Q.The organisms which cause diseases in plants and animals are called:
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
| Transmission Type | Sub-type | Example Disease | Key Interruption Strategy |
|---|---|---|---|
| Direct | Contact | Common cold, scabies | Hand hygiene, avoid sharing personal items |
| Direct | Droplet | Influenza, COVID-19 | Masks, physical distancing |
| Direct | Congenital | HIV (mother to child) | Antiretroviral therapy during pregnancy |
| Indirect | Vehicle (water) | Cholera, typhoid | Boil water, improve sanitation |
| Indirect | Vehicle (food) | Food poisoning | Proper cooking and storage |
| Indirect | Vehicle (air) | Tuberculosis, measles | Ventilation, masks |
| Indirect | Vector (mosquito) | Malaria, dengue | Mosquito nets, insecticide, drain stagnant water |
| Indirect | Vector (flea) | Plague | Rodent control, flea repellents |
The NCERT textbook also mentions vertical transmission (from mother to foetus) as a special case of direct transmission, and horizontal transmission (between any two individuals, directly or indirectly) as the broader category covering everything else. You may encounter these terms in exam questions.
One final thought
You do not need to memorise every disease name. What matters is the logic: every germ has a preferred travel route. If you block that route, you stop the disease. That is the core idea — and it applies whether you are studying biology, economics, or public policy.
This topic shows up often in student searches, usually phrased as "NCERT biology syllabus disease transmission modes", "Disease Transmission Modes class 12 biology", or "Disease Transmission Modes diagram and explanation". This concept is directly part of the Human Health and Disease chapter in the NCERT/CBSE Class 12 Biology syllabus, and it is also an important topic for NEET and state medical/CET entrance exams, making it worth mastering for both board and competitive-exam preparation.
Pathogens are biological agents that cause disease or illness in their host organisms, which can be plants or animals. This broad category includes various microorganisms such as viruses, bacteria, fungi, protozoans, and even some parasitic worms.
In contrast, vectors are organisms that transmit pathogens from an infected host to another host, but they do not cause the disease themselves. For example, a mosquito is a vector for the malarial parasite, which is the actual pathogen. While some insects and worms can indeed be pathogens or act as vectors, "pathogen" is the precise and comprehensive term for any organism that directly causes disease.
The organisms which cause diseases in plants and animals are called (A) Pathogens.
Pathogens are the biological agents that directly cause diseases in both plants and animals.
When we talk about diseases, whether they affect humans, other animals, or plants, we are referring to conditions that disrupt the normal functioning of an organism. These disruptions are often triggered by specific biological entities that invade the host and interfere with its physiological processes. Understanding the precise terminology for these disease-causing agents is fundamental.
Let's break down the options provided:
-
Pathogens (A): This term is derived from Greek words, where "pathos" means suffering and "genes" means producer. A pathogen is, by definition, a biological agent that causes disease or illness to its host. Pathogens are capable of invading a host organism, multiplying within it, and causing damage that manifests as symptoms of disease. This category is very broad and includes a wide array of microorganisms and parasites.
- Pathogens can affect virtually all forms of life. For instance:
- Viruses like the influenza virus in humans or the tobacco mosaic virus in plants.
- Bacteria such as Salmonella typhi causing typhoid in humans, or Xanthomonas oryzae causing bacterial blight in rice plants.
- Fungi responsible for diseases like ringworm in humans or rusts and smuts in crops.
- Protozoans like Plasmodium causing malaria, or Entamoeba histolytica causing amoebiasis.
- Helminths (parasitic worms) such as Ascaris (roundworm) or Wuchereria (filarial worm).
-
Important
Pathogens are the direct causative agents of disease, meaning they are the organisms that actively infect and harm the host.
- Pathogens can affect virtually all forms of life. For instance:
-
Vectors (B): A vector is an organism that does not cause disease itself but transmits pathogens from one host to another. Vectors act as intermediaries, carrying the disease-causing agents. For example, mosquitoes are well-known vectors for the Plasmodium parasite (which causes malaria) and various viruses (like dengue or chikungunya). The mosquito itself is not the pathogen; it merely transports the pathogen from an infected individual to a healthy one. Similarly, houseflies can act as mechanical vectors, transferring pathogens from contaminated surfaces to food.
-
Note
While vectors are crucial in the spread of many diseases, they are not the pathogens themselves. They are the carriers or transmitters of pathogens.
