A series of questions was used to clarify the concept of cell receptors. How does the chemical messenger recognize the target cell? Where on the cell are these receptors found? What specifically must occur between the messenger and the receptor? Once chemical binding occurs, what is produced by the cell? What is meant by specificity of messenger-receptor binding? Using molecular models to show the geometric shape of messengers , and lego blocks, the definition of specificity was demonstrated. Affinity was demonstrated using the "fit" of lego blocks into each other, a greater affinity shown by a better fit. An example of typical responses was listed.