NEET Human Health and Disease Previous Year Questions with Solutions

The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes.

• • All blood cells including B and T lymphocytes are produced in the bone marrow; T-lymphocytes mature in the thymus.

After maturation, lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine, and appendix. These organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.

• • The spleen is a large bean-shaped organ containing lymphocytes and phagocytes, acting as a filter for blood-borne microorganisms.

The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant against gastrointestinal and respiratory pathogens.

• • This provides natural passive immunity because preformed antibodies are transferred directly to the infant.

Secretory IgA is typically a dimer joined by a J-chain and protected by a secretory component against proteolytic digestion in the infant’s stomach and intestines.

• • IgG provides prenatal passive immunity via placental transfer, whereas IgA provides postnatal passive immunity via colostrum.

Morphine is a natural opiate alkaloid obtained from the latex of the opium poppy plant, Papaver somniferum. It binds to specific opioid receptors present in our central nervous system and gastrointestinal tract.

• • Diacetylation of morphine yields heroin (diacetylmorphine, or smack).

In clinical medicine, morphine is widely used as a potent analgesic (painkiller) and sedative for managing severe acute pain, particularly in patients undergoing surgery or dealing with terminal cancer pain.

• • However, when taken for purposes other than medicinal use, it leads to severe psychological and physical dependence.

Plasmodium requires two hosts to complete its life cycle. The infectious stage is the sporozoite, injected into the human bloodstream through the bite of an infected female Anopheles mosquito. Sporozoites reach the liver and reproduce asexually (schizogony), bursting hepatocytes and invading RBCs where further asexual cycles cause paroxysms of fever due to hemozoin release.

• • Gametocytes (sexual stages) develop in the peripheral RBCs of the human host.

When a female Anopheles mosquito bites an infected person, it takes up gametocytes with the blood meal. Fertilization and development take place in the mosquito’s gut. The resulting motile ookinete penetrates the stomach wall, forms an oocyst, and divides by sporogony to produce mature sporozoites that migrate to the mosquito’s salivary glands.

• • Option (4) is completely correct.

Detection of cancers in internal organs (such as brain, lungs, liver, pancreas) requires non-invasive cross-sectional and high-contrast imaging:

• • Computed tomography (CT) uses X-rays to generate a three-dimensional image of the internals of an object.
• • Magnetic resonance imaging (MRI) uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in living tissue.
• • NCERT states: "Computed tomography and magnetic resonance imaging are very useful to detect cancers of the internal organs." Thus, Statement A is correct.

Chemotherapy involves cytotoxic chemical drugs that inhibit rapid cell division:

• • Chemotherapeutic drugs are designed specifically to kill rapidly dividing cancerous cells. Although hair loss and anaemia occur due to collateral damage to normal proliferating cells, stating they are "used to kill non-cancerous cells" is completely false. Thus, Statement B is incorrect.
• • Statement D claims chemotherapeutic drugs are biological response modifiers. Biological response modifiers (BRMs) are immuno-stimulatory proteins (such as $\alpha$-interferon) that boost the host immune surveillance, whereas chemotherapeutic drugs are small-molecule synthetic chemicals or antibiotics (e.g., cisplatin, vincristine, methotrexate). Thus, Statement D is incorrect.

Immunotherapy in cancer treatment:

• • Tumour cells frequently evade immune surveillance because they are self-derived.
• • Administration of biological response modifiers such as $\alpha$-interferon activates natural killer (NK) cells and cytotoxic T-lymphocytes, aiding the immune destruction of the tumour.
• • Thus, Statement C is correct.

Leukaemia is a malignant neoplasm of hematopoietic stem cells in the bone marrow characterized by abnormal, uncontrolled proliferation and massive accumulation of immature or abnormal white blood cells (leukocytes) in circulating blood. The leukocyte count is markedly elevated (often > 100,000/mm³), not decreased. Thus, Statement E is incorrect.

Only Statements A and C are correct, matching Option (4).

