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Human Health and Disease

NCERT Class 12 · Biology Based on NCERT Class 12 Biology textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the concept of health as a state of complete physical, mental, and social well-being, moving beyond the mere absence of disease. It covers common infectious diseases caused by pathogens like bacteria, viruses, protozoans, and helminths, and delves into the immune system's role in defending the body. The chapter also addresses major public health challenges such as AIDS, cancer, and drug and alcohol abuse, emphasizing prevention, control, and the importance of a healthy lifestyle. The one big idea is that health is a dynamic state maintained by the immune system, personal hygiene, and societal measures, and that many diseases can be prevented through awareness and vaccination.
Key Concepts (48)
Health
A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.
e.g. A person who exercises regularly, eats a balanced diet, and has strong social connections is considered healthy.
Disease
A condition where the functioning of one or more organs or systems of the body is adversely affected, characterized by the appearance of various signs and symptoms.
e.g. Typhoid fever is a disease characterized by sustained high fever, weakness, and stomach pain.
Pathogen
Disease-causing organisms such as bacteria, viruses, fungi, protozoans, and helminths.
e.g. Salmonella typhi is a pathogenic bacterium that causes typhoid fever.
Vector
An organism that transmits a pathogen from an infected individual to a healthy individual.
e.g. The female Anopheles mosquito is the vector for the malarial parasite Plasmodium.
Immunity
The overall ability of the host to fight disease-causing organisms, conferred by the immune system.
e.g. A person who has recovered from chickenpox is immune to future infections due to memory cells.
Innate Immunity
Non-specific type of defence that is present at the time of birth, consisting of physical, physiological, cellular, and cytokine barriers.
e.g. Skin acts as a physical barrier preventing entry of microorganisms.
Acquired Immunity
Pathogen-specific immunity characterized by memory, involving primary and secondary responses mediated by B-lymphocytes and T-lymphocytes.
e.g. Vaccination induces acquired immunity by generating memory B and T cells.
Antibody
Proteins produced by B-lymphocytes in response to pathogens, having a structure of four peptide chains (two heavy and two light) represented as H2L2.
e.g. IgA antibodies are abundant in colostrum and protect the newborn infant.
Active Immunity
Immunity developed when the host is exposed to antigens, producing antibodies; it is slow but long-lasting.
e.g. Natural infection with measles or vaccination with a weakened measles virus induces active immunity.
Passive Immunity
Immunity obtained by injecting readymade antibodies into the body; it is immediate but short-lived.
e.g. The injection of antitoxin for tetanus or snake venom antivenom provides passive immunity.
Vaccination
Introduction of a preparation of antigenic proteins of a pathogen or inactivated/weakened pathogen (vaccine) into the body to generate memory B and T cells.
e.g. The hepatitis B vaccine is produced using recombinant DNA technology in yeast.
Allergy
The exaggerated response of the immune system to certain antigens (allergens) present in the environment, mediated by IgE antibodies.
e.g. Sneezing and watery eyes due to pollen grains is an allergic reaction.
Auto-immune Disease
A condition where the body attacks its own cells due to genetic and other unknown reasons.
e.g. Rheumatoid arthritis is an auto-immune disease.
Lymphoid Organs
Organs where origin, maturation, and proliferation of lymphocytes occur; divided into primary (bone marrow and thymus) and secondary (spleen, lymph nodes, tonsils, Peyer's patches, appendix, MALT).
e.g. The thymus is a primary lymphoid organ located near the heart, which reduces in size with age.
AIDS
Acquired Immuno Deficiency Syndrome, a fatal disease caused by the Human Immunodeficiency Virus (HIV), a retrovirus, leading to progressive destruction of helper T-lymphocytes.
e.g. A person with AIDS becomes susceptible to opportunistic infections like tuberculosis.
Cancer
A disease characterized by uncontrolled cell division due to breakdown of regulatory mechanisms, leading to the formation of tumors (benign or malignant).
e.g. Lung cancer is often caused by chemical carcinogens present in tobacco smoke.
Metastasis
The property of malignant tumors where cells sloughed from the primary tumor reach distant sites through blood and start new tumors.
e.g. Breast cancer cells can metastasize to the bones or lungs.
Carcinogen
Physical, chemical, or biological agents that induce transformation of normal cells into cancerous neoplastic cells.
e.g. Ionising radiations like X-rays and gamma rays are physical carcinogens.
Drug Abuse
Use of drugs for a purpose other than medicinal use or in amounts/frequency that impairs one's physical, physiological, or psychological functions.
e.g. Taking heroin (smack) for euphoria is drug abuse.
Addiction
A psychological attachment to certain effects (e.g., euphoria) associated with drugs and alcohol, driving repeated use even when self-destructive.
