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Diffusion and Osmosis
- A “Moving” Topic -
Another Potato Demo...
1) Send two group members to obtain:
- Two Beakers
- Dry-Erase Marker
- Triple Beam Balance
Another Potato Demo...
1) Send two group members to obtain:
- Two Beakers
- Dry-Erase Marker
- Triple Beam Balance
2) Get two slices of potato
that are approximately
the same size.
Another Potato Demo...
3) Using the balance, determine the mass of
each potato slice. Record in your table.
4) Using the dry-erase marker, label one beaker
“water” and the other one
“sugar solution.”
5) Using the beaker,
measure 100mL of water for
each beaker.
Another Potato Demo...
6) Put a piece of paper on the balance. Measure
out 30 grams of sugar and then add it to the
“sugar solution” beaker. Mix.
7) Place one potato slice in
each beaker.
8) Wait.
Passive Transport
• Cells maintain stable internal conditions by
controlling what enters and leaves the cell.
Passive Transport
• Cells maintain stable internal conditions by
controlling what enters and leaves the cell.
What word do we use to describe
“maintaining stable internal conditions?”
(think 7 characteristics of life)
Passive Transport
• Cells maintain stable internal conditions by
controlling what enters and leaves the cell.
Homeostasis!
Passive Transport
• Cells maintain stable internal conditions by
controlling what enters and leaves the cell.
Homeostasis!
• Some substances can cross the cell
membrane without the cell having to use
any energy.
• This is known as passive transport.
Passive Transport
• There are three types of passive transport:
1) Diffusion
2) Osmosis
3) Facilitated Diffusion
Diffusion
• Diffusion is the simplest type of passive
transport.
Diffusion
• Diffusion is the simplest type of passive
transport.
• Diffusion – the movement of molecules
from an area of high concentration to an
area of low concentration.
Diffusion
• Diffusion is the simplest type of passive
transport.
• Diffusion – the movement of molecules
from an area of high concentration to an
area of low concentration.
• Concentration –
Diffusion
• Diffusion is the simplest type of passive
transport.
• Diffusion – the movement of molecules
from an area of high concentration to an
area of low concentration.
• Concentration – the amount of a
substance present.
(Smelly) Example of Diffusion
• Mrs. Shepherd sprays some cologne in
the room.
• Eventually, everyone in the room will be
able to smell it.
(Smelly) Example of Diffusion
• Mr. Mathis sprays some cologne in the
room.
• Eventually, everyone in the room will be
able to smell it.
Why?
(Smelly) Example of Diffusion
• After the initial spray, there is a high
concentration of the cologne in one spot.
• The smell diffuses across the room,
moving to areas where the concentration
is low.
Another Example of Diffusion
• If you place a cube of sugar into a beaker
of water, the concentration of sugar is
highest at the bottom of the beaker.
Another Example of Diffusion
• If you place a cube of sugar into a beaker
of water, the concentration of sugar is
highest at the bottom of the beaker.
• As the cube dissolves, the sugar
molecules diffuse through the solution,
moving toward the top of the beaker,
where the concentration is lowest.
Diffusion
• Diffusion occurs because molecules are in
constant motion.
• Molecules tend to move from areas of high
concentration to areas of low
concentration.
Diffusion
• In the absence of other influences, diffusion
will eventually lead to equilibrium.
• At equilibrium, the concentration of
molecules is the same throughout the space
that the molecules occupy.
Diffusion and the Cell Membrane
• Cell membranes allow some molecules
(but not others) to pass through.
Diffusion and the Cell Membrane
• If a molecule can diffuse through the cell
membrane, it will diffuse until it reaches
equilibrium.
• Diffusion across the cell membrane is
called simple diffusion.
Diffusion and the Cell Membrane
• Simple diffusion of molecules across the
cell membrane depends on the size,
charge and polarity of the molecule.
Diffusion and the Cell Membrane
• For example:
– The cell membrane is made of phospholipids.
– Oxygen and carbon dioxide are capable of
dissolving in lipids, so can easily diffuse
through the membrane.
Diffusion and the Cell Membrane
• For example:
– Small molecules that can not dissolve in lipids
may pass into the cell via pores in the
membrane.
Back to the Potato Lab
1) Remove the potato slices from the water
solutions.
2) Pat them dry with paper towels and then
measure the mass of each one on the triple
beam balance.
3) Using the formula below, determine the
percent change in mass and record in your
table.
