Final answer:
The degradation of obsolete cellular parts like defective mitochondria is carried out by the process of autophagy, where lysosomes break down the cell's own components.
Step-by-step explanation:
The mechanism used for degrading obsolete parts of a cell, such as a defective mitochondrion, is autophagy. This process involves the digestion of the cell's own structures by lysosomes, which contain enzymes that break down cellular components. During autophagy, the organelles to be degraded are encased in a membrane, forming an autophagosome, which then fuses with a lysosome. The lysosomal enzymes then digest the contents of the autophagosome. Unlike phagocytosis, which deals with external particles, or apoptosis, which is programmed cell death, autophagy serves as the cell's internal waste disposal system.