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HUMAN HEALTH & DISEASE

MASTER REVISION SHEET · NCERT CLASS 12 BIOLOGY (RATIONALISED) CH. 7 · OLD NCERT CH. 8

NEET / NTA–NMC Zoology · Biology & Human Welfare 4-Page PYQ-Weighted Edition
Official NEET syllabus statement for this chapter

Pathogens; parasites causing human diseases (malaria, filariasis, ascariasis, typhoid, pneumonia, common cold, amoebiasis, ringworm, dengue, chikungunya); basic concepts of immunology – vaccines; cancer; HIV & AIDS; adolescence, drug and alcohol abuse.  2–3 Qs / year  Highest-yield: Malaria cycle · Immunity types · Drug abuse

A · COMMON HUMAN DISEASES — THE MASTER TABLE (learn column-wise, not row-wise)

DiseasePathogen (genus–species) GroupTransmission / VectorTarget organ & hallmark signs
TyphoidSalmonella typhiBacteriumContaminated food & water Enters small intestine → blood → other organs. Sustained fever 39–40 °C, weakness, stomach pain, constipation, headache, loss of appetite. Severe: intestinal perforation & death. Test: Widal. Classic case: Mary Mallon “Typhoid Mary”, a cook, spread it via the food she prepared.
PneumoniaStreptococcus pneumoniae, Haemophilus influenzaeBacteriumInhaling droplets/aerosols; sharing glasses & utensils Alveoli fill with fluid → severe breathing problems. Fever, chills, cough, headache; severe: lips & finger nails turn grey to bluish.
Common coldRhino virusesVirusDroplets, contaminated objects (pen, book, cup, doorknob) Infects nose & respiratory passage — NOT the lungs. Nasal congestion & discharge, sore throat, hoarseness, cough, headache, tiredness; lasts 3–7 days.
MalariaPlasmodium vivax, P. malariae, P. falciparum (falciparum = malignant, most fatal)ProtozoanBite of female Anopheles (vector + secondary host) Liver cells → RBCs. RBC rupture releases haemozoin (toxin) → chill & high recurring fever every 3–4 days.
Amoebiasis
(amoebic dysentery)		Entamoeba histolyticaProtozoanContaminated food/water; houseflies = mechanical carrier Large intestine. Constipation, abdominal pain & cramps, stools with excess mucous and blood clots.
AscariasisAscaris lumbricoides (round worm)HelminthEggs in faeces → contaminated soil, water, vegetables, fruits Internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
Filariasis
(Elephantiasis)		Wuchereria bancrofti, W. malayiHelminthBite of female Culex mosquito Lymphatic vessels of the lower limbs → chronic inflammation, gross deformity; genital organs also often affected. Pathogens take many years to show symptoms.
RingwormMicrosporum, Trichophyton, EpidermophytonFungusSoil; towels, clothes, comb of infected person Skin, nails, scalp (esp. groin & between toes). Dry, scaly lesions + intense itching. Heat & moisture favour growth.
Dengue & ChikungunyaVirusesVirusAedes aegypti (day-biting) Listed by name in the NEET syllabus — remember vector + viral nature; that is what is asked.

B · NCERT FIGURE — LIFE CYCLE OF PLASMODIUM (most-drawn figure of the chapter)

HUMAN — secondary host FEMALE ANOPHELES — primary host 1. Mosquito bite injects SPOROZOITES into blood 2. Multiply in LIVER cells, then attack RBCs 3. RBCs RUPTURE, releasing HAEMOZOIN toxin = chill + fever every 3-4 days 4. Some parasites form GAMETOCYTES in RBC ASEXUAL CYCLE occurs here Infective stage to man = SPOROZOITE Infective to mosquito = GAMETOCYTE Man = intermediate host 5. Mosquito sucks blood with gametocytes 6. In the MOSQUITO GUT gametes fuse: fertilisation + development = SEXUAL cycle 7. SPOROZOITES formed and stored in the mosquito SALIVARY GLAND 8. Next bite: the cycle repeats SEXUAL CYCLE occurs here Mosquito = primary / definitive host Vector = FEMALE Anopheles only Read the cycle clockwise
Fig. 7.1 — Stages in the life cycle of Plasmodium. Arrow direction and the gut/salivary-gland split are the two most examined details.