In cancer biology, transformation of normal cells into cancerous neoplastic cells is driven by loss of contact inhibition and uncontrolled mitotic proliferation:

• • Tumours are classified into two major types: Benign tumours and Malignant tumours.
• • Benign tumours remain strictly confined to their anatomical site of origin, do not spread or infiltrate surrounding tissues, and usually cause relatively little damage (Feature D).

Malignant tumours consist of true neoplastic cells displaying distinct aggressive pathological hallmarks:

• • A mass of actively proliferating cells (Feature A): Cells lose regular cell cycle checkpoints and proliferate autonomously.
• • Rapid growth (Feature B): High mitotic index and accelerated doubling times starve surrounding normal cells by competing for vital nutrients.
• • Invasiveness and tissue destruction (Feature C): Neoplastic cells degrade extracellular matrix, infiltrate neighboring normal parenchyma, damage local structures, and enter blood/lymphatic vessels to establish secondary distant metastases (the most feared property of malignant neoplasms).

Features A, B, and C define the neoplastic characteristics of malignant tumor cells, whereas Feature D characterizes benign tumors. Thus, A, B, C only are correct.

An antibody (immunoglobulin) is a Y-shaped glycoprotein composed of four polypeptide chains:

• • Two identical light (L) chains of lower molecular weight (~25 kDa each).
• • Two identical heavy (H) chains of higher molecular weight (~50 kDa each).
• • The four chains are held together in a Y-configuration by covalent interchain disulfide (-S-S-) bonds and non-covalent interactions. Hence, statements (1) and (2) are correct.

Functional differentiation between the variable tips and constant stalk:

• • Variable regions ($V_L$ and $V_H$): Located at the N-terminal (amino-terminal) ends of the Y-shaped arms. The hypervariable segments (complementarity-determining regions / CDRs) form the unique antigen-binding site (paratope) that binds specifically to an epitope.
• • Constant regions ($C_L$ and $C_H$): Located towards the C-terminal (carboxyl-terminal) end. They mediate effector functions such as complement fixation and binding to Fc receptors on phagocytes. Hence, statement (4) is correct.

Statement (3) claims that the "Antigen binding site is located at C-terminal region of antibody molecules". This is biologically false; the antigen-binding site is located at the N-terminal region.

Lymphoid organs are categorized into primary and secondary lymphoid organs based on their anatomical and immunological roles:

• • Primary Lymphoid Organs: Organs where immature lymphocytes originate, proliferate, and differentiate into antigen-sensitive mature lymphocytes. In humans, these are Bone marrow (B) and Thymus (A).
• • After maturation, these immunocompetent T and B lymphocytes migrate via the bloodstream into secondary lymphoid organs.

Sites of antigen capture, presentation, and clonal expansion:

• • C. Spleen: A large bean-shaped organ containing lymphocytes and phagocytes; filters blood by trapping blood-borne microorganisms and acts as a reservoir of erythrocytes.
• • D. Lymph nodes: Small solid structures located along the lymphatic system; trap antigens carried in lymph and tissue fluid, activating lymphocytes to elicit immune responses.
• • E. Peyer's patches: Unencapsulated aggregates of mucosal lymphoid follicles located in the submucosa of the small intestine (ileum), representing Gut-Associated Lymphoid Tissue (GALT).
• • All three (C, D, E) provide the microenvironment where lymphocytes interact with trapped antigens.

Secondary lymphoid organs/tissues among the choices are C, D, and E only, corresponding to Option (4).

Innate immunity represents the body's first line of natural immunological defence:

• • It is congenital, meaning it is genetically predetermined and fully operational at the time of birth.
• • It is non-specific, meaning it does not discriminate between distinct antigenic molecular determinants; it provides broad-spectrum resistance against invasion by foreign infectious agents.

How non-specific protection is maintained:

• • Physical barriers: Skin acts as the principal barrier preventing entry; mucus coatings of respiratory, GI, and urogenital tracts trap microbes.
• • Physiological barriers: Gastric acid (HCl) in stomach, saliva in the mouth, and lysozyme in tears prevent microbial growth.
• • Cellular barriers: Phagocytes like polymorphonuclear leukocytes (PMNL-neutrophils), monocytes, and tissue macrophages, plus Natural Killer (NK) cells.
• • Cytokine barriers: Virus-infected cells secrete interferons which protect non-infected cells from further viral infection.

