A scientist is comparing the outer layer of an onion cell to the outer layer of a human skin cell. What is unique about the outer layer of the onion cell compared to the skin cell?

An onion cell is a plant cell, so outside its cell membrane it has a rigid cell wall made largely of cellulose. A human skin cell has a cell membrane but no cellulose cell wall. Both cell membranes contain proteins and carbohydrates and are selectively permeable, so those features are not unique to the onion cell.

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