Multicellular organisms consist of communities of cells with several notable features (see next page and Chapter 28). First, and most obviously, cells adhere to one another. Most cells in multicellular organisms are physically attached to other cells or to substances in their surroundings. Second, cells communicate with one another. As we saw in Chapter 9, cells respond to signals from neighboring cells and the physical environment. In addition, as we will see, cells in tissues have pathways for the movement of molecules from one cell to another. Third, cells are specialized to carry out different functions as a result of development and differentiation. The different shapes of cells often reflect these specialized functions.