Human Health and DiseaseNEET Zoology · Class 12 · NCERT Chapter 7

You can expect 3 to 4 questions from Human Health and Disease in NEET 2027. It is the highest-yield zoology chapter and one of the most tested chapters across all of biology. The most reliable scoring topics are disease-pathogen matching (especially Plasmodium species, typhoid, filariasis), the difference between active and passive immunity, antibody types (IgG, IgA, IgM, IgD, IgE), and HIV pathology.

Innate immunity is non-specific and present from birth. It has four barriers: physical (skin, mucus), physiological (saliva, stomach acid, tears), cellular (macrophages, neutrophils, NK cells), and cytokine (interferons). Acquired immunity is specific, pathogen-targeted, and develops after exposure. It is mediated by B cells (humoral) and T cells (cell-mediated) and shows memory, which is why a second exposure to the same pathogen gives a faster, stronger response.

Active immunity is when your own body produces antibodies after exposure to a pathogen or vaccine. It is slow to develop but long-lasting (sometimes lifelong). Examples: recovering from chickenpox, vaccination with BCG. Passive immunity is when ready-made antibodies are transferred to you from someone else. It acts fast but does not last long. Examples: a baby getting antibodies through the placenta and through colostrum from the mother, and tetanus or snake-bite antiserum injections.

Malaria is caused by Plasmodium, a protozoan parasite. It is transmitted by the bite of an infected female Anopheles mosquito. Four species infect humans: P. vivax, P. malariae, P. ovale, and P. falciparum. P. falciparum is the most lethal because it causes malignant malaria with possible coma and death. NEET asks this every other year.

The five antibody isotypes are: IgG (most abundant in plasma, crosses placenta, secondary response), IgA (in secretions like saliva, tears, breast milk, mucosa), IgM (largest, pentamer, first antibody made in primary response), IgD (on naive B-cell surface), and IgE (allergy and parasitic infections, binds mast cells). A common mnemonic is "GAMED".

An antibody is a Y-shaped molecule with the formula H2L2: two heavy (H) chains and two light (L) chains held together by disulphide bonds. Each chain has a variable region (the tip of the Y, which binds the antigen and is called the paratope) and a constant region. The part of the antigen the antibody binds to is called the epitope. The constant region of the heavy chain decides the isotype (IgG, IgA, IgM, IgD or IgE).

HIV is a retrovirus carrying single-stranded RNA and the enzyme reverse transcriptase. After entering the body, HIV infects helper T cells (CD4 cells). Inside the cell, reverse transcriptase makes a DNA copy of the viral RNA, which is integrated into the host chromosome. The infected T cell makes new viral particles that destroy more T cells. As CD4 T-cell numbers drop, the immune system cannot fight ordinary infections. The patient is now in AIDS stage. HIV is detected by the ELISA test. There is no cure, but antiretroviral drugs slow the disease.