Whereas an onion epidermal cell has a cell wall, a human cheek cell does not. Instead, a semi-permeable membrane surrounds the cytoplasm of the cheek cell. While there are chloroplasts present in onion cells, they are absent in cheek cells.
Another difference is that the cytoplasm of a cheek cell is more granular, is denser and occupies a larger space than the cytoplasm of an onion epidermal cell. While both cells have a nucleus, the positioning is different, as it is at the periphery of an onion cells’ cytoplasm, while the nucleus of a cheek cell is positioned centrally. The vacuole of an onion cell is prominent, but it is very small in a cheek cell, and is absent in some other cells.
While cheek cells are spherical, onion epidermal cells are rectangular. Cheek cells have lysosomes but onion epidermal cells do not. The two cells are similar in the fact that they both have cell membranes, organelles, mitochondria, plastids, endoplasmic reticulum, ribosomes, Golgi bodies and cytoplasm.
One can simply obtain a cheek cell by gently scraping the mucous membrane found on the inner lining of the human mouth. These cells are akin to those situated around the digestive system. One can obtain an onion epidermal cell by peeling an ordinary onion.