e.g. A person addicted to alcohol experiences cravings and continues drinking despite health problems.
Dependence
The tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued.
e.g. An alcoholic may experience anxiety, shakiness, and nausea when stopping alcohol consumption.
Withdrawal Syndrome
A set of symptoms (anxiety, shakiness, nausea, sweating) that occur when a dependent person abruptly stops taking a drug or alcohol.
e.g. A heroin addict may experience severe withdrawal symptoms like muscle pain and insomnia.
Humoral Immune Response
The antibody-mediated immune response carried out by B-lymphocytes, where antibodies are found in the blood.
e.g. When a pathogen enters the blood, B-cells produce antibodies to neutralize it.
Cell-mediated Immunity (CMI)
The immune response mediated by T-lymphocytes, responsible for graft rejection and defense against intracellular pathogens.
e.g. T-cells attack and destroy cells infected with viruses.
Contact Inhibition
A property of normal cells where contact with other cells inhibits their uncontrolled growth; cancer cells lose this property.
e.g. Normal skin cells stop dividing when they touch each other, but cancerous skin cells continue to divide and form a tumor.
Benign Tumor
A tumor that remains confined to its original location, does not spread to other parts, and causes little damage.
e.g. A benign mole on the skin that does not invade deeper tissues.
Malignant Tumor
A mass of proliferating neoplastic cells that grow rapidly, invade surrounding tissues, and can metastasize.
e.g. A malignant tumor in the breast that spreads to the lymph nodes.
Oncogenic Virus
Cancer-causing viruses that have genes called viral oncogenes.
e.g. Human papillomavirus (HPV) is an oncogenic virus linked to cervical cancer.
Proto-oncogene
Normal cellular genes (c-onc) that, when activated under certain conditions, can lead to oncogenic transformation of cells.
e.g. A mutation in the RAS proto-oncogene can lead to uncontrolled cell division.
ELISA
Enzyme Linked Immuno-Sorbent Assay, a widely used diagnostic test for AIDS.
e.g. A blood sample is tested using ELISA to detect HIV antibodies.
NACO
National AIDS Control Organisation, an Indian government body that educates people about AIDS.
e.g. NACO runs programs for free distribution of condoms and safe blood transfusion.
MALT
Mucosa-Associated Lymphoid Tissue, lymphoid tissue located within the lining of major tracts (respiratory, digestive, urogenital), constituting about 50% of the lymphoid tissue in the human body.
e.g. Peyer's patches in the small intestine are part of MALT.
Interferons
Proteins secreted by virus-infected cells that protect non-infected cells from further viral infection; they are a type of cytokine barrier in innate immunity.
e.g. When a cell is infected by influenza virus, it releases interferons to warn neighboring cells.
Haemozoin
A toxic substance released from the rupture of red blood cells during malaria, responsible for chill and high fever recurring every three to four days.
e.g. The release of haemozoin during Plasmodium infection causes the classic malarial paroxysm.
Sporozoites
The infectious form of Plasmodium that enters the human body through the bite of an infected female Anopheles mosquito.
e.g. Sporozoites are injected into the blood when a mosquito bites a person.
Colostrum
The yellowish fluid secreted by the mother during the initial days of lactation, rich in antibodies (IgA) that provide passive immunity to the newborn.
e.g. A breastfed infant receives IgA antibodies from colostrum, protecting against infections.
Reverse Transcriptase
An enzyme present in retroviruses like HIV that converts viral RNA into viral DNA, which then gets incorporated into the host cell's DNA.
e.g. HIV uses reverse transcriptase to make a DNA copy of its RNA genome inside the host cell.
Retrovirus
A group of viruses with an RNA genome and an envelope, which replicate by converting RNA into DNA using reverse transcriptase; e.g., HIV.
e.g. HIV is a retrovirus that causes AIDS.
Helper T-lymphocytes (TH)
A type of T-cell that is attacked by HIV; their progressive decrease leads to immunodeficiency in AIDS patients.
e.g. HIV enters and replicates in helper T-lymphocytes, destroying them over time.
Biopsy
A diagnostic procedure where a piece of suspected tissue is cut into thin sections, stained, and examined under a microscope for cancer detection.
e.g. A biopsy of a breast lump can confirm whether it is malignant or benign.
Radiography
A technique using X-rays to detect cancers of internal organs.
e.g. A chest X-ray can reveal a lung tumor.
CT (Computed Tomography)
A technique that uses X-rays to generate a three-dimensional image of the internals of an object, useful for cancer detection.
e.g. A CT scan of the abdomen can detect a liver tumor.
MRI (Magnetic Resonance Imaging)
A technique that uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in living tissue.
e.g. An MRI of the brain can detect a brain tumor.
Opioids
Drugs that bind to specific opioid receptors in the central nervous system and gastrointestinal tract; e.g., heroin (diacetylmorphine) obtained from morphine extracted from Papaver somniferum.
e.g. Heroin is an opioid depressant that slows down body functions.
