Human Health and Disease — NEET Revision Weapon

📊 PYQ Weightage Map — Last 10–15 Years

Judgment ranking of how often each sub-topic has appeared in NEET / AIPMT (2010 → 2024). 🔥 counts approximate frequency. NEET typically pulls 5–6 questions/year from this chapter — one of the highest-yield Zoology chapters. Study the 🔥🔥🔥🔥 topics first.

1. Diseases table (pathogen ↔ disease ↔ vector)

🔥🔥🔥🔥🔥

2–3 Q/yr · almost guaranteed

2. Immunity (innate vs acquired, humoral vs cell-mediated)

🔥🔥🔥🔥🔥

1–2 Q/yr · antibody types loved

3. AIDS — HIV type, target cell, diagnostic

🔥🔥🔥🔥🔥

1 Q/yr · ELISA + T-helper

4. Drugs — plant sources & categories

🔥🔥🔥🔥🔥

1 Q/yr · match plant→drug is classic

5. Cancer — types, oncogenes, treatment

🔥🔥🔥🔥🔥

1 Q/yr · benign vs malignant

6. Antibody structure (Y-shape, 2H+2L, IgG etc.)

🔥🔥🔥🔥🔥

Assertion-Reason favourite

7. Malaria life cycle (Plasmodium stages)

🔥🔥🔥🔥🔥

Sporozoite → merozoite sequence

8. Vaccines — active vs passive; PEP

🔥🔥🔥🔥🔥

Passive = preformed antibody

9. Lymphoid organs — primary vs secondary

🔥🔥🔥🔥🔥

Bone marrow & thymus = primary

10. Allergy & auto-immunity

🔥🔥🔥🔥🔥

IgE + histamine; RA autoimmune

11. α-interferon & monoclonal antibodies

🔥🔥🔥🔥🔥

Occasional single-Q trap

12. Prevention / warning signs / NACO / RCH

🔥🔥🔥🔥🔥

One-mark match items

🔥 Priority order for revision: Diseases → Immunity → AIDS → Drugs → Cancer → everything else. If time is very short, master the diseases table and immunity types — that alone locks ~ 3 of 5 chapter Qs.

🗓️ 7-Day Mastery Protocol + Zero-Miss Rules

A protocol adapted from the personal study plan (HHD Mastery Pack PDF). Because almost every NEET question from this chapter is a direct NCERT line (a name, a number, a vector, a chemical), a miss here is a memory failure, not a concept failure. That's exactly what a fixed protocol fixes.

Day	Task	How to do it (this is the part that matters)
Day 0	Cold diagnostic	Take the self-test (Section 11 below) before studying. 45 min, no book. Score with NEET marking (+4 / −1). The score doesn't matter; the error list does.
Day 1	NCERT read #1 — narrative	Read the whole chapter start to finish without highlighting. Goal: know the shape (5 blocks — Diseases → Immunity → AIDS → Cancer → Drugs).
Day 2	NCERT read #2 — extraction	Read with a pencil. Circle every italicised scientific name, every number, every proper noun, every vector, every symptom list. Nothing else has ever been asked.
Day 3	Rebuild the tables	Rewrite the disease/immunity/drug tables above from memory on blank paper. Correct in red pen. Blank-paper recall beats re-reading by a wide margin.
Day 4	Figures + captions	Redraw and label: antibody (H₂L₂), Plasmodium life cycle, HIV replication cycle. Read every NCERT figure caption aloud — NEET lifts questions from captions.
Day 5	PYQ drill	10 years of PYQs in one sitting. For every wrong answer, write the exact NCERT sentence that contained the answer into an error log.
Day 6	Retest	Retake the Day-0 test. Target: 44 / 45 or better. Anything below → go back to the specific weak block only.
Day 7	Compress	Reduce the whole chapter to one A4 sheet in your own handwriting. That sheet is what you revise later — never the textbook again.

Spaced-revision schedule

🔁 Revise the one-page sheet on Day 10 · Day 24 · Day 55 · Day 120 — then every fortnight in the final 3 months. Each revision under 12 minutes. Re-take the 45-Q test once a month; the aim is a stable 45/45, not a first-time 45/45.

The 5 "Zero-Miss" Rules 🎯 Non-negotiable

1. Line-level fidelity. If NCERT says "sustained high fever (39–40 °C)", learn the numbers. NEET has asked exactly that.
2. Never learn a disease alone. Always learn the quartet: pathogen → vector/mode → site in body → hallmark symptom. Most NEET questions are a mismatch in one of those four slots.
3. Learn the exceptions loudly. Rhinoviruses do not infect the lungs. Thymus is primary, not secondary. Male Anopheles does not transmit malaria. These are the traps.
4. Do assertion–reason & match-the-column deliberately. Since 2024, NEET leans heavily on statement-based questions where partial knowledge scores zero.
5. Keep an error log, not a notebook. One line per mistake, with the NCERT sentence. Before the exam, read only the log.

🦠 Common Diseases in Humans

Five pathogen groups. Learn each row as a 4-tuple: pathogen · vector/mode · main symptoms · site. NEET repeatedly asks "match the disease to its pathogen" or "vector of ___". The bacterial & protozoan rows are the most-tested.

A · Bacterial diseases 🔥🔥🔥🔥

Disease	Pathogen	Mode / Vector	Symptoms & site
Typhoid	Salmonella typhi	Contaminated food/water	Sustained high fever (39–40 °C), weakness, headache, stomach pain, constipation. Confirmed by Widal test. Site: small intestine (Peyer's patches). Mary Mallon = "Typhoid Mary" — asymptomatic carrier.
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae	Droplet infection (sneeze/cough)	Fluid fills alveoli → breathing difficulty; fever, chills, cough, headache. Severe: lips/nail-beds turn grey/bluish.

B · Viral diseases 🔥🔥🔥

Disease	Pathogen	Mode	Symptoms
Common cold	Rhinoviruses	Droplet inhalation, contaminated objects	Nasal congestion & discharge, sore throat, cough, headache, tiredness. Lasts 3–7 days. Infects nose & upper respiratory passages, NOT lungs.
Dengue / Chikungunya	Dengue & Chikungunya viruses (arboviruses)	*Aedes aegypti* mosquito	Named explicitly in NTA/NMC NEET syllabus even though NCERT treats them only in passing. Dengue = high fever, muscle/joint pain, rash, low platelet count. Chikungunya = high fever, debilitating joint pain.

