NEET Biology — Human Health and Disease Complete Chapter Guide

Chapter Overview & Weightage

Human Health and Disease covers common diseases (pathogens, symptoms, transmission), the immune system (innate and adaptive immunity), AIDS, cancer, and drugs/alcohol abuse. Disease-pathogen matching and immunity concepts are NEET staples.

Key Concepts You Must Know

Tier 1 (Core)

• Common diseases: malaria (Plasmodium, Anopheles mosquito), typhoid (Salmonella typhi), pneumonia (Streptococcus pneumoniae), amoebiasis (Entamoeba histolytica), dengue (Aedes mosquito), filariasis (Wuchereria bancrofti)
• Immunity types: innate (non-specific, present from birth) vs adaptive (specific, acquired)
• Adaptive immunity: humoral (B-cells, antibodies) vs cell-mediated (T-cells)
• Active immunity (body makes antibodies — vaccination) vs passive immunity (ready-made antibodies given — mother’s milk, antiserum)
• Vaccination principle: memory B-cells formed on first exposure → rapid response on second exposure

Tier 2 (Frequently tested)

• AIDS: HIV destroys helper T-cells (CD4+), transmitted through blood/sexual contact, diagnosed by ELISA
• Cancer: uncontrolled cell division, benign vs malignant tumours, metastasis, oncogenes, tumour suppressor genes
• Antibody structure: 4 polypeptide chains (2 heavy + 2 light), Y-shaped, antigen-binding sites
• Allergies: exaggerated immune response, IgE antibodies, histamine release, mast cells

Tier 3 (Occasionally tested)

• Drugs and alcohol abuse: opioids, cannabinoids, coca alkaloids — effects and addiction
• Interferons: proteins released by virus-infected cells to protect neighboring cells
• Primary vs secondary lymphoid organs: bone marrow/thymus vs spleen/lymph nodes/MALT

Important Formulas

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: The

definitive host of Plasmodium is:

(A) Human (B) Female Anopheles mosquito (C) Male Anopheles mosquito (D) Culex mosquito

Solution:

The definitive host is where sexual reproduction occurs. Plasmodium undergoes sexual reproduction (gametocyte fusion → zygote → oocyst → sporozoites) inside the female Anopheles mosquito. Humans are the intermediate host (asexual reproduction occurs here).

Answer: (B) Female Anopheles mosquito

PYQ 2 — NEET 2023

Problem: Which cells does HIV primarily attack?

(A) B-lymphocytes (B) Helper T-lymphocytes (CD4+) (C) Killer T-cells (D) Red blood cells

Solution:

HIV specifically targets helper T-lymphocytes (CD4+ cells) by binding to the CD4 receptor on their surface. As helper T-cell count drops below 200 per μL (normal: 500-1500), the immune system collapses, leading to opportunistic infections characteristic of AIDS.

Answer: (B) Helper T-lymphocytes (CD4+)

PYQ 3 — NEET 2022

Problem: Active immunity differs from passive immunity in that:

(A) Active involves ready-made antibodies (B) Active involves the body producing its own antibodies (C) Passive provides long-term protection (D) Active immunity has no memory

Solution:

In active immunity, the body encounters the antigen (through infection or vaccination) and produces its own antibodies. Memory cells are formed, providing long-term protection. In passive immunity, preformed antibodies are provided (e.g., mother’s milk, antiserum) — protection is immediate but short-lived (no memory cells formed).

Answer: (B) Active involves the body producing its own antibodies

Difficulty Distribution

Expert Strategy

Day 1: Build the disease table — pathogen, type (bacterial/viral/protozoan/helminth/fungal), transmission route. This single table answers 2-3 NEET questions per paper.

Day 2: Immunity — innate vs adaptive, humoral vs cell-mediated, active vs passive. Understand vaccination as a form of active immunity. Know antibody structure (Y-shaped, 4 chains).

Day 3: AIDS, cancer, and drugs. For AIDS, know the life cycle of HIV inside helper T-cells. For cancer, know benign vs malignant, metastasis, and the role of oncogenes. For drugs, know the classification (opioids, cannabinoids, coca alkaloids) and one example each.

Common Traps