Human Health and Disease - Class 12 Biology

Class 12 Biology | Unit IX — Biology in Human Welfare

Chapter 8: Human Health and Disease

Immunity • Malaria • AIDS • Cancer • Drugs & Alcohol

1. Health and Immunity

Health (WHO definition): A state of complete physical, mental and social well-being, and not merely an absence of disease or infirmity.

1.1 Types of Immunity

Type	Subdivisions	Features / Examples
Innate (Natural / Non-specific)	Physical barriers	Skin, mucus membranes, cilia of respiratory tract
Innate (Natural / Non-specific)	Physiological barriers	Stomach acid (HCl kills bacteria), saliva (lysozyme), tears (lysozyme), fever
Innate — Cellular	Phagocytosis, NK cells	Monocytes, neutrophils, macrophages engulf pathogens. Natural Killer (NK) cells kill virus-infected/ tumour cells.
Acquired (Adaptive / Specific)	Active immunity	Body produces its own antibodies after exposure to antigen (natural infection or vaccination). Long-lasting. Memory cells formed.
Acquired (Adaptive / Specific)	Passive immunity	Ready-made antibodies transferred from another source. Fast but short-lived. Examples: maternal antibodies via placenta/colostrum; anti-snake venom; tetanus antitoxin.

1.2 Active vs Passive Immunity

Feature	Active Immunity	Passive Immunity
Antigen exposure	Required	Not required
Antibody source	Self (host)	External (another organism)
Onset	Slow (days)	Immediate
Duration	Long-lasting (years)	Short-lived (weeks)
Memory cells	Yes	No
Examples	Vaccination, natural infection	Colostrum, anti-venom, IgG transfer via placenta

1.3 Lymphoid Organs

Organ	Primary / Secondary	Function
Bone Marrow	Primary	Site of B-lymphocyte maturation. Source of all blood cells (haematopoiesis).
Thymus	Primary	Site of T-lymphocyte maturation. Largest at birth, involutes with age. Secretes thymosins.
Spleen	Secondary	Largest lymphoid organ. Filters blood. Destroys old RBCs (graveyard of RBCs). Produces antibodies and B-cells.
Lymph Nodes	Secondary	Filter lymph; trap antigens. Proliferation of lymphocytes and macrophages.
Tonsils, MALT	Secondary	Mucosa-Associated Lymphoid Tissue (MALT) — lining of digestive, respiratory, urogenital tracts.
Peyer's Patches	Secondary	In small intestine wall; important for gut immunity.

⚠️ NEET Focus (2013, 2016, 2019, 2022): Thymus = primary lymphoid organ, T-cell maturation, secretes thymosins. Bone marrow = B-cell maturation + all blood cells. Spleen = largest lymphoid organ + graveyard of RBCs. Colostrum = IgA rich (first milk, passive immunity). Passive immunity via placenta = IgG.

2. Antibodies and Immune Response

2.1 Antibody Structure

Antibody (Immunoglobulin): Y-shaped glycoprotein produced by plasma cells (activated B-cells). Structure = 4 polypeptides: 2 heavy (H) chains + 2 light (L) chains connected by disulphide bonds. Variable region = antigen-binding site. Constant region = determines antibody class.

2.2 Types of Immunoglobulins

Antibody	Location / Role
IgG	Most abundant in blood. Crosses placenta (passive immunity to foetus). Long-lived.
IgA	Found in secretions: saliva, tears, mucus, colostrum (first milk). Gut immunity.
IgM	First antibody produced in primary immune response. Pentamer (largest). ABO blood group antibodies.
IgE	Involved in allergy and hypersensitivity. Binds mast cells; causes histamine release.
IgD	Found on B-cell surface; role in B-cell activation. Least understood.

