In order to detect a signal (that is, to be a target cell), a neighbor cell must have the right receptor for that signal. When a signaling molecule binds to its receptor, it alters the shape or activity of the receptor, triggering a change inside of the cell. Signaling molecules are often called ligands, a general term for molecules that bind specifically to other molecules (such as receptors).
A chunk paragraph is just a way of developing your skill in writing - it is a style or format which forces you to explain your ideas and arguments. Here's you do chunk writing: Write your topic sentence.
Chunking (writing) Chunking is a method of presenting information which splits concepts into small pieces or chunks of information to make reading and understanding faster and easier. Chunking is especially useful for material presented on the web because readers tend to scan for specific information on a web page rather than read the page sequentially.