteins and ATP


In some cases, ions such as K+ (potassium ion),
must move across the membrane from LOW
concentration to HIGH concentration
Called going against the concentration gradient
http://www.wisconline.com/objects/ViewObject.aspx?ID=AP11203





Maintain pH levels
Temperature
Active and Passive Transport of particles
Water balance
Glucose balance


pH balance  Acids and bases. Remember
them???
Buffers are used  A buffer is an aqueous solution
(a chemical dissolved in water) that resists major
changes in the pH of the solution.

Acidosis occurs when acid builds up

Alkalosis occurs when bases build up

Blood maintains a pH between 7.38 and 7.42
(slightly above neutral)






An acid is basically a solution with numerous
hydrogen ions (H+)
A base is a solution with hydroxide (OH-) ions
Blood pH is regulated by the lungs and the
kidneys
Blood contains large amounts of carbonic acid,
a weak acid, and bicarbonate, a base.
If blood pH falls below 6.8 or rises above 7.8,
one can become sick or die.
The bicarbonate neutralizes excess acids in the
blood while the carbonic acid neutralizes
excess bases.


If blood temperature rises too high, blood
vessels dilate, more blood flows close to the
body surface and excess heat radiates from the
body.
If it doesn’t cool enough, the brains induces
sweating


If the blood temperature falls too low, arteries
that supply blood to the skin constrict and
warm blood is retained.
If it gets too cold, the brain activates shivering.
Each muscle tremor in shivering releases heat
energy and helps warm the body.

Monitored by cells in the pancreas

Hormones  chemicals that carry messages from
organs of your body to your cells. Work in large part
to keep the body’s natural balance in check.
 Glucagon secreted by the pancreas – RAISE blood
glucose levels
 Insulin – Helps to LOWER blood glucose levels