OSMOSIS AND
DIFFUSION
By: Raelee Robinson and Chantal Jabbour
INTRODUCTION TO OSMOSIS AND
DIFFUSION
Diffusion
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Osmosis
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All living things have certain
requirements they must satisfy in
order to stay alive
A cell membrane allows some
substances to leave or enter the
cell.
Diffusion plays a part in moving
substances into and out of a cell
Concentration determines the
direction that a substance takes
through the cell membrane
Particles move from areas of
higher concentration to areas of
lower concentration until there is a
balance – “equilibrium”
The diffusion of water through a
selectively permeable membrane is
LESSON SEQUENCE
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Diffusion
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The movement of a substance from an area of high
concentration to an area of low concentration
Diffusion is a passive process where substances move
across a concentration gradient from high to low
The process of diffusion creates equilibrium
Molecules are in constant motion
Lesson Sequence
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Osmosis
A special type of diffusion
 Occurs when water
molecules move across a
partially permeable
membrane (like a cell
membrane) from a lower
concentrated solution of a
higher concentrated
solution
 Solute particles are too
large to pass through the
membrane, so the water
moves
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Lesson Sequence
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Diffusion and Osmosis in plant and animal cells
Cell membranes are selectively permeable
 Solutions can be classified as hypotonic, hypertonic, and
isotonic relative to their solute concentrations
 Water potential describes the tendency of water to leave one
area in favour of another, it is affected by 2 factors: pressure
and amount of solute (use examples of this in red blood cells, as
well as potato cells)
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CURRICULUM EXPECTATIONS
Grade 8: Understanding Life Systems: Cells
Overall Expectations:
2. investigate functions and processes of plant and animal
cells;
3. demonstrate an understanding of the basic structure and
function of plant and animal cells and cell processes.
Specific Expectations:
3.3 compare the structure and function of plant and animal
cells
3.4 explain the processes of diffusion and osmosis and their
roles within a cell
TEACHING APPROACH
Video demonstration on Diffusion and Osmosis
TEACHING APPROACH
Gizmo activity on diffusion. Students explore the motion of
particles as they bounce across the screen and through an
adjustable gap. Temperature, mass and initial number of
particles can be altered.
Lab Activity
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Investigation of Diffusion and Osmosis Using Eggs
Prior to the lab, the teacher will dissolve the shells of 4 eggs using vinegar so that only the
membrane remains on the egg to create a simulation of a cell.
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Materials:
 Eggs (see above)
 Water
 Water coloured with blue food colouring
 Molasses
 Corn syrup
 4 beakers
 Toothpicks
Procedure:
 Students will determine the mass of the eggs and record it in a table
 They should pour 150 ml of each substance into it’s own beaker, and then add an
egg to each beaker and store in the fridge for 24 hours
 After 24 students remove the eggs from their beakers and record their
observations. Students should record the volume of liquid in the beaker as well as
the mass of the egg
 After recording their observations, students should use a toothpick to pop the egg
membrane and record their observations
Safety
 Students should wear safety goggles while popping the egg membrane with a
toothpick
 The lab floor area should be cleared of all backpacks, stools etc
 The teacher should ask students if there are any allergies to the materials being
used in the lab
See teacher notes below, taken from sciencespot.net
POTENTIAL STUDENT DIFFICULTIES
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Difficulty understanding the abstract concept of molecules and
how they permeate a cell membrane
 Visuals including the Gizmo activity, web video animations,
and lab activity may help the students to conceptualize the
membrane’s qualities
Difficulty with the concept of solutions’ “desire” to reach
equilibrium
 The teacher can demonstrate this by using simple familiar
demonstrations such as food colouring in water
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Difficulty applying and using vocabulary such as hypotonic vs.
hypertonic, solute, solvent, concentration gradient etc
correctly
Students will have plenty of exposure to the correct use of
vocabulary through the Gizmo, and multimedia introduced.
They will practice their vocabulary and knowledge during the
lab activity to identify the hypertonic and hypotonic solutions
 A Word Wall with the words and their definitions can be used
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REAL WORLD APPLICATIONS
 Diffusion
How odours travel
through air
 Pollution and air
quality
 Mixing of
substances
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 Osmosis
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Water passing
through plants
from their roots
Cooking with
water
Osmosis in
medicine (red
blood cell, kidneys)
Preservation of
fruits and meets
Water Filters
DIFFERENTIATED ASSESSMENT
Students will work in partners and
choose one of the following
activities for their final assessment
Interpersonal:
Find someone who uses diffusion
or osmosis in their career and
conduct an interview asking them
questions related to osmosis or
diffusion and their job
Spatial:
Create a 2D or 3D display
depicting the processes of diffusion
and osmosis. Be sure to show both
as separate processes.
Spatial:
Create a 2D or 3D
display depicting
the processes of
diffusion and
osmosis. Be sure
to show both as
separate
processes.
Linguistic:
Write a diary or journal entry of a
water molecule going through
osmosis and diffusion. The entry
should describe
the process, and
Logical:
the
differences
thethe
two.
The
studentsbetween
will use
computer in some way to
create a demonstration of
diffusion and osmosis.
They can use any
program the teacher
approves. A summary
chart must be included
highlighting the similarities
and differences of the two
processes.
Linguistic:
Create a poem or mind map
describing osmosis and diffusion,
be sure to use as much unit
vocabulary as possible.