C · Protozoan diseases 🔥🔥🔥🔥

Disease	Pathogen	Vector	Symptoms & site
Malaria	Plasmodium (vivax, malariae, falciparum, ovale)	Female Anopheles mosquito	Chill + high fever recurring every 3–4 days; RBCs rupture releasing haemozoin toxin. *P. falciparum* = most severe (malignant malaria).
Amoebiasis (Amoebic dysentery)	Entamoeba histolytica	Housefly (mechanical carrier)	Constipation, abdominal pain, stools with mucus & blood clots. Site: large intestine.

D · Helminthic diseases 🔥🔥🔥

Disease	Pathogen	Mode / Vector	Symptoms & site
Ascariasis	Ascaris lumbricoides (roundworm)	Contaminated food/water; through faeces	Internal bleeding, muscular pain, fever, anaemia, intestinal blockage.
Filariasis (Elephantiasis)	Wuchereria bancrofti, W. malayi	Female Culex mosquito	Chronic inflammation of lymphatic vessels of lower limb (elephantiasis) & scrotum (hydrocele).

E · Fungal diseases 🔥🔥

Disease	Pathogen (fungal genera)	Mode	Symptoms
Ringworms	Microsporum, Trichophyton, Epidermophyton	Contact — soil, towels, clothes; heat & moisture-friendly	Dry, scaly lesions with intense itching; skin, nails, scalp (groin, between toes common).

Prevention (universal): personal hygiene · clean drinking water · food handling · vector control (Anopheles, Culex, housefly) · vaccination where available · educating on transmission routes.

🛡️ Immunity

Two broad types — innate (present since birth, non-specific, quick) and acquired (learned after antigen exposure, specific, has memory). All the classic NEET splits below are single-mark tests waiting to happen.

A · Innate vs Acquired 🔥🔥🔥🔥

Feature	Innate (non-specific)	Acquired (specific)
Present from	Birth (inborn)	Develops after antigen exposure
Specificity	Non-specific — same defence for all invaders	Specific — targets a particular pathogen
Memory	None	Yes — primary vs secondary response
Speed	Rapid (minutes-hours)	Slow first time, fast on re-exposure
4 barriers	Physical (skin, mucus) · Physiological (HCl, saliva, tears) · Cellular (neutrophils, monocytes, macrophages, NK cells) · Cytokine (interferons from virus-infected cells)	Handled by B & T lymphocytes → antibodies + memory cells

B · Humoral vs Cell-mediated (both are acquired) 🔥🔥🔥🔥

Feature	Humoral (AMI)	Cell-mediated (CMI)
Cell type	B-lymphocytes	T-lymphocytes
Mechanism	Antibody secretion into blood/lymph	Direct killing (cytotoxic T-cells)
Best against	Extracellular pathogens (bacteria, toxins)	Intracellular pathogens (virus-infected cells, tumours) & graft rejection
Named after	"Humor" = body fluid	Cells directly involved

C · Active vs Passive immunity 🔥🔥🔥

Feature	Active	Passive
How acquired	Body makes its own antibodies after antigen contact (infection or vaccine)	Pre-formed antibodies given directly (mother→baby, antiserum injection)
Onset	Slow (days-weeks)	Immediate
Duration	Long-lasting (memory)	Short-lived (no memory)
Examples	Recovery from measles; DPT / MMR vaccination	Colostrum (IgA to newborn); anti-tetanus serum (ATS); anti-snake venom; anti-rabies immunoglobulin

D · Antibody Structure (Y-shape) 🔥🔥🔥

🔥Y-shaped protein with 2 heavy (H) chains + 2 light (L) chains ⇒ formula H₂L₂.
Two arms: Fab (antigen-binding, variable region) — very specific to one antigen.
Stem: Fc (constant region) — determines class.
5 antibody classes: IgG, IgA, IgM, IgE, IgD.
IgG — most abundant in serum; crosses placenta; long-lasting protection.
IgM — largest (pentamer); first antibody produced in primary response.
IgA — in colostrum, saliva, tears, mucus; mucosal immunity for newborns.
IgE — mediates allergy (binds mast cells → histamine release).
IgD — B-cell receptor; role unclear.

E · Lymphoid Organs 🔥🔥

Type	Organs	Function
Primary (production & maturation)	Bone marrow · Thymus	Origin (both B & T) & maturation (T-cells in thymus; B-cells in bone marrow)
Secondary (interaction with antigen)	Spleen · Lymph nodes · Tonsils · Peyer's patches (of small intestine) · Appendix · MALT (mucosa-associated)	Sites where lymphocytes meet antigen and multiply

F · Allergy & Auto-immunity 🔥🔥🔥

Allergy — exaggerated response to environmental antigens (allergens: dust, pollen, animal dander, mites). Mediated by IgE. Chemicals released: histamine & serotonin.
Treatment of allergy: anti-histamines, adrenaline, steroids.
Auto-immunity — body attacks self-cells. Classic NCERT example: Rheumatoid arthritis (RA). Others: Type I diabetes, MS, lupus (beyond NCERT depth).

💉 AIDS 🔥🔥🔥🔥 · 1 Q/yr

Acquired Immuno-Deficiency Syndrome. Caused by HIV — Human Immunodeficiency Virus, a member of the retrovirus family (RNA genome + reverse transcriptase). First reported 1981.

Transmission (routes) 🔥🔥🔥

Sexual contact with infected person (most common).
Contaminated blood/blood products (transfusion).
Sharing infected needles (drug abusers).
Infected mother → foetus via placenta (vertical transmission).
NOT transmitted by handshake, hugging, sharing food, mosquito bite, toilet seats, casual contact.

Mechanism inside body

HIV enters body → attaches to macrophage → RNA replicated via reverse transcriptase → DNA integrates into host genome (provirus).
New virus particles bud off, infect more Helper T-lymphocytes (T_H).
T_H count drops → immunity collapses → opportunistic infections (Mycobacterium, virus, fungi, parasites).
Karposi's sarcoma (skin cancer) — common in AIDS.
Time to AIDS symptoms: months to 10+ years (variable).

