Cell Transport: Moving molecules
in and out of the cell
Label the following parts of your diagram
 Plasma membrane (about 6-7 nm wide)

A. Phospholipids (A1 is the phosphate head, A2 is the fatty acid tail)

F, G. Proteins
 Some have channels (G)

D. Carbohydrate
 Glycoproteins (C)
– this is a molecule where a carb is attached to a protein
 Glycolipids (B)


The is a molecule where a carb is attached to a phospholipid
E. Cholesterol
Plasma membrane
 Phospholipid
bilayer that
surrounds all
cells and certain
organelles
within the cell
Phospholipids
Hydrophilic Phosphate head
Hydrophobic Fatty acid Tails
In water what will happen?
Water on outside of cell
Water on outside of cell
Also Water on Inside of cell
Double Layer Allows:
 All hydrophobic
parts to be away
from water
 All hydrophilic parts
to be near water
Membranes are MORE than just phospholipids
Key components
The role of four key membrane components
 Phospholipids

allow only small non-polar molecules to enter
 Proteins
 Act
as transport for some larger molecules
 All transport of polar or charged molecules
 Increase contact with the water
 Cholesterol
 Fluidity
control (not too rigid, not too loose (more
cholesterol = more rigid.
The role of membrane components
 Carbohydrates
 Chains
act as “ID” tags
 help the body to
recognize whether a
cell is “self” or
“foreign”
Review of vocabulary
 Homeostasis

Maintenance of the cells internal conditions (pH, water,
temperature, size, etc)
 The main job of the cell membrane is to maintain
internal conditions!
Review of Vocabulary
 Solution
 Homogeneous
mixture
 Solute: what is dissolved (in living things this can
be glucose, amino acids, salts, etc)
 Solvent: What is the dissolver (in living things,
this is water)
What needs to enter and leave the cell
 What needs to enter the cell (what goes IN)?
 Gases
like O2, N2, CO2
 Ions
 Small
polar molecules (water)
 Polar molecules (glucose, amino acids, fatty acids,
nucleotides)
 What needs to leave the cell (OUT)?
 excess H2O, CO2, other waste products, glucose (in a leaf
cell or in an intestinal cell), ions, large polar molecules
(proteins) , N2, O2 (in the case of plant cells)
Selective Permeability
 The membrane allows some, but not all molecules into
the cell
 The membrane DOES NOT necessarily protect the cell
from “Bad things”!
http://www.youtube.com/watch?v=Pt4Ch-YW-xs
Polar molecules
like Glucose and
water
Not everything that passes through the
phospholipids of the membrane are good!
What passes through the phospholipid bilayer?
 Gases
Oxygen
(O2) and nitrogen (N2) and CO2
 http://education.seattlepi.com/kinds-molecules-can-
pass-through-plasma-membrane-through-simplediffusion-4587.html
 Sometimes things that aren’t good for us!!!!
What types require a membrane protein
 Look at the diagram (slide 25)…what cannot go through
the membrane but is required by cells?
What do cells need that CAN’T pass through the
phospholipid bilayer?
 Small polar molecules (H2O)
 Ions
(Na+, Cl-, K+, Ca++)
 Large polar molecules
(Sugars, Amino Acids)
How do these things get into the cell????
These must go through proteins to get in
 Need the proteins to “help” (facilitate)
moving the molecule into the cell or
out of the cell

http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation
.html

http://www.youtube.com/watch?v=NC8pIzNzqrc
Passive Transport
Requires no energy; molecules move from an
area of high concentration to an area of low
concentration.
Molecules “roll down the hill” to spread out
Three types of Passive Transport
 Diffusion
 Facilitated Diffusion
 Osmosis
Diffusion
 Movement of solutes from areas of high concentration
to areas of low concentration until concentrations are
equal
 Move due to a concentration gradient.
 Concentration Gradient = differences in Concentration
Diffusion – Do we need a membrane?
High Conc.
Low Conc.
Can occur without a membrane
Think of it as “spreading out”
Progression of Liquid Diffusion
http://www.youtube.com/watch?v=aVc_LEuiZ4
High Conc.
Low Conc.
The dye moves from an area of HIGH CONCENTRATION to an area of LOW concentration
(of the dye)
?
Facilitated Diffusion
 movement of solute from high concentration to low
concentration
…………..BUT requires transport protein
…………..WHY? to move molecule that are too big or polar
to get through the phospholipid bilayer
EXAMPLE:
GLUCOSE
too big for the PL
membrane
Facilitated Diffusion compared to Diffusion
 One requires “help” or facilitation to get through the
membrane
Osmosis
 A Passive Process where water moves across a cell
membrane from an area that is hypotonic (lots of water,
little solute) to an area that is hypertonic (little water, lots
of solute). THE SOLUTE DOES NOT MOVE!!!!
 PICTURE: Think of water as trying to dilute the
concentrated side to make the concentrations equal (it
can only do this if water moves, but not the solute!).
Eventually both sides are “medium”
Weak Iced Tea
Strong Iced Tea
Osmosis
 http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/ani
mation__how_osmosis_works.html
Osmosis and Tonicity
 Water will move from an area of high concentration of
WATER (low solute) to low concentration of water ( high
solute)
 Tonicity is concerned with the concentration of solute
 Water moves from LOW tonicity (high water) to HIGH
tonicity (low water)

