Transcript Transportation of materials

A Cell
Cytoplasm
Mitochondrion
Nucleus
Selectively permeable cell membrane
Selective Membrane
Why do cells need to transport
materials across the cell membrane?
• Cells need to obtain various substances in
order to carry out life processes
• What are some of the substances that
they need to obtain?
• e.g. nutrients, oxygen, water, etc.
Why do cells need to transport
materials across the cell membrane?
• Cells also need to get rid of substances
that are useless and harmful to them
• What are some of the substances that
must be removed?
• e.g. carbon dioxide, metabolic wastes, etc.
Transportation of Materials
There are 3 different processes for
transporting materials in and out of a cell:
• Diffusion
• Osmosis
• Active Transport
DIFFUSION
Hi. I am Moley.
I am a gas
molecule. I am
constantly moving
around. This is
because I possess
kinetic energy.
Here I am with my
brothers and sisters.
Notice that we are all
cramped to one side of
the area. In other words,
there is a HIGH
CONCENTRATION of
molecules on the left side
of the area.
Area of High Concentration
Well, since we are
moving all the time,
we will eventually
spread out to cover
the rest of the area.
That is, we will move
along the
concentration gradient,
from an area of HIGH
CONCENTRATION to
an area of LOW
CONCENTRAION!
CONCENTRATION GRADIENT
Area of High Concentration
Area of Low Concentration
EQUILIBRIUM – Particles are evenly distributed
Diffusion
• Diffusion is the net movement of the
particles of a substance from a region
of higher concentration to a region of
lower concentration
• It is a passive process and no
external energy is required
• It can occur in a liquid or gaseous
medium
We can also pass
through a
selectively
permeable
membrane because
we are so small!!!
Area of High Concentration
CONCENTRATION GRADIENT
Area of High Concentration
Area of Low Concentration
CONCENTRATION GRADIENT
Area of High Concentration
Area of Low Concentration
EQUILIBRIUM – Particles are evenly distributed
Diffusion
A small amount of ink is
added to a beaker of
water. What do you
think will happen?
Diffusion
- Can you explain the
color change?
- Do you think the ink
particles will continue
to move even after they
have spread out evenly
in the water?
- Will the result be the
same if this is carried out
in hot water?
Factors Affecting
the Rate of Diffusion
• Molecular size – will small or large particles
diffuse faster?
• Concentration gradient – will diffusion occur
more rapidly if there is a large or small
difference in concentration between two
regions?
• Distance of diffusion – will diffusion be
faster or slower if the distance of
diffusion is long?
Factors Affecting
the Rate of Diffusion
• Medium – is diffusion faster in a
gaseous or liquid medium?
• Surface area – will diffusion occur
faster in a large or small surface
area?
Factors Affecting
the Rate of Diffusion
Factors Affecting
the Rate of Diffusion
• Medium – is diffusion faster in
gaseous or liquid medium?
• Surface area – will diffusion occur
faster in a large or small surface
area?
• Temperature – will diffusion be faster
under high or low temperature?
Examples of Diffusion
• Exchange of gases (i.e. oxygen and
carbon dioxide) in the air sacs of
lungs
• Absorption of digested food in the gut
• The detection of smell e.g. perfume
• The movement of carbon dioxide
through the stomata during
photosynthesis
OSMOSIS
Osmosis
• Osmosis is the net movement (i.e.
diffusion) of water molecules from a
less concentrated solution (with a
higher water potential) to a more
concentrated solution (with a lower
water potential) through a selectively
permeable membrane
This is a water molecule
This is a sucrose molecule
Region A – Dilute sucrose solution
Region B – Concentrated sucrose solution
This is a water molecule
This is a sucrose molecule
Region A – Dilute sucrose solution
Region B – Concentrated sucrose solution
INVESTIGATION #1
Illustration of osmosis using a
dialysis tubing
Introduction to Investigation
• In this experiment, osmosis will be
demonstrated by using a dialysis
tubing, which acts as a selectively
permeable membrane
Procedure
• Please refer
to pages 83
and 84 in
your ARISTO
text book
Results Table
Time
After 5 minutes
After 10 minutes
After 15 minutes
After 20 minutes
Distance from
initial mark
Distance risen by the
sucrose solution
Plot the data on a graph
What will the graph look like?