Cannabinoids
A group of chemicals that interact with cannabinoid receptors in the brain, obtained from Cannabis sativa; e.g., marijuana, hashish, charas, ganja.
e.g. Cannabinoids affect the cardiovascular system and are often inhaled or ingested orally.
Cocaine
A coca alkaloid obtained from Erythroxylum coca, which interferes with dopamine transport; a stimulant that produces euphoria and increased energy.
e.g. Cocaine is usually snorted and can cause hallucinations in excessive doses.
Nicotine
An alkaloid present in tobacco that stimulates the adrenal gland to release adrenaline and nor-adrenaline, raising blood pressure and heart rate.
e.g. Smoking tobacco increases the risk of lung cancer due to nicotine and other chemicals.
Anabolic Steroids
Drugs misused by sportspersons to increase muscle strength and bulk, with side effects including masculinisation in females and testicular shrinkage in males.
e.g. Anabolic steroid use can lead to premature baldness and liver dysfunction.
Formulas & Equations (3)
H2L2
Reads as: H two L two
Variables: H = heavy chain, L = light chain; an antibody molecule consists of two heavy and two light peptide chains.
Use when: Describing the structure of an antibody molecule in a diagram or short answer question.
⚠ Students often write H2L2 as a chemical formula or think it means two heavy and two light chains are identical; actually, heavy and light chains are different types of polypeptide chains.
C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + energy
Reads as: Glucose plus six oxygen molecules yields six carbon dioxide molecules plus six water molecules plus energy
Variables: C6H12O6 = glucose, O2 = oxygen, CO2 = carbon dioxide, H2O = water
Use when: Explaining cellular respiration; not directly in this chapter but relevant to understanding metabolic effects of drugs/alcohol.
⚠ Students confuse this with the equation for photosynthesis; ensure you write the correct direction (oxidation of glucose).
C21H23NO5 (morphine) → C21H23NO5 + 2(CH3CO)2O → C21H23NO5(COCH3)2 (heroin)
Reads as: Morphine plus acetic anhydride yields heroin (diacetylmorphine)
Variables: C21H23NO5 = morphine, (CH3CO)2O = acetic anhydride, C21H23NO5(COCH3)2 = heroin
Use when: Describing the chemical conversion of morphine to heroin in the context of drug abuse.
⚠ Students often write heroin as simply 'morphine' or forget that acetylation is involved.
How It Works
Life Cycle of Plasmodium
  1. Step 1: An infected female Anopheles mosquito bites a human, injecting sporozoites (infectious form) into the blood.
  2. Step 2: Sporozoites initially multiply within the liver cells of the human host.
  3. Step 3: Parasites then attack red blood cells (RBCs), causing their rupture.
  4. Step 4: Rupture of RBCs releases a toxic substance called haemozoin, which causes chills and high fever recurring every three to four days.
  5. Step 5: When a female Anopheles mosquito bites an infected person, the parasites enter the mosquito's body.
  6. Step 6: The parasites multiply within the mosquito to form sporozoites, which are stored in the mosquito's salivary glands.
  7. Step 7: When the mosquito bites another human, sporozoites are introduced, initiating the cycle again.
💡 The malarial parasite requires two hosts (human and mosquito) to complete its life cycle; the female Anopheles mosquito is both the vector and a host for the sexual phase of the parasite.
Replication of HIV (Retrovirus)
  1. Step 1: HIV enters the body and infects macrophages, where its RNA genome is present.
  2. Step 2: The enzyme reverse transcriptase converts viral RNA into viral DNA.
  3. Step 3: This viral DNA gets incorporated into the host cell's DNA.
  4. Step 4: The integrated viral DNA directs the infected cell to produce new virus particles.
  5. Step 5: Macrophages continue to produce virus, acting like an HIV factory.
  6. Step 6: Simultaneously, HIV enters helper T-lymphocytes (TH), replicates, and produces progeny viruses.
  7. Step 7: Progeny viruses are released into the blood and attack other helper T-lymphocytes.
  8. Step 8: This repeated cycle leads to a progressive decrease in the number of helper T-lymphocytes, causing immunodeficiency.
💡 HIV does not kill the host immediately; there is a time lag of 5-10 years between infection and appearance of AIDS symptoms. The virus specifically targets helper T-lymphocytes, not all T-cells.
Immune Response (Primary and Secondary)
  1. Step 1: First encounter with a pathogen: B-lymphocytes and T-lymphocytes recognize the antigen.
  2. Step 2: B-cells produce antibodies (humoral response) and T-cells mediate cell-mediated immunity.
  3. Step 3: This primary response is of low intensity and takes time to develop.
  4. Step 4: Memory B and T cells are generated during the primary response.
  5. Step 5: Subsequent encounter with the same pathogen: memory cells recognize the antigen quickly.
  6. Step 6: A highly intensified secondary (anamnestic) response occurs, with massive production of antibodies.
  7. Step 7: The pathogen is overwhelmed and eliminated rapidly.
💡 The secondary response is faster and more intense than the primary response due to immunological memory. This is the basis of vaccination.
Cancer Development (Oncogenic Transformation)
