# Human Health and Disease (NEET Biology Class 12): Pathogens, Immunity, AIDS & Cancer Source: https://tracknation.in/story/human-health-and-disease-neet-biology-class-12-pathogens-immunity-aids-cancer (TrackNation — free UPSC notes with PYQs) > NEET Class 12 Human Health and Disease, mined from NCERT: a complete disease-pathogen-vector-symptom master table (typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis, filariasis, ringworm), the Plasmodium life cycle, prevention measures, innate immunity's four barriers tabulated, acquired immunity (primary vs secondary response, B vs T lymphocytes, antibody structure, graft rejection), allergy and autoimmunity, a primary vs secondary lymphoid organ table with MALT, AIDS, and cancer ## Infectious Diseases, Pathogens & Vectors 🎯 **NEET priority: High-yield.** *4–5 questions a year — about 10% of the Biology paper. **Immunity + the disease/pathogen/vector table + cancer** make up roughly 80% of this chapter's questions, and **cancer (oncogenes, metastasis, carcinogens) has been tested increasingly since 2019**.* ### Infectious diseases — the master table NEET asks from | **Disease** | **Pathogen** | **Type** | **Transmission / vector** | **Key symptoms & facts** | | Typhoid | Salmonella typhi | Bacterium | Contaminated FOOD and WATER; enters via the small intestine, migrates through blood | Sustained high fever 39–40°C, weakness, stomach pain, constipation, headache, loss of appetite. Intestinal perforation and death in severe cases. Confirmed by the WIDAL TEST. Classic case: Mary Mallon, 'Typhoid Mary', a cook | | Pneumonia | Streptococcus pneumoniae and Haemophilus influenzae | Bacterium | Inhaling DROPLETS/aerosols from an infected person, or sharing glasses and utensils | Infects the ALVEOLI, which fill with fluid. Fever, chills, cough, headache; in severe cases lips and fingernails turn GREY TO BLUISH | | Common cold | Rhino viruses | Virus | Inhaled droplets from cough/sneeze, or contaminated objects (pens, books, cups, doorknobs, keyboard) | Infects the NOSE and RESPIRATORY PASSAGE but NOT the lungs. Nasal congestion and discharge, sore throat, hoarseness, cough — lasts 3–7 days | | Malaria | Plasmodium (P. vivax, P. malariae, P. falciparum) | Protozoan | Bite of the infected FEMALE ANOPHELES mosquito | MALIGNANT malaria by P. FALCIPARUM is the most serious and can be fatal. Chill and high fever recur every 3–4 days, caused by the toxin HAEMOZOIN | | Amoebiasis (amoebic dysentery) | Entamoeba histolytica | Protozoan | Contaminated food/water; HOUSEFLIES act as MECHANICAL CARRIERS | Lives in the LARGE INTESTINE. Constipation, abdominal pain and cramps, stools with excess mucous and blood clots | | Ascariasis | Ascaris (the common round worm) | Helminth | Contaminated water, vegetables, fruits — eggs excreted in faeces contaminate soil/water | Internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage | | Filariasis (elephantiasis) | Wuchereria bancrofti and W. malayi | Helminth | Bite of FEMALE MOSQUITO vectors | Slow chronic inflammation of the LYMPHATIC VESSELS of the lower limbs, over many years. Genital organs often affected, causing gross deformities | | Ringworm | Microsporum, Trichophyton, Epidermophyton | Fungus | From SOIL, or shared towels, clothes, or combs | Dry scaly lesions on skin, nails and scalp with intense itching. HEAT and MOISTURE help them thrive — hence skin folds like the groin and between the toes | ### The Plasmodium life cycle — the sequence NEET tests - Plasmodium enters the human body as **SPOROZOITES — the infectious form** — through the bite of an **infected female Anopheles** mosquito. The parasites multiply in **liver cells**, then attack **red blood cells**, rupturing them and releasing the toxin **haemozoin**, which causes the chill and high fever recurring every **3–4 days**. - When a female Anopheles bites an infected person, parasites enter the mosquito, develop further, and form **sporozoites stored in the mosquito's SALIVARY GLANDS** — ready to infect the next human. **Plasmodium needs TWO hosts** — humans and mosquitoes — to complete its life cycle; the **female Anopheles is the VECTOR**. ### Prevention - **Personal and public hygiene** is critical — especially for **food/water-borne** diseases (typhoid, amoebiasis, ascariasis). For **air-borne** diseases (pneumonia, common cold) also avoid close contact with infected persons or their belongings. For **vector-borne** diseases (malaria, filariasis), the key is **eliminating vectors and breeding places** — avoid stagnant water, clean coolers regularly, use mosquito nets, and introduce larvivorous fish like **Gambusia**. ## Immunity: Innate, Acquired, Allergy & Lymphoid Organs ### Innate immunity — four types of barrier | **Barrier** | **What it is** | | Physical | Skin; mucus coating of the epithelium lining respiratory, gastrointestinal and urogenital tracts traps microbes | | Physiological | ACID in the stomach, SALIVA in the mouth, TEARS from the eyes — all prevent microbial growth | | Cellular | Leukocytes — polymorpho-nuclear leukocytes (PMNL/neutrophils), monocytes and NATURAL KILLER lymphocytes in blood, plus MACROPHAGES in tissues — phagocytose and destroy microbes | | Cytokine | Virus-infected cells secrete INTERFERONS, which protect NON-infected cells from further viral infection | ### Acquired immunity — pathogen-specific, with memory - First encounter → a low-intensity **primary response**. A subsequent encounter with the same pathogen → a highly intensified **secondary or ANAMNESTIC response**, because the body remembers. - **B-lymphocytes** produce **antibodies** → **humoral immune response** (antibody-mediated). **T-lymphocytes** mediate **cell-mediated immunity (CMI)**; **T-cells do NOT secrete antibodies** — they help B cells produce them. - An antibody has **four peptide chains** — two short **light** and two longer **heavy** chains — hence represented as **H₂L₂**. Types include **IgA, IgM, IgE, IgG**. - **Graft rejection** is due to **cell-mediated immunity** — the body distinguishes 'self' from 'non-self'. Tissue and blood group matching are essential before transplant, and the patient still takes **immunosuppressants for life**. ### Allergy & autoimmunity - **Allergy** is an exaggerated immune response to environmental antigens called **allergens** (dust mites, pollen, animal dander). The antibodies produced are **IgE type**. Symptoms — sneezing, watery eyes, running nose, difficulty breathing — come from the release of **histamine and serotonin from MAST CELLS**. Treated with **anti-histamine, adrenalin and steroids**. - **Autoimmune disease:** the body attacks its own self-cells. **Rheumatoid arthritis** is the NCERT example. ### Lymphoid organs | **Type** | **Organs** | **Role** | | PRIMARY lymphoid organs | Bone marrow and THYMUS | Where IMMATURE lymphocytes differentiate into antigen-sensitive lymphocytes. Bone marrow makes all blood cells; the thymus is lobed, near the heart beneath the breastbone, LARGE at birth but shrinks to a very small size by puberty | | SECONDARY lymphoid organs | Spleen, lymph nodes, tonsils, Peyer's patches of the small intestine, appendix | Where MATURE lymphocytes interact with antigen and proliferate into effector cells. The SPLEEN is bean-shaped, contains lymphocytes and phagocytes, and holds a large reservoir of ERYTHROCYTES. LYMPH NODES trap microbes from lymph and tissue fluid | | MALT | Mucosa-Associated Lymphoid Tissue, in the lining of respiratory, digestive and urogenital tracts | Constitutes about 50 PER CENT of the lymphoid tissue in the human body | ## AIDS & Cancer ### AIDS - **AIDS = Acquired Immuno Deficiency Syndrome**, caused by **HIV — a retrovirus**. The widely used diagnostic test is **ELISA (enzyme linked immuno-sorbent assay)**. - Treatment with **anti-retroviral drugs is only PARTIALLY effective** — it can prolong life but cannot prevent death. **Prevention is the best option.** In India, **NACO (National AIDS Control Organisation)** and NGOs lead education efforts. - Preventive steps: making blood-bank blood HIV-safe, ensuring only **disposable needles and syringes**, free distribution of condoms, controlling drug abuse, advocating safe sex, and regular check-ups in susceptible populations. NCERT's message: **"don't die of ignorance"** — infected people need help and sympathy, not shunning. ### Cancer — increasingly tested since 2019 - Normal cells show **CONTACT INHIBITION** — contact with other cells stops their growth. **Cancer cells have LOST this property**, so they divide continuously into masses called **tumors**. | **Tumor type** | **Behaviour** | | BENIGN | Remains CONFINED to its original location, does NOT spread, causes little damage | | MALIGNANT | A mass of proliferating NEOPLASTIC/tumor cells that grow rapidly, INVADE and damage surrounding tissue, and STARVE normal cells by