Module 4: Immunity
These free OCR A Level Biology Immunity revision notes have been written for specification point 4.1.1(j).
Types of Immunity
Immunity is the ability to resist infection by pathogens by having complementary antibodies or memory cells that can rapidly make them.
Immunity can be either active or passive:
- Active: The host’s immune system makes its own antibodies after being exposed to a pathogen.
- Passive: The host receives antibodies from an external source.
Immunity can be acquired either naturally or artificially:
- Natural: A normal biological process confers immunity.
- Artificial: Medical intervention confers immunity.
The table below summarises these types of immunity with examples:
| Natural | Artificial | |
|---|---|---|
| Active | The immune system produces antibodies after infection (e.g. chickenpox) | Antigen introduced via vaccine (e.g. MMR, TB) |
| Passive | Antibodies from the mother via the placenta or breast milk | Antibodies injected (e.g. antivenom, hepatitis treatment) |