  1. Step 1: Normal cell growth and differentiation are highly controlled and regulated.
  2. Step 2: Normal cells exhibit contact inhibition, where contact with other cells stops uncontrolled growth.
  3. Step 3: Carcinogens (physical, chemical, or biological agents) cause DNA damage.
  4. Step 4: Proto-oncogenes (c-onc) in normal cells may be activated, leading to oncogenic transformation.
  5. Step 5: Cancer cells lose contact inhibition and continue to divide uncontrollably.
  6. Step 6: A mass of cells called a tumor forms; benign tumors remain localized, malignant tumors invade and metastasize.
💡 Metastasis is the most feared property of malignant tumors; it is the spread of cancer cells to distant sites via blood or lymph.
Drug Addiction and Dependence Cycle
  1. Step 1: Initial use of a drug or alcohol out of curiosity, peer pressure, or to escape stress.
  2. Step 2: The user experiences perceived benefits like euphoria or temporary well-being.
  3. Step 3: With repeated use, tolerance develops: receptors respond only to higher doses.
  4. Step 4: The user increases dosage to achieve the same effect, leading to addiction (psychological attachment).
  5. Step 5: The body becomes dependent; abrupt discontinuation causes withdrawal syndrome (anxiety, shakiness, nausea, sweating).
  6. Step 6: The user continues use to avoid withdrawal symptoms, entering a vicious cycle of abuse.
💡 Addiction is psychological; dependence is physiological. Withdrawal symptoms can be severe and even life-threatening, requiring medical supervision.
Exam Traps — Don't Make These Mistakes
⚠ Confusing 'Innate' and 'Acquired' Immunity
✗ Innate immunity is specific and has memory, while acquired immunity is non-specific.
→ It is the opposite: innate immunity is non-specific and present at birth, while acquired immunity is pathogen-specific and has memory.
✓ Innate immunity is non-specific, present at birth, and includes physical, physiological, cellular, and cytokine barriers. Acquired immunity is pathogen-specific, develops after exposure, and has memory (primary and secondary responses).
⚠ Mixing Up Active and Passive Immunity
✗ Active immunity is when antibodies are injected from outside, and passive immunity is when the body produces its own antibodies.
→ Active immunity involves the body producing its own antibodies after exposure to an antigen (natural infection or vaccination). Passive immunity involves receiving readymade antibodies from an external source (e.g., colostrum, antitoxin).
✓ Active immunity: host produces antibodies in response to an antigen; slow but long-lasting. Passive immunity: readymade antibodies are directly given; immediate but short-lived.
⚠ Thinking HIV Directly Causes Death
✗ HIV directly kills the person by destroying all immune cells.
→ HIV does not directly kill; it progressively destroys helper T-lymphocytes, leading to immunodeficiency. The patient dies from opportunistic infections (e.g., tuberculosis, fungal infections) that the weakened immune system cannot fight.
✓ HIV causes a progressive decrease in helper T-lymphocytes, leading to immunodeficiency. The patient becomes susceptible to opportunistic infections, which ultimately cause death.
⚠ Confusing Benign and Malignant Tumors
✗ Benign tumors are cancerous and spread to other parts of the body.
→ Benign tumors are not cancerous; they remain confined to their original location and do not spread (no metastasis). Malignant tumors are cancerous, invade surrounding tissues, and metastasize.
✓ Benign tumors remain localized and cause little damage. Malignant tumors are masses of neoplastic cells that grow rapidly, invade nearby tissues, and can metastasize to distant sites via blood.
⚠ Thinking All Drugs of Abuse are Illegal or Street Drugs
✗ Only illegal drugs like heroin and cocaine are abused.
→ Many drugs that are legally used as medicines (e.g., barbiturates, amphetamines, benzodiazepines, morphine) are also abused when taken for non-medicinal purposes or in excessive amounts.
✓ Drug abuse includes misuse of both illegal drugs (heroin, cocaine, cannabinoids) and legal medicinal drugs (barbiturates, amphetamines, benzodiazepines, morphine) when taken for purposes other than prescribed or in harmful amounts.
⚠ Misidentifying the Vector for Malaria
✗ Malaria is transmitted by the bite of any mosquito.
→ Only the female Anopheles mosquito transmits malaria. Male mosquitoes do not bite, and other mosquito species (e.g., Aedes, Culex) transmit different diseases (dengue, filariasis).
✓ Malaria is transmitted by the bite of an infected female Anopheles mosquito, which injects sporozoites of Plasmodium into the human blood.
Compare & Contrast
Specificity and memory
Innate Immunity
Acquired Immunity
Innate immunity is non-specific and lacks memory; it is present at birth. Acquired immunity is pathogen-specific and has memory, with a stronger secondary response on subsequent exposure.
Source of antibodies
Active Immunity
Passive Immunity
In active immunity, the host's body produces its own antibodies after exposure to an antigen (natural infection or vaccination). In passive immunity, readymade antibodies are introduced from an external source (e.g., colostrum, antitoxin).
Growth and spread
Benign Tumor
Malignant Tumor
