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 cdmpared to the skin cell? It contains proteins. It contains cellulose. It contains carbohydrates It is selectively permeable.

## Step 1<br />The question is asking us to identify a unique characteristic of the outer layer of an onion cell that sets it apart from a human skin cell. The options provided are: it contains proteins, it contains cellulose, it contains carbohydrates, and it is selectively permeable.<br /><br />## Step 2<br />The outer layer of an onion cell is the cell wall, which is primarily composed of cellulose. This is a unique characteristic of plant cells, including onion cells.<br /><br />## Step 3<br />Human skin cells, on the other hand, do not have a cell wall. Instead, they have a cell membrane, which is composed of lipids and proteins.<br /><br />## Step 4<br />While both the onion cell and the human skin cell contain proteins and carbohydrates, these are not unique to the onion cell. Both types of cells contain these components.<br /><br />## Step 5<br />The term "selectively permeable" refers to the ability of a cell to control what substances can enter or leave the cell. While this is a characteristic of both onion cells and human skin cells, it is not unique to the onion cell.