2.3 Humoral vs Cell-Mediated Immunity

Feature	Humoral (Antibody-Mediated)	Cell-Mediated (CMI)
Cell type	B-lymphocytes	T-lymphocytes
Effectors	Antibodies (secreted by plasma cells)	Cytotoxic T-cells (CD8+), Helper T-cells (CD4+)
Targets	Extracellular pathogens, bacteria, toxins	Intracellular pathogens (viruses), fungi, transplanted cells, cancer cells
Memory	Memory B-cells	Memory T-cells

2.4 Primary vs Secondary Immune Response

Primary immune response: First exposure to antigen. Response is slow and low. Mainly IgM produced. Memory cells are generated.
Secondary (Anamnestic) immune response: Second exposure. Response is fast, large, and prolonged. Mainly IgG. Basis of vaccination and immunological memory.

⚠️ NEET Focus: IgG = placenta + most abundant. IgA = colostrum + secretions. IgE = allergy. IgM = first to appear in primary response. Secondary response = anamnestic response. B-cells = Humoral. T-cells = CMI. CD4+ T-cells (Helper T) targeted by HIV.

3. Diseases and Pathogens

3.1 Common Infectious Diseases

Disease	Pathogen	Type	Key Facts
Typhoid	Salmonella typhi	Bacterium	Via contaminated food/water. Widal test for diagnosis. Vidal agglutination test. Rose-coloured spots on body.
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae	Bacterium	Alveoli filled with fluid. Rust-coloured sputum. Lips/nails may turn grey.
Common Cold	Rhinovirus	Virus	Affects nose and respiratory tract. Spread by droplets, contaminated objects. NOT spread by cold weather.
Malaria	Plasmodium sp.	Protozoan	Vector: female Anopheles mosquito. P. vivax (benign tertian), P. malariae (quartan), P. falciparum (most deadly — malignant tertian). Drug: quinine, chloroquine.
Amoebiasis	Entamoeba histolytica	Protozoan	Housefly = carrier/vector. Bloody diarrhoea, cramps. Intestinal (caecum/colon) infection.
Ascariasis	Ascaris lumbricoides	Helminth	Roundworm. Feco-oral route. Worms in intestine. Symptoms: internal bleeding, muscular pain.
Filariasis	Wuchereria bancrofti, W. malayi	Helminth	Vector: female Culex mosquito. Elephantiasis (lymph nodes). Lymphatic obstruction. W. bancrofti in lymph vessels.
Ringworm	Trichophyton, Microsporum	Fungus	Dry, scaly lesions on skin. Spreads by direct/indirect contact with infected material.

3.2 Life Cycle of Plasmodium (Malaria)

In female Anopheles mosquito (Definitive host): Sexual reproduction occurs (gametogony → fertilisation → zygote → ookinete → oocyst → sporozoites). Sporozoites migrate to salivary glands.
In Human liver (Exo-erythrocytic cycle): Sporozoites enter liver cells → multiply → release merozoites (hepatic schizogony).
In Human RBCs (Erythrocytic cycle): Merozoites infect RBCs → Ring stage → Trophozoite → Schizont → Merozoites released (rupture RBCs) → causes chills and fever.

Chill and fever cycle: P. vivax / P. ovale: every 48 hrs (tertian). P. malariae: every 72 hrs (quartan). P. falciparum: irregular (malignant). Fever caused by release of toxins when RBCs rupture (haemozoin = malarial pigment).

⚠️ NEET Focus (2013, 2015, 2017, 2019, 2021, 2022): Most virulent malaria = P. falciparum (malignant tertian). Vector = female Anopheles. Filariasis vector = Culex. Definitive host of Plasmodium = mosquito. Intermediate host = human. Amoebiasis carrier = housefly. Widal test = typhoid. Rhinovirus = common cold.

4. AIDS (Acquired Immuno-Deficiency Syndrome)

Cause: HIV (Human Immunodeficiency Virus). A retrovirus (ssRNA genome + reverse transcriptase enzyme). Discovered by Luc Montagnier (France, 1983) and Robert Gallo (USA). Nobel Prize 2008: Montagnier and Barré-Sinoussi.

4.1 Transmission Routes

Sexual contact with infected person
Transfusion of contaminated blood/blood products
Sharing infected needles (intravenous drug users)
Mother to child: via placenta, breast milk, or during birth (vertical transmission)

NOT transmitted by: casual contact (shaking hands, hugging, coughing, sneezing, insect bites, sharing utensils).

