investigation 4: diffusion and osmosis

part 1: surface area and cells — basic setup

demonstrate relationship between SA and volume and how this ratio affects diffusion rates.

• block of agar that has indicator dye that changes colour when pH drops

• cut blue agar into 3 different block sizes with diff SA-volume ratios (SA:V)

• each block is dropped into a solution & diffuses. Track the time it took to fully diffuse

part 1: surface area and cells — results

larger SA = slowest diffusing time

• high SA:V ratio is important for any cell that relies on high diffusion rate.

• eg. the linings of ur small intestines and lungs have many folds in order to create the highest SA possible in the smallest amount of space

Part 2: modelling diffusion and osmosis — basic setup

dialysis tubing, selectively permeable to water and some solutes

Part 2: modelling diffusion and osmosis — results

when molarities are equal (eg 1 mol sucrose & 1 M NaCl) and the solution becomes lighter after 30 minutes for example, ionization constant from solute potential equation becomes the deciding factor. NaCl ionizes but sucrose doesn’t (i = 2). Thus water diffuses out of the bag into surrounding NaCl solution

part 3: observing osmosis in living cells — basic setup

surcose solutions (0 mol to 3 mol) and use potato cores to find out the relative concentrations of these solutions. U can then calculate %change in weight of potato cores & get the water potential of potato tissue

bigger the difference in water potential between a cell and solution, the bigger the movement of water (into our out)

part 3: observing osmosis in living cells — results

• arrange change in weight from most negative to positive

  • very (-) means heavy loss of water

  • very (+) means heavy water gain (hypotonic), greater the weight, the lower the molarity of the solution

• graph %changes in weight and find x intercept which indicates the molarity when there would be no net change in weight.

  • if water potential of the solution = cell water potential