Diagnosis & Management

Diagnosis: ELISA (Enzyme-Linked Immuno-Sorbent Assay) detects antibodies against HIV.
Treatment: Anti-retroviral therapy (ART) — prolongs life; no cure.
Governing body in India: NACO (National AIDS Control Organisation).
Awareness by WHO — free condoms, safe blood, disposable needles, no stigma.

🎗️ Cancer 🔥🔥🔥 · 1 Q/yr

Uncontrolled cell division. Cancerous cells show loss of contact inhibition — they don't stop dividing when they touch other cells. NEET loves the benign/malignant split and the metastasis definition.

Benign vs Malignant tumours 🔥🔥🔥

Feature	Benign	Malignant (cancerous)
Growth	Slow	Rapid, uncontrolled
Metastasis	No — confined to original site	Yes — cells detach, travel via blood/lymph, form secondary tumours at distant sites
Damage	Minimal (may compress nearby tissue)	Extensive; damages normal tissue & steals nutrients (competes)
Effect on host	Rarely fatal	Often fatal without treatment

Types of cancer (by tissue of origin)

Type	Origin tissue	Examples
Carcinoma	Epithelial tissue	Skin, breast, lung, colon cancer
Sarcoma	Connective tissue (bone, cartilage, muscle)	Osteosarcoma, fibrosarcoma
Leukemia	Blood-forming tissues (bone marrow)	"Blood cancer" — WBC ↑↑
Lymphoma	Lymphatic tissue	Hodgkin's & non-Hodgkin's lymphoma

Causes (Carcinogens) 🔥🔥

Physical: Ionising radiation — X-rays, γ-rays (mutate DNA); Non-ionising — UV rays.
Chemical: Chemicals in tobacco smoke (major cause of lung cancer).
Biological / oncogenic viruses: genes called viral oncogenes (v-onc). Cellular counterparts = cellular oncogenes / proto-oncogenes (c-onc). Under certain conditions proto-oncogenes turn into oncogenes → cancer.

Detection & Diagnosis

Biopsy — tissue sample stained & examined microscopically (histopathology).
Blood/bone-marrow tests — for leukemia.
Imaging: Computed Tomography (CT) — X-rays generate a 3-D image. MRI (Magnetic Resonance Imaging) — strong magnetic fields + non-ionising radiation. Both detect internal tumours.
Molecular biology — identify genes with cancer susceptibility.
Antibodies against tumour antigens — detect certain cancers.

Treatment

Surgery — physical removal.
Radiotherapy — irradiate cancer cells (surrounding normal tissue also affected).
Chemotherapy — anti-cancer drugs (some kill hair follicles too → hair loss).
Immunotherapy — biological response modifiers like α-interferon activate immune system to destroy tumour.

💊 Drugs and Alcohol Abuse 🔥🔥🔥🔥 · 1 Q/yr

Match the drug ↔ plant ↔ effect. NEET repeatedly tests: name of source plant, category (opioid/cannabinoid/coca alkaloid), and target site in body.

A · Categories & sources 🔥🔥🔥🔥

Category	Drug (example)	Plant source	Effect & site
Opioids	Heroin (Smack) = diacetylmorphine (white, odourless, bitter powder)	Papaver somniferum (opium poppy) — from latex	Binds specific opioid receptors — depressant. Slows body functions. Usually taken by snorting & injection.
Cannabinoids	Marijuana, Hashish, Charas, Ganja	Cannabis sativa — from inflorescences (flower tops)	Bind cannabinoid receptors in the brain. Affect cardiovascular system. Being abused by sportspersons.
Coca alkaloid	Cocaine (Coke, Crack)	Erythroxylum coca — from leaves	Interferes with dopamine transport → strong euphoria + increased energy. Usually snorted. Excessive use → hallucinations.
Others (hallucinogens/CNS depressants)	Atropa belladonna, Datura (hallucinogens); Barbiturates, Amphetamines, LSD, Benzodiazepines	Various plants + synthetic	Medicinal use for depression, insomnia; abused for altered states.

B · Tobacco 🔥🔥🔥

Plant: Nicotiana tabacum. Active: nicotine — stimulates adrenal glands → adrenaline & nor-adrenaline release → BP & heart rate ↑.
Modes: smoking (cigarettes, cigars, hookah), chewing.
Diseases: lung cancer, oral cancer, urinary bladder cancer, bronchitis, emphysema, coronary heart disease, gastric ulcers, Buerger's disease.
Increases CO in blood → less O₂ carrying capacity of Hb.

C · Warning signs of drug/alcohol abuse

Drop in academic performance, unexplained absence from school.
Isolation, depression, fatigue, aggressive/rebellious behaviour.
Weight loss/gain, weakness, change in sleeping/eating habits.
Change of friend circle; hostility toward family.

D · Prevention & help

Avoid undue peer pressure; parents provide caring counsel; identify problems early.
Seek help — highly qualified psychologists & psychiatrists; de-addiction & rehabilitation programmes.
Do not just accept that a child is right — be observant.

🔢 Numbers & Data

Fact	Value
Antibody structure	2H + 2L chains → H₂L₂ (Y-shape)
Antibody classes	5 — IgG, IgA, IgM, IgE, IgD
Most abundant Ig in serum	IgG
Largest Ig (pentamer)	IgM (first produced)
Ig that crosses placenta	IgG
Ig in colostrum	IgA
Ig for allergy	IgE
Typhoid diagnostic test	Widal test
AIDS diagnostic test	ELISA
HIV target cell	Helper T-lymphocyte (T_H)
HIV enzyme	Reverse transcriptase
Malaria fever cycle	Every 3 or 4 days depending on species
Most severe malaria species	P. falciparum (malignant)
Filariasis vector	Female Culex
Malaria vector	Female Anopheles
Amoebiasis vector	Housefly (mechanical)
First reported year of AIDS	1981
Heroin chemical name	Diacetylmorphine
Opioids source	Papaver somniferum (latex)
Cocaine source	Erythroxylum coca (leaves)
Cannabinoids source	Cannabis sativa (inflorescences)
Tobacco alkaloid	Nicotine (from Nicotiana tabacum)
Cancer immunotherapy agent	α-interferon

🎯 ILTS Target Sprint — Life Cycles & Definitions

1. Plasmodium life cycle — 5 stages · dual host

Vector: female Anopheles mosquito · Definitive host: mosquito (sexual reproduction) · Intermediate host: human (asexual). NCERT figure is a guaranteed 1-mark Q every 2-3 years.

