In the last lesson, MG and I conducted a series of science experiments, using starch, yeast, flour, water, oranges, apples, orange juice, apple juice, sugar, balloons, potatoes, and iodine (diluted). Our first experiment was bread making. We wanted to see how yeast could make bread fluffier (which is generally considered yummier). First, we took some flour, added some sugar (food for the yeast, and it also acts like a shovel to create air pockets while mixing), and then, in a bowl (we had to separate bowls), we added some yeast. We then also added water. We set these two bowls aside on a radiator and began our next (also yeast) experiment. 

We took three glasses, filled them with an identical amount of water, and added sugar into two and yeast into two, so that we had one glass with sugar and water, one with yeast and water, and one with yeast, sugar, and water. We then mixed all three into plastic bottles and put balloons on top instead of lids. The purpose was to see which would release the most carbon dioxide. I theorized that the sugar, yeast, and water solution would win, as it has yeast, which produces Carbon Dioxide when it respires anaerobically, and sugar, which feeds the yeast. I was right.

Next, we experimented with a starch tester, using iodine. As it turns out, starch has a helix structure, and it has little pockets in which the iodine gets trapped. This means that the color turns black. So, we tested potatoes, apples, cheese, and even starch itself (that one was the coolest. It turned blue-black almost instantly).

Our last experiment (as we were in a rush to get to the airport and it was already 10:10 AM) was a vitamin C test. Basically, vitamin C cancels out the effects of iodine on starch, or at least makes it temporary. So, by putting starch into a glass with water and then pouring in a liquid, you can test if the liquid has vitamin C by checking dripping some diluted iodine in and checking if the blue-black effect is either temporary or nonexistent, in which case it has vitamin C.

Questions:
Why does the fact that iodine gets trapped in the helix formation of starch mean that it gets darker? That implies its absorbing more light, but what does the iodine getting trapped bit have to do with it?

How does vitamin C cancel out the effects of iodine on starch?