Percent Change in Mass:
____(final mass – initial mass)___
initial mass
Exit-Slip
1) Diffusion is the movement of molecules
from an area of ____ concentration to
____ concentration.
a) High ; Low
b) Medium ; High
c) Low ; High
d) High ; Medium
2) Diffusion is a type of _____ ______,
because it requires no energy input from
the cell.
a) active transport
b) molecular transport
c) effective transport
d) passive transport
3) Assuming the pink dots
can pass through the
cell membrane, in what
direction will they move?
a) Out of the Cell
b) Remain Constant
c) Into the Cell
4) The dots will move until they reach a state of ...
a) Equality
b) Equilibrium
c) Homeostasis
d) Concentration
Bell-Ringer
True or False
1) Diffusion is the movement of molecules
from an area of low concentration to an
area of high concentration.
2) Cells use diffusion in order to move
important molecules, such as oxygen, in
and out of themselves.
3) Cells must use ATP in order to power
diffusion.
Bell-Ringer
True or False
4) In the picture to the right,
the dots will diffuse into
the cell.
5) The cell pictured below
is at equilibrium.
Osmosis
• Osmosis is the movement of water from
an area of high concentration to an area of
low concentration.
• In other words, osmosis is the diffusion of
water.
The Direction of Movement
• The direction of osmosis depends on the
concentration of molecules dissolved in
water.
• We use three important terms to describe
solutions:
– Hypotonic
– Hypertonic
– Isotonic
Hypotonic
• A solution is hypotonic when the
concentration of molecules outside the cell
is lower than the concentration of
molecules inside the cell.
Hypotonic
• To determine how water will move, we
must first determine the concentration of
the water.
• Assume that each solution is made up
only of water and the molecule dissolved
in it.
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
What is the concentration of water
inside the cell?
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
100% - 5% =95% Water
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
What is the concentration of water
outside the cell?
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
100% - 1% =99% Water
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
How will the water move?
Hypotonic
• To determine the concentration of water,
subtract the concentration of the
molecules dissolved in it from 100%
Into the Cell!
Hypotonic
• When a solution is hypotonic to the cell,
water will diffuse from outside the cell into
the cell.
• This will cause the cell to swell.
Hypertonic
• A solution is hypertonic when the
concentration of molecules outside the cell
is higher than the concentration of
molecules inside the cell.
Hypertonic
What is the concentration of water
inside the cell?
Hypertonic
100% - 7% = 93% Water
Hypertonic
What is the concentration of water
outside the cell?
Hypertonic
100% - 10% = 90% Water
Hypertonic
How will the water move?
Hypertonic
Out of the cell!
Hypertonic
• When a solution is hypertonic to the cell,
water will diffuse from inside the cell out
into the solution.
• This will cause the cell to shrivel.
Isotonic
• A solution is isotonic when the
concentration of molecules outside the cell
is the same as the concentration of
molecules inside the cell.
Isotonic
What is the concentration of water
inside the cell?
Isotonic
100% - 10% = 90% Water
Isotonic
What is the concentration of water
outside the cell?
Isotonic
100% - 10% = 90% Water
Isotonic
How will the water move?
Isotonic
In and out of the cell at equal rates
Isotonic
• When a solution is isotonic to the cell,
water will move both in and out of the cell
at the same rate.
• The cell will show no change.
-Tonic Pictures
• Pick an object and sketch it in three
different environments:
Isotonic, Hypotonic and Hypertonic
• Be sure to show how would these three
environments change this object.
Exit Slip
Match the words on the left to the
corresponding picture on the right.
1) Hypotonic
2) Hypertonic
3) Isotonic
A
B
C
Bell-Ringer
1) What is the concentration of water outside the
cell?
2) What is the concentration of water inside the cell?
3) How will the water move?
4) The solution is ______tonic
Observing
Osmosis
Observing Osmosis...
1) Send one group member to obtain:
- A Glass Slide and Cover
- Small piece of Red Onion
2) Tear off a thin slice of the red onion skin.
Place the skin and a drop of water on the
slide. Cover with the cover slip.
Observing Osmosis...
3) Observe the onion cells at 4x, 10x and
40x magnification. Sketch the cells.
4) After everyone in the group has sketched
the cells, remove the cover slip and use a
paper towel to dry off the onion and slide.
5) Place two drops of salt water (front desk)
on the onion skin and re-cover.
6) Repeat step #3.
7) Answer questions.
Exit-Slip
1) Osmosis is, specifically, the diffusion of...
a) Ions
b) Lipids
c) Molecules
d) Water
2) The cells to the right
are mostly likely found
in a ______ solution.
a) Hypertonic
b) Hypotonic
c) Isotonic
3) In the example to the
right, water will move...
a) Out of the cell
b) Into the cell
c) In and Out of the cell at the same rate
4) After the water moves, the cell will look
like which picture below?