Q.AIDS is caused by HIV. Among the following, which one is not a mode of transmission of HIV?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Disease Transmission Modes
Let’s begin with something you already know. When someone in your family catches a cold, you instinctively avoid sharing their glass or sitting too close. That instinct is your brain recognising that something — a disease — can travel from one person to another. The how of that travel is what we call disease transmission modes.
In everyday language, a transmission mode is simply the route a germ takes to leave an infected person and reach a healthy one. Think of it as the germ’s travel plan. If the germ cannot travel, it cannot cause new infections. So understanding these routes is the first step in stopping outbreaks — whether it’s a common flu or a more serious epidemic.
The two big families: Direct and Indirect transmission
The NCERT textbook (Class XII, Biology, Chapter 8 — Human Health and Disease) divides transmission into two main categories. This is the standard classification you need to remember.
1. Direct Transmission — The germ moves straight from the infected person to the healthy person, with no intermediate object or living being involved. This can happen through:
- Physical contact: Touching, shaking hands, kissing, or sexual contact. Diseases like the common cold, scabies, and sexually transmitted infections (e.g., syphilis, HIV) spread this way.
- Droplet infection: When an infected person coughs, sneezes, or even talks, tiny droplets of saliva or mucus fly out. If you are within about a metre, you can inhale them. This is how influenza, the common cold, and COVID-19 spread.
- Direct exposure to infected tissue or blood: For example, a needle-stick injury in a hospital, or a mother passing an infection to her baby during pregnancy (congenital transmission).
Direct transmission is often the easiest to interrupt. Simple actions — like maintaining distance, wearing a mask, or washing hands — break the chain because the germ has no vehicle to ride on.
2. Indirect Transmission — Here, the germ needs a middleman to reach a new host. The middleman can be:
- A vehicle: This is a non-living thing that carries the germ. Common vehicles include:
- Air: Dust particles or droplet nuclei (the dried remnants of droplets) can float for hours. Measles and tuberculosis spread through air.
- Water: Contaminated drinking water spreads cholera, typhoid, and hepatitis A.
- Food: Improperly cooked or stored food can carry salmonella or E. coli.
- Fomites: Inanimate objects like door handles, towels, syringes, or surgical instruments. Hepatitis B can spread through contaminated needles.
- A vector: This is a living organism — usually an insect or animal — that carries the germ from one host to another. The vector itself is not infected (or is only incidentally infected). Classic examples:
- Mosquitoes: Female Anopheles mosquito transmits malaria; Aedes mosquito transmits dengue and chikungunya.
- Fleas: Rat fleas transmit the plague bacterium.
- Ticks: Spread Lyme disease.
The key difference between a vehicle and a vector is that a vehicle is non-living, while a vector is a living creature. Both are intermediate agents — the germ does not jump directly from person to person.
Why this matters beyond biology
For a commerce or humanities student, the importance of transmission modes is not just medical — it is social and economic. Think about it:
- If a disease spreads through water (like cholera), the solution is not a vaccine alone — it is clean water supply, sanitation infrastructure, and public awareness campaigns. That is a government policy and budget issue.
- If a disease spreads through vectors (like malaria), the solution involves mosquito nets, insecticide spraying, and urban planning to eliminate stagnant water. That is a logistics and community management problem.
- If a disease spreads through direct contact (like HIV), the solution involves education, behaviour change, and stigma reduction — which is a social science challenge.
In short, the mode of transmission determines the type of intervention needed. That is why public health officials always ask: “How is this disease spreading?” before they decide what to do.
A quick summary for revision …
HIV spreads only through specific body fluids that carry the virus in sufficient quantities to cause infection. Blood, semen, vaginal fluids, and breast milk are the main vehicles of transmission because they contain high viral loads.
Transfusion of contaminated blood directly introduces the virus into the bloodstream. Sharing infected needles allows blood-to-blood contact, which is why intravenous drug users face high risk. Sexual contact with an infected person permits exchange of semen or vaginal secretions, making unprotected intercourse a major route of HIV spread. …
HIV spreads through direct exchange of body fluids (blood, sexual fluids), not through casual physical contact like handshakes.
HIV, the Human Immunodeficiency Virus, attacks the immune system and leads to AIDS (Acquired Immunodeficiency Syndrome). Understanding how this virus actually transmits is crucial, because much of the fear and stigma around HIV comes from misconceptions about how it spreads.
The virus lives in specific body fluids — blood, semen, vaginal fluids, and breast milk — and requires direct access to the bloodstream or mucous membranes to establish infection. This is why certain activities carry risk while others, despite involving close human contact, carry none at all.
