PATHOLOGY

Detailed explanation-1: -If cells are no longer needed, they commit suicide by activating an intracellular death program. This process is therefore called programmed cell death, although it is more commonly called apoptosis (from a Greek word meaning “falling off, ‘’ as leaves from a tree).

Detailed explanation-2: -Apoptosis typically involves only a single signaling pathway. Apoptosis occurs randomly during embryonic development of a nematode. Apoptosis is triggered only by signals from outside the cell. All of the listed responses are correct.

Detailed explanation-3: -The two main pathways of apoptosis are extrinsic and intrinsic as well as a perforin/granzyme pathway. Each requires specific triggering signals to begin an energy-dependent cascade of molecular events.

Detailed explanation-4: -In some cases, the mechanism that generates cells that are needed also fortuitously generates unneeded ones as well (as happens in the immune system). And some cells that die are needed, but only transiently. “Cells die either because they are harmful or because it takes less energy to kill them than to maintain them.