Cambridge O Level Biology · Syllabus 5090 · Disease and Immunity
Memory Cell
What is Memory Cell?
A lymphocyte that remains in the body after an immune response to a particular antigen. Memory cells persist long after the antibodies themselves have disappeared, and on a second exposure to the same antigen they allow antibodies to be produced far more quickly and in far greater quantity, so the pathogen is often destroyed before symptoms develop.
This definition is part of the Disease and Immunity chapter in Cambridge O Level Biology.
Common mistakes with Memory Cell
- "Phagocytes produce specific antibodies." Phagocytes are non-specific and do not produce antibodies. Lymphocytes do. Write Lymphocytes produce specific antibodies and form memory cells; phagocytes engulf and digest pathogens.
- "Vaccination gives passive immunity." A vaccine supplies antigens, not antibodies, and your own lymphocytes do the work. Write Vaccination stimulates active immunity: the person's own lymphocytes produce antibodies and memory cells are formed.
- "Passive immunity produces memory cells." The recipient's own lymphocytes never met the antigen, so there is nothing to remember. Write Passive immunity gives immediate protection but no memory cells are formed, so protection is short-term.
Questions students ask about Memory Cell
If a vaccine contains the pathogen, why does it not give you the disease?
Because of the form it is in. A vaccine may contain weakened pathogens, inactivated pathogens, or just the antigens, and none of these can establish a normal infection. What survives is the antigen's shape, which is all the lymphocytes need in order to produce complementary antibodies and form memory cells.
Is passive immunity ever given deliberately?
Yes, ready-made antibodies can be given as a medical treatment when immediate protection is needed and there is no time to build a response. The syllabus examples you must know are the natural ones — antibodies crossing the placenta and antibodies in breast milk — and both share the same limitation: immediate protection, no memory cells, short duration.