What does the appendix do?

The appendix is a small, tube-like structure attached to the large intestine, and while it has been historically viewed as a vestigial organ with no significant function, it does play a role in the immune system. Specifically, the appendix is known to contain lymphoid tissue, which is involved in the production and storage of white blood cells, particularly lymphocytes and other immune-related cells. These components are essential for fighting infections in the body.

In addition, the appendix is thought to serve as a reservoir for beneficial gut bacteria, which can help repopulate the gut after gastrointestinal disturbances. This dual role in immune response and gut health underscores why the correct answer aligns with its function relating to white blood cells.

Other options such as producing digestive enzymes, storing food, or filtering waste don't accurately reflect the specific role of the appendix. While the digestive system includes organs that perform these functions, the appendix is not involved in enzyme production or food storage to any significant extent, nor does it function as a waste filter.