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.
A: The chunk size is the amount of data contiguous on the virtual device that is also contiguous on the physical device. In this HOWTO, chunk and stripe refer to the same thing: what is commonly called the stripe in other RAID documentation is called the chunk in the MD man pages.