- Perform a first-hand investigation to model the selectively permeable nature of a cell membrane

Beakers A and B

The dialysis tubing has small pores which allow certain substances of appropriate size to pass through.

Allows iodine and water to pass through but stops large starch molecules

Analysis Increase of mass of bag in BEAKER A indicates osmosis occurring, through

tubing into the bag (WATER) Colour of Iodine: BROWN > BLUE-BLACK by presence of starch BLUE-BLACK colour of bag indicates that iodine has diffused through the tubing

and since the Iodine solution in the beaker did not change, no starch diffused out In BEAKER B, mass of bag decreases indicates diffusion through the bag into

starch solution Iodine solution diffuses through the bag into the beaker, causing the Blue-Black

change No starch has diffused into the bag, hence no change of Brown colour The tubing acts as a semi permeable membrane, allowing water and iodine

solutions to pass through pores, but not allow starch

- Perform a first-hand investigation to demonstrate the difference between osmosis and diffusion

BEAKERS C AND D

The mvt of water from areas of low(glucose) concentration to high(glucose) concentration

Beaker Mass of tubing bag (g) Colour after a day in beaker

Colour after a day in bag

A Initial: 24.6Final: 30.2

Brown Blue-black

B Initial: 22.4Final: 18.6

Blue-Black Brown

The mvt of glucose is in the opposite direction, from high concentration to low concentration

Analysis In BEAKER C it is clear that the water has diffused into the bag through the

tubing, from low glucose to high glucose concentration In BEAKER D it is clear that the water has diffused out the bag through the tubing

into the glucose solution which is much higher concentration Testing with Benedicts Solution it is clear that the GLUCOSE has moved from

areas of to low concentration(water) Water and Glucose move in opposite directions Water diffuses from a low to high concentration Starch turns from white to purple Glucose from aqua to orange

Beaker Mass of dialysis tubing bag (G)

Colour of solution in beaker after a day

Colour of solution after a day in bag

C Initial: 23.5Final: 28.2

Blue to Orange Blue to Orange

D Initial: 19.6Final: 14.7

Blue to Orange Blue to Orange