Which type of immunity is characterised by memory?

The correct answer is Option (3) → Acquired immunity

Memory means that the body remembers its first meeting with a pathogen. The first encounter gives a low-intensity primary response; a later encounter with the same pathogen gives a much stronger secondary or anamnestic response. This is the mark of acquired immunity.

Option (1) Innate immunity — Incorrect. Innate immunity is a non-specific defence present at birth. It works through barriers and does not depend on an earlier exposure, so it has no memory.

Option (2) Passive immunity — Incorrect. In passive immunity, ready-made antibodies are given to the body. The body does not make them itself, so no memory is formed.

Option (3) Acquired immunity — Correct. Acquired immunity is pathogen specific and is characterised by memory. This memory is also the basis of vaccination.

NCERT Extract:
Acquired Immunity – “Acquired immunity, on the other hand is pathogen specific. It is characterised by memory. This means when our body encounters a pathogen for the first time it produces a response called primary response which is of low intensity. Subsequent encounter with the same pathogen elicits a highly intensified secondary or anamnestic response. This is ascribed to the fact that our body appears to have memory of the first encounter.”