4.2 Pathogenesis of HIV

HIV enters body → infects and multiplies in CD4+ T-helper lymphocytes (also macrophages and dendritic cells).
HIV genome (RNA) → reverse transcriptase makes viral DNA → integrates into host chromosome → latent period.
CD4+ T-cell count progressively drops over years (3–10 years).
When CD4+ count falls below 200 cells/μL (normal ~800–1200/μL): AIDS stage.
Opportunistic infections take over: Toxoplasma, Cryptococcus, Mycobacterium, Candida, CMV, Kaposi's sarcoma.

4.3 Diagnosis and Treatment

Diagnosis: ELISA test (enzyme-linked immunosorbent assay) for HIV antibodies; Western Blot for confirmation.
Treatment: ART (Antiretroviral Therapy) — combination of reverse transcriptase inhibitors (AZT — azidothymidine) and protease inhibitors. Not a cure, but prolongs life.
Prevention: Safe sexual practices, blood screening, clean needles, mother-to-child transmission prevention.

⚠️ NEET Focus (2014, 2016, 2018, 2020, 2022): HIV = retrovirus. Infects CD4+ T helper cells. Enzyme = reverse transcriptase. Diagnosis = ELISA. AZT = azidothymidine (first antiretroviral). Not transmitted by casual contact or mosquitoes. Western Blot = confirmatory test. Montagnier + Barré-Sinoussi = Nobel 2008.

5. Cancer

Definition: Cancer is a disease characterised by uncontrolled and abnormal cell division (loss of contact inhibition) resulting in the formation of a mass called tumour (neoplasm).

5.1 Types of Tumours

Feature	Benign Tumour	Malignant Tumour (Cancer)
Growth	Slow, localised	Rapid, invasive
Spread	Does not spread	Spreads via blood/lymph (metastasis)
Capsule	Enclosed in capsule	No capsule
Danger	Less dangerous	Life-threatening

5.2 Types of Cancer

Carcinoma: Cancer of epithelial cells (skin, lung, breast, colon). Most common type.
Sarcoma: Cancer of connective tissue (bone, cartilage, muscle).
Leukaemia: Cancer of blood (uncontrolled proliferation of WBCs/stem cells in bone marrow). “Blood cancer.”
Lymphoma: Cancer of lymph nodes (Hodgkin's disease).

5.3 Causes and Diagnosis

Carcinogens: Physical (UV, X-rays, gamma rays), chemical (tobacco smoke, asbestos, benzene), biological (oncogenic viruses: HPV, EBV, HBV).
Oncogenes: Mutated proto-oncogenes that cause cancer. E.g., ras gene mutation in many cancers.
Tumour suppressor genes: p53, Rb — when these are inactivated, cancer may develop.
Diagnosis: Biopsy, radiography (X-ray, CT scan), MRI, PET scan, Pap smear (cervical cancer), blood tests (AFP, PSA), immunological methods.

5.4 Treatment

Surgery: Remove primary tumour.
Radiation therapy: Ionising radiation kills tumour cells (but damages normal tissues too).
Chemotherapy: Drugs that inhibit cell division (e.g., taxol from Taxus tree for ovarian cancer). Side effects: hair loss, nausea.
Immunotherapy: α-interferon activates NK cells to kill tumour cells. Antibody-based (monoclonal antibodies).

⚠️ NEET Focus (2015, 2018, 2021): Cancer = loss of contact inhibition. Metastasis = spread of malignant cells via blood/lymph. Leukemia = blood cancer (WBCs). Lymphoma = lymph nodes. Taxol (from Taxus tree) = anticancer drug (inhibits microtubule depolymerisation, stops mitosis). α-interferon = immunotherapy for cancer (activates NK cells).

