Subject: Why can a photo negative be printed onto a plant's leaf after photosynthesi

My science project is to put a plant in the dark and then in 
fluorescent light with a black and white photo negative attached. 
After this, I am supposed to treat the leaf with alcohol and then 
tincture of iodine over heat to cause the photo image to appear 
on the leaf.  It is a really cool project, but I don't understand 
how photosynthesis is affecting this.  Is it the starch, or is 
the leaf just acting as a piece of photo paper?

Re: Why can a photo negative be printed onto a plant's leaf after photosynthesi