Iodine Lab

We poured 100 ml. of water inside the plastic bag. Then got one spoonful of starch into the bag. We filled the beaker half way with water and put iodine inside. We put the bag inside the beaker and waited. After 15 min. the starch didn't change at all. We put in more iodine and waited another 5-10 min. Then we checked the bag again and the bottom of the starch was purple. The whole purpose of the lab was to show that the cell membrane (bag) lets certain things through (iodine). We were showing that iodine can go through the "cell membrane" and change the starch. So in the end we learned that cell membranes are semi permeable.