Suppose you use a microscope yo look at a skin of a n onion what struturce will you see that would not be found in your skin cell.

Onion skin is a plant cell. And your skin cell is a animal cell.
Basically as simple all the structures in animal cell can be found in plant cells. But plant cells has some extra structure and part where doesn't exist in animal cells.
In animal cell, it contains a cytoplasm, nucleus and a cell membrane.
But in plant cell, they have chloroplast, cell wall and vacuole in additional.

In my own word cell technology can  lead to advances in the understanding of diseases mechanism and transmission because diseases is very bad