Actual modes of HIV transmission include:
- Transfusion of contaminated blood: If infected blood enters your bloodstream directly, the virus transfers efficiently. This was a significant problem before blood screening became routine.
- Sharing infected needles: Intravenous drug users who share needles can transmit the virus because traces of infected blood remain in the syringe and enter the next person's bloodstream.
- Sexual contact with infected persons: Unprotected sex allows the virus in semen or vaginal fluids to enter through the mucous membranes of the genital tract, which are permeable to the virus.
- Mother to child: During pregnancy, childbirth, or breastfeeding, an infected mother can pass the virus to her baby. …
Method: Single Filter — "Does This Exchange Body Fluid?"
The same single-test method used for crop2m applies here, adapted to HIV: apply one
yes/no filter to all four options — "Does this activity involve exchanging blood, semen, vaginal fluid, or breast milk between two people?"
- (a) Transfusion of contaminated blood — Yes, direct blood exchange → real transmission route.
- (b) Sharing infected needles — Yes, blood-to-blood via the shared needle → real transmission route.
- (c) Shaking hands with an infected person — No fluid is exchanged; intact skin is an effective barrier and HIV does not survive on skin in infectious quantity → not a transmission route.
- (d) Sexual contact with an infected person — Yes, exchange of semen/vaginal fluid through mucous membranes → real transmission route.
Result: the only option that fails the fluid-exchange filter is (c), so it is the …
Showing the 12 most recent of 50 on this concept.
- AP EAPCET 2026Set ap-2026-05-19-FN1 markMCQQ.Statement I: Due to presence of mitochondria, Entamoeba histolytica is a facultative anaerobe. Statement II: Entamoeba histolytica causes abscesses in the wall of large intestine of man. (A) Both statements I and II are true (B) Both statements I and II are false (C) Statement I is true. But II is false (D) Statement I is false. But II is true
›Reveal solutionSolution
Entamoeba histolytica is actually an amitochondriate anaerobic parasite (statement I is false for the wrong reason given), while it genuinely does cause abscesses/ulcers in the large intestine wall (statement II is true).
Concept and Intuition
Entamoeba histolytica is the protozoan parasite responsible for amoebiasis (amoebic dysentery) in humans. It lives in the human large intestine, where it can invade the mucosal lining, forming characteristic flask-shaped ulcers and abscesses in the intestinal wall; in severe cases it can travel via the bloodstream to cause liver abscesses. Unlike many free-living or aerobic protozoans, E. histolytica is adapted to the low-oxygen environment of the gut and lacks classical, fully-functional mitochondria — it possesses reduced mitochondrion-derived organelles ("mitosomes") instead, and its energy metabolism is essentially anaerobic, not facilitated by conventional mitochondria.
Step-by-Step Solution
- Statement I claims the parasite is a facultative anaerobe "due to presence of mitochondria" — but E. histolytica is notable precisely for lacking standard mitochondria; its anaerobic lifestyle is not attributable to having mitochondria. So statement I is false. …
- AP EAPCET 2026Set ap-2026-05-19-AN1 markMCQQ.Study the following statements: Statement I: Malaria fever occurs due to release of haemozoin into the blood. Statement II: Haemozoin is formed during the digestion of haem by Plasmodium in RBC. (A) Statement I and II are correct (B) Statement I and II are incorrect (C) Statement I is correct II is incorrect (D) Statement I is incorrect II is correct
›Reveal solutionSolution
Both statements describe the same well-established malaria pathophysiology correctly: haemozoin formation during haemoglobin digestion, and its release causing the fever paroxysm.
Concept and Intuition
Plasmodium feeds on the haemoglobin inside the red blood cell it has invaded. Haemoglobin's haem component is toxic to the parasite in its free form (it generates reactive oxygen species), so Plasmodium neutralises it by polymerising/crystallising the haem into an insoluble, biologically inert pigment called haemozoin ("malaria pigment"). When the infected RBC finally ruptures to release a new generation of merozoites (schizogony), haemozoin and other cellular debris/toxins spill into the bloodstream. The host's immune system reacts to this material (triggering cytokines such as TNF-α), producing the classic cyclical fever, chills and rigor that define a malarial paroxysm.
Step-by-Step Solution
- Track the parasite's intra-erythrocytic cycle: invasion → trophozoite feeding on haemoglobin → schizont → merozoite release via RBC rupture.