Benign tumors remain confined to their original location, do not invade surrounding tissues, and do not metastasize. Malignant tumors grow rapidly, invade nearby tissues, and can metastasize to distant sites via blood or lymph.
Nature of attachment
Addiction
Dependence
Addiction is a psychological attachment to the effects of a drug (e.g., euphoria). Dependence is a physiological state where the body requires the drug to function normally, and abrupt discontinuation leads to withdrawal syndrome.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1-2 Very Short Answer (1 mark each), 1 Short Answer (2-3 marks), 1 Long Answer (5 marks) — total approximately 10-12 marks in the board exam.
Most asked: Types of immunity (innate vs. acquired, active vs. passive) · Life cycle of Plasmodium and malaria transmission · Structure and replication of HIV · Cancer: properties of malignant tumors, metastasis, carcinogens · Drug and alcohol abuse: types of drugs, effects, prevention · Common diseases: typhoid, pneumonia, amoebiasis, ascariasis, filariasis, ringworm · Lymphoid organs (primary and secondary) · Vaccination and immunisation
Don't skip: Diagram of antibody structure (H2L2) and labeling; Life cycle of Plasmodium with diagram; Replication of HIV and its mechanism of causing immunodeficiency; Differentiation between benign and malignant tumors; Comparison of active and passive immunity with examples; Prevention and control of drug/alcohol abuse
One-Line Revision (read aloud before the exam)
  1. Health is a state of complete physical, mental, and social well-being, not merely the absence of disease.
  2. Pathogens are disease-causing organisms including bacteria, viruses, fungi, protozoans, and helminths.
  3. Typhoid fever is caused by Salmonella typhi, confirmed by Widal test, and transmitted through contaminated food and water.
  4. Pneumonia is caused by Streptococcus pneumoniae or Haemophilus influenzae, infecting the alveoli of the lungs.
  5. Common cold is caused by Rhino viruses, infecting the nose and respiratory passage but not the lungs.
  6. Malaria is caused by Plasmodium species (P. vivax, P. malaria, P. falciparum) and transmitted by the female Anopheles mosquito.
  7. Haemozoin released from ruptured RBCs causes the recurring chills and fever in malaria.
  8. Amoebiasis (amoebic dysentery) is caused by Entamoeba histolytica and transmitted through contaminated food and water.
  9. Ascariasis is caused by the roundworm Ascaris, leading to internal bleeding, muscular pain, and intestinal blockage.
  10. Filariasis (elephantiasis) is caused by Wuchereria bancrofti or W. malayi, transmitted by female mosquito vectors.
  11. Ringworm is a fungal infection caused by Microsporum, Trichophyton, or Epidermophyton, characterized by dry, scaly lesions.
  12. Innate immunity consists of physical, physiological, cellular, and cytokine barriers present at birth.
  13. Acquired immunity is pathogen-specific and has memory, with primary and secondary responses.
  14. Antibodies are H2L2 proteins produced by B-lymphocytes; types include IgA, IgM, IgE, IgG.
  15. Active immunity: body produces its own antibodies (slow, long-lasting); Passive immunity: readymade antibodies given (immediate, short-lived).
  16. Vaccination is based on immunological memory; vaccines contain weakened or inactivated pathogens or antigenic proteins.
  17. Colostrum provides passive immunity to newborns via IgA antibodies.
  18. Allergy is an exaggerated immune response to allergens, mediated by IgE, involving histamine release from mast cells.
  19. Rheumatoid arthritis is an auto-immune disease where the body attacks its own cells.
  20. Primary lymphoid organs: bone marrow and thymus; Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches, appendix, MALT.
  21. AIDS is caused by HIV, a retrovirus that uses reverse transcriptase to convert RNA to DNA.
  22. HIV targets helper T-lymphocytes, progressively decreasing their number and causing immunodeficiency.
  23. ELISA is a diagnostic test for AIDS.
  24. Cancer cells lose contact inhibition and divide uncontrollably, forming tumors.
  25. Malignant tumors metastasize; benign tumors remain localized.
  26. Carcinogens include ionising radiations (X-rays, gamma rays), UV, chemical carcinogens (tobacco smoke), and oncogenic viruses.
  27. Cancer detection methods: biopsy, histopathology, radiography, CT, MRI, and molecular biology techniques.
  28. Cancer treatment includes surgery, radiotherapy, chemotherapy, and immunotherapy (e.g., alpha-interferon).
  29. Opioids (e.g., heroin) bind to opioid receptors; heroin is diacetylmorphine from Papaver somniferum.
  30. Cannabinoids from Cannabis sativa interact with cannabinoid receptors in the brain.
  31. Cocaine from Erythroxylum coca interferes with dopamine transport and is a central nervous system stimulant.
  32. Nicotine in tobacco stimulates adrenaline release, raising blood pressure and heart rate.
  33. Drug addiction is psychological; dependence is physiological, with withdrawal symptoms on abrupt discontinuation.
  34. Anabolic steroids misuse causes masculinisation in females and testicular shrinkage in males.
  35. Prevention of drug abuse: avoid peer pressure, seek education and counselling, look for danger signs, seek professional help.

