Uneeb Q. answered • 03/21/19
Head/Neck Surgeon, Ivy League, Military Veteran,Teach for America Alum
The key to answering this question is to understand what a "phospholipid" bilayer means.
It is essentially two layers of membrane, where the polar ("phospho") head of the phospholipid is facing polar solutions (e.g. the inside of the cell and the outside of the cell). And the lipid portion is facing inside, creating a non-polar inside.
In order to cross this non-polar inside area the molecule in question must be of the same type. Remember in chemistry "Like Dissolves Like". So in order for a molecule to cross the membrane it must be a steroid.
Another way to answer this question is to understand how all the remaining choices are the same. A globular molecule (tertiary/quaternary structure) like a protein is composed of many peptide moieties bound together, peptides in turn consist of amino acids. So the remaining three choices you're given are all the same, and in true multiple choice fashion if multiple answers refer to the same thing then none of those can be true! :)