- During haemoglobin digestion, the haem moiety is detoxified into haemozoin (Statement II — describes the formation correctly). …
- AP EAPCET 2026Set ap-2026-05-19-AN1 markMCQQ.Pneumonia mainly affects (A) Bronchi (B) Trachea (C) Alveoli (D) Larynx
›Reveal solutionSolution
Pneumonia is an alveolar disease — inflammation and fluid-filling of the alveoli impairs gas exchange, distinguishing it from airway diseases like bronchitis or laryngitis.
Concept and Intuition
The respiratory tract can be divided into conducting airways (larynx, trachea, bronchi, bronchioles) that merely transport air, and the respiratory zone (alveoli) where actual gas exchange with blood happens across a thin epithelial-capillary membrane. Pneumonia specifically targets this respiratory zone: infectious agents provoke an inflammatory response, and the alveolar spaces (normally air-filled for efficient diffusion) become filled with inflammatory exudate, pus and fluid. This directly compromises oxygen diffusion into the pulmonary capillaries, explaining the hypoxia and laboured breathing seen in pneumonia patients, and why it appears radiographically as opacities ("consolidation") of lung tissue.
Step-by-Step Solution
- Recall the functional distinction between conducting airways (bronchi, trachea, larynx) and the exchange surface (alveoli).
- Recall pneumonia's defining pathology: alveolar inflammation with exudate/fluid accumulation. …
- AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQQ.Assertion (A): Ascaris lumbricoides completes its entire life cycle within the small intestine. Reason (R): Larvae of Ascaris undergo extra intestinal migration. (A) Both (A) and (R) are true. (R) is correct explanation for (A) (B) Both (A) and (R) are true. (R) is not correct explanation for (A) (C) (A) is true. But (R) is false (D) (A) is false. But (R) is true
›Reveal solutionSolution
Ascaris larvae leave the intestine and migrate through blood, liver, heart and lungs before returning to mature in the gut — so the life cycle is NOT confined to the small intestine, making the Assertion false while the Reason (which describes exactly this migration) is true.
Concept and Intuition
Many intestinal nematodes, including Ascaris lumbricoides, have a life cycle where the adult and egg-laying stage occurs in the intestine, but the larval stage takes a detour through the circulatory and respiratory systems — this is called extra-intestinal (or hepato-pulmonary/tracheal) migration, and it is central to how the parasite establishes and matures.
Step-by-Step Solution
- Ingested embryonated eggs hatch into larvae in the small intestine.
- The larvae penetrate the intestinal wall and enter the portal blood/lymphatics, travelling to the liver, then the heart, then the lungs.
- In the lungs the larvae break into the alveoli, migrate up the bronchi, trachea, and pharynx, and are then swallowed again.
- Only after re-entering the small intestine a second time do the larvae mature into egg-laying adults. …
- AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQQ.Statement I: Ringworm is caused by Epidermophyton. Statement II: Ringworm commonly affects skin folds such as groin or among toes. (A) Statement I and II are correct (B) Statement I and II are incorrect (C) Statement I is correct II is incorrect (D) Statement I is incorrect II is correct
›Reveal solutionSolution
Both statements about ringworm are textbook-accurate: it is caused by dermatophyte fungi including Epidermophyton, and it typically affects moist skin folds like the groin and toe-webs.
Concept and Intuition
Ringworm (dermatophytosis) is a fungal skin infection, not caused by a worm despite the name. The causative fungi (genera Trichophyton, Microsporum, Epidermophyton) thrive in warm, moist environments, which is exactly why body folds — groin, armpits, and between toes — are the classic sites of infection.
Step-by-Step Solution
- Confirm causative organism: ringworm is a dermatophytosis, and NCERT/standard texts name Trichophyton, Microsporum, and Epidermophyton as the causative fungal genera — so Statement I is accurate.
- Confirm site of infection: dermatophyte fungi favour keratinized, moist skin — groin folds and interdigital spaces of the feet are the most commonly affected regions, matching Statement II. …
- AP EAPCET 2026Set ap-2026-05-20-AN1 markMCQQ.Assertion (A): Elephantiasis is due to the obstruction of lymphatic vessels by accumulation of dead filarial worms. Reason (R): First stage microfilaria larva is the infective stage to humans. (A) Both (A) and (R) are true. (R) is correct explanation for (A) (B) Both (A) and (R) are true. (R) is not correct explanation for (A) (C) (A) is true. But (R) is false (D) (A) is false. But (R) is true
›Reveal solutionSolution
This tests filarial worm life cycle and pathology — elephantiasis truly results
from lymphatic blockage by dead worms (A, true), but the human-infective stage
is the mosquito-borne third-stage (L3) larva, not the first-stage microfilaria
(R, false).