6. Drugs and Alcohol Abuse

6.1 Commonly Abused Drugs

Drug	Source	Chemical	Effect
Morphine / Heroin	Papaver somniferum (opium poppy)	Morphine; Heroin = diacetylmorphine	Opioid narcotic. Sedation, analgesia, euphoria, addiction.
Cannabinoids	Cannabis sativa (hemp)	THC (tetrahydrocannabinol)	Marijuana, hashish, charas, ganja. Hallucinations, sedation.
Cocaine	Erythroxylum coca	Cocaine hydrochloride	Stimulant. Euphoria, increased heart rate. “Crack” is free base form.
LSD	Synthetic (ergot fungus derivative)	Lysergic acid diethylamide	Hallucinogen. Severe perceptual distortions.
Barbiturates	Synthetic	E.g., phenobarbitone	CNS depressants. Sedation, hypnosis. Often abused with alcohol.
Amphetamines	Synthetic	E.g., methamphetamine	CNS stimulants. Increased alertness, reduced fatigue, addiction.

6.2 Effects of Alcohol

Depresses CNS (GABA agonist). Short term: impaired judgment, slurred speech, ataxia.
Chronic use: cirrhosis of liver, pancreatitis, cardiomyopathy, Korsakoff's syndrome (thiamine deficiency), polyneuropathy.
Foetal alcohol syndrome (FAS) — if used during pregnancy.

6.3 Addiction and Dependence

Psychological dependence: Craving for the drug without physical symptoms on withdrawal.
Physical dependence (addiction): Severe withdrawal symptoms (tremors, nausea, sweating) on stopping the drug.
Tolerance: Progressively higher doses needed for same effect.

⚠️ NEET Focus (2013, 2016, 2018, 2020): Heroin / Morphine from Papaver somniferum. Cocaine from Erythroxylum coca. Cannabinoids from Cannabis sativa. LSD = lysergic acid diethylamide (hallucinogen). Smack = diacetylmorphine (heroin). THC = tetrahydrocannabinol (active compound in ganja/marijuana). Cirrhosis = chronic alcohol damage to liver.

🎓 Key NEET Questions (Previous Years)

Q1. [NEET 2022] Which organ is the primary site of T-lymphocyte maturation?

(a) Spleen (b) Lymph node (c) Thymus (d) Bone marrow

Answer: (c) Thymus is the primary lymphoid organ where T-cells mature. Bone marrow = primary site of B-cell maturation. Spleen = largest secondary lymphoid organ.

Q2. [NEET 2021] HIV preferentially infects which type of lymphocytes?

(a) CD8+ T-cells (b) B-cells (c) NK cells (d) CD4+ T-helper cells

Answer: (d) HIV infects and destroys CD4+ T-helper lymphocytes (also macrophages). CD4 acts as the receptor. As CD4+ count falls, immune response is compromised → AIDS.

Q3. [NEET 2019] Plasmodium falciparum causes which type of malaria?

(a) Benign tertian (b) Quartan (c) Malignant tertian (d) Ovale tertian

Answer: (c) P. falciparum = Malignant tertian malaria (most deadly). P. vivax = Benign tertian. P. malariae = Quartan. P. ovale = Ovale tertian.

Q4. [NEET 2018] Which immunoglobulin is present in colostrum?

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

Answer: (b) IgA is the predominant antibody in colostrum (first mother's milk) and other secretions (saliva, tears, gut mucus). It provides passive immunity to the newborn. IgG crosses the placenta.

Q5. [NEET 2017] Drug smack (heroin) is obtained from:

(a) Cannabis sativa (b) Papaver somniferum (c) Erythroxylum coca (d) Atropa belladonna

Answer: (b) Heroin (diacetylmorphine / Smack) is obtained from the latex of Papaver somniferum (opium poppy). Cocaine = Erythroxylum coca. Cannabis products (THC) = Cannabis sativa.

Q6. [NEET 2016] Widal test is used for diagnosis of:

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

Answer: (c) Widal test detects agglutinating antibodies against Salmonella typhi and is used for typhoid fever diagnosis.

