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Transcript
Transport Through
Cell Boundaries
Every living cell exists in a liquid
environment that it needs to
survive.
In order to understand how
water and particles move
through the cell boundaries,
we have to understand
concentration.
The cytoplasm of a cell contains
a solution of many different
substances.
The substances dissolved in the
solution are called solutes.
Measuring concentration
The amount of solute in a solution
is called the concentration.
Concentration is the mass of the
solute in a given volume of solution.
Ex. If you dissolve 12 grams of salt in 3
liters of water the concentration is
12 g/3 L = 4g/L
Passive Transport
There are 3 ways in which
particles or water move through
the cell membrane which require
no energy:
-diffusion (particles)
-osmosis (water)
-facilitated diffusion (particles)
Diffusion
Diffusion: When particles move from
an area of higher concentration to an
area of lower concentration.
(See diagram on board.)
Particles that move freely by diffusion
are small non-polar molecules.
Diffusion
Requires no energy.
When the concentration of a solute is
the same throughout a system (inside
and outside the cell), the system has
reached equilibrium.
Osmosis
Osmosis is the passing of water through
a selectively permeable membrane.
Why does water do this? Again it all has
to do with concentration.
Osmosis
Water will tend to move across
membranes until equilibrium is reached
(when the concentration is the same on
both sides of the cell membrane). This
state is called isotonic (which means
same strength).
(See diagrams on board.)
A solution outside the cell that is more
concentrated than inside the cell is
called hypertonic to the cell.
A solution outside the cell that is less
concentrated than inside the cell is
called hypotonic to the cell.
When we are talking about a solution
that is hypertonic or hypotonic, we
always assume that the solution is
outside the cell.
Osmotic Pressure
Osmotic pressure is the force required
to oppose osmosis.
Facilitated Diffusion
There are hundreds of different
protein channels that allow
particular substances to diffuse
across cell membranes. This
diffusion through protein channels
in the membrane is called
facilitated diffusion.
• In passive transport, molecules are
said to move with the concentration
gradient.
Sometimes molecules
have to move against
their concentration
gradient? How?
By using energy.
Active Transport
• Requires energy (ATP)
• May move against the
concentration gradient
Active Transport
In three different
ways, by:
- protein carrier
- endocytosis
- phagocytosis
- pinocytosis
- exocytosis
Ions requiring active
transport:
• Calcium
• Potassium
• Sodium
ATP
Adenosine-5'-triphosphate is
a multifunctional
nucleotide used by the cell
as a co-enzyme.
Carrier Proteins
• Are embedded in the cell membrane
• One molecule at a time binds to a
carrier protein, is transported through
the cell membrane and is released on
the other side of the membrane.
Taking
material
into a cell
by the in
folding of a
membrane.
Endocytosis
2 Types of Endocytoses
• PhagocytosisSolid particles are
ingested into the
cell
• Pinocytosis –
liquids taken into
the cell.
Exocytosis
Moves materials
out of the cell
The
membrane of
the vacuole
fuses with the
cell
membrane,
forcing the
contents out
of the cell.
Crash Course: Transport and Cell Membranes
Endocytosis