Which of the following best describes the concept of immunity?

Explanation: Active immunity. Active immunity is acquired when the immune system is exposed to a pathogen, either through natural infection or vaccination. It results in the production of memory cells that provide long-term protection against future exposures to the same pathogen.
Incorrect choices:

a. Passive immunity is acquired when preformed antibodies are transferred from one individual to another. It provides immediate but temporary protection and does not involve the production of memory cells.

b. Innate immunity is the body's first line of defense against infections and provides immediate, non-specific protection, but it does not involve the production of antibodies specific to a particular pathogen.

d. Acquired immunity is a general term that includes both active and passive immunity, but it does not specifically describe the type of immunity acquired through vaccination or exposure to a specific pathogen.

Explanation: Memory in the immune system refers to the ability of immune cells, particularly memory B cells and memory T cells, to recognize and respond more quickly and effectively to specific antigens upon subsequent exposure. This leads to a faster and stronger secondary immune response.

Incorrect choices:
b. The ability of immune cells to differentiate between self and non-self antigens refers to the concept of immune tolerance, which helps prevent the immune system from attacking the body's own cells and tissues.
c. The process of phagocytosis by macrophages is a mechanism by which immune cells engulf and destroy pathogens and cellular debris, but it is not directly related to memory in the immune system.
d. The ability of B cells to produce antibodies is an essential part of the primary immune response, but it is not specific to memory in the immune system.