Health Disease Pathogens

8 MCQs9-step worked example
Source: NCERT Cell: The Unit of LifePYQ coverage: NEET 2020, 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

The trap that costs marks: confusing the vector (the organism that transmits) with the causative agent (the pathogen that causes disease). When a question asks "causative agent of malaria," students who write Anopheles instead of Plasmodium lose marks on what should be a free recall point.

Core framework — pathogen, transmission, prevention:

NCERT Class 12 Biology Chapter 7 (page 148) organises human diseases by pathogen type: bacterial, viral, protozoan, helminthic, and fungal. For NEET, you need three facts per disease: (1) causative organism, (2) mode of transmission, and (3) one prevention/control measure.

Key diseases by pathogen type:

  • Bacterial: Typhoid (Salmonella typhi, contaminated food/water), Pneumonia (Streptococcus pneumoniae/Haemophilus influenzae, droplet inhalation)
  • Viral: Common cold (Rhinovirus, droplet/contaminated objects), Dengue (Dengue virus, Aedes mosquito vector)
  • Protozoan: Malaria (Plasmodium spp., female Anopheles mosquito vector), Amoebiasis (Entamoeba histolytica, contaminated food/water)
  • Helminthic: Ascariasis (Ascaris lumbricoides, contaminated soil/water), Filariasis (Wuchereria bancrofti, Culex mosquito vector)

The vector–agent distinction: The mosquito is the delivery vehicle; the parasite/virus is the disease-maker. Anopheles carries Plasmodium. Aedes carries Dengue virus. Culex carries Wuchereria. Never swap them.

Prevention principles: Personal hygiene, safe drinking water, vector control (eliminating breeding sites), vaccination where available, and avoiding contact with infected individuals.

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

The causative agent of typhoid fever is:

MCQ 2Easy RecallPractice

Which mosquito genus serves as the vector for malaria?

MCQ 3Easy RecallPractice

Which of the following diseases is transmitted through contaminated food and water?

MCQ 4Direct ApplicationPractice

A student states: "The causative agent of malaria is *Anopheles*." What is wrong with this statement?

MCQ 5Direct ApplicationPractice

Match the disease with its correct vector:

MCQ 6Direct ApplicationPractice

Which of the following is NOT a protozoan disease?

MCQ 7Direct ApplicationPractice

A public health officer wants to control malaria in a region. Which strategy directly targets the transmission route?

MCQ 8CalculationPractice

A patient has *Wuchereria bancrofti* infection. Which of the following correctly identifies the disease AND its vector?

Worked Example

Pattern: Disease–vector–pathogen identification (from NEET pattern: unit bundle — similar-term-confusion distractor type)

  1. 1

    Given

    A question states: "Identify the disease, causative agent, and vector from the following description: A patient presents with periodic fever and chills. The infection is transmitted by a female mosquito that breeds in stagnant water. Blood smear shows ring-shaped trophozoites."

  2. 2

    Required

    Name the disease, causative organism, and vector.

  3. 3

    Concept

    Vector-borne protozoan diseases — the vector transmits the pathogen but does not cause the disease itself. Ring-shaped trophozoites in blood smear are diagnostic for *Plasmodium*.

  4. 4

    Formula/Rule

    