C · HEALTH, PATHOGENS & PREVENTION

  • Health = a state of complete physical, mental and social well-being, not merely the absence of disease (WHO framing used by NCERT).
  • Maintained by: balanced diet, personal hygiene, regular exercise, yoga, awareness, vaccination, waste disposal, vector control.
  • Pathogens = disease-causing organisms. Parasites live in/on the host and derive nourishment from it.
  • Two prevention pillars: (i) maintaining personal & public hygiene, (ii) vector control + immunisation.
  • Public hygiene: proper disposal of waste & excreta, periodic cleaning & disinfection of water reservoirs, standard practices for drinking water and food.
  • Vector control: eliminate breeding places, remove stagnant water, clean coolers & tanks, mosquito nets, spray insecticides, introduce larvivorous fish like Gambusia into ponds.
Killer traps NEET has actually used
  • Common cold does NOT infect the lungs — only nose & respiratory passage.
  • Anopheles = malaria; Culex = filariasis; Aedes = dengue/chikungunya. Never swap.
  • Housefly in amoebiasis is a mechanical carrier, not a biological vector.
  • P. falciparum is malignant malaria; P. vivax is the commonest — “most fatal ≠ most common”.
  • Widal → typhoid; ELISA → AIDS. Do not attach Widal to any other disease.
Mnemonics that survive the exam hall

Vectors “ACA”: Anopheles–malAria, Culex–filariasis (Chronic limbs), Aedes–dengue.

Ringworm “MTE”: Microsporum, Trichophyton, Epidermophyton.

Ascaris = Anaemia + blockage; Entamoeba = Excess mucous + blood in stool.

Human Health & Disease · Master Revision SheetPage 1 of 4 — Diseases & Malaria Cycle

IMMUNITY — THE HIGHEST-SCORING HALF OF THE CHAPTER

Page 2 · Innate · Acquired · Antibodies · Vaccines · Allergy

D · INNATE IMMUNITY — NON-SPECIFIC, PRESENT FROM BIRTH

BarrierComponents (exact NCERT wording)
PhysicalSkin; mucus coating of the epithelium lining the respiratory, gastrointestinal & urogenital tracts — traps microbes.
PhysiologicalAcid of the stomach, saliva in the mouth, tears from the eyes — prevent microbial growth.
CellularPMNL–neutrophils, monocytes, natural killer (NK) lymphocytes in blood + macrophages in tissues — phagocytose and destroy microbes.
CytokineVirus-infected cells secrete interferons which protect non-infected neighbouring cells.

E · ACQUIRED (ADAPTIVE) IMMUNITY — PATHOGEN-SPECIFIC + MEMORY

  • Primary response — first encounter, low intensity, slow.
  • Secondary / anamnestic response — subsequent encounter, highly intensified and fast, because of memory B and T cells.
  • Two cell types: B-lymphocytes produce an army of proteins = antibodies. T-lymphocytes do not make antibodies themselves — they help B cells produce them.
TypeKey identity
Humoral / Antibody-mediated (AMI)Carried out by antibodies in body fluids (blood) produced by B cells.
Cell-mediated (CMI)Carried out by T-lymphocytes. Responsible for graft rejection; the body is able to differentiate “self” from “non-self”.

F · ACTIVE vs PASSIVE IMMUNITY

ACTIVEPASSIVE
MechanismHost is exposed to antigens (live/dead microbes or proteins) and makes its own antibodies.Ready-made antibodies are directly given to the body.
SpeedSlow — takes time to give its full effective response.Immediate.
MemoryPresent (long-lasting).Absent (short-lived).
ExamplesNatural infection; vaccination.Colostrum → IgA for the newborn; foetus gets IgG through the placenta; tetanus antitoxin; antivenom for snake bite.

G · NCERT FIGURE — STRUCTURE OF AN ANTIBODY MOLECULE

Antigen-binding site Antigen-binding site Light chain (L) Light chain (L) Heavy chain (H) Disulphide bond Fc region H₂L₂
Fig. 7.2 — Each antibody = 4 peptide chains: two small light (L) + two longer heavy (H) → represented as H₂L₂.