-
-
Insects (C): Insects are a vast and diverse class of invertebrates within the phylum Arthropoda. They are characterized by a segmented body, an exoskeleton, three pairs of jointed legs, and usually wings. While many insects can indeed act as vectors (like mosquitoes and flies), and some might directly cause harm through bites or stings, the term "insect" is a broad taxonomic classification. It does not inherently define an organism by its disease-causing ability. Not all insects cause disease, and not all disease-causing organisms are insects. Therefore, "insect" is too general and not precise enough to describe all organisms that cause disease.
-
Worms (D): "Worms" is a general term often used to describe various elongated, soft-bodied, legless invertebrates. In the context of disease, it typically refers to parasitic worms, specifically helminths (e.g., roundworms, tapeworms, flukes). These helminths are indeed pathogens, causing diseases like ascariasis, taeniasis, or filariasis. However, "worms" is not a comprehensive term for all organisms that cause diseases. Viruses, bacteria, fungi, and protozoans are also major categories of pathogens, and they are not classified as worms. Thus, "worms" is too specific and does not encompass the full range of disease-causing organisms.
Comparing these options, "Pathogens" is the most accurate and all-encompassing term for organisms that directly cause diseases in both plants and animals. It correctly includes all the diverse biological agents responsible for illness.
The organisms which cause diseases in plants and animals are called Pathogens.
Method: Classify Each Option by What KIND of Term It Is
Rather than describing examples of pathogens, this method classifies each option by its
own category — a term-type filter that works even without recalling specific disease
examples.
- (A) Pathogens — this is the general biological category for "any agent that directly causes disease" — it covers viruses, bacteria, fungi, protozoans, and parasitic worms alike, in both plants and animals. This is a causal category.
- (B) Vectors — this is a transport category: an organism that carries a pathogen between hosts without causing the disease itself (e.g. a mosquito carrying Plasmodium). A vector is never itself the cause.
- (C) Insects — this is a taxonomic category (a class within Arthropoda) — most insects aren't disease-causing agents at all, and disease-causing agents aren't restricted to insects (bacteria and viruses aren't insects).
- (D) Worms — this is another taxonomic category (helminths specifically) — too narrow, since it excludes viruses, bacteria, fungi, and protozoans entirely.
The filter: the question asks for the category that means "causes disease" — only
option (A) is defined by that causal role; (B) is defined by transport, and (C)/(D) are
defined by what kind of organism it is, not by whether it causes disease. This lets you
answer correctly even for an unfamiliar pathogen you've never studied, since the test is
about the role of the term, not a memorised example.
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.
- Statement II states it causes abscesses in the wall of the large intestine — this matches the well-documented pathology of amoebic dysentery (ulcers/abscesses in the colon wall). So statement II is true.
- Hence I is false, II is true.
Common Mistakes
- Assuming any anaerobic organism must simply "have fewer" mitochondria rather than genuinely lacking the canonical organelle — E. histolytica is a classic amitochondriate/mitosome-bearing example.
✓Final answerThe correct option is (D) — Statement I is false. But II is true.
ANSWER: D
- 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).
- RBC rupture releases haemozoin (and other toxins) into circulation, and this release is what is understood to precipitate the fever/chill cycle (Statement I — describes the cause of fever correctly).
- Both are independently true and mutually consistent (II explains where the substance in I comes from).
Common Mistakes
- Thinking haemozoin is formed outside the RBC — it is formed inside, during digestion, and only released upon rupture.
- Confusing haemozoin (a haem-derived pigment) with haemoglobin itself.
✓Final answerThe correct option is (A) — Statement I and II are correct.
ANSWER: A
- 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.
- Eliminate bronchi/trachea/larynx — these are affected in bronchitis, tracheitis and laryngitis respectively, not the hallmark of pneumonia.
- Select alveoli as the primary site affected in pneumonia.
Common Mistakes
- Confusing pneumonia (alveolar) with bronchitis (bronchial) — both cause cough/breathlessness but affect different structures.
- Assuming pneumonia is confined to the upper airway (larynx/trachea) rather than the deep lung tissue.
✓Final answerThe correct option is (C) — Alveoli.
ANSWER: C
- 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.
- This means the life cycle genuinely leaves the intestine during larval development — so "completes entire life cycle within the small intestine" (the Assertion) is false, while "larvae undergo extra-intestinal migration" (the Reason) is a true and directly relevant fact.
