Hi Na, 

This is a common exam question, so it would be good to understand the reason for the colour change. 

a) We know that iodine solution starts off brown, but turns blue when it is in contact with starch. 

Since the iodine can move into the dialysis tube, it can change the colour of solution X if it contains starch. The iodine outside the dialysis tube will stay brown, because starch cannot exit the dialysis tube to trigger complete colour change. 

Since solution X in the dialysis tube turned blue, we know that Solution X must contain starch. [1m]

b) The dialysis tube is a partially-permeable membrane. The Cell Membrane [1m] is also a partially permeable membrane. 

If this helped, please like and accept the answer so others can learn too!

-Michelle [www.dingletutors.com]

a) Solution X contains starch as starch will turn Iodine blue. 

b) Cell membrane. 

Thank you so much dingle tutors and Zappy for the answer