Antibody isotypes — remember the five, remember two

IgA · IgM · IgE · IgG · IgD.  IgA = colostrum & secretions; IgE = allergy; IgG = crosses placenta; IgM = first antibody of primary response; IgD = surface receptor of B cells.

H · LYMPHOID ORGANS

OrganFunction & exam point
PRIMARY
Bone marrow, Thymus		Where immature lymphocytes differentiate into antigen-sensitive lymphocytes. Bone marrow = main lymphoid organ; all blood cells including lymphocytes are produced here. Thymus: lobed, large at birth, very small by puberty.
SECONDARY
Spleen, Lymph nodes, Tonsils, Peyer’s patches, Appendix		Sites where lymphocytes interact with the antigen, then proliferate to become effector cells. Spleen: large bean-shaped; filters blood by trapping blood-borne micro-organisms; reservoir of erythrocytes. Lymph nodes: trap microbes/antigens in lymph & tissue fluid.
MALTMucosa-Associated Lymphoid Tissue — lining of the respiratory, digestive & urogenital tracts. Constitutes about 50 % of the lymphoid tissue in the human body.
Antibody titre Time after exposure to the antigen 1st exposure 2nd exposure PRIMARY low, slow SECONDARY (anamnestic) fast and highly intensified
Primary vs secondary antibody response — the shape of this curve is itself an exam question.

I · VACCINATION & IMMUNISATION

  • Principle: memory of the immune system. A preparation of antigenic proteins of a pathogen or inactivated/weakened pathogen (= vaccine) is introduced.
  • Antibodies are produced and, crucially, memory B & T cells form — these recognise the pathogen quickly on real infection.
  • If a person is already infected (deadly microbes, quick response needed) → give preformed antibodies / antitoxin = passive immunisation. Example: tetanus.
  • Snake bite: injection of antivenom = preformed antibodies against snake venom.
  • Recombinant DNA technology: antigenic polypeptides produced in bacteria/yeast → large-scale vaccines. Hepatitis B vaccine produced from yeast.

J · ALLERGY — EXAGGERATED RESPONSE

  • Response to certain antigens present in the environment = allergens (mites in dust, pollens, animal dander).
  • Antibodies produced are of IgE type.
  • Symptoms: sneezing, watery eyes, running nose, difficulty in breathing.
  • Due to histamine and serotonin released from mast cells.
  • Drugs: anti-histamine, adrenalin, steroids quickly reduce the symptoms.
  • Diagnosis: a small dose of the suspected allergen is injected into the skin and the reaction studied.
  • Modern-city children show more allergies — protected environment early in life lowers immunity development.

K · AUTOIMMUNITY & TRANSPLANT

  • Memory-based immunity sometimes goes wrong: the body attacks self-cells → auto-immune disease. NCERT example: rheumatoid arthritis.
  • Graft/organ transplant: tissue matching & blood group matching are essential; even then the patient takes immuno-suppressants lifelong.
  • The rejection is due to cell-mediated immunity — T-lymphocytes.
Immunity traps
  • Interferon = cytokine barrier (innate), NOT acquired.
  • NK cells are lymphocytes but belong to innate cellular barrier.
  • Colostrum → IgA; placenta → IgG. Reversing these is the single commonest error.
  • Appendix & tonsils are secondary lymphoid organs; thymus is primary.
Human Health & Disease · Master Revision SheetPage 2 of 4 — Immunology