Time (Mins.)
Can you predict the results in the
following situations?
Treatment
Inside tubing
In beaker
Change in
level
1
Sucrose
solution
Distilled
water
Rises
2
Distilled water
Sucrose
solution
?
3
Concentrated
sucrose solution
Distilled
water
?
4
Distilled water
Distilled
water
?
Variations to the Experiment
• Instead of dialysis tubing, we can
also use living tissues, such as
potatoes, to illustrate the
process of osmosis
Variations to the Experiment
What do you think is the result of this experiment?
Water Potential
• Water potential is represented by the
Greek letter “psi”
• A measure of the free energy of water or
the energy for water molecules in a solution
to move about
• Water potential is dependent on the
proportion of free water molecules in a
solution (free water molecules = water
molecules that are not engaged with other
molecules)
Water Potential
• The water potential of pure water is
defined as zero
• If solutes are dissolved in water, the
proportion of free water molecules will
decrease. The water potential will
also decrease to less than zero
Water Potential
• A concentrated solution has a lower
water potential than a dilute solution
• The net movement of water molecules
is always from a region of HIGHER
water potential to a region of LOWER
water potential
Tonicity
• Osmotic movements across cell
membranes are affected by the
tonicity: the relative concentrations
of solutes in 2 fluids, e.g. the
cytoplasm of a cell and the fluid
outside the cell
Tonicity
• We are going to use a red blood cell
as an example. On a piece of paper,
draw three beakers. In each of the
beaker, add a RBC. We will discuss
what happen to the RBC when it is put
into 3 different types of solutions of
different concentrations of sodium
chloride (i.e. salt)
Isotonic
Salty Water
CELL
The water potential
inside the cell is the
same as that outside
the cell. There is no
net movement of water
into or out of the cell
Hypertonic
Very Salty Water
CELL
There is less water
molecules outside the
cell, and therefore the
solution outside has a
lower water potential
than that of the cell
What will happen to
the cell?
Hypotonic
Pure Water
CELL
There is more water
molecules outside the
cell, and therefore the
solution outside has a
higher water potential
than that of the cell.
What will happen to
the cell?
Effects of Osmosis on Plant Cells
Turgid Cells
Flaccid Cells
Plant cells placed in a hypertonic solution will undergo plasmolysis,
a condition where the plasma membrane pulls away from the cell wall
as the cell shrinks. The cell wall is rigid and does not shrink.
Effects of Osmosis on Animal Cells
Effects of Osmosis on Animal Cells
Effects of Osmosis on Animal Cells
Shrinking RBC
Swelling RBC
Active Transport
Active Transport
• Some solutes have a higher concentration
inside the cell than outside so they have to
cross the membrane against the
concentration gradient. These solutes need
to enter the cell by means of active
transport
• Why is this called ACTIVE transport?
Active Transport
Low concentration
outside the cell
High concentration
inside the cell
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
Cell membrane
Active Transport
What is this???
Cell membrane
Active Transport
• Active transport requires special
protein carriers. These carriers are
embedded within the cell membrane
• Active transport also requires energy
obtained from respiration
• The energy is used to change the
shape of the protein carriers so that
the molecules can attach to the
carriers for transportation
Active Transport
• The process of active transport is
useful when there is no concentration
gradient or when diffusion is too slow
for the transportation of substances
Examples of Active Transport
• Nutrients are actively transported
into the small intestine
• Substances that are useful to the
body are actively reabsorbed into the
blood vessels surrounding the kidney
tubules
• Root hairs actively absorb mineral
salts from the soil
Comparison of
Passive and Active Transport