Membrane Structure and Transport
Plasma Membrane
 A
membrane that surrounds the cytoplasm of a
cell

the contents of the cell from the outside environment
 Regulates what
and
the cell.
Fluid Mosaic Model
 A model that describes the cell membrane as a flexible mosaic composed
of embedded
dispersed in a fluid
of
 Think of how many mosaic tiles make a complete picture.
Membrane Structure
 Composed of:

Made of amphiphatic
molecules, meaning the molecules have both a
and
non-polar portion

Helps
phospholipids
and affects fluidity

Used for
recognition
(communication/”name tag”)
Membrane Function
 To
transport
and
of the cell:
 Simple Diffusion, Osmosis, Active Transport,
Endocytosis/Exocytosis
 Adhesion
 Cell Communication
Simple Diffusion “down the concentration gradient”
 The movement of molecules from an area of their
concentration
to an area of their
concentration.
 At Equilibrium:
 Particles are
in
motion, there is just no NET
movement
 Passive Transport
 Diffusion across a biological membrane with
expenditure of
energy by the cell
Osmosis
 A
kind of passive transport
 Diffusion of
through a semi-permeable membrane from an area
of the
H2O concentration to an area of the
H2O
concentration
 Ex: Dialysis, Kidney Filtration
Tonicity
The relative
concentration of one solution compared to another
solution
 Hypotonic:

solute concentration
 Hypertonic:

solute concentration
 Isotonic:
 Solutions with
solute concentrations (it does not
necessarily mean that there is no solute)
Osmosis and Tonicity
 In osmosis, the

 “Salt sucks”
, typically H2O, moves from the:
solution to the
solution.
Cell Physiology and Tonicity
 Lysed: In a
solution, the blood cell
to intake of water.
 Shriveled: In a
solution, the blood cell will
shrivel due to loss of water.
or burst due
or
Cell Physiology and Tonicity

: When placed in a
solution, the plant cell’s
vacuoles
with water and develop a
pressure.

: When placed in an
solution, the cell will
neither gain nor lose water.

: When placed in a
solution, the cell’s
vacuoles will
water and the cytoplasm will shrink (
).
Selective Permeability
 Simple Diffusion
 Facilitated Diffusion (
)

Active Transport
Facilitated Diffusion
 Passive Transport:

expenditure of energy
 Movement of particles (ions and polar molecules)
a
concentration gradient via a
that is embedded in
a plasma membrane
Active Transport
 Requires expenditure of energy in the form of
 Typically, involves movement of solutes
gradient, but not always
 Requires a transport protein
 The sodium/potassium pump is an example
(
)
the concentration
Endocytosis
 An
process for the movement of materials
cell via membranous vesicles.
 2 Types:

cytosis
 Cell “
”

cytosis
 Cell “
”
Exocytosis
 An
process for the movement of materials
of a cell via membranous vesicles (example: hormones)
a