competing for nutrients | **METASTASIS** — the most feared property of malignant tumors — is when cells sloughed from the tumor travel through the **blood**, lodge elsewhere, and **start a new tumor there**. | **Cause of cancer (carcinogen)** | **Detail** | | Ionising radiation | X-rays and gamma rays — cause DNA damage leading to neoplastic transformation | | Non-ionising radiation | UV radiation | | Chemical carcinogens | Those in TOBACCO SMOKE are a major cause of LUNG CANCER | | Oncogenic viruses | Cancer-causing viruses carrying VIRAL ONCOGENES | | Cellular oncogenes (c-onc) / proto-oncogenes | Genes ALREADY present in NORMAL cells which, when activated under certain conditions, cause oncogenic transformation | **Detection and diagnosis:** **BIOPSY** — a piece of suspected tissue is cut into thin sections, stained and examined microscopically (**histopathological studies**) by a pathologist. **Blood and bone marrow tests** detect increased cell counts in **leukemias**. **Radiography (X-rays), CT (computed tomography) and MRI (magnetic resonance imaging)** detect cancers of internal organs. ## Why This Matters for NEET ### Why this matters for NEET - High-value one-liners: typhoid → **Salmonella typhi**, confirmed by the **Widal test**; pneumonia infects the **alveoli**; common cold infects the nose **but NOT the lungs**; malaria's infectious form is the **sporozoite** and the toxin is **haemozoin**; filariasis affects **lymphatic vessels**; antibody = **H₂L₂**; allergy antibody = **IgE**, from **mast cells**; graft rejection = **CMI**; **MALT = 50%** of lymphoid tissue; AIDS test = **ELISA**; loss of **contact inhibition** defines cancer. - **Trap:** **T-cells do NOT secrete antibodies** — only B-cells do; T-cells merely help. Also, **bone marrow and thymus are PRIMARY** lymphoid organs (where lymphocytes mature) while **spleen and lymph nodes are SECONDARY** (where they meet antigen) — inverting these is a classic error. And **proto-oncogenes are NORMAL genes** already present in healthy cells — they are not viral in origin, unlike viral oncogenes. - **Second trap:** **malignant** malaria is caused by **P. falciparum** specifically, not by all Plasmodium species. And **houseflies in amoebiasis are MECHANICAL carriers** (they merely carry the parasite on their body) — unlike the female Anopheles in malaria, which is a true **biological vector** where the parasite develops. ## Test Yourself: MCQs, PYQs & Active Recall Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one. ## Practice Questions **Q1.** Typhoid fever is confirmed by which diagnostic test? - (a) Widal test - (b) Biopsy - (c) ELISA - (d) Gram staining **Answer: (a)** — The Widal test confirms typhoid, caused by Salmonella typhi entering via contaminated food and water. **Q2.** Pneumonia primarily infects which part of the lungs? - (a) The alveoli - (b) The trachea - (c) The pleura - (d) The bronchi **Answer: (a)** — Streptococcus pneumoniae and Haemophilus influenzae infect the alveoli, which fill with fluid causing respiratory difficulty. **Q3.** In severe pneumonia, a characteristic sign is that the lips and fingernails: - (a) Show no change - (b) Turn grey to bluish - (c) Become white - (d) Turn yellow **Answer: (b)** — In severe cases of pneumonia, the lips and finger nails may turn grey to bluish in colour. **Q4.** The common cold, caused by rhino viruses, infects: - (a) The nose and respiratory passage but NOT the lungs - (b) The lungs - (c) The intestines - (d) The alveoli only **Answer: (a)** — Rhino viruses infect the nose and respiratory passage but not the lungs; symptoms last 3-7 days. **Q5.** The infectious form of Plasmodium that enters the human body is the: - (a) Trophozoite - (b) Gametocyte - (c) Sporozoite - (d) Merozoite **Answer: (c)** — Plasmodium enters as sporozoites through the bite of an infected female Anopheles mosquito. **Q6.** The toxic substance released when Plasmodium ruptures red blood cells is: - (a) Serotonin - (b) Interferon - (c) Haemozoin - (d) Histamine **Answer: (c)** — Haemozoin, released on rupture of RBCs, is responsible for the chill and high fever recurring every three to four days. **Q7.** The most serious form of malaria, which can be fatal, is caused by: - (a) Plasmodium malariae - (b) Plasmodium falciparum - (c) Plasmodium vivax - (d) All equally **Answer: (b)** — Malignant malaria caused by Plasmodium falciparum is the most serious and can even be fatal. **Q8.