Distinguishing features of adaptive defence:

• • Acquired (adaptive) immunity (including humoral and cell-mediated branches) is NOT present at birth; it is acquired post-natally upon exposure to specific pathogens and is characterized by exquisite antigenic specificity and long-lasting memory.

The immunity present at birth providing non-specific defence is Innate Immunity, corresponding to Option (2).

Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings (A -> IV). Leishmania is a flagellated protozoan causing visceral leishmaniasis (B -> III).

Many fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton are responsible for ringworms in humans (C -> I). Wuchereria (W. bancrofti and W. malayi), the filarial worms, are nematodes causing slowly developing chronic inflammation in lymphatic vessels of the lower limbs (D -> II).

A-IV, B-III, C-I, D-II matches Option (4).

Autoimmunity is a condition where the body’s immune system loses self-tolerance and generates auto-antibodies or autoreactive T-cells that attack host tissues.

- Myasthenia gravis (A): Autoimmune disorder affecting neuromuscular junctions leading to fatigue and paralysis of skeletal muscles. - Rheumatoid arthritis (B): Autoimmune disease affecting joint synovial membranes, highlighted in NCERT. - Systemic Lupus Erythematosus (E): Multiorgan autoimmune disease. - Gout (C): Inflammation of joints due to accumulation of uric acid crystals (metabolic). - Muscular dystrophy (D): Progressive degeneration of skeletal muscle mostly due to genetic mutation in dystrophin protein.

Disorders A, B, and E are autoimmune, giving A, B & E only (Option 4).

Morphine is extracted from the latex of poppy plant Papaver somniferum and is a very effective sedative and painkiller used for surgical patients (C -> I). Heroin (smack) is chemically diacetylmorphine, also obtained from Papaver somniferum (B -> IV). Cannabinoids like marijuana, hashish, charas and ganja are obtained from the inflorescences of Cannabis sativa (D -> II).

Coca alkaloid or cocaine is obtained from the coca plant, Erythroxylum coca, native to South America (A -> III).

A-III, B-IV, C-I, D-II matches Option (2).

Rhinoviruses represent one such group of viruses which cause one of the most infectious human ailments - the common cold (A -> III). The rupture of RBCs during malaria is associated with the release of a toxic substance, haemozoin, which is responsible for the chill and high recurring fever (B -> I).

Typhoid fever caused by Salmonella typhi is confirmed by the classic Widal test (C -> II). Common examples of allergens that trigger IgE-mediated allergic responses include mites in dust, pollens, animal dander, etc. (D -> IV).

A-III, B-I, C-II, D-IV matches Option (1).

NCERT explicitly states: "The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced." Therefore, Statement I is completely true.

NCERT explicitly states: "The thymus is a lobed organ located near the heart and beneath the breastbone... Both bone-marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes." (Progenitor T-cells originate in bone marrow and migrate to thymus). Therefore, Statement II is completely true.

Both Statement I and Statement II are correct statements, matching Option (3).

HIV envelope glycoprotein gp120 binds specifically to the CD4 surface marker present on monocytes/macrophages and helper T-cells ($T_H$ lymphocytes):

NCERT states verbatim: "Simultaneously, HIV enters into helper T-lymphocytes (TH), replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person."

Eosinophils fight allergic reactions and helminth infections; B-lymphocytes produce humoral antibodies; basophils release histamine and heparin during inflammation. None of these support HIV replication.

Analyzing the specific physiological targets described in NCERT:

NCERT states under Drugs and Alcohol Abuse: - "Heroin is a depressant and slows down body functions." - "Cannabinoids are known for their effects on cardiovascular system of the body." - "Cocaine interferes with the transport of the neuro-transmitter dopamine." - "Morphine is a very effective sedative and painkiller, and is very useful in patients who have undergone surgery."

Matching A-II and B-I immediately isolates Option (2) uniquely.