Sporozoite injection — infected female Anopheles bites human · injects sporozoites via saliva into bloodstream.
Liver phase — sporozoites reach liver · multiply asexually → release merozoites into blood.
RBC phase — merozoites attack RBCs · multiply inside · RBCs rupture in synchrony → releases haemozoin (toxic pigment) → causes chill + fever (every 48-72 h).
Gametocyte formation — some merozoites in RBCs form male + female gametocytes (sexual forms).
Mosquito uptake & sporogony — another female Anopheles bites patient · takes up gametocytes · in mosquito gut: fertilisation → zygote → oocyst → new sporozoites in salivary glands → cycle continues.

Species severity: P. falciparum (most severe · cerebral malaria) > P. vivax > P. malariae > P. ovale.

2. HIV replication cycle — 5 steps

HIV is a retrovirus targeting CD4+ T-helper cells · has an RNA genome + reverse transcriptase. Long asymptomatic phase (5-10 yr) — virus is silently integrated.

Attachment & entry — viral gp120 envelope glycoprotein binds CD4 receptor on T-helper cell · virus fuses with membrane · RNA + enzymes enter cytoplasm.
Reverse transcription — viral reverse transcriptase converts RNA → complementary DNA (cDNA). This is the "retro" step.
Integration — viral integrase inserts cDNA into host chromosome → becomes a provirus. This is why HIV cannot be cured — it hides in the host genome.
Transcription & translation — host machinery reads provirus → produces viral RNA + proteins.
Assembly & budding — new virions assemble at cell membrane · bud out taking host membrane as envelope. Progressive T-cell depletion → immunity collapses → opportunistic infections (Pneumocystis, Mycobacterium, Karposi's sarcoma) → AIDS.

3. ELISA vs Western blot — which and when

Feature	ELISA	Western blot
Full form	Enzyme-Linked Immuno-Sorbent Assay	Immunoblot (transfer to membrane)
Detects	Antibodies to HIV in serum	Antibodies to specific HIV proteins
Role	Screening (fast, cheap, sensitive)	Confirmatory (specific)
Cost / speed	Cheap · minutes	Expensive · hours
Order	1st test	Only if ELISA is positive
False +	Possible	Very rare

Also used: PCR — detects viral nucleic acid directly (useful in early window before antibodies form, and in newborns of HIV+ mothers).

4. Cancer — 4 definitions you must own cold

Contact inhibitionNormal cells stop dividing when they touch a neighbour. Cancer cells have lost contact inhibition → pile up → form tumour.

MetastasisCancer cells break off · travel via blood or lymph · seed secondary tumours elsewhere. Only malignant tumours metastasise · benign do not.

OncogeneA normal cellular gene (proto-oncogene) that has mutated / been activated · now drives uncontrolled division. Example: src, myc, ras. Contrast: tumour-suppressor genes (p53, Rb) when inactivated also cause cancer.

Benign vs MalignantBenign: encapsulated · slow · no metastasis · non-lethal. Malignant: invasive · fast · metastasises · life-threatening. Only malignant = "cancer".

5. Cancer types — 4 categories

Type	Origin	Common examples
Carcinoma	Epithelial tissue	Lung, breast, skin, colon
Sarcoma	Connective tissue (muscle, bone, cartilage)	Osteosarcoma · Karposi's sarcoma (in AIDS)
Leukaemia	Blood — bone marrow WBC	ALL, AML, CML
Lymphoma	Lymphoid tissue (lymph nodes)	Hodgkin's, non-Hodgkin's

Detection: biopsy · histology · MRI / CT · radioactive tracers · monoclonal antibodies for tumour markers. Treatment: surgery + radiotherapy + chemotherapy + immunotherapy (α-interferon).

⚠️ Trap Pairs / Confusables

Malaria: Anopheles ♀ vs Filaria: Culex ♀ — both mosquitoes; NEET swaps.

Amoebiasis: housefly (mechanical) — not a mosquito.

IgG crosses placenta · IgA in colostrum · IgE for allergy · IgM first produced.

Active immunity = your body makes antibodies · Passive = preformed antibodies given.

Primary lymphoid organs: bone marrow, thymus · Secondary: spleen, lymph nodes, MALT.

Humoral = B-cells, antibodies · Cell-mediated = T-cells, direct killing.

Benign = no metastasis · Malignant = metastasis via blood/lymph.

Carcinoma (epithelial) vs Sarcoma (connective) vs Leukemia (blood) vs Lymphoma (lymph).

HIV is a retrovirus (RNA) — uses reverse transcriptase.

Heroin = diacetylmorphine from Papaver. Cocaine from Erythroxylum. Don't confuse plants.

Cannabinoids affect cardiovascular system (not just brain).

Widal test = typhoid diagnostic · ELISA = AIDS diagnostic.

Karposi's sarcoma — associated with AIDS, not with tobacco.

Innate immunity = born with (non-specific) · Acquired = learned after exposure (specific + memory).

Auto-immunity classic NCERT example = Rheumatoid arthritis.

α-interferon = cancer immunotherapy · Interferons in general = innate defence vs viruses.

🧠 Mnemonics

4 innate barriers — "PPCC": Physical (skin) · Physiological (HCl, saliva, tears) · Cellular (neutrophils, macs, NK) · Cytokine (interferons).

5 antibody classes — "GAMED" → IgG · IgA · IgM · IgE · IgD.

Ig quick tags — "Goes across placenta · Abundant in colostrum · Most first / largest · Extreme (allergy) · Drifter on B-cell surface."

