Osmosis for IA

Your challenge…

How do different concentrations of a specific solution affect the rate of osmosis in

plant/vegetable tissue?or…

How do different concentrations of a specific solution diffuse across a semi permeable

membrane?

There are 6 sections to your design IA

1. Research question2. Background information3. Accurately defined variables (independent,

dependent, controlled)4. Apparatus5. Risk assessment6. Assessment of potential errors and uncertainties7. Materials and Method used

3

Challenge 1: Background information and your

Research Question!Remind yourselves what osmosis

is!

Osmosis

‘Net movement of solvent molecules (typically water) through a semi-permeable membrane in order to equalise solute concentrations on either

side of the membrane’Let’s remind ourselves…McGraw Hill animation

What are the factors which affect osmosis?

These will be your dependent and independent variables

What are the factors which can affect osmosis?

1. Temperature: The higher the temperature, the higher the rate of osmosis

2. Concentration gradient across the semi-permeable membrane

3. Surface Area for osmosis4. Difference in water potential*5. Pressure difference across the semi-permeable membrane6. Light and dark?....7. Resources can be accessed here…From APEC water systems

Factors which affect osmosis

• One of these factors will be your independent variable (what you manipulate)

• You must ensure that all other factors are controlled

Investigating osmosis across vegetable cell membranes

• Check out the amyloplasts, storing starch granules…

• Cell membrane: - which solutes can diffuse through the plant cell membrane?

• What solutes can’t diffuse through the plant cell membrane?

• What about the cell wall?• What are the intracellular

concentrations of [Na+], [glucose], [sucrose]?

…So how could we ‘measure’ osmosis in plant

tissue?(i.e. What will be your dependent

variable?)

Your ideas…

Other folks ideas…

• Mr Bozeman's tips• Any alternatives?....Let’s brainstorm• Rate of osmosis could be measured as mass

change per unit time (gmin-1 or gh-1)• In a closed chamber, [where temperature was

controlled, and not manipulated], rate of osmosis could be measured as pressure change per unit time (kPamin-1)

Investigating osmosis across a semi-permeable membrane

• It depends on the semi-permeable membrane!

• There are many types of dialysis tubing• If using a semi-permeable

membrane, you need to ensure you have a solute

which cannot pass through the dialysis membrane

Investigating osmosis across a semi-permeable membrane

• Permeability of a solute depends on mass and volume

• The molecular weight cut-off will show you which molecules will be able to pass through the semi-permeable membrane

Molecular Weights of various solutes

For reference, note that the molecular weights of the molecules of interest here are:sucrose = 342 daltonsglucose = 180 daltonsglycerol = 92 daltonsmethylene blue = 319 daltonswater = 18 daltonsPermLab Dialysis information

How could we ‘measure’ osmosis in

dialysis tubing?

What could we ‘measure’ if you are using dialysis tubing?

• Your ideas…

Other folk’s ideas…

• Dialysis Mr Science• Advanced Diffusion Lab• Vernier Osmosis Lab• Rate of osmosis could be measured as mass

change per unit time (gmin-1 or gh-1)• In a closed chamber, [where temperature was

controlled, and not manipulated], rate of osmosis could be measured as pressure change per unit time (kPamin-1)

Section 2: Identification of Independent, Dependent,

controlled and measured variables

Make a table of accurately defined variables

Variable Definition, Units

Independent

Dependent Rate of osmosis

Controlled

Measured