💡 Rapid Revision — Key Facts

Thymus = T-cell maturation | Bone Marrow = B-cell maturation | Spleen = largest lymphoid organ
IgG = placenta + most abundant | IgA = colostrum + secretions | IgE = allergy | IgM = first in primary response
HIV = retrovirus | Target = CD4+ T-helper cells | Enzyme = reverse transcriptase | Diagnosis = ELISA
Most deadly malaria = P. falciparum | Vector = female Anopheles | Definitive host = mosquito
Cancer = loss of contact inhibition | Metastasis = spread via blood/lymph
Heroin = P. somniferum | Cocaine = E. coca | Cannabinoids = Cannabis sativa (THC)
Widal test = typhoid | Wuchereria = filariasis, vector = Culex | Housefly = amoebiasis carrier
Taxol (from Taxus tree) = anticancer drug | α-interferon = immunotherapy

NCERT Solutions - Human Health and Disease - Class 12

CLASS 12 BIOLOGY | NCERT SOLUTIONS

Chapter 8 — Human Health and Disease

All NCERT Exercise Questions with Detailed Solutions

📋 Note: All questions from NCERT Class 12 Biology Chapter 8 Exercise. Answers as per NCERT and CBSE marking scheme.

NCERT Exercise Questions & Solutions

2 MarksQ1. What are the various public health measures to control infectious diseases in a community?

✓ Answer
Public health measures to control infectious diseases:

Proper disposal of waste and excreta to prevent feco-oral disease transmission (typhoid, amoebiasis, polio).
Regular disinfection of water supply and food handling facilities.
Vector control: Eliminating breeding sites of mosquitoes (draining stagnant water), using insecticides, insect repellents, mosquito nets.
Vaccination programmes: National immunization against polio, measles, TB, DPT, hepatitis B.
Quarantine and isolation of infected individuals to prevent spread.
Awareness campaigns about hygiene, safe sex, blood safety (to prevent HIV/hepatitis B).
Food safety regulations; combating housefly populations (amoebiasis carrier).

3 MarksQ2. In what ways is the study of microbiology useful in the control of disease?

✓ Answer
Microbiology contributes to disease control in the following ways:

Identification of pathogens: Culture, staining, serology help identify the causative organism so proper treatment can be given.
Antibiotic production: Microbes like Penicillium produce antibiotics (penicillin) that kill bacterial pathogens.
Vaccine development: Understanding microbes enables preparation of vaccines (attenuated/killed organisms or toxoids) for active immunisation.
Diagnostic tests: Microbiology-based tests (ELISA, Widal test, Mantoux test) aid in diagnosis.
Understanding disease mechanisms: Knowledge of pathogen biology leads to targeted drug development.
Epidemiology: Tracking microbes helps identify outbreaks and implement control measures.

5 MarksQ3. Describe the life cycle of Plasmodium in the human body and in the mosquito.

✓ Answer
Life cycle of Plasmodium:

In Female Anopheles Mosquito (Definitive / Sexual Host):

When mosquito bites an infected human, it ingests gametocytes (male and female) along with blood.
In mosquito midgut: gametogony → microgamete (male) + macrogamete (female) fuse → zygote.
Zygote → motile ookinete → penetrates gut wall → oocyst.
Oocyst → sporozoites (sporogony) → migrate to salivary glands.

In Human (Intermediate / Asexual Host):

Liver stage (Exo-erythrocytic schizogony): Mosquito injects sporozoites → sporozoites enter liver cells → multiply → release merozoites.
RBC stage (Erythrocytic schizogony):
- Merozoites infect RBCs → ring stage (trophozoite) → schizont → ruptures RBC releasing many new merozoites.
- Rupture releases haemozoin (malarial pigment) → causes fever and chills.
- Some merozoites develop into gametocytes (ready to be ingested by next mosquito).

Fever cycle: P. vivax/ovale: 48 hrs (tertian). P. malariae: 72 hrs (quartan). P. falciparum: irregular.