4 Plasmodium species — "V-M-F-O": Vivax · Malariae · Falciparum · Ovale.

Mosquito vector — "ANopheles → Malaria · CUlex → filariasis" (both female).

Cancer types — "C-S-L-L" → Carcinoma (epithelial) · Sarcoma (connective) · Leukemia (blood) · Lymphoma (lymph).

Drug plants — "PEC + N": Papaver (heroin) · Erythroxylum (cocaine) · Cannabis (marijuana) · Nicotiana (tobacco).

Ringworm 3 genera — "MET" (or "TEM"): Microsporum · Epidermophyton · Trichophyton.

Passive immunity examples — "Colostrum + serum": IgA from mother's colostrum, ATS injection for tetanus.

Lymphoid organs — "Primary = BT" (Bone marrow, Thymus). "Secondary = SLAP-T-M" (Spleen, Lymph nodes, Appendix, Peyer's patches, Tonsils, MALT).

🎯 High-Yield Top 25 Master these first

Typhoid → Salmonella typhi · diagnosed by Widal test · Mary Mallon = "Typhoid Mary" carrier.
Pneumonia → Streptococcus pneumoniae + Haemophilus influenzae. Alveoli fill with fluid.
Common cold → Rhinoviruses. Infects nose & upper respiratory (NOT lungs).
Malaria → Plasmodium (4 spp) via female Anopheles. Toxin: haemozoin. Most severe: P. falciparum.
Amoebiasis → Entamoeba histolytica via housefly. Site: large intestine.
Ascariasis → Ascaris lumbricoides. Filariasis → Wuchereria via female Culex.
Ringworms → Microsporum, Trichophyton, Epidermophyton (fungal).
Innate immunity = 4 barriers (PPCC) · Acquired = B/T cells + memory.
Humoral (B, antibodies) vs Cell-mediated (T, direct killing).
Active (own antibodies, slow, lasting) vs Passive (given, immediate, short).
Antibody = Y-shape · H₂L₂ · Fab (variable) · Fc (constant).
5 Ig classes = GAMED. IgG most abundant + crosses placenta.
IgM = largest pentamer, first produced. IgA = colostrum + tears. IgE = allergy.
Primary lymphoid = Bone marrow + Thymus. Secondary = Spleen, lymph nodes, MALT, Peyer's patches, tonsils.
Allergy — IgE-mediated · histamine + serotonin · treated by anti-histamines, adrenaline, steroids.
Auto-immunity classic example = Rheumatoid arthritis.
AIDS → HIV (retrovirus, RNA) → targets Helper T-cells → diagnosed by ELISA.
HIV transmission: sexual · blood · needles · mother→foetus. NOT by casual contact.
Cancer: Benign (no metastasis) vs Malignant (metastasis via blood/lymph). Loss of contact inhibition.
Cancer types: Carcinoma/Sarcoma/Leukemia/Lymphoma. Detection: biopsy, CT, MRI, monoclonal antibodies.
Oncogenes: proto-oncogene (c-onc) → oncogene (v-onc). Cancer treatment: surgery, radio, chemo, α-interferon.
Opioids = Heroin (diacetylmorphine) from Papaver somniferum.
Cannabinoids from Cannabis sativa (inflorescences) — affect cardiovascular.
Cocaine from Erythroxylum coca (leaves) — dopamine transport interference → euphoria.
Tobacco = Nicotiana tabacum → nicotine → BP ↑, lung/oral cancer, Buerger's disease.

📝 Self-Test — 15 NEET-style MCQs

Q1. Widal test is used to diagnose:

(a) Typhoid (b) Malaria (c) AIDS (d) Pneumonia

Answer

(a) Typhoid — detects antibodies against Salmonella typhi.

Q2. The vector for filariasis is:

(a) Female Anopheles (b) Female Culex (c) Female Aedes (d) Housefly

Answer

(b) Female Culex — carries Wuchereria bancrofti. Anopheles is for malaria.

Q3. Which antibody crosses the placenta?

(a) IgA (b) IgE (c) IgG (d) IgM

Answer

Q4. HIV primarily attacks:

(a) Erythrocytes (b) Neutrophils (c) Cytotoxic T-cells (d) Helper T-cells

Answer

(d) Helper T-cells (T_H) — their depletion collapses immunity → AIDS.

Q5. Diacetylmorphine is commonly known as:

(a) Cocaine (b) Heroin (c) Marijuana (d) LSD

Answer

(b) Heroin (Smack) — extracted from latex of Papaver somniferum.

Q6. Primary lymphoid organs include:

(a) Spleen & lymph nodes (b) Bone marrow & thymus (c) Tonsils & MALT (d) Peyer's patches & appendix

Answer

(b) Bone marrow & thymus — sites of lymphocyte origin/maturation. Others are secondary.

Q7. The first antibody produced in response to a new antigen is:

(a) IgA (b) IgG (c) IgM (d) IgE

Answer

Q8. Which of the following is a helminthic disease?

(a) Malaria (b) Typhoid (c) Ascariasis (d) Amoebiasis

Answer

Q9. Cancer characterised by loss of contact inhibition means:

(a) Cells recognise other cells and stop dividing (b) Cells do NOT stop dividing when touching other cells (c) Cells stop responding to hormones (d) Cells cannot undergo apoptosis

Answer

(b) Cells don't stop dividing on contact — normal cells respect this signal; cancer cells ignore it, causing uncontrolled growth.

Q10. Which is an example of passive immunity?

(a) MMR vaccine (b) Recovery from measles (c) Anti-tetanus serum injection (d) BCG vaccine

Answer

Q11. Cocaine is obtained from:

(a) Cannabis sativa (b) Papaver somniferum (c) Erythroxylum coca (d) Nicotiana tabacum

Answer

Q12. Rheumatoid arthritis is an example of:

(a) Allergy (b) Auto-immune disease (c) Immunodeficiency (d) Cancer

Answer

(b) Auto-immune disease — body attacks its own joint tissue.

Q13. The most severe form of malaria is caused by:

(a) P. vivax (b) P. malariae (c) P. falciparum (d) P. ovale

Answer

Q14. ELISA is used to detect:

(a) TB (b) Typhoid (c) HIV (d) Cancer

Answer

Q15. Assertion: Interferons are used in cancer treatment. Reason: They are biological response modifiers that activate the immune system to destroy tumours.

