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 question 2.Background information 3.Accurately defined variables (independent, dependent, controlled) 4.Apparatus 5.Risk assessment 6.Assessment of potential errors and uncertainties 7.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 osmosis 4.Difference in water potential* 5.Pressure difference across the semi-permeable membrane 6.Light and dark? 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 daltons glucose = 180 daltons glycerol = 92 daltons methylene blue = 319 daltons water = 18 daltons PermLab 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 VariableDefinition, Units Independent DependentRate of osmosis Controlled Measured