Unicellular organisms use cell division primarily to reproduce themselves, whereas in multicellular organisms cell division also plays important roles in growth and in the repair of tissues (Figure 9.1). In order for any cell to divide, four events must occur:
► There must be a reproductive signal. This signal, which may come either from inside or outside the cell, initiates the cellular reproductive events.
► Replication of DNA (the genetic material) and other vital cell components must occur so that each of the two new cells will be identical and have complete cell functions.
► The cell must distribute the replicated DNA to each of the two new cells. This process is called segregation.
► New material must be added to the cell membrane (and the cell wall, in organisms that have one) in order to separate the two new cells in a process called cytokinesis.
These four events occur in somewhat different ways in prokaryotes and eukaryotes.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.