(a) Both true, R explains A (b) Both true, R doesn't explain (c) A true, R false (d) A false, R true

Answer

(a) Both true & connected. α-interferon is a standard immunotherapy — it stimulates immune cells to attack tumour tissue.

Page built 2026-07-26 · content strictly from NCERT Class 12 Ch 7 (Human Health & Disease). Weightage rankings reflect 10–15 years of NEET / AIPMT PYQ frequency.

⚠️ Exceptions The "only / not / except" traps NEET loves

Every one-line "except / only / does NOT" statement from the chapter. If you can rattle these off from memory, half the exam's assertion-reason questions are already yours.

🔥Rhinoviruses — infect the nose & upper respiratory passage but NOT the lungs. Common trap in "sites of infection" questions.
🔥Male Anopheles does NOT transmit malaria — only the female does (needs blood meal for egg development).
Same for Culex (filariasis) and Aedes (dengue/chikungunya) — females only.
🔥Housefly is NOT a vector — it's a mechanical carrier (spreads amoebic cysts on legs/body without hosting the parasite).
🔥Ringworm is NOT caused by a worm — despite the name, the pathogens are fungi (Microsporum, Trichophyton, Epidermophyton).
Innate immunity has NO memory — every response is a first-time response.
Innate immunity is non-specific — same defence for all invaders (unlike acquired).
🔥Thymus is a PRIMARY lymphoid organ (not secondary). Common trap. Same for bone marrow.
Thymus is large at birth, keeps shrinking with age, very small at puberty.
🔥IgG is the ONLY Ig that crosses the placenta (natural passive immunity to foetus).
IgA is the Ig in colostrum, tears, saliva & mucus — not IgG in colostrum.
IgM is the first Ig produced in a primary immune response (not IgG).
IgE mediates allergy — NOT IgG.
Cortisol/steroids treat allergy but are NOT antihistamines.
🔥HIV is NOT transmitted by: handshake, hugging, sharing food/utensils, mosquito bite, toilet seats, casual contact.
HIV is a retrovirus (RNA genome) — NOT a DNA virus.
Reverse transcriptase makes DNA from RNA — opposite of the normal Central Dogma direction (unique to retroviruses).
Anti-retroviral therapy (ART) prolongs life but does NOT cure AIDS.
🔥Not all tumours are cancerous — benign tumours are localised, don't metastasize, and usually aren't fatal.
Cancer cells lose contact inhibition — normal cells respect this signal.
α-interferon is used in cancer immunotherapy — it activates the immune system, it is NOT a chemotherapy drug.
Chemotherapy kills cancer cells but ALSO kills hair follicle cells → hair loss side-effect.
🔥Heroin ≠ Cocaine ≠ Cannabis — all three come from different plants: Papaver, Erythroxylum, Cannabis. Never swap.
Cannabinoids affect the cardiovascular system — NOT primarily the nervous system (unlike opioids/cocaine).
Cocaine acts on dopamine transport (interferes with it) — this is the euphoria mechanism.
Tobacco raises BP/HR by stimulating adrenal medulla to release adrenaline/noradrenaline — nicotine does NOT directly act on the heart.
Dengue & Chikungunya are in the NTA/NMC syllabus even though NCERT covers them only in passing. Vector = Aedes aegypti.
Karposi's sarcoma is associated with AIDS, not with tobacco use.
Rheumatoid arthritis is auto-immune, NOT an allergy.
MALT constitutes ~50 % of the lymphoid tissue in the human body.

🧑‍🔬 Scientists & Agencies (NCERT-named)

NCERT Chapter 7 is unusually light on named individual scientists (compared to Evolution or Genetics). The named contributors are as below, plus the government/global agencies you must recognise.

Name	NCERT-named contribution
Mary Mallon ("Typhoid Mary")	Historic asymptomatic carrier of Salmonella typhi who worked as a cook and spread typhoid to many people. Named directly in the NCERT typhoid section.
Rudolf Virchow	Cell theory extension — "all cells arise from pre-existing cells" (relevant to the cancer section's concept of uncontrolled cell division; the NCERT chapter builds on this idea from Ch 6/Bio-2).
WHO — World Health Organization	Runs the global programme on AIDS control & disease prevention; publishes the definitions and disease-classification standards NCERT uses.
NACO — National AIDS Control Organisation	Government of India body running AIDS awareness, safe-blood-supply, and free-condom programmes. Named directly in NCERT AIDS section.
CDRI, Lucknow	Central Drug Research Institute — developed Saheli, the non-steroidal once-a-week oral pill (referenced in RH but often cross-tested here).
ELISA developers	Not named individually in NCERT — but the test itself (Enzyme-Linked Immuno-Sorbent Assay) is the standard for detecting antibodies against HIV.

NEET-typical Q: "Who was Mary Mallon?" ⇒ Typhoid carrier (a cook). This is the highest-yield "scientist" question from this chapter.

📚 Examples Bank — from NCERT

Every "which of the following is an example of ___" trap in the chapter. If you can complete each Category ↔ Examples row without looking, this trap is closed.

