Osmosis Diffusion

Osmosis Diffusion - Osmosis
&
Diffusion
...

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Unformatted text preview: Osmosis
&
Diffusion
 Diffusion
 Definition
­
The
movement
of
molecules
in
a
liquid
or
a
gas
from
an
area
of
higher
 concentration
to
an
area
of
lower
concentration,
caused
solely
as
a
result
of
their
 random
thermal
motion:
the
different
concentrations
gradually
“average
out”.
 Factors
Affecting
Diffusion
Rate
 1) Temperature
–
The
higher
the
temperature,
the
greater
the
speed
of
 molecular
movement
and
hence
the
faster
the
rate
of
diffusion.
 2) Mass
of
the
Molecule
–
Larger
molecules
have
a
slower
speed
(at
a
given
 temperature)
than
smaller
molecules,
and
thus
diffuse
more
slowly.
 3) Surface
Area
–
The
greater
the
surface
area
between
two
regions,
the
greater
 the
space
available
for
diffusion
and
the
higher
the
rate
of
diffusion.
 4) Medium
–
Molecules
diffuse
more
rapidly
in
air
than
in
water
because
of
less
 frequent
collisions.

Similarly
when
a
membrane
is
involved
in
diffusion,
its
 chemical
composition
affects
the
rate
of
diffusion
 Types
of
Diffusion
 Diffusion
Through
Membranes
 ‐ ‐ Non‐polar
molecules
diffuse
rapidly
through
cell
membranes
because
they
 can
dissolve
in
the
non‐polar
regions
of
the
cell
membrane.
 o Non‐Polar
Molecules
 Oxygen

 Carbon
dioxide
 Fatty
acids
 Steroid
hormones
 Polar
molecules
have
a
much
lower
lipid
solubility
so
they
diffuse
into
cells
 very
slowly
or
not
at
all
 o Organic
molecules
that
make
up
the
intermediate
stages
of
various
 metabolic
pathways
are
ionized
or
polar
molecules
 Diffusion
Through
Protein
Channels
 ‐ ‐ Integral
membranes
can
span
the
lipid
bilayer,
forming
ion
channels
that
 allow
ions
such
as
sodium,
potassium
and
calcium
to
diffuse
at
a
rate
much
 faster
than
what
would
be
predicted
based
on
their
membrane
solubility.
 Gated
Ion
Channels
–
channels
that
can
be
opened
or
closed,
affecting
the
 permeability
of
a
membrane
to
a
specific
ion
 o Ligand‐gated
channels
–
A
channel
in
which
the
binding
of
specific
 molecules
to
channel
proteins
my
produce
an
allosteric
or
covalent
 change
in
the
shape
of
the
channel
protein,
thus
either
closing
or
 opening
the
channel.
 o Voltage‐gated
channels
–
A
channel
that
responds
to
the
membrane
 potential:
changes
in
the
membrane
potential
can
cause
movement
of
 the
charged
region
on
a
channel
protein,
altering
its
shape.
 o Mechanically‐Gated
channels
–
A
channel
which
responds
to
 physically
deforming
the
membrane
by
changing
the
conformation
of
 the
channel
proteins.
 Facilitated
Diffusion
 ‐ ‐ ‐ The
process
of
facilitated
diffusion
allows
large
molecules
that
are
not
 permeable
to
the
cell
membrane
to
move
down
the
concentration
gradient
 via
integral
membrane
proteins
called
transporters.
 Not
coupled
to
the
use
of
ATP
 Used
to
transport
glucose
across
cell
membranes
 
 Osmosis
 Definition
–
The
net
diffusion
of
a
water
across
a
membrane
from
an
area
of
low
 solute
concentration
to
an
area
of
high
solute
concentration:
again,
this
causes
the
 different
solute
concentrations
to
gradually
“average
out”.
 Terms
 Osmotic
Pressure
–
the
pressure
that
must
be
applied
to
a
solution
to
prevent
the
 net
flow
of
water
into
it.
The
greater
the
osmolarity
of
a
solution,
the
greater
its
 osmotic
pressure.
 Isotonic
–
a
solution
that
has
the
same
concentration
of
nonpenetrating
solutes
 outside
the
cell
as
inside
the
cell.

If
a
cell
is
placed
in
an
isotonic
solution
there
is
no
 change
in
cell
size.
 Hypertonic
–
a
solution
that
has
a
greater
concentration
of
nonpenetrating
solutes
 outside
the
cell
than
inside
the
cell.

If
a
cell
is
placed
in
a
hypertonic
solution,
 osmotic
pressure
will
cause
water
to
diffuse
out
of
the
cell
and
the
cell
will
shrink.
 Hypotonic
–
a
solution
that
has
a
lower
concentration
of
nonpenetrating
solutes
 outside
the
cell
than
inside
the
cell.

If
a
cell
is
place
in
a
hypotonic
solution,
osmotic
 pressure
will
cause
water
to
diffuse
into
the
cell
and
the
cell
will
swell.
 ...
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This note was uploaded on 03/29/2012 for the course LS 2 taught by Professor Andrewa.biewener,petert.ellison,anddaniele.lieberman during the Fall '10 term at Harvard.

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