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