Biology
The immune system — quick study summary
The immune system defends the body in two layers: innate (fast, non-specific) and adaptive (slower, specific, with memory). Innate responses include skin, mucus, phagocytes, and inflammation. The adaptive response involves B cells (which secrete antibodies) and T cells (which kill infected cells or coordinate the response). Memory cells persist after infection, giving lifelong immunity to many pathogens — the principle vaccines exploit.
Key points
- Innate: physical barriers, phagocytes, inflammation, complement — fast but non-specific
- Adaptive: B cells make antibodies; T cells kill infected cells or help B cells
- Antibodies bind specific antigens and tag them for destruction
- Memory B and T cells give long-lasting immunity (basis of vaccination)
- Autoimmune disease = immune system attacks self; allergy = overreaction to harmless antigen
Practice quiz
Click each question to reveal the answer.
1. Which cells produce antibodies?
- T cells
- B cells
- Macrophages
- Natural killer cells
Answer: B cells (B lymphocytes)
B cells differentiate into plasma cells that secrete antibodies specific to the antigen they recognised.
2. What is the main difference between innate and adaptive immunity?
Answer: Innate is fast and non-specific; adaptive is slower, specific, and produces memory
Innate immunity attacks any pathogen the same way. Adaptive immunity learns the pathogen and remembers it for next time.
3. Why does vaccination give lasting immunity?
Answer: It creates memory B and T cells without causing disease, so the immune system reacts faster on real exposure
Memory cells persist for years or decades and trigger a rapid, strong secondary response to the same pathogen.
Last reviewed: May 2026