Do cells have to be in a thick layer?

Cells do not have to be in a thick layer; they can exist in single layers or as part of complex structures. The arrangement depends on the type of tissue and its function. For example, epithelial tissues can be a single layer (simple epithelium) or multiple layers (stratified epithelium), while muscle and nervous tissues have their own specific arrangements. The thickness is determined by the specific needs of the organ or system they are part of.