Answer:
The correct answer is option D, Receptor protein
Explanation:
A Receptor protein is found on the outer side of the cell and they provide receptor sites where a foreign chemical messenger can get associated and perform its function. As the name also suggest , “receptor” which receives chemical signals from outside a cell. Some common example of receptor proteins are ion channels such as ligand gated ion channels , enzymes etc.
Thus, it can be a receptor protein which has the ability to bind to hormones or other chemical messengers.