MCQs — 10 Questions with Answers

Q1. Health is defined as a state of:

  • A. Complete physical, mental, and social well-being ✓
  • B. Only absence of physical disease
  • C. Absence of genetic disorders alone
  • D. Physical fitness without mental stress

Answer: A — WHO defines health as complete physical, mental, and social well-being, not merely the absence of disease.

Q2. Salmonella typhi enters the human body primarily through:

  • A. Inhalation of respiratory droplets
  • B. Contaminated food and water ✓
  • C. Insect vector bites
  • D. Direct skin contact with infected person

Answer: B — Salmonella typhi is a pathogenic bacterium that enters via the gastrointestinal route through contaminated food and water, then migrates to other organs via blood.

Q3. Which test is used to confirm typhoid fever diagnosis?

  • A. Widal test ✓
  • B. PCR test
  • C. ELISA for antibodies only
  • D. Blood culture alone

Answer: A — The Widal test detects antibodies against Salmonella typhi antigens (O and H) and is the classic confirmatory test for typhoid fever diagnosis.

Q4. Pneumonia caused by Streptococcus pneumoniae primarily affects which part of the lungs?

  • A. Trachea and bronchi
  • B. Pleura (lung membrane)
  • C. Alveoli (air sacs) ✓
  • D. Diaphragm muscle

Answer: C — The alveoli (air-filled sacs in lungs) are infected and filled with fluid, leading to severe respiratory problems and reduced oxygen exchange.

Q5. Which of the following is NOT a vector-borne parasitic disease? (A) Malaria — Anopheles mosquito (B) Dengue — Aedes mosquito (C) Amoebiasis — Entamoeba histolytica in contaminated water (D) Filariasis — Culex mosquito

  • A. Malaria transmitted by Anopheles mosquito
  • B. Dengue transmitted by Aedes mosquito
  • C. Amoebiasis transmitted via contaminated water, not a vector ✓
  • D. Filariasis transmitted by Culex mosquito

Answer: C — Amoebiasis is transmitted through contaminated water and food containing Entamoeba histolytica cysts, not via a biological vector like a mosquito.

Q6. During a malaria infection, the Plasmodium parasite destroys red blood cells in the human host. Which phase of the Plasmodium life cycle occurs in the human body?

  • A. Gametogenesis and zygote formation only
  • B. Asexual reproduction in liver (schizogony) and blood (erythrocytic stage) ✓
  • C. Sporozoite injection and sexual reproduction only
  • D. All developmental stages from sporozoite to gamete

Answer: B — In humans, Plasmodium undergoes asexual multiplication in liver cells (pre-erythrocytic) and then in RBCs (erythrocytic stage), causing hemolysis and fever; sexual stages occur in the mosquito.

Q7. Which statement best distinguishes innate immunity from acquired immunity? (Both correct in themselves, choose the MOST complete distinction)

  • A. Innate immunity involves antibodies; acquired immunity involves only T-cells
  • B. Innate immunity is present from birth and includes physical barriers and phagocytes; acquired immunity develops after antigen exposure and involves specific B and T cell responses ✓
  • C. Innate immunity is stronger than acquired immunity
  • D. Acquired immunity is always passive, while innate immunity is always active

Answer: B — Innate immunity is always present (barriers, lysozyme, phagocytes) and non-specific; acquired immunity requires prior exposure to antigen and is specific due to B-cell antibodies and T-cell responses.

Q8. A person receives a tetanus vaccination. This triggers active immunity. Which cells are responsible for producing the protective antibodies in this case?

  • A. T-helper cells alone
  • B. Macrophages and neutrophils
  • C. B-lymphocytes (plasma cells) ✓
  • D. Memory cells without any involvement of B-cells

Answer: C — B-lymphocytes differentiate into plasma cells that secrete specific antibodies against tetanus toxoid antigen; memory B-cells provide long-term immunity.

Q9. HIV replicates by first binding to CD4+ receptors on T-helper cells. Which of the following correctly describes what happens next? (A) Reverse transcriptase synthesizes DNA from HIV RNA (B) Viral DNA integrates into host chromosome (C) New viral particles bud from cell surface (D) All of the above occur in sequence

  • A. Only reverse transcriptase activity occurs
  • B. Only integration into chromosome occurs
  • C. Only budding of new virions occurs
  • D. All three steps occur in sequence during HIV replication cycle ✓

Answer: D — HIV replication involves reverse transcription of RNA to DNA, integration of DNA into host chromosome, and budding of new viral particles that destroy the T-cell, progressively depleting CD4+ cells.

Q10. A benign tumour differs from a malignant tumour in that it is: (I) Non-invasive and localized (II) Slow-growing (III) Does not metastasize (IV) Always fatal if untreated

  • A. Only I and II are correct
  • B. Only I, II, and III are correct ✓
  • C. Only II and IV are correct
  • D. All four statements are correct

Answer: B — Benign tumours are non-invasive, localized, and do not metastasize; malignant tumours are invasive and spread to distant sites; statement IV is false because benign tumours are often not fatal.

Flashcards

Define health according to WHO.

Health is a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity.

What is a pathogen?

A disease-causing organism (bacterium, virus, protozoan, fungus, helminth) that enters the body, multiplies, and damages host tissues.

How does Salmonella typhi cause typhoid fever?

It enters the small intestine via contaminated food/water, migrates through blood to other organs, and causes sustained high fever (39–40°C), weakness, stomach pain, and constipation; diagnosis is confirmed by Widal test.

