Movement in and out- Classwork

1 Some students investigated osmosis in raw potato sticks. (a) Define the term osmosis

(b) The students measured the mass of four of the potato sticks using an electronic balance. Fig. 4.1 shows an electronic balance.

(i) Predict which of the liquids would cause the largest decrease in mass of a potato stick.

(ii) The students dried the potato sticks with paper towels before putting them on the electronic balance. Suggest why

(c) After the experiment the students noticed that the potato stick with the lowest mass was soft and floppy. Explain why the potato stick had become soft and floppy.

(d) The students followed the same experimental procedure with boiled potato sticks and found no overall change in mass in any of the solutions. Suggest why the mass of the boiled potato sticks remained the same.

2. A student investigated the diffusion of substances through Visking tubing, an artificial membrane which has some of the properties of cell membranes. The student made a bag of Visking tubing as shown in Fig. 4.1

The student added some iodine solution to the water in the test-tube. After 30 minutes at room temperature, the contents of the Visking bag were stained blue-black, but the water outside remained a yellow colour. (a) (i) Explain these results.

(ii) State three factors that influence the movement of molecules through membranes.