A
B
A
B
TONICITY
 Term used to compare the concentrations (of solute) of
two solutions
 The
tonicity will determine in WHICH DIRECTION the
water flows
3 Conditions
Hypotonic
Isotonic
Hypertonic
Terms used to describe tonicity
 The solution with the higher concentration is
called Hypertonic.
 The solution with the lower concentration is
called Hypotonic
 If the concentrations are equal, they are
called Isotonic
Assume the yellow
circle is a cell. Is the
salt solution outside
the cell hypotonic,
hypertonic or isotonic
to the cell?
10% Salt Solution
20%
Salt Solution
Outside is Hypertonic
Animal cells swell and
Could break open
(CYTOLYSIS)
Plant cells exhibit
HIGH TURGOR
PRESSURE
(they like this)
Is the solution
hypotonic or
hypertonic to the
cell?
20% Salt Solution
10%
Salt Solution
?
Outside is
Hypertonic
Animal cells
shrivel. This is
called CRENATION
The cell membrane
of plant cells pulls
Away from the cell w
PLASMOLYSIS
Isotonic:
20% Salt Solution
20%
Salt Solution
Isotonic
Animal cells like this
environment
(Isotonic cell)
While the Plant
Cell is at equilibrium,
It prefers that the
environment is
hypotonic)
Crenation
Cytolysis
Comparing animal cells at different
Plasmolysis
Vs.
Turgidity in Plant cells
- Turgor pressure: Pressure that
the water INSIDE the cell puts on
the cell wall. Supports plant
http://highered.mcgrawhill.com/sites/9834092339/student_view0/cha
pter38/animation_-_osmosis.html
A
B
A
B
Active Transport
Cell must use energy to force molecules to
move across the membrane from a low
concentration to a high concentration.
Usually used to move ion and since ions can
not go through the phospholipids requires a
transport protein . Usually moving from a
low to high concentration
Active Transport:
Vesicle transport: when molecules are
too big for the proteins!
EXOCYTOSIS – moves molecules
OUT of the cell
ENDOCYTOSIS – moves
molecules INTO the cell.
Vesicle Transport
 Vesicle transport is
different from Diffusion,
Osmosis, facilitated
diffusion and active
transport
 HOW IS IT DIFFERENT?
 Moves
large quantities
(many molecules) at a
time.
 Requires
 Must
energy
package the
molecules in a vesicle
(efficient transport)
Vesicle Transport
 Making a vesicle requires the cell to exert energy in the form
of ATP.
 Concentration differences don’t matter
Vesicle transport is named based on the direction the vesicle is
moving (into or out of the cell)
 Moving materials out of a cell in a vesicle is called exocytosis.
Moving materials into the cell is called endocytosis.
Exocytosis – Bulk Transport out of cell
Way of releasing large quantities of stuff from the
cell including : Hormones, mucus and cell wastes
NEEDS ATP
Bulk transport into cell
PHAGOCYTOSIS
(SOLIDS)
Endocytosis
PINOCYTOSIS
(LIQUIDS)
PHAGOCYTOSIS: “CELL EATING”
PROTEINS, BACTERIA, DEAD CELLS
ARE ENCLOSED IN A PL. MEMB. SAC.
NEEDS ATP
PINOCYTOSIS: “Cell Drinking”
Plasma membrane “sinks” below a liquid
containing small solutes and the sides “fuse”
creating a vesicle
OCCURS IN MOST CELLS, EXP: KIDNEYS AND
INTESTINES
 REVIEW of CELL STRUCTURES AND FUNCTIONS
(Eukaryotes)

Hperlink for Cell Structure and Function