AIDS & CANCER — THE TWO GUARANTEED SCORERS

Page 3 · HIV replication · Diagnosis · Oncogenes · Therapy

L · AIDS — ACQUIRED IMMUNO-DEFICIENCY SYNDROME

  • “Acquired” = not congenital, “Immuno-Deficiency” = drop in immunity, “Syndrome” = a group of symptoms.
  • Caused by HIV — a member of the retrovirus group, which has an RNA genome and an envelope. First reported in 1981; killed more than 25 million people in about two decades.
  • Transmission (4 routes only): ① sexual contact with an infected person; ② transfusion of contaminated blood; ③ sharing infected needles (drug addicts); ④ from infected mother to child through the placenta.
  • High-risk groups: individuals with multiple sexual partners, drug addicts taking drugs intravenously, those needing repeated blood transfusions, children born to an HIV-positive mother.
  • HIV does NOT spread by casual physical contact — hugging, shaking hands, sharing food, mosquito bite. AIDS patients need care, not isolation.
  • Time lag between infection and appearance of symptoms: a few months to many years (usually 5–10 years).
  • Symptoms of full-blown AIDS: bouts of fever, diarrhoea and weight loss; the patient becomes so immuno-deficient that he/she cannot protect against even Mycobacterium, viruses, fungi and parasites like Toxoplasma.
  • Diagnosis: ELISA (Enzyme Linked Immuno-Sorbent Assay).
  • Treatment: anti-retroviral drugs — only partially effective; they prolong life but cannot prevent death.
  • Prevention (NACO & NGOs; WHO programme): use of disposable needles & syringes, free distribution of condoms, controlled drug abuse, advocating safe sex, routine blood screening in blood banks. Prevention is far better than cure — infection always leads to death.
HIV enters the body and attacks a MACROPHAGE Viral RNA makes viral DNA by REVERSE TRANSCRIPTASE the single most-asked enzyme of this chapter Viral DNA is incorporated into the host cell DNA It directs the cell to produce virus particles: the macrophage becomes an HIV FACTORY HIV also enters HELPER T-LYMPHOCYTES, replicates in them and releases progeny viruses into the blood Progeny attack fresh helper T cells, cycle repeats Helper T-lymphocyte number FALLS progressively = AIDS
Fig. 7.3 — Replication of the retrovirus (HIV) in the host cell. Note the order: macrophage first, then TH cells.

M · CANCER

Normal vs cancer cell — the defining property

  • Normal cells show contact inhibition: contact with other cells inhibits their uncontrolled growth. Cancer cells appear to have lost this property.
  • Cancer cells divide continuously → a mass of cells called a tumour.
  • Benign tumour: normally remains confined to its original location, does not spread, causes little damage.
  • Malignant tumour: a mass of proliferating cells called neoplastic / tumour cells. They grow very rapidly, invading and damaging surrounding normal tissue, and starve the normal cells by competing for vital nutrients.
  • METASTASIS — the most feared property: cells sloughed from the tumour reach distant sites through the blood and start a new tumour there.

Causes of cancer — carcinogens

TypeExamples
PhysicalIonising radiation: X-rays, gamma rays. Non-ionising: UV. Cause DNA damage → neoplastic transformation.
ChemicalChemicals of tobacco smoke → major cause of lung cancer.
BiologicalOncogenic viruses, which carry viral oncogenes.

Proto-oncogenes: normal cells contain cellular oncogenes (c-onc) or proto-oncogenes; when activated under certain conditions they can lead to the oncogenic transformation of the cell.

Benign vs malignant — the exact discriminators
FeatureBenignMalignant
SpreadConfined to original siteInvades surrounding tissue
MetastasisAbsentPresent — via blood
Growth rateSlowVery rapid
Effect on hostLittle damageStarves normal cells of nutrients

Cancer detection & diagnosis

  • Biopsy & histopathological studies of the tissue — a piece of tissue is cut, stained and examined under a microscope by a pathologist.
  • Blood and bone-marrow tests — used for leukaemias (cancers of the blood).
  • Radiography (X-rays), CT and MRI to detect internal cancers. CT uses X-rays to build a three-dimensional image of the internals. MRI uses strong magnetic fields and non-ionising radiation to accurately detect pathological and physiological changes in living tissue.
  • Antibodies against cancer-specific antigens are used for detection.
  • Molecular biology techniques detect genes in individuals with an inherited susceptibility to certain cancers — such people can be advised to avoid carcinogens.

Treatment

  • Surgery, radiation therapy and chemotherapy — most cancers are treated by a combination of these.
  • In radiotherapy tumour cells are irradiated lethally, taking proper care of the normal surrounding tissues.
  • Chemotherapeutic drugs kill cancerous cells; most have side effects such as hair loss and anaemia.
  • Immunotherapy: tumour cells largely avoid detection and destruction by the immune system, so patients are given biological response modifiers such as α-interferon, which activates their immune system and helps in destroying the tumour.
AIDS & cancer traps
  • HIV is a retrovirus — RNA genome; reverse transcriptase makes DNA from RNA, not the reverse.
  • ELISA diagnoses AIDS; biopsy is the definitive cancer test.
  • Benign ≠ harmless in every option set — it is defined by remaining confined, not by size.
  • MRI = non-ionising; CT = X-ray based. Frequently swapped in options.
  • α-interferon = treatment (immunotherapy); interferon in immunity = innate cytokine barrier. Same molecule, two different questions.