5 MarksQ4. Explain the mechanism by which HIV virus causes immunodeficiency in an individual.

✓ Answer
HIV Pathogenesis:

HIV (a retrovirus with ssRNA genome) enters the body and attaches to CD4 receptors on CD4+ T-helper lymphocytes, macrophages, and dendritic cells.
HIV injects its RNA + reverse transcriptase into the host cell.
Reverse transcriptase makes viral DNA from RNA template → viral DNA integrates into host's chromosomal DNA (provirus).
After latent period, viral genes are expressed → new HIV virions bud off → infect more CD4+ T-cells.
Over 3–10 years, CD4+ T-cell count progressively drops from normal ~800–1200/μL to <200/μL → AIDS.
With severely reduced CD4+ T-cells: helper function lost → B-cells cannot make effective antibodies → cytotoxic T-cells become ineffective → complete immunodeficiency.
Opportunistic infections (tuberculosis, Candida, Toxoplasma, CMV) and cancers (Kaposi's sarcoma) take over and cause death.

Diagnosis: ELISA (screening) → Western Blot (confirmatory).
Treatment: ART (Antiretroviral Therapy): AZT, protease inhibitors. Not a cure; prolongs life.

3 MarksQ5. Differentiate between active and passive immunity.

✓ Answer

Feature	Active Immunity	Passive Immunity
Definition	Immunity developed by the host after antigen exposure	Immunity acquired by transfer of ready-made antibodies from another source
Antibody source	Self-produced by host	External source (another organism)
Onset	Slow (days to weeks)	Immediate
Duration	Long-lasting (years)	Short-lived (weeks to months)
Memory	Yes — memory cells formed	No memory cells
Examples	Vaccination, natural infection recovery	Colostrum (IgA), anti-snake venom, tetanus antitoxin; IgG via placenta

3 MarksQ6. What are lymphoid organs? Briefly describe their roles in immunity.

✓ Answer
Lymphoid organs are organs where lymphocytes (B and T cells) are produced, mature, and/or function.

Primary Lymphoid Organs:

Bone Marrow: Site of origin of all blood cells (haematopoiesis). B-lymphocytes mature here. Only primary organ throughout life.
Thymus: Site where T-lymphocytes mature and differentiate. Largest at birth. Secretes peptide hormones called thymosins that promote T-cell maturation. Gradually involutes with age.

Secondary Lymphoid Organs:

Spleen: Largest lymphoid organ. Filters blood. Blood-borne antigen extraction. Graveyard of old RBCs. Produces antibodies.
Lymph Nodes: Filters lymph; traps antigens; proliferation of lymphocytes and macrophages.
MALT (Mucosa-Associated Lymphoid Tissue): Peyer's patches, tonsils, appendix — protect mucosal surfaces.

3 MarksQ7. What is cancer? How does a normal cell become cancerous? What are the various means of treating cancer?

✓ Answer
Cancer = uncontrolled and abnormal cell proliferation due to loss of contact inhibition.

Normal cell → Cancer cell:

Mutation in proto-oncogenes → activated oncogenes → uncontrolled cell division.
Inactivation of tumour suppressor genes (p53, Rb) → loss of cell cycle control.
Carcinogens cause these mutations: physical (UV, X-rays), chemical (tobacco, asbestos), biological (oncogenic viruses: HPV, EBV, HBV).
Transformed cells lose contact inhibition → form tumour → malignant cells invade and spread (metastasis) via blood/lymph.

Treatment:

Surgery: Removal of tumour mass.
Radiotherapy: Ionising radiation kills dividing cells.
Chemotherapy: Cytotoxic drugs (e.g., taxol from Taxus tree) inhibit cell division.
Immunotherapy: α-interferons activate NK cells and immune response against tumour.

3 MarksQ8. Name the source plant and the chemical compound responsible for the following drugs: (a) Heroin (b) Cocaine (c) Marijuana.

✓ Answer

Drug	Source Plant	Chemical Compound
Heroin (Smack)	Papaver somniferum (opium poppy)	Diacetylmorphine (modified morphine)
Cocaine	Erythroxylum coca	Cocaine hydrochloride (cocaine alkaloid)
Marijuana / Ganja / Hashish	Cannabis sativa	THC (Tetrahydrocannabinol)

Note: All three are subject to strict legal control in India and globally under the Narcotic Drugs and Psychotropic Substances (NDPS) Act.

