Final answer:
Lysosomes are the organelles responsible for breaking down cellular debris, foreign material such as bacteria and viruses, and worn-out cell parts. They contain digestive enzymes and are important components of autophagy and the immune system's defense mechanism.
Step-by-step explanation:
The organelle responsible for breaking down old cell parts, enzymes, viruses, and bacteria is the lysosome. Lysosomes contain digestive enzymes and act similarly to a waste disposal system in the cell, breaking down not only cellular debris and worn-out organelles but also foreign invaders such as viruses and bacteria. In the process of autophagy, lysosomes are involved in 'self-eating,' where a cell digests its own structures. They are also a key component of the immune defense system, where white blood cells engulf bacteria and then digest them with lysosomal enzymes.
In plant cells, the function similar to that of lysosomes is often carried out by vacuoles, which also help in the degradation process. However, plant cells may contain lysosome-like organelles as well. Christian de Duve discovered lysosomes in the 1960s. These organelles are part of the endomembrane system, which also includes the Golgi apparatus, endoplasmic reticulum, and nucleus amongst others.