Final answer:
Reaper is the molecule unique to Drosophila that inhibits IAPs, leading to the activation of caspases and promotion of cell death, which is crucial for both normal development and in various disease conditions.
Step-by-step explanation:
Reaper is the molecule that is found only in Drosophila (fruit flies) and inhibits IAPs (inhibitor of apoptosis proteins), which promotes cell death (apoptosis). Reaper does this by binding to IAPs, thus preventing them from inhibiting caspases, which are the enzymes responsible for carrying out apoptosis. The activation of caspases leads to the systematic breakdown of cell components, ultimately resulting in cell death. This process is important for the development and homeostasis of organisms, as well as in disease states where cell death is dysregulated.