Common Mistakes
- Assuming that because the adult worm and the eggs are both intestinal, the whole life cycle must be intestinal — the crucial larval detour through blood/liver/lungs is easy to overlook.
✓Final answerThe correct option is (D) — (A) is false, but (R) is true.
ANSWER: D
- 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.
- Both statements hold, so the joint answer is that both are correct.
Common Mistakes
- Assuming "ringworm" implies a helminth infection because of the name — it is fungal, not parasitic-worm related.
- Overlooking that moist, occluded skin regions (not just visible ring-shaped patches anywhere) are the classic sites.
✓Final answerThe correct option is (A) — Statement I and II are correct.
ANSWER: A
- 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.
- Evaluate (R): it claims the first-stage microfilaria larva is infective to humans. In reality, microfilariae are the stage found in human blood (picked up from humans by mosquitoes), while the stage that is infective to humans is the third-stage (L3) larva developed inside the mosquito. (R) is false.
- Since (A) is true and (R) is false, and (R) does not correctly explain (A) regardless, the correct choice is "(A) is true, (R) is false."
Common Mistakes
- Assuming microfilaria (the blood stage found in infected humans) is also the stage transmitted back to new hosts — the infective stage requires further development inside the mosquito to become the L3 larva.
✓Final answerThe correct option is (C) — (A) is true. But (R) is false.
ANSWER: C
- 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.
- Statement II: "Salmonella typhi is a gram-positive bacterium" — in reality, Salmonella typhi is Gram-negative. Incorrect.
- So Statement I is correct and Statement II is incorrect, matching option (C).
Common Mistakes
- Assuming all disease-causing rod-shaped bacteria are Gram-positive; many important enteric pathogens (Salmonella, E. coli, Shigella) are in fact Gram-negative.
✓Final answerThe correct option is (C) — Statement I is correct II is incorrect.
ANSWER: C
- 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).
- Wuchereria bancrofti — infects a new host when an infected mosquito introduces the 3rd-stage (infective) larva (II) during a bite.
- This gives A-IV, B-I, C-III, D-II, matching option (C).
Common Mistakes
- Confusing the infective stage (entering the new host) with the diagnostic stage (found in blood/stool samples, e.g. trophozoite or microfilaria).
✓Final answerThe correct option is (C) — A-IV, B-I, C-III, D-II.
ANSWER: C
- 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.
- Wuchereria — causes lymphatic filariasis, not sleeping sickness.
- Hence the correct causative agent is Trypanosoma.
Common Mistakes
- Confusing Trypanosoma (sleeping sickness, tsetse fly vector) with Plasmodium (malaria, Anopheles mosquito vector) — both are blood/tissue protozoan parasites but cause very different diseases.
✓Final answerThe correct option is (B) — Trypanosoma.
ANSWER: B
- 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.
- (C) Ascaris lumbricoides - Mammillated eggs — correctly matched, a classic identifying feature of fertilized Ascaris eggs.
- (D) Wuchereria bancrofti - Oviparous — incorrect; Wuchereria bancrofti is ovoviviparous (produces live microfilariae, not laid eggs).
- Hence (D) is the wrongly matched pair.
Common Mistakes
- Assuming all worm parasites lay eggs (oviparous); filarial worms specifically retain and hatch eggs internally, releasing live larvae.
✓Final answerThe correct option is (D) — Wuchereria bancrofti - Oviparous.
ANSWER: D
- 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.
- Microsporum is a fungus causing ringworm (a skin infection), not pneumonia.
- Only option (B) correctly names a pneumonia-causing organism.
Common Mistakes
- Confusing Salmonella (typhoid) with pneumonia-causing bacteria.
- Assuming any respiratory-sounding virus (like Rhinovirus) must cause pneumonia rather than the common cold.
✓Final answerThe correct option is (B) — Haemophilus.
ANSWER: B
- 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.
- Filariasis is caused by the nematode Wuchereria bancrofti — pair (D) is correct.
- Hence the wrongly matched pair is (C).
Common Mistakes
- Assuming any parasite name automatically fits a human skin disease.
- Not recalling that Sacculina is a well-known example of a barnacle parasite on crabs from the Animal Kingdom/parasitism topic, unrelated to fungal skin infections.
✓Final answerThe correct option is (C) — Ring worm - Sacculina (wrongly matched; ringworm is
caused by a fungus, not by Sacculina).
ANSWER: C
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