Which of the following best describes the role of plasma cells?

Plasma cells play a crucial role in the immune response by producing antibodies, which are proteins that specifically target and neutralize foreign substances such as bacteria and viruses. When B cells, a type of white blood cell, encounter an antigen (a substance that induces an immune response), they differentiate into plasma cells. These plasma cells can then produce large quantities of antibodies, which circulate in the bloodstream to identify and mark pathogens for destruction by other immune cells.

The function of plasma cells is vital for adaptive immunity, allowing the body to remember previous infections and respond more effectively upon re-exposure to the same pathogens. This capability forms the basis of how vaccines work, as they introduce a harmless form of the pathogen to stimulate an antibody response and "train" the immune system for future encounters.

In contrast, the other options describe roles that are essential for different biological functions but do not pertain to plasma cells. Gas exchange is primarily facilitated by the lungs and blood in the context of respiratory physiology. Blood clotting involves platelets and clotting factors to prevent excessive bleeding. Storing nutrients is a function associated with organs like the liver, rather than plasma cells. Thus, the correct choice highlights the specific role plasma cells play in the immune system.