Textbook in PDF format Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Muscle cells contract to maintain a heartbeat and allow us to move, neurons form networks that give rise to memories and enable thought processes. This book provides an overview of the state of knowledge in the study of cellular structure and function. The book is also intended to present information on the importance of mechanisms for generating cellular order