Concept and Intuition
Lymphatic filariasis (elephantiasis) is caused by thread-like filarial worms
(e.g. Wuchereria bancrofti) that lodge in the lymphatic vessels and lymph nodes.
Chronic infection, with accumulation of both living and dead adult worms, provokes
inflammation and fibrosis that progressively blocks lymphatic drainage — this
obstruction is what causes the grotesque swelling (elephantiasis) of limbs and
other body parts. This makes Assertion (A) an accurate description of the disease
mechanism.
The filarial life cycle, however, has a specific infective-stage detail that
Reason (R) gets wrong: microfilariae (first-stage larvae) circulate in the
peripheral blood of an infected person and are picked up by a biting mosquito.
Inside the mosquito, these larvae undergo further development (moulting through
additional larval stages) to become the third-stage (L3) infective/filariform larva. It is this L3 stage — not the original microfilaria — that the mosquito
then transmits into a new human host during a subsequent bite, where it develops
into an adult worm.
Step-by-Step Solution
- Evaluate (A): elephantiasis is caused by lymphatic vessel obstruction due to accumulated (living and dead) filarial worms — this is the well-established disease mechanism. (A) is true. …
- AP EAPCET 2026Set ap-2026-05-20-AN1 markMCQQ.Statement I: Typhoid bacteria are transmitted through contaminated food and water. Statement II: Salmonella typhi is a gram-positive bacterium. (A) Statement I and II are correct (B) Statement I and II are incorrect (C) Statement I is correct II is incorrect (D) Statement I is incorrect II is correct
›Reveal solutionSolution
This tests basic microbiology of typhoid fever — transmission via contaminated
food/water is correctly stated (I, true), but Salmonella typhi is Gram-negative,
not Gram-positive as claimed in II (false).
Concept and Intuition
Typhoid fever is a classic water/food-borne bacterial disease. Its causative
agent, Salmonella typhi (also called Salmonella enterica serovar Typhi), is
transmitted through the faecal-oral route: contaminated drinking water or food
handled/prepared under poor hygienic conditions carries the bacterium from an
infected person (or carrier) to a new host, who ingests it. On Gram staining,
Salmonella typhi is a Gram-negative, rod-shaped bacterium (it has a thin
peptidoglycan layer surrounded by an outer membrane, characteristic of
Gram-negative bacteria, and appears pink/red after Gram staining) — it is not
Gram-positive.
Step-by-Step Solution
- Statement I: "Typhoid bacteria are transmitted through contaminated food and water" — this matches the well-documented faecal-oral transmission route of typhoid. Correct. …
- AP EAPCET 2025Set ap-2025-05-19-FN1 markMCQQ.Match the following. Parasites - Infective stages to man A) Entamoeba histolytia - I. Sporozoite B) Plasmodium vivax - II. 3rd stage microfilaria C) Ascaris lumbricoides - III. 2nd stage rhabditiform larva D) Wuchereria bancrofti - IV. Tetranucleate cyst
- V. Gametocyte (A) A - III, B - IV, C - II, D - I (B) A - IV, B - I, C - V, D - II (C) A - IV, B - I, C - III, D - II (D) A - I, B - IV, C - III, D - II
›Reveal solutionSolution
This tests recall of the human-infective stage for four medically important parasites; the correct match is A-IV, B-I, C-III, D-II.
Concept and Intuition
Each parasite has a specific developmental stage that is capable of infecting a new human host, and this stage differs across life cycles:
- Amoebic and protozoan cysts are ingested.
- Malarial sporozoites are injected by mosquito bite.
- Nematode eggs/larvae are either ingested (Ascaris) or transmitted by insect vectors (Wuchereria).
Step-by-Step Solution
- Entamoeba histolytica — infects a new host via ingestion of the tetranucleate cyst (IV) present in contaminated food/water.
- Plasmodium vivax — infects a new host when an infected female Anopheles mosquito injects sporozoites (I) during a blood meal.
- Ascaris lumbricoides — infects a new host via ingestion of eggs containing the 2nd-stage rhabditiform larva (III). …
- AP EAPCET 2025Set ap-2025-05-19-FN1 markMCQQ.Parasite that causes african sleeping sickness. (A) Ascaris (B) Trypanosoma (C) Plasmodium (D) Wuchereria
›Reveal solutionSolution
This tests the causative agent of African sleeping sickness, which is the flagellate protozoan Trypanosoma.
