OSMOSIS AND DIFFUSION By: Raelee Robinson and Chantal Jabbour
Mar 31, 2015
OSMOSIS AND DIFFUSION
By: Raelee Robinson and Chantal Jabbour
INTRODUCTION TO OSMOSIS AND DIFFUSION
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 called Osmosis
Diffusion
Osmosis
LESSON SEQUENCE
Diffusion 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
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
Lesson Sequence 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)
CURRICULUM EXPECTATIONS
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
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.
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.
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 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. 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 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 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 for easy student reference
REAL WORLD APPLICATIONS
DiffusionHow odours
travel through airPollution and air
qualityMixing of
substances
OsmosisWater 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