** In amoebiasis, houseflies act as: - (a) Intermediate hosts - (b) Biological vectors - (c) Mechanical carriers - (d) Definitive hosts **Answer: (c)** — Houseflies act as mechanical carriers, transmitting Entamoeba histolytica from faeces of infected persons to food. **Q9.** Wuchereria bancrofti causes chronic inflammation of the: - (a) Large intestine - (b) Lymphatic vessels of the lower limbs - (c) Alveoli - (d) Liver **Answer: (b)** — Filarial worms cause slowly developing chronic inflammation of the lymphatic vessels of the lower limbs — elephantiasis. **Q10.** Ringworm is caused by fungi belonging to the genera: - (a) Entamoeba and Plasmodium - (b) Ascaris and Wuchereria - (c) Microsporum, Trichophyton and Epidermophyton - (d) Salmonella and Streptococcus **Answer: (c)** — These three fungal genera cause ringworm, thriving in the heat and moisture of skin folds. **Q11.** Interferons, which protect non-infected cells from viral infection, are an example of which innate barrier? - (a) Physical barrier - (b) Cytokine barrier - (c) Physiological barrier - (d) Cellular barrier **Answer: (b)** — Virus-infected cells secrete interferons — the cytokine barrier of innate immunity. **Q12.** The highly intensified response on a second encounter with the same pathogen is called the: - (a) Primary response - (b) Allergic response - (c) Secondary or anamnestic response - (d) Innate response **Answer: (c)** — Acquired immunity is characterised by memory; the second encounter elicits a highly intensified secondary or anamnestic response. **Q13.** An antibody molecule is represented as H2L2 because it has: - (a) Two lipid and two protein chains - (b) Four identical chains - (c) Two heavy chains only - (d) Two heavy and two light peptide chains **Answer: (d)** — Each antibody has four peptide chains — two short light and two longer heavy chains — hence H2L2. **Q14.** Graft rejection following organ transplantation is due to: - (a) Cell-mediated immunity - (b) Innate immunity - (c) Passive immunity - (d) Humoral immunity **Answer: (a)** — The body distinguishes self from non-self, and cell-mediated immune response is responsible for graft rejection. **Q15.** The antibodies produced in an allergic reaction are of which type? - (a) IgA - (b) IgE - (c) IgG - (d) IgM **Answer: (b)** — Allergens elicit IgE-type antibodies; symptoms result from histamine and serotonin released from mast cells. **Q16.** Which of the following is a PRIMARY lymphoid organ? - (a) Thymus - (b) Lymph nodes - (c) Spleen - (d) Tonsils **Answer: (a)** — Bone marrow and thymus are primary lymphoid organs where immature lymphocytes differentiate; spleen, lymph nodes and tonsils are secondary. **Q17.** MALT constitutes approximately what percentage of the lymphoid tissue in the human body? - (a) 50 per cent - (b) 25 per cent - (c) 90 per cent - (d) 10 per cent **Answer: (a)** — Mucosa-associated lymphoid tissue constitutes about 50 per cent of the lymphoid tissue in the human body. **Q18.** The property that normal cells possess but cancer cells lose is: - (a) Cell division - (b) Phagocytosis - (c) Metastasis - (d) Contact inhibition **Answer: (d)** — Normal cells show contact inhibition — contact with other cells inhibits growth. Cancer cells have lost this property. **Q19.** Metastasis refers to: - (a) The formation of benign tumors - (b) Loss of the nucleus - (c) Uncontrolled cell division at the original site - (d) Cells sloughed from a tumor travelling through blood to start new tumors elsewhere **Answer: (d)** — Metastasis — the most feared property of malignant tumors — is the spread of tumor cells through blood to new sites. **Q20.** Genes present in NORMAL cells that can cause oncogenic transformation when activated are called: - (a) Viral oncogenes - (b) Cellular oncogenes or proto-oncogenes - (c) Interferons - (d) Allergens **Answer: (b)** — Cellular oncogenes (c-onc) or proto-oncogenes exist in normal cells and, when activated, can lead to oncogenic transformation. **Q21.** The chains marked A are - (a) light chains - (b) heavy chains - (c) Fc chains - (d) J chains **Answer: (a)** — An antibody (H2L2) has four polypeptide chains: two small light chains [A] and two longer heavy chains [B], held together by disulphide bonds. **Q22.