Question

how did the iodine solution affect the image the onion cell

Answer 1

Iodine dyes cells a purple color. This enables things to be seen easier under a microscope.

Answer 2

Iodine reacts with the starch present inonion cells, producing a coloration that makes the cells easily visible under a microscope. Onion cells are naturally transparent, so it is difficult to properly visualize them without using a solution to increase contrast.