Final answer:
A lysosome is the organelle that degrades worn-out cellular components and digests macromolecules and particles taken into the cell, particularly through the processes of autophagy and phagocytosis.
Step-by-step explanation:
The organelle that functions as a small sac of digestive enzymes, responsible for degrading worn-out organelles and breaking down macromolecules and particles that are taken into the cell by endocytosis, is known as a lysosome. Lysosomes are part of the endomembrane system and are crucial for the process of autophagy where a cell digests its own structures. They also play a significant role in the digestion of foreign material, such as bacteria ingested by white blood cells through phagocytosis.