NCERT LINES THAT BECOME QUESTIONS ALMOST WORD-FOR-WORD

  • “Cancer cells appear to have lost the property of contact inhibition.”
  • “Metastasis — the property that makes cancer so feared.”
  • “HIV is a retrovirus with an RNA genome and an envelope.”
  • “The macrophage continues to produce virus and acts like an HIV factory.”
  • “Anti-retroviral drugs are only partially effective.”
  • “MRI uses strong magnetic fields and non-ionising radiations.”
  • “α-interferon activates the immune system and helps in destroying the tumour.”
  • “Proto-oncogenes, when activated, could lead to oncogenic transformation.”
  • “Prevention is far better than cure” — the AIDS message NCERT ends on.
Human Health & Disease · Master Revision SheetPage 3 of 4 — AIDS & Cancer

DRUGS & ALCOHOL ABUSE + LAST-MINUTE RECALL

Page 4 · Adolescence · Drugs · PYQ trend · 40 one-liners

N · ADOLESCENCE, DRUG & ALCOHOL ABUSE

Adolescence = the period between 12 and 18 years of age; it is both a period and a process during which a child becomes mature — a bridge linking childhood and adulthood. It is mentally and psychologically a very vulnerable phase.

Drug groupSource / receptorForms, route & effect on the body
OpioidsBind to opioid receptors in the CNS and gastro-intestinal tract. From the latex of the poppy plant Papaver somniferum. Heroin = diacetylmorphine = “smack”: white, odourless, bitter crystalline compound, obtained by acetylation of morphine. Taken by snorting and injection. It is a DEPRESSANT — slows down body functions.
CannabinoidsInteract with cannabinoid receptors present principally in the brain. From Cannabis sativa. Obtained from the inflorescences — flower tops, leaves and resin give marijuana, hashish, charas, ganja. Taken by inhalation and oral ingestion. Affects the CARDIOVASCULAR system. Also abused by some sportspersons.
Coca alkaloid
(cocaine / coke / crack)		From Erythroxylum coca, native to South America. Interferes with the transport of the neurotransmitter dopamine. Usually snorted. Potent STIMULATING action on the CNS → sense of euphoria and increased energy. Excessive dose → hallucinations.
HallucinogensAtropa belladonna, DaturaOther well-known plants with hallucinogenic properties.
Medicinal drugs abusedMorphine, barbiturates, amphetamines, benzodiazepines, LSDNormally used as medicines to help patients cope with depression and insomnia, but are frequently abused.
TobaccoNicotiana tabacum — used for more than 400 years. Contains the alkaloid nicotine. Smoked, chewed or used as snuff. Nicotine stimulates the adrenal gland to release adrenaline & nor-adrenaline → raise blood pressure and increase heart rate. Smoking raises CO in blood, lowering haem-bound oxygen → oxygen deficiency.
Alcohol—Damages the nervous system and the liver → cirrhosis.

Tobacco-linked disorders: cancers of the lung, urinary bladder and throat; bronchitis, emphysema, coronary heart disease, gastric ulcer. Tobacco chewing → cancer of the oral cavity.

Why adolescents start

  • Curiosity, need for adventure and excitement, and the desire to experiment — the commonest causes.
  • To escape facing problems; academic/exam stress; perceived need to “do more than others”.
  • Peer pressure; unstable or unsupportive family structures.
  • Media and TV glamorising the behaviour.

Addiction, dependence & withdrawal

  • Addiction — a psychological attachment to the euphoria and temporary well-being; the user ignores the harm and takes higher doses to get the same effect (tolerance).
  • Dependence — the body’s tendency to manifest a characteristic and unpleasant withdrawal syndrome if regular dose is abruptly discontinued: anxiety, shakiness, nausea and sweating, which may be severe.