** The regions marked C bind to the antigen. They are - (a) the constant regions - (b) the complement-binding sites - (c) the hinge - (d) the variable regions **Answer: (d)** — Antigen-binding sites are formed by the variable regions of a heavy and a light chain; each antibody therefore has two identical antigen-binding sites. **Q23.** The chains of the molecule are held together by the bonds marked D, which are - (a) phosphodiester bonds - (b) peptide bonds - (c) disulphide bonds - (d) glycosidic bonds **Answer: (c)** — Disulphide (S-S) bonds between cysteine residues join the heavy chains to each other and to the light chains. ### NEET Previous Year Questions (PYQs) *Real NEET previous-year questions on this chapter. Immunity, the disease/pathogen table and cancer together make up about 80% of this chapter's questions, so this bank is deliberately larger. Explanations in our own words.* **Q24.** The vector for malaria is: (NEET PYQ) - (a) Female Anopheles mosquito - (b) Female Culex mosquito - (c) Male Anopheles mosquito - (d) Housefly **Answer: (a)** — The female Anopheles mosquito is the vector; Plasmodium needs two hosts — humans and mosquitoes — to complete its life cycle. **Q25.** Which of the following diseases is caused by a helminth? (NEET PYQ) - (a) Typhoid - (b) Ascariasis - (c) Ringworm - (d) Amoebiasis **Answer: (b)** — Ascariasis is caused by Ascaris, a helminth (round worm); typhoid is bacterial, amoebiasis protozoan and ringworm fungal. **Q26.** Which cells do NOT secrete antibodies? (NEET PYQ) - (a) T-lymphocytes - (b) B-lymphocytes - (c) None of these - (d) Plasma cells **Answer: (a)** — T-cells themselves do not secrete antibodies — they help B cells produce them. B-lymphocytes produce antibodies. **Q27.** The widely used diagnostic test for AIDS is: (NEET PYQ) - (a) ELISA - (b) Biopsy - (c) Widal test - (d) MRI **Answer: (a)** — Enzyme linked immuno-sorbent assay (ELISA) is the widely used diagnostic test for AIDS. **Q28.** Chemical carcinogens present in tobacco smoke are a major cause of: (NEET PYQ) - (a) Liver cancer - (b) Leukemia - (c) Skin cancer - (d) Lung cancer **Answer: (d)** — The chemical carcinogens in tobacco smoke have been identified as a major cause of lung cancer. **Q29.** Cancer detection by examining thin stained sections of suspected tissue under a microscope is called: (NEET PYQ) - (a) Biopsy and histopathological study - (b) ELISA - (c) Radiography - (d) CT scan **Answer: (a)** — In biopsy, a piece of suspected tissue is cut into thin sections, stained and examined microscopically by a pathologist. **Q30.** Rheumatoid arthritis is an example of: (NEET PYQ) - (a) A deficiency disease - (b) An allergic reaction - (c) An infectious disease - (d) An auto-immune disease **Answer: (d)** — In auto-immune disease the body attacks its own self-cells; rheumatoid arthritis is the NCERT example. **Q31.** Which larvivorous fish is introduced into water bodies to control mosquito breeding? (NEET PYQ) - (a) Rohu - (b) Gambusia - (c) Hilsa - (d) Catla **Answer: (b)** — Introducing larvivorous fish like Gambusia is a recommended measure to control mosquito vectors. **Q32.** Allergy symptoms result from the release of histamine and serotonin from: (NEET PYQ) - (a) T-lymphocytes - (b) Mast cells - (c) Neutrophils - (d) Macrophages **Answer: (b)** — Allergy is due to the release of chemicals like histamine and serotonin from the mast cells. **Q33.** The thymus, a primary lymphoid organ, is: (NEET PYQ) - (a) Absent in humans - (b) Large at birth and reduces to a very small size by puberty - (c) Located in the abdomen - (d) Small at birth and enlarges with age **Answer: (b)** — The thymus is quite large at the time of birth but keeps reducing in size with age, becoming very small by puberty. ### Active Recall Prompt Write everything you can recall about **Human Health and Disease**, naming each part first: every **infectious disease** with its pathogen, type, mode of transmission and symptoms (typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis, filariasis, ringworm); the **Plasmodium life cycle**; **prevention** measures; **innate immunity** (all four barriers); **acquired immunity** (primary vs secondary response, B vs T lymphocytes, antibody structure, graft rejection); **allergy and autoimmunity**; the **lymphoid organs** (primary vs secondary, and MALT); **AIDS** (pathogen, test, treatment, prevention); and **cancer** (contact inhibition, benign vs malignant, metastasis, every carcinogen type, and the detection methods). Begin each fact with its topic and end it with a full stop.