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