Adverse effects

  • Reckless behaviour, vandalism and violence.
  • Excessive doses → coma and death due to respiratory failure, heart failure or cerebral haemorrhage.
  • Combination of drugs, or intake along with alcohol → overdose and death.
  • Use during pregnancy adversely affects the foetus.
  • Anabolic steroids misused in sports: females — masculinisation, abnormal menstrual cycles, excessive facial/body hair, enlargement of clitoris, deepening of voice; males — acne, aggressiveness, mood swings, depression, reduction in size of testicles, decreased sperm production, kidney & liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland. In adolescent females also premature closure of the growth centres of long bones → stunted growth.

Warning signs & prevention

  • Drop in academic performance, unexplained absence from school, lack of interest in personal hygiene, withdrawal and isolation, depression, fatigue, aggressive and rebellious behaviour, change in sleeping and eating habits, fluctuations in weight and appetite.
  • Prevention: avoid undue peer pressure; education and counselling to channel energy into sports, reading, music, yoga; seeking help from parents and peers; looking for danger signs; seeking professional and medical help from psychologists, psychiatrists and de-addiction/rehabilitation programmes.

O · WHERE THE MARKS ACTUALLY COME FROM — PYQ PATTERN

Very high frequency: pathogen–disease matching · malaria life-cycle stage & host · innate immunity barrier classification · active vs passive immunity examples · HIV replication order · contact inhibition & metastasis · nicotine on adrenal gland.

Assertion–Reason favourites: “Common cold does not infect lungs” · “Cancer cells lose contact inhibition” · “Colostrum gives passive immunity” · “Cannabinoids affect the cardiovascular system” · “Thymus is a primary lymphoid organ”.

Match-the-column favourites: disease ↔ pathogen ↔ vector · drug ↔ source plant ↔ receptor · immunoglobulin ↔ role · lymphoid organ ↔ primary/secondary. Learn these as triplets, never as isolated pairs.

P · 40-SECOND RECALL — ONE-LINERS TO SCAN JUST BEFORE THE EXAM

1. Widal test → typhoid.

2. Typhoid Mary → Mary Mallon, a cook.

3. Grey-blue nails & lips → pneumonia.

4. Rhinovirus → common cold, 3–7 days, no lungs.

5. Haemozoin → chill + fever every 3–4 days.

6. Sporozoite → infective stage to humans.

7. Gametocyte → stage taken up by the mosquito.

8. Sexual cycle of Plasmodium → mosquito’s gut.

9. Sporozoites stored → mosquito salivary gland.

10. P. falciparum → malignant malaria.

11. Entamoeba histolytica → large intestine.

12. Housefly → mechanical carrier of amoebiasis.

13. Ascaris → anaemia + intestinal blockage.

14. Wuchereria → lymph vessels of lower limbs.

15. Ringworm → heat & moisture; 3 genera.

16. Gambusia → larvivorous fish, vector control.

17. Interferons → cytokine barrier, protect uninfected cells.

18. NK cells, macrophages → cellular barrier.

19. Tears, saliva, stomach acid → physiological barrier.

20. Secondary response = anamnestic, high intensity.

21. Antibody = H₂L₂, 4 chains.

22. Graft rejection → cell-mediated immunity.

23. Colostrum → IgA; placenta → IgG.

24. Snake antivenom, tetanus antitoxin → passive.

25. Hepatitis B vaccine → made in yeast (rDNA).

26. Allergy → IgE, mast cells, histamine + serotonin.

27. Rheumatoid arthritis → auto-immune.

28. Bone marrow & thymus → primary lymphoid organs.

29. MALT ≈ 50 % of lymphoid tissue.

30. Spleen → reservoir of erythrocytes.

31. HIV → retrovirus, reverse transcriptase.

32. Macrophage → “HIV factory”.

33. AIDS → fall in helper T-lymphocytes.

34. ELISA → AIDS diagnosis.

35. Metastasis → spread via blood to distant sites.

36. α-interferon → cancer immunotherapy.

37. Heroin → depressant, from Papaver somniferum.

38. Cocaine → stimulant, blocks dopamine transport.

39. Cannabinoids → from inflorescence, hit the heart.

40. Nicotine → adrenal gland → adrenaline ↑ BP, ↑ HR.

Human Health & Disease · Master Revision Sheet · Prepared for NEET (NTA–NMC) aspirantsPage 4 of 4 — Drug Abuse & Rapid Recall