Category	NCERT examples
Bacterial diseases	Typhoid (Salmonella typhi) · Pneumonia (Streptococcus pneumoniae, Haemophilus influenzae)
Viral diseases	Common cold (Rhinoviruses) · Dengue & Chikungunya (arboviruses via Aedes)
Protozoan diseases	Malaria (Plasmodium vivax, malariae, falciparum, ovale) · Amoebiasis (Entamoeba histolytica)
Helminthic diseases	Ascariasis (Ascaris lumbricoides) · Filariasis (Wuchereria bancrofti, W. malayi)
Fungal diseases	Ringworms — Microsporum · Trichophyton · Epidermophyton
Mosquito vectors (all female)	Anopheles → Malaria · Culex → Filariasis · Aedes aegypti → Dengue/Chikungunya
Mechanical carriers (non-mosquito)	Housefly → Amoebiasis
Innate — physical barriers	Skin · mucus lining of respiratory / GI / urogenital tracts
Innate — physiological	HCl in stomach · saliva (lysozyme) · tears
Innate — cellular	PMNL-neutrophils · monocytes · natural killer (NK) lymphocytes · macrophages
Innate — cytokine	Interferons (from virus-infected cells)
Primary lymphoid organs	Bone marrow · Thymus
Secondary lymphoid organs	Spleen · Lymph nodes · Tonsils · Peyer's patches (small intestine) · Appendix · MALT
Active-immunity examples	Recovery from measles · BCG / MMR / DPT vaccination
Passive-immunity examples	Colostrum (IgA) → newborn · IgG through placenta → foetus · Tetanus antitoxin (ATS) · Snake antivenom · Anti-rabies immunoglobulin
Antibody classes (5)	IgA · IgD · IgE · IgG · IgM (mnemonic: GAMED)
Allergens	Mites in dust · pollen · animal dander
Allergy chemicals	Histamine · Serotonin (both from mast cells)
Allergy drugs	Anti-histamines · Adrenaline · Steroids
Auto-immune disease (NCERT example)	Rheumatoid arthritis
Cancer types (by tissue)	Carcinoma (epithelial) · Sarcoma (connective) · Leukemia (blood/bone marrow) · Lymphoma (lymph)
Physical carcinogens	X-rays · γ-rays (ionising) · UV rays (non-ionising)
Chemical carcinogen	Chemicals in tobacco smoke (lung cancer)
Biological carcinogens	Oncogenic viruses (carry v-onc genes)
Cancer detection tools	Biopsy · Histopathology · Blood/bone-marrow tests (leukemia) · Radiography · CT · MRI · Monoclonal antibodies
Cancer treatments	Surgery · Radiotherapy · Chemotherapy · Immunotherapy (α-interferon)
Opioid drug & source	Heroin (Smack) = diacetylmorphine · Papaver somniferum (opium poppy) latex
Cannabinoids & source	Marijuana · Hashish · Ganja · Charas — Cannabis sativa inflorescences
Coca alkaloid	Cocaine (Coke, Crack) — Erythroxylum coca leaves
Hallucinogens	Atropa belladonna · Datura
Depressants / stimulants (medical)	Barbiturates · Amphetamines · LSD · Benzodiazepines
Tobacco & effects	Nicotiana tabacum → nicotine · Diseases: lung/oral/bladder cancer · Buerger's disease · Bronchitis · Emphysema · Coronary heart disease · Gastric ulcers
HIV-associated malignancy	Karposi's sarcoma (skin cancer)

📖 NCERT Chapter-End Exercises — Brief Answers

The exercises at the end of NCERT Ch 7. Answers are compressed to what NEET actually tests — one clean paragraph per question, no padding.

Q1. What are the various public health measures which you would suggest as safeguard against infectious diseases?

Answer

Personal hygiene (bathing, washing hands before food) · clean drinking water & safe food · sanitary disposal of waste & excreta · vector control (mosquito nets, breeding-site elimination) · vaccination against major diseases (typhoid, DPT, MMR, polio, hepatitis-B) · isolation of infected persons in outbreaks · education / awareness. Prevention is cheaper & kinder than cure.

Q2. Transmission modes of: (a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia?

Answer

(a) Amoebiasis — contaminated food/water; housefly is a mechanical carrier. (b) Malaria — bite of female Anopheles. (c) Ascariasis — eggs of Ascaris in soil/water/vegetables contaminated by faeces. (d) Pneumonia — droplet infection (sneeze/cough); sharing utensils/glasses.

Q3. What measures would you take to prevent water-borne diseases?

Answer

Boil / filter / chlorinate drinking water · dispose of sewage properly · avoid mixing sewage with drinking-water sources · keep flies away from food · wash raw vegetables/fruits before eating · maintain personal hygiene. Diseases prevented: typhoid, cholera, amoebiasis, hepatitis-A.

Q4. Discuss the differences between: (a) Innate vs Acquired immunity (b) Active vs Passive immunity.

Answer

(a) Innate — inborn, non-specific, no memory, immediate; 4 barriers (physical, physiological, cellular, cytokine). Acquired — learned after antigen exposure, specific, has memory (primary vs secondary response), takes time first exposure. (b) Active — body makes its own antibodies (slow, lasting); e.g. vaccine, recovery from infection. Passive — preformed antibodies given (immediate, short); e.g. colostrum IgA, tetanus antitoxin.

Q5. Draw a well-labelled diagram of an antibody molecule.

Answer

Y-shaped structure with 2 heavy (H) + 2 light (L) chains ⇒ formula H₂L₂. Two Fab arms carry the variable (antigen-binding) regions. The Fc stem is constant. Disulfide bonds hold the chains together. Five classes: IgA, IgD, IgE, IgG, IgM.

Q6. Routes of HIV transmission?

Answer

Sexual contact with infected person · transfusion of contaminated blood · sharing infected needles (drug abusers) · from infected mother to foetus through placenta. NOT transmitted by casual contact, mosquito, hugging.

Q7. Mechanism by which HIV causes immunodeficiency?

Answer

HIV enters body → attaches to macrophage → reverse transcriptase makes viral DNA from viral RNA → viral DNA integrates into host DNA → host directed to produce new virus particles. Virus simultaneously infects helper T-lymphocytes (T_H), replicates, and progressively reduces their number → immunity collapses → opportunistic infections (Mycobacterium, virus, fungi, parasites) & Karposi's sarcoma.

Q8. How is a cancerous cell different from a normal cell?

Answer

Normal cells show contact inhibition — they stop dividing on touching neighbours. Cancer cells lose this and divide uncontrollably → tumour. Malignant tumours also show metastasis — cells detach, travel via blood/lymph, form secondary tumours at distant sites. They compete with normal cells for nutrients, starving them.

Q9. Explain what is meant by metastasis.

Answer

The property (unique to malignant tumours) by which cells detach from the primary tumour, enter blood/lymph vessels, travel to distant sites in the body, and start new (secondary) tumours there. It is the most feared property of cancer — the reason cancer is often fatal.

Q10. Harmful effects caused by alcohol/drug abuse?

