Transcript Cellular Transport

Cellular Transport
8.1 Notes
I. Plasma Membrane
maintains homeostasis in
the cell
Controls the passage of
materials into and out
of the cell.
Plasma membrane is
selectively permeable
because it allows some
materials to pass
through while keeping
others out
Plasma Membrane
II. Diffusion
DIFFUSION: All objects in
motion have energy called
kinetic energy.
A. Process of diffusion
1. Diffusion – net movement of
particles from an area of
higher concentration to
Diffusion
an area of lower concentration.
Example: perfume
Diffusion results from random
movement of particles.
B. The selectivity of
membranes1. Only molecules of water,
oxygen, nitrogen, carbon
dioxide, and a few other small,
nonpolar molecules can
diffuse directly across the
lipid bilayer.
III. Osmosis
How osmosis occurs
1. Osmosis is the diffusion of
water molecules through a
selectively permeable
Osmosis
Osmosis
membrane from an area of
higher water concentration to
an area of lower water
concentration.
2. Unequal distribution of
particles, called a
concentration gradient, is
one factor that controls
osmosis.
B. Cells in an isotonic solution1. Isotonic solution – the
concentration of dissolved
substances (solute) in the
solution is the same as the
concentration of dissolved
substances inside the cell;
therefore, the concentration of
water in the solution is the
same as the concentration of
water inside the cell.
2. Cells in an isotonic solution
do not experience osmosis
and they retain their normal
shape.
Isotonic Solution
Most solutions (immunizations
your doctor gives) are isotonic
so that cells are not damaged
by the loss or gain of water.
C. Cells in a hypotonic solution-
1. Hypotonic solution –
concentration of dissolved
substances is lower in the
solution outside the cell
than the concentration
inside the cell; therefore,
there is more water outside
the cell than inside.
2. In a hypotonic solution, water
enters a cell by osmosis.
3. The cell swells.
4. Turgor pressure, which is the
pressure inside a cell,
increases in a hypotonic
solution.
Hypotonic Solution
Hypotonic
Solution
5. The rigid property, due to the
cell wall, produced by turgor
pressure gives plant cells their
shape and support. As the
pressure increases inside the cell,
the plasma membrane is pressed
against the cell wall. They do not
burst when placed in a hypotonic
solution. Instead of bursting, the
plant cell becomes more firm.
6. Animal cells in a hypotonic
solution may swell and burst.
(The plasma membrane may
be unable to withstand the
pressure.)
7. An adaptation that some
animals have to keep their cells
from rupturing is called a
contractile vacuole.
How do they work? Like medicine
droppers; they collect excess
water from the cell, contract,
and squeeze water out.
D. Cells in a hypertonic solution
1. Hypertonic solution –
concentration of dissolved
substances outside the cell is
higher than the concentration
inside the cell; therefore, there is
less water outside the cell than
inside.
2. In a hypertonic solution, water
leaves a cell by osmosis.
3. The cell shrinks.
4. Turgor pressure decreases
when a cell is placed in a
hypertonic solution.
Hypertonic Solution
5. Plant cells lose water in a
hypertonic solution, mainly from
the central vacuole. The plasma
membrane and cytoplasm shrink
away from the cell wall. The
process in which plants wilt due to
a loss of turgor pressure in a
hypertonic solution is called
plasmolysis.
Plasmolysis
6. Animal cells will shrivel in a
hypertonic solution because of
decreased pressure.
7. You should not salt meat before
cooking because the salt forms a
hypertonic solution on the meat’s
surface; water inside the meat
cells diffuse out, leaving the
cooked meat dry and tough.
IV. Passive Transport – Movement
of particles across membranes by
diffusion.
A. Passive transport requires NO
energy.
B. Examples of passive transport
include: diffusion, osmosis,
facilitated diffusion
C. Passive transport by proteins1. Transport proteins are
embedded in the lipid bilayer of
the plasma membrane, and they
allow needed substances or
waste materials to move across
the plasma membrane.
2. Facilitated diffusion is the
passive transport of materials
across the plasma membrane with
the aid of transport proteins.
Transport proteins provide
convenient openings for particles
(ions) to pass through.
Passive and Facilitated Diffusion
3. Facilitated diffusion helps move
sugars and amino acids across
membranes.
V. Active transport – Movement of
particles across membranes from
areas of lower concentrations (the
environment) to higher
concentrations (inside the cell);
Moves against a concentration
gradient
Active Transport
A. Active transport requires
energy.
B. Examples of active transport:
endocytosis, exocytosis,
sodium-potassium pump
C. Endocytosis –process by
which a cell surrounds & takes
in material from its
environment.
This material does not pass
directly through the
membrane. Instead, it is
engulfed and enclosed by a
portion of the cell’s plasma
membrane. That portion of the
membrane then breaks away,
and the resulting vacuole with
its contents moves inside the
cell.
(Example: Amoebas feed by
phagocytosis, which is an
example of endocytosis.)
D. Exocytosis – expulsion or
secretion of materials from a cell.
Cells use exocytosis to expel
wastes, such as indigestible
particles, from the interior to the
exterior environment. Substances
such as hormones are secreted by
this process.
Exocytosis
E. Sodium-Potassium Pumps
a. Uses energy stored in the
form of ATP
b. Moves sodium ions (Na+)
out through the cell’s
membrane
c. Help to transport food
particles into cells
d. Pumps potassium ions (K+) in
e. Example: Nerve cells use the
differences in sodium and
potassium ion concentrations
produced by sodium-potassium
pumps to send signals
throughout the body, like
electrical signals passing over
wires.