The correct option is C.
The outer structure of an onion is made up of cellulose cell wall. Cellulose is a material that is found only in plant cells, it is not present in the animal cells. The plant cell wall is made up of cellulose; cellulose is a polysaccharide, which gives the cell wall its form and rigidity. Structure Y on the other hand, which is cell membrane is found in both plants and animals cells.