Answer

Immediate: reckless behaviour, vandalism, violence; overdose → coma / death. Long-term: loss of academic productivity, drop in health, tolerance & addiction, mental disorders, damage to liver (cirrhosis), kidney, heart. Family/social: financial ruin, damaged relationships, criminal behaviour to fund the addiction. Sharing needles → HIV/Hepatitis-B.

Q11. Can friends influence one to take alcohol/drugs? How to protect oneself?

Answer

Yes — peer pressure is a major cause. Protective moves: pick friends carefully · learn to say "no" firmly · seek help from parents / teachers / peers when uncomfortable · engage in sports, music, hobbies, other constructive activities · if temptation arises, seek professional counselling early.

Q12. Why is alcohol use during adolescence not advisable?

Answer

Adolescence is a period of major physical, mental & behavioural change. Alcohol interferes with brain development, disrupts studies, causes aggressive/rebellious behaviour, damages liver & other organs at a formative age, and — most dangerously — very often becomes the entry point to addiction that persists lifelong.

Q13. What motivates youngsters to take alcohol/drugs and how can this be avoided?

Answer

Motivators: curiosity · thrill/adventure/experimentation · peer pressure · academic/family stress · desire to look "cool" or independent · unstable family environments · media glamorisation. Avoidance: parents' watchful care · open communication · positive peer groups · sports/hobbies · counselling · avoid undue pressure on academic performance · seek professional help early.

⚖️ Comparison Tables — every side-by-side split NEET tests

A · Innate vs Acquired Immunity

Feature	Innate (non-specific)	Acquired (specific)
Present from	Birth (inborn)	Develops after antigen exposure
Specificity	Non-specific (same for all invaders)	Specific (targets a particular antigen)
Memory	None	Yes — primary vs secondary response
Speed	Rapid (min–hrs)	Slow first time, faster on re-exposure
Cells / mediators	Neutrophils, macrophages, NK cells, interferons	B-cells (antibodies), T-cells (cytotoxic)

B · Active vs Passive Immunity

Feature	Active	Passive
Antibody source	Body makes its own	Preformed antibodies given
Onset	Slow (days-weeks)	Immediate
Duration	Long — memory	Short — no memory
Examples	Vaccination · recovery from infection	Colostrum (IgA) · placental IgG · Tetanus antitoxin · Anti-snake venom

C · Humoral vs Cell-Mediated Immunity (both are acquired)

Feature	Humoral (AMI)	Cell-mediated (CMI)
Cell type	B-lymphocytes	T-lymphocytes
Mechanism	Antibody secretion into blood/lymph	Direct killing (cytotoxic T-cells)
Best against	Extracellular pathogens (bacteria, toxins)	Intracellular (virus-infected cells, tumours) · graft rejection
Named for	"Humor" = body fluid	Cells directly involved

D · B-cells vs T-cells

Feature	B-lymphocyte	T-lymphocyte
Maturation site	Bone marrow	Thymus
Product	Antibodies (immunoglobulins)	Directly kills / helps B-cells (helper T; cytotoxic T)
Involved in	Humoral immunity	Cell-mediated immunity + graft rejection
HIV target	—	Helper T-cell (T_H) — attacked by HIV

E · Primary vs Secondary Lymphoid Organs

Feature	Primary	Secondary
Role	Origin & maturation of lymphocytes	Interaction with antigen · proliferation
Organs	Bone marrow · Thymus	Spleen · Lymph nodes · Tonsils · Peyer's patches · Appendix · MALT
Antigen contact	Not the site	The site of contact & response

F · Benign vs Malignant Tumours

Feature	Benign	Malignant (cancerous)
Growth	Slow	Rapid, uncontrolled
Metastasis	No — confined	Yes — via blood/lymph → secondary tumours
Damage	Minimal, local compression	Extensive; competes with normal cells for nutrients
Effect on host	Rarely fatal	Often fatal without treatment

G · Cancer Types by Origin Tissue

Type	Origin tissue	NCERT example
Carcinoma	Epithelial	Skin, breast, lung, colon
Sarcoma	Connective (bone, cartilage, muscle)	Osteosarcoma, fibrosarcoma
Leukemia	Blood-forming (bone marrow)	"Blood cancer" — WBC ↑↑
Lymphoma	Lymphatic	Hodgkin's · non-Hodgkin's

H · Immunoglobulin Classes

Class	Distinguishing feature	Special role
IgG	Most abundant in serum	Only Ig that crosses placenta
IgA	In colostrum, saliva, tears, mucus	Mucosal immunity for newborn
IgM	Largest (pentamer)	First Ig produced in primary response
IgE	Binds mast cells	Mediates allergy (histamine release)
IgD	B-cell surface receptor	Role unclear

I · Vectors — Which Mosquito or Fly?

Vector	Disease(s)	Notes
Female Anopheles	Malaria (Plasmodium)	Only the female needs a blood meal
Female Culex	Filariasis (Wuchereria)	Lymphatic vessels affected
Female Aedes aegypti	Dengue & Chikungunya	Named in NEET syllabus
Housefly	Amoebiasis	Mechanical carrier (NOT true vector)

J · Drug Categories — Source & Effect

Category	Drug	Plant source	Effect
Opioids	Heroin (Smack)	Papaver somniferum (latex)	Depressant · opioid receptors
Cannabinoids	Marijuana, Hashish, Ganja, Charas	Cannabis sativa (inflorescences)	Affects cardiovascular system
Coca alkaloid	Cocaine	Erythroxylum coca (leaves)	Blocks dopamine transport → euphoria
Hallucinogens	—	Atropa belladonna · Datura	Altered perception
Stimulant	Nicotine (tobacco)	Nicotiana tabacum	Adrenal release → BP & HR ↑

K · Allergy vs Auto-immunity vs Immunodeficiency

Feature	Allergy	Auto-immunity	Immunodeficiency
What goes wrong	Immune system over-reacts to harmless antigen	Immune system attacks own body cells	Immune system is weakened / absent
Mediator	IgE + mast-cell histamine/serotonin	Auto-antibodies	—
NCERT example	Dust, pollen, mite allergy	Rheumatoid arthritis	AIDS (acquired) · SCID (inherited)