Immunity is the overall ability of your body to fight disease-causing organisms. NCERT defines it as the defence given by the immune system that lets you meet many germs each day but fall sick only a few times. Memory hook: IMMUNITY = "I'M-you-NEE-tea" — your body's built-in tea that keeps germs out. It has two types: innate (present at birth) and acquired (built after exposure).
The two types of immunity: innate (present at birth, non-specific, no memory) and acquired (built later, specific, with memory). Both are given by the immune system.
Your doubts, answered
What is the exact NCERT definition of immunity?
NCERT says: the overall ability of the host to fight the disease-causing organisms, conferred by the immune system, is called immunity. In simple words, immunity is your body's power to defend itself. You meet many germs every day, but you get sick only a few times because immunity stops most of them.
What is the difference between immunity and the immune system?
They are not the same. The immune system is the group of cells and organs (like WBCs, thymus, spleen, lymph nodes). Immunity is the ability or protection that this system gives you. So the immune system is the machine, and immunity is the work it does.
What are the two types of immunity?
There are two types: (i) Innate immunity, which is non-specific and present at the time of birth, and (ii) Acquired immunity, which is specific and develops during your life after you meet a germ. NEET often asks you to name these two types, so remember them clearly.
Why do we not fall sick every day even though germs are all around us?
Because the body defends itself. NCERT says we are exposed to a large number of infectious agents every day, but only a few exposures cause disease. Immunity, given by the immune system, blocks most germs before they can harm us.
Is immunity the ability to tell self-cells from foreign cells?
Yes, this is a key job of the immune system. It can tell the body's own cells (self) from outside germs (non-self). If this power is lost due to a genetic problem and the body attacks its own cells, it causes autoimmune disease. NEET has tested this idea directly.
Which type of immunity is present at birth?
Innate immunity is present at the time of birth. It is non-specific, meaning it acts the same way against all germs. It works through four barriers: physical, physiological, cellular, and cytokine barriers. Acquired immunity, in contrast, builds up later after exposure to a germ.
⚠️ The NEET trap ✗ Innate immunity is present at birth because it makes memory cells and specific antibodies for a fast second response. ✓ Innate immunity is present at birth because it is non-specific and uses cells like natural killer cells, neutrophils and macrophages that phagocytose (engulf) and destroy microbes. Memory cells and specific antibodies belong to ACQUIRED immunity, not innate. 🧠 Trap word: 'memory' and 'specific'. If you see these attached to innate immunity, it is wrong. Innate = non-specific, no memory. Acquired = specific, has memory.
Real NEET questions
NEET 2019 (Odisha)
Humans have an acquired immune system that produces antibodies to neutralize pathogens. Still, the innate immune system is present at the time of birth because it:
A · is very specific and uses different macrophages.
B · produces memory cells for mounting a fast secondary response.
C · has natural killer cells which can phagocytose and destroy microbes. ✓
D · provides passive immunity.
Solution: Innate immunity is the non-specific defence present at birth. Its cellular barrier includes natural killer cells, neutrophils and macrophages that phagocytose (engulf) and destroy microbes, giving immediate protection before acquired immunity develops. Options A and B describe acquired immunity (specific, memory cells), and passive immunity is a sub-type of acquired immunity, so they are wrong.
NEET 2016 (Phase 1)
In higher vertebrates, the immune system can distinguish self-cells and non-self. If this property is lost due to genetic abnormality and it attacks self-cells, then it leads to:
A · Allergic response
B · Graft rejection
C · Auto-immune disease ✓
D · Active immunity
Solution: A core function of immunity is telling self from non-self. When the body, due to genetic or unknown reasons, attacks its own self-cells, the damage is called auto-immune disease (for example, rheumatoid arthritis). Allergy is an over-reaction to outside antigens, graft rejection is against non-self transplanted tissue, and active immunity is normal antibody production, so they do not fit.
Solved Human Health and Diseases NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
