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.
The preview statement is something you will actually say in the speech. You are to speak directly to the audience here. The preview statement is nothing more than your main point headings linked together in sentence form using connector words. Connector words are words such as first, next, and finally.. If your main points in the speech are as follows... I. Materials needed to make spaghetti. II. How to make spaghetti.