The signal for apoptosis can come from outside or inside the cell. Give one example when the signal comes from outside the cell and two examples of cellular occurrences that would prompt an apoptosis signal from inside the cell.

- A signal for apoptosis that comes from outside the cell is when a cell detaches from extracellular matrix. If this happens, a transmembrane signal is triggered.

- Two examples of cellular occurrences that would prompt an apoptosis signal from inside the cell are:

1. Damaged DNA

2. Increase of cytosolic calcium concentration

Explanation:

Apoptosis can be activated from an intrinsic or an extrinsic pathway. The intrinsic pathway is activated when a cell senses stress (for example, damaged DNA or high cytosolic calcium concentration) and triggers death proteins to activate apoptosis mechanism inside of it; the extrinsic pathway refers to the apoptosis triggered by signals that come from other cells. In this scenario, ligands bind to cell-surface death receptors and activates a death-inducing signal.