Facts Capsule - Human Health and Disease - Class 12

CLASS 12 BIOLOGY | NEET RAPID CAPSULE

Facts & High-Yield Points

Chapter 8 — Human Health and Disease | 30 Key Facts for NEET

🛡️ Immunity

FACT #01 — Active vs Passive

Active: slow, long-lasting, memory cells, self-produced Abs. Passive: immediate, short-lived, no memory. Examples of passive: colostrum, anti-snake venom, tetanus antitoxin, IgG via placenta.

FACT #02 — Primary Lymphoid Organs

Bone Marrow: B-cell maturation + haematopoiesis. Thymus: T-cell maturation, secretes thymosins, largest at birth, involutes with age.

FACT #03 — Secondary Lymphoid Organs

Spleen = largest lymphoid organ + graveyard of RBCs. Lymph nodes, tonsils, Peyer's patches, appendix, MALT. All trap antigens and support immune response.

FACT #04 — Immunoglobulins

IgG: most abundant, crosses placenta. IgA: colostrum + secretions (saliva, tears). IgE: allergy/hypersensitivity. IgM: first in primary response, pentamer, largest. IgD: B-cell surface.

FACT #05 — Antibody Structure

Y-shaped glycoprotein. 2 heavy + 2 light chains, joined by disulphide bonds. Variable region = antigen-binding site. Made by plasma cells (activated B-cells).

FACT #06 — B-cells vs T-cells

B-cells: Humoral immunity; secrete antibodies. T-cells: Cell-mediated immunity (CMI); cytotoxic T-cells kill infected/tumour cells. CD4+ T-helper: coordinator of immune response (target of HIV). CD8+: cytotoxic.

😵 Infectious Diseases

FACT #07 — Disease-Pathogen-Vector

Malaria: Plasmodium sp. — vector: female Anopheles.
Filariasis: Wuchereria bancrofti — vector: female Culex.
Amoebiasis: Entamoeba histolytica — carrier: housefly.

FACT #08 — Malaria Types

P. vivax: Benign tertian (48 hrs). P. malariae: Quartan (72 hrs). P. ovale: Ovale tertian. P. falciparum: Malignant tertian (most deadly). Fever = haemozoin release.

FACT #09 — Plasmodium Host

Definitive host (sexual reproduction): female Anopheles mosquito. Intermediate host (asexual): human. Sporozoites → liver → merozoites → RBCs → gametocytes.

FACT #10 — Diagnostic Tests

Typhoid: Widal test. HIV: ELISA (screening) + Western Blot (confirmatory). Malaria: blood smear + RDT. Tuberculosis: Mantoux test (tuberculin skin test).

FACT #11 — Helminth Diseases

Ascariasis: Ascaris lumbricoides (roundworm), feco-oral. Filariasis: Wuchereria bancrofti, lymphatic obstruction → elephantiasis. Vector: female Culex mosquito.

FACT #12 — Bacterial/Viral Diseases

Typhoid: Salmonella typhi, contaminated food/water. Pneumonia: Streptococcus pneumoniae. Common Cold: Rhinovirus (NOT spread by cold weather). Ringworm: Trichophyton / Microsporum (fungi).

🧠 AIDS / HIV

FACT #13 — HIV Basics

HIV = retrovirus (ssRNA + reverse transcriptase). Discovered by Luc Montagnier (1983, France) and Robert Gallo (USA). Nobel Prize 2008: Montagnier + Barré-Sinoussi.

FACT #14 — HIV Target

Infects CD4+ T-helper lymphocytes (also macrophages). CD4 = receptor + co-receptor (CCR5/CXCR4). Reverse transcriptase: RNA → DNA → integrates into host genome. Latent period: 3–10 years.

FACT #15 — AIDS Stage

CD4+ count drops below 200/μL (normal: 800–1200/μL) = AIDS. Opportunistic infections: Toxoplasma, Candida, Cryptococcus, Mycobacterium. Kaposi's sarcoma (opportunistic cancer).

FACT #16 — HIV Transmission

Sexual contact, contaminated blood, shared needles, mother→child (placenta/breast milk). NOT by: casual contact, sneezing, coughing, sharing utensils, insect bites. Treatment: ART (AZT = azidothymidine).

