Question

Which best describes the structure labeled X in the diagram?

Answer 1

The structure labeled X in the diagram is a membrane protein.
Membrane proteins are integral parts of the cell membrane that enable the transfer of ions like sodium, potassium and chlorine and small molecules like glucose through the lipid bilayer. They differ from other types of cell proteins by their structure. As you can see on the diagram, hey form channels that enable specific ions or molecules to pass to the other side of the membrane.

Answer 2

Actually choose A:  membrane protein

Source: protein quantification

https://www.creative-proteomics.com/services/protein-quantification.htm