Transcript Powerpoint

TRANSPORT AND
THE PLASMA
MEMBRANE
NELSON 11
CHAPTER 2
CELL TRANSPORT
All cells must exchange materials with
their environment to maintain
homeostasis. The cell can use a variety of
methods to move things from the internal
environment to the external environment
and vice versa.
 There are two main types of cell transport;
passive transport and active transport.

CELL TRANSPORT
PASSIVE TRANSPORT

Passive transport is
the movement of
materials across the
plasma membrane
without the use of
cellular energy and it
includes diffusion,
osmosis, and
facilitated diffusion.
DIFFUSION

The random
movement of
molecules from an
area of high
concentration to an
area of low
concentration.
BROWNIAN MOTION
This can be defined as the random
movement of molecules.
 Molecules will move about randomly in a
solution or gas and collide with one
another with equal frequency.
 This random motion is the reason why
molecules move from an area of high
concentration to one of low concentration.

CONCENTRATION GRADIENT

The difference in
concentration
between a region of
high concentration
and a region of low
concentration.
EQUILIBRIUM


A condition in which all
acting influences are
balanced resulting in a
stable environment.
Once equilibrium has
been reached there are
now as many molecules
moving into an area as
there are moving out.
DIFFUSION AND THE
PLASMA MEMBRANE
Particles that are soluble in lipids or small
enough to fit through the spaces between
the polar heads will diffuse across a
plasma membrane IF a concentration
gradient exists.
 Diffusion will continue until equilibrium is
reached.

OSMOSIS



The diffusion of water
across a semi-permeable
membrane from an area
of high concentration to
one of low.
Water will also move as a
result of osmotic pressure
from high to low.
In the image on the right
water is represented by
the small red dots.
OSMOTIC BALANCE


Water molecules are
small and can diffuse
easily across the plasma
membrane. The direction
of osmosis will depend on
the concentration
gradient.
When equilibrium is
reached in osmosis it is
known as osmotic
balance.
EFFECTS OF OSMOSIS
Cells will react differently to different
solutions.
 Plant cells and animal cells will also react
differently to different solutions.
 There are three types of solutions that
have an effect on cells; isotonic, hypotonic
and hypertonic solutions.

ISOTONIC SOLUTION


A solution where the
concentration of water
and solute molecules
outside a cell is equal to
the concentration of water
and solute molecules
inside the cell.
Isotonic solutions are the
ideal solution for cells to
be contained in. A cell
will be at equilibrium in
this solution.
HYPOTONIC SOLUTION


A solution where the
concentration of water outside
a cell is greater than that found
inside the cell. (so less
solutes)
Cells placed in this solution will
experience a net movement of
water into the cell by osmosis.
This will result in increased
pressure inside the cells.
Effects of a hypotonic solution
Animal cells cannot withstand a high
amount of osmotic pressure and the
plasma membrane will burst.
 Plant cells build up turgor pressure.
Plant cells can stand up to the pressure
due to the presence of the cell wall.
Turgor pressure helps keep a plant cell
rigid.

HYPERTONIC SOLUTION



A solution where the
concentration of water
molecules outside a cell is
lower than that found inside the
cell. (more solutes)
Cells placed in this solution will
experience a net movement of
water out of the cell by
osmosis.
The cytoplasm of the cell will
shrink due to the loss of water.
The shrinking of the cytoplasm
in cells is known as
plasmolysis.
Effect of Solutions on Plant and
Animal Cells
FACILITATED DIFFUSION

Many particles needed by the cell are too large
to diffuse across the membrane on their own.
Proteins located in the plasma membrane can
act as carriers to aid or facilitate passive
transport.
FACILITATED DIFFUSION
ACTIVE TRANSPORT

Active transport is the
movement of particles
across the cell membrane
against the concentration
gradient with the use of
cellular energy and it
includes endocytosis
and exocytosis.
ACTIVE TRANSPORT



Active transport plays a very important role in
homeostasis. Many molecules needed by the
cell cannot enter the cell through passive
transport because they are too large.
The cell must use energy to move these
molecules across the plasma membrane.
There are two types of active transport;
endocytosis and exocytosis.
ENDOCYTOSIS



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Endocytosis is the process used to ingest materials and
bring them inside the cell.
Due to the fluidity of the plasma membrane it is able to
fold around materials in the external environment and
bring them inside within a small pouch called a vesicle.
Once inside the cell these vesicles often fuse with a
lysosome that contains the digestive enzymes needed to
break down the ingested molecules.
There are two types of endocytosis; pinocytosis and
phagocytosis.
PINOCYTOSIS


Pinocytosis involves
liquid droplets being
engulfed by the cell.
For example, the cells
in your small intestine
engulf fat droplets by
pinocytosis.
PHAGOCYTOSIS


Phagocytosis involves
solid particles being
engulfed by the cell.
For example, your
white blood cells
engulf foreign
microbes that invade
your blood stream by
phagocytosis.
EXOCYTOSIS



Exocytosis is the process used by cells to move
large molecules to the external environment.
These molecules are often waste products.
Some molecules released by exocytosis are
products that have been made by that cell and
they are needed elsewhere in the organism. For
example, our nerve cells produce transmitter
chemicals that leave the cells by exocytosis.
EXOCYTOSIS