Name two bacteria that cause pneumonia.

Streptococcus pneumoniae and Haemophilus influenzae infect lung alveoli, filling them with fluid and causing respiratory distress.

Which protozoan causes malaria and how is it transmitted?

Plasmodium species (P. vivax, P. falciparum) is transmitted by female Anopheles mosquito during blood meal, enters liver and blood cells causing fever, chills, and hemolysis.

What is the difference between innate and acquired immunity?

Innate immunity is present from birth and includes physical barriers (skin, stomach acid) and phagocytes; acquired immunity develops after exposure to antigen and involves B-cell antibodies and T-cell responses.

How do B-lymphocytes protect against pathogens?

B-cells produce specific antibodies (immunoglobulins) that bind to pathogen antigens, marking them for destruction by phagocytes and forming immune memory for rapid future responses.

What is active vs. passive immunity?

Active immunity results from the body producing its own antibodies (vaccination or infection); passive immunity occurs when antibodies are directly transferred (maternal antibodies, antiserum injection).

How does HIV destroy the immune system?

HIV binds to CD4+ receptors on T-helper cells, replicates inside them, causes cell death, and gradually depletes T-helper cells, leading to opportunistic infections (AIDS).

Distinguish between benign and malignant tumours.

Benign tumours are localized, slow-growing, and non-invasive; malignant tumours are invasive, metastasize to distant sites, and have high mortality if untreated.

Important Board Questions

Define 'health' according to WHO. Give one example of how mental health affects physical health. [2 marks]

State WHO definition (complete physical, mental, social well-being). Example: stress → weakened immunity → infections. Or: depression → poor sleep → reduced antigen response.

Describe the life cycle of Plasmodium vivax in the human host and Anopheles mosquito. Explain why repeated fever occurs during malaria infection. [5 marks]

Human: sporozoite in liver → schizogony → RBCs → lysis releases merozoites + toxins → fever. Mosquito: ingested RBCs → gametogenesis → zygote → sporozoites in salivary glands. Repeated fever = cyclic RBC rupture every 48–72 hours (P. vivax fever every third day due to synchronized schizont release).

Explain the role of B-lymphocytes and T-lymphocytes in acquired immunity. How does vaccination provide protection without causing disease? Justify why some vaccines require booster doses. [6 marks]

B-cells produce antibodies (humoral); T-cells kill infected cells (cell-mediated). Vaccination: antigen primes immune response without pathogenic replication → memory cells form. Booster doses: refresh memory cell populations to maintain high antibody titre and long-term protection against waning immunity.

Assertion-Reason Questions for Human Health and Disease

Q1. Assertion (A):

Health is defined solely as the absence of disease in the body.

Reason (R):

The WHO definition of health includes physical, mental, and social well-being, not just absence of disease.

Answer: D — A is false but R is true — Both the assertion and reason are false. The assertion is incorrect because health includes mental and social dimensions. The reason is true but doesn't contradict the assertion being false; it demonstrates why the assertion is incomplete.

Q2. Assertion (A):

Salmonella typhi pathogens enter the human body through the small intestine and then migrate to other organs via blood.

Reason (R):

The low pH of the stomach and presence of digestive enzymes make it difficult for pathogens to survive passage through the stomach.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both statements are true, but the reason does not explain the assertion. The reason explains why pathogens must survive the stomach, while the assertion describes the entry and migration route. They are related but not causally connected in explanation.

Q3. Assertion (A):

Pneumonia caused by Streptococcus pneumoniae primarily affects the alveoli of the lungs.

Reason (R):

When alveoli fill with fluid due to infection, gas exchange is severely impaired, leading to respiratory problems and cyanosis.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both assertion and reason are true, and the reason correctly explains why pneumonia in the alveoli is problematic. The fluid in alveoli directly causes the respiratory symptoms observed in pneumonia patients.

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Case-Based Questions (CBQ) for Human Health and Disease

Case Study:

A public health department in Delhi investigated a typhoid outbreak in a densely populated residential area. Over 150 cases were confirmed using the Widal test, and epidemiologists traced the source to a food vendor's stall. The vendor's water supply was contaminated with Salmonella typhi, which had survived the low pH of the stomach in affected individuals and caused infection in the small intestine. Many customers reported symptoms including sustained high fever (39-40°C), stomach pain, and constipation. Interestingly, the vendor himself showed no symptoms but was later identified as an asymptomatic carrier, similar to the historical case of Mary Mallon.

Q1. Why did the Widal test serve as a critical diagnostic tool in this outbreak investigation?

  • A. It could identify asymptomatic carriers like the food vendor
  • B. It is the classic confirmatory test for typhoid fever caused by Salmonella typhi ✓
  • C. It determines whether contaminated water is the source
  • D. It measures the pH of the stomach to assess bacterial survival

Answer: B

Q2. Why did Salmonella typhi survive passage through the stomach of infected individuals?