🦀 Cancer

FACT #17 — Cancer Basis

Cancer = loss of contact inhibition + uncontrolled cell division. Malignant cells undergo metastasis (spread via blood/lymph). Benign tumour = enclosed, localised, NOT life-threatening.

FACT #18 — Types of Cancer

Carcinoma: epithelial (most common; skin, breast, lung). Sarcoma: connective tissue (bone, muscle). Leukaemia: blood/WBCs. Lymphoma: lymph nodes (Hodgkin's).

FACT #19 — Oncogenes

Proto-oncogenes → mutated by carcinogens → oncogenes. Oncogenic viruses: HPV (cervical ca.), EBV (Burkitt's lymphoma), HBV (liver ca.). Tumour suppressors: p53, Rb (when inactivated → cancer).

FACT #20 — Cancer Treatment

Surgery | Radiation | Chemotherapy (Taxol from Taxus tree — inhibits microtubule depolymerisation) | Immunotherapy (α-interferon activates NK cells). Taxol = ovarian cancer treatment.

💊 Drugs & Alcohol

FACT #21 — Drug Sources

Heroin/Morphine: Papaver somniferum (opium poppy). Cocaine: Erythroxylum coca. Cannabinoids (THC): Cannabis sativa (ganja, hashish, charas). LSD: synthetic (ergot fungus derivative).

FACT #22 — Drug Types

Opioids (narcotic): morphine, heroin — sedation/analgesia/addiction. Cannabinoids: hallucinogen + sedation. Cocaine: stimulant (sympathomimetic). LSD: hallucinogen. Barbiturates: CNS depressants.

FACT #23 — Smack vs Cocaine

Smack = Heroin = diacetylmorphine (acetylated morphine). White powder. Depressant. Crack cocaine = free base form of cocaine. Both highly addictive.

FACT #24 — Alcohol Effects

CNS depressant (GABA agonist). Chronic: cirrhosis of liver, pancreatitis, cardiomyopathy, Korsakoff's syndrome (thiamine deficiency), polyneuropathy. Foetal alcohol syndrome (FAS) if used in pregnancy.

🧠 Mnemonics — Remember Fast

Immunoglobulins: “GAEMD” G=placenta | A=secretions (colostrum) | E=allergy | M=primary response (first) | D=B-cell surface.

Malaria Types: “Vivax=48, Malariae=72” P. vivax/ovale = tertian (48 hrs). P. malariae = quartan (72 hrs). P. falciparum = malignant (irregular). Most deadly = falciparum.

Drug Sources: “Poppy-Coca-Cannabis” Heroin = Papaver somniferum. Cocaine = Erythroxylum coca. Ganja/marijuana = Cannabis sativa. LSD = synthetic.

Cancer Types: “CALL” Carcinoma (epithelial) | Adenoma (glandular) | Leukaemia (blood) | Lymphoma (lymph nodes). Sarcoma = connective tissue.

📊 Disease — Pathogen — Vector Quick Chart

Disease	Pathogen	Type	Vector/Carrier	Diagnostic Test
Malaria	Plasmodium	Protozoan	Female Anopheles	Blood smear / RDT
Filariasis	Wuchereria bancrofti	Helminth	Female Culex	Blood smear (microfilariae)
Amoebiasis	Entamoeba histolytica	Protozoan	Housefly (carrier)	Stool examination
Typhoid	Salmonella typhi	Bacterium	Contaminated food/water	Widal test
AIDS	HIV	Retrovirus	Sexual/blood/vertical	ELISA + Western Blot
Common Cold	Rhinovirus	Virus	Droplets / contact	Clinical
Ringworm	Trichophyton	Fungus	Direct contact	KOH mount

🔢 Critical Numbers — Never Forget

CD4+ <200/μL — AIDS stage 800–1200/μL — normal CD4+ count 2H + 2L chains — antibody structure IgM — first in primary response IgG — crosses placenta IgA — in colostrum + secretions 3–10 years — HIV latent period 1983 — HIV discovered (Montagnier) 2008 — Nobel Prize for HIV discovery 48 hrs — P. vivax fever cycle 72 hrs — P. malariae fever cycle

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