Concept and Intuition
African trypanosomiasis, commonly called "sleeping sickness," is caused by protozoan parasites of the genus Trypanosoma (subspecies T. brucei gambiense and T. brucei rhodesiense), transmitted through the bite of the tsetse fly (Glossina). The parasite invades the bloodstream and eventually the central nervous system, causing the characteristic disturbed sleep-wake cycle that gives the disease its name.
Step-by-Step Solution
- Ascaris — a roundworm causing intestinal ascariasis, not sleeping sickness.
- Trypanosoma — the flagellate protozoan parasite that causes African sleeping sickness, transmitted by the tsetse fly.
- Plasmodium — causes malaria, not sleeping sickness. …
- AP EAPCET 2025Set ap-2025-05-19-FN1 markMCQQ.Pick up the wrongly matched pair. (A) Entamoeba histolytica - Cart wheel shaped nucleus (B) Plasmodium vivax - Haemozoin granules (C) Ascaris lumbricoides - Mammillated eggs (D) Wuchereria bancrofti - Oviparous
›Reveal solutionSolution
This tests distinguishing features of common human parasites; the wrongly matched pair is Wuchereria bancrofti-Oviparous, since filarial worms are ovoviviparous, not oviparous.
Concept and Intuition
Each parasite has a well-documented diagnostic feature used in identification:
- Entamoeba histolytica trophozoites/cysts show a characteristic cartwheel-shaped nucleus (central karyosome with radiating chromatin).
- Plasmodium vivax infected red blood cells contain haemozoin (malarial pigment), a breakdown product of haemoglobin digestion.
- Ascaris lumbricoides fertilized eggs have a characteristic mammillated (bumpy) outer coating.
- Wuchereria bancrofti females do not lay eggs that hatch externally; instead eggs develop and hatch within the female's uterus, and she releases already-motile larvae (microfilariae) directly — this reproductive mode is called ovoviviparous, not oviparous.
Step-by-Step Solution
- (A) Entamoeba histolytica - Cart wheel shaped nucleus — correctly matched, a genuine diagnostic feature.
- (B) Plasmodium vivax - Haemozoin granules — correctly matched, the malarial pigment seen in infected RBCs/tissues. …
- AP EAPCET 2025Set ap-2025-05-20-AN1 markMCQQ.Pneumonia is caused by (A) Salmonella (B) Haemophilus (C) Rhino virus (D) Microsoprum
›Reveal solutionSolution
This tests knowledge of causative organisms of common human diseases. Pneumonia (alveolar
infection) is caused by bacteria such as Streptococcus pneumoniae and Haemophilus influenzae — the answer is (B) Haemophilus.
Concept and Intuition
Human Health and Disease pairs each common illness with its causative agent so that
similar-sounding organisms are not confused. Pneumonia specifically inflames the alveoli,
filling them with fluid and impairing gas exchange; this is classically produced by the
bacteria Streptococcus pneumoniae and Haemophilus influenzae.
Step-by-Step Solution
- Salmonella typhi is the causative agent of typhoid fever, not pneumonia.
- Haemophilus influenzae is a well-known bacterial cause of pneumonia (and also of meningitis/ear infections) — this matches the question.
- Rhinovirus is one of the viruses responsible for the common cold, not pneumonia. …
- AP EAPCET 2025Set ap-2025-05-20-AN1 markMCQQ.Pick up the wrongly matched pair (A) Typhoid - Salmonella (B) Pneumonea - Streptococcus (C) Ring worm - Sacculina (D) Filaria - Wuchereria
›Reveal solutionSolution
Three of the four pairs correctly link a disease to its causative organism; only the
ringworm pairing is wrong because Sacculina is a parasitic barnacle of crabs, not a
fungus, and does not cause ringworm.
Concept and Intuition
This is a disease-organism matching question. Each disease must be checked against the
correct kingdom and species of its causative agent, since superficially plausible
pairings (organism names that "sound right") are the usual distractors.
Step-by-Step Solution
- Typhoid is caused by the bacterium Salmonella typhi — pair (A) is correct.
- Pneumonia is caused by bacteria including Streptococcus pneumoniae — pair (B) is correct.
- Ringworm is a fungal skin disease caused by fungi of the genera Microsporum, Trichophyton, or Epidermophyton — not by Sacculina, which is a parasitic barnacle (crustacean) that castrates crabs; it has nothing to do with human skin infection. Pair (C) is therefore wrong. …
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