Matching infectious diseases to their respective etiological agents:

NCERT states under Common Diseases in Humans: - "Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans." - "Malaria is caused by Plasmodium (P. vivax, P. malaria and P. falciparum)." - "Wuchereria (W. bancrofti and W. malayi), the filarial worms cause a slowly developing chronic inflammation of the organs... (elephantiasis or filariasis)." - "Many fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton are responsible for ringworms."

A-II, B-III, C-IV, D-I uniquely and definitively selects Option (2).

- (a) Filariasis (Elephantiasis): Caused by the filarial roundworm nematodes _Wuchereria bancrofti_ and _Wuchereria malayi_. The adult worms lodge in the lymphatic vessels of the lower limbs and genital organs, triggering chronic inflammation and gross lymphedema. - (b) Amoebiasis (Amoebic Dysentery): Caused by the protozoan parasite _Entamoeba histolytica_ in the large intestine of humans. Symptoms include constipation, abdominal cramps, and stools with excess mucus and blood clots. - (c) Pneumonia: A bacterial pulmonary infection caused by _Streptococcus pneumoniae_ and _Haemophilus influenzae_, which infects the alveoli of the lungs, causing them to fill with fluid. - (d) Ringworm: A superficial cutaneous fungal infection caused by dermatophyte fungi of the genera _Microsporum_, _Trichophyton_, and _Epidermophyton_, characterized by dry, scaly pruritic lesions on skin, scalp, and nails.

Matching sequence is: (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii). This corresponds precisely to Option (2).

- (a) Typhoid Fever: Caused by the pathogenic Gram-negative rod bacterium _Salmonella typhi_, which enters the small intestine via contaminated food and water, migrating to other organs via blood (diagnosed by Widal test). - (b) Pneumonia: An acute pulmonary infection caused by _Streptococcus pneumoniae_ and _Haemophilus influenzae_, leading to fluid accumulation within alveolar sacs. - (c) Filariasis (Elephantiasis): Caused by the filarial nematode roundworms _Wuchereria bancrofti_ and _W. malayi_, which chronically obstruct lymphatic vessels of the lower limbs. - (d) Malaria: Caused by the protozoan parasite _Plasmodium_ (_P. vivax_, _P. malariae_, _P. falciparum_), transmitted by the bite of female _Anopheles_ mosquitoes.

Matching sequence is: (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii). This corresponds precisely to Option (2).

_Plasmodium_ is a digenetic protozoan parasite requiring two hosts to complete its life cycle: 1. Inoculation: When an infected female _Anopheles_ mosquito pierces human skin for a blood meal, it injects saliva containing anticoagulants and thousands of sickle-shaped, motile sporozoites directly into the capillary bloodstream. 2. Hepatic Schizogony: Circulating sporozoites travel to the liver within 30 minutes, penetrating hepatocytes to undergo asexual multiple fission (pre-erythrocytic schizogony) to produce merozoites. 3. Erythrocytic Cycle: Merozoites rupture hepatocytes and invade red blood cells, developing into amoeboid feeding trophozoites, which digest hemoglobin into toxic hemozoin crystals. 4. Gametocytes: A subpopulation of merozoites differentiates into male and female gametocytes, which are taken up by a biting mosquito to complete sexual reproduction (syngamy and sporogony) in the mosquito gut wall.

- Trophozoites: The intraerythrocytic actively feeding vegetative stage inside human RBCs. - Female & Male Gametocytes: The sexual stages formed in human peripheral blood that serve as the infectious stage for the mosquito, not the human.

When a host is exposed to antigens (living or dead microbes or other proteins), antibodies are synthesized in the host's body. This is called active immunity. However, active immunity is slow and takes time to develop and mount its full effective response.

When ready-made antibodies are directly administered to the body (e.g., antivenom for snake bite, anti-tetanus serum), it is called passive immunity. Passive immunity acts immediately (quick response).

The foetus receives maternal antibodies (IgG) across the placenta during pregnancy, and the newborn receives secretory IgA in mother's yellowish milk (colostrum) during initial days of lactation. These are classic examples of natural passive immunity.

Statement (3) asserts that "Active immunity is quick and gives full response." This directly contradicts immunology fundamentals: active immunity is notoriously slow during the primary response.