  • A. The stomach's high pH provided a favorable environment for bacterial growth
  • B. The bacteria were resistant to low pH and digestive enzymes in the stomach ✓
  • C. The vendor supplied alkaline water that neutralized stomach acid
  • D. Patients had underlying genetic deficiencies in stomach acid production

Answer: B

Q3. The identification of the vendor as an asymptomatic carrier is significant because:

  • A. It shows that individuals without symptoms can still spread infectious disease to others ✓
  • B. It proves that Mary Mallon's case is not relevant to modern disease transmission
  • C. It demonstrates that contaminated water is safer than contaminated food
  • D. It indicates that the Widal test cannot identify carriers

Answer: A

Q4. Which preventive measure would have been most effective in stopping this outbreak?

  • A. Screening all customers for Widal test seropositivity
  • B. Restricting access to the market for one week
  • C. Providing antibiotics to all symptomatic patients only
  • D. Regular health screening and treatment of food vendors, particularly asymptomatic carriers ✓

Answer: D

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Previous Year Questions (PYQ) for Human Health and Disease

Real CBSE board exam questions from past papers — free to attempt.

CBSE 2026 · Set 57/1/1 · 3 marks

(a) Mention the scientific name of the source plant and the part from which opioids are extracted. (1 mark) (b) How are morphine and heroin related? Mention the effect each one of them has on human body. (2 marks)

CBSE 2026 · Set 57/2/2 · 2 marks

Differentiate between opioids and cannabinoids on the basis of their (a) Receptor site in human body. (b) Mode of action in human body.

CBSE 2026 · Set 57/3/2 · 1 mark

Some statements regarding drugs and alcohol are given below : (i) Adolescents are more vulnerable to peer pressure. (ii) Drug addiction leads to increased tolerance level of the receptors present in our body. (iii) Alcohol affects the central nervous system. (iv) Excessive use of drugs helps to increase energy. (v) Anabolic steroids decrease aggressiveness. Choose the option with correct statement(s).

  • Statements (i), (iv) and (v) are correct
  • Statements (i), (ii) and (iii) are correct
  • Only statements (i) and (v) are correct
  • Only statement (iii) is correct

CBSE 2026 · Set 57/3/3 · 1 mark

Some statements regarding drugs and alcohol are given below: (i) Adolescents are more vulnerable to peer pressure. (ii) Drug addiction leads to increased tolerance level of the receptors present in our body. (iii) Alcohol affects the central nervous system. (iv) Excessive use of drugs helps to increase energy. (v) Anabolic steroids decrease aggressiveness. Choose the option with correct statement(s).

  • Statements (i), (iv) and (v) are correct
  • Statements (i), (ii) and (iii) are correct
  • Only statements (i) and (v) are correct
  • Only statement (iii) is correct

CBSE 2026 · Set 57/3/3 · 3 marks

Study the following cases: Case I: A person bitten by a rabid dog is immediately given an injection of antitoxin for rabies. Case II: A child is given rabies vaccine as a preventive measure. (a) Identify the type of immunity provided in both the cases. (b) Differentiate between the two types of immunity. (c) What is a vaccine ? How does it help in preventing a disease ?

CBSE 2026 · Set 57/1/1 · 1 mark

Which of the following is not a component of immune system?

  • Lymphocytes
  • Plasma Proteins
  • Red Blood Cells
  • Bone Marrow

CBSE 2026 · Set 57/1/1 · 2 marks

(a) Define Humoral immune response. (1 mark) (b) Name any two types of antibodies found to give humoral immune response in humans. (1 mark)

CBSE 2026 · Set 57/1/1 · 5 marks

(a) (i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. (0.5 marks) (ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place. (2 marks) (iii) How does the parasite damage the human body after entering the blood stream? (1.5 marks) (iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions. (1 mark)

CBSE 2026 · Set 57/1/2 · 5 marks

(a) (i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. (½ mark) (ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place. (2 marks) (iii) How does the parasite damage the human body after entering the blood stream? (1½ marks) (iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions. (1 mark) OR (b) (i) What are bio-fertilizers? (1 mark) (ii) Name the different types of microorganisms used as bio-fertilizers in organic farming and explain how each contributes to soil fertility. (3 marks) (iii) Write two advantages of using bio-fertilizers over chemical fertilizers. (1 mark)

CBSE 2026 · Set 57/1/3 · 1 mark

Interferons are most effective in making non-infected cells resistant against the spread of which of the following diseases?

  • Malaria
  • Ascariasis
  • Pneumonia
  • Cancer

CBSE 2026 · Set 57/1/3 · 2 marks

A health officer visiting two different regions reported the following symptoms in patients: Region A – Sustained high fever with stomach pain, constipation and loss of appetite. Region B – Inflammation in the lower limbs and genital organs. Name the diseases likely affecting the patients in regions A and B. Write the scientific name of the causative organisms in both the cases.

CBSE 2026 · Set 57/1/3 · 5 marks

Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. Name the host in which the parasite completes its sexual stages and explain the changes taking place. How does the parasite damage the human body after entering the blood stream? Suggest two effective preventive measures to control the spread of this disease in endemic regions.

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Class 12 Biology Previous Year Questions, Chapter-wise

All 1074 CBSE board questions from 2022–2026, sorted by chapter and question type. Free PDF download.

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