Ace the PLTW Biomedical Science Challenge 2026 – Dive into Discovery and Innovation!

The primary purpose of the lymphatic system is to defend against pathogens. This system plays a crucial role in the body's immune response by filtering lymph, a fluid that circulates throughout the body, and by providing a site for lymphocytes, which are a type of white blood cell responsible for fighting infections. The lymphatic system includes lymph nodes, which trap bacteria and viruses and facilitate their destruction by immune cells.

In addition to acting as a key component of the immune system, the lymphatic system also helps to maintain fluid balance in the body and absorb fats from the digestive system, but its primary and most vital role remains in the protection against diseases and infections. Therefore, the correct answer highlights the lymphatic system's essential function in maintaining health through immune defense mechanisms.