Final answer:
Apoptosis is a default pathway that requires external survival signals to be stopped for any cell to live. It allows a cell to die in a controlled manner and prevents the release of damaging molecules. External signaling, like binding to the extracellular matrix, can initiate apoptosis.
Step-by-step explanation:
Apoptosis is a default pathway and must be stopped by external survival signals for any cell to live. Apoptosis allows a cell to die in a controlled manner, preventing the release of potentially damaging molecules from inside the cell. External signaling, such as the binding of cellular receptors to the extracellular matrix, can initiate apoptosis. Moving away from the extracellular matrix ceases the signaling, leading to cell death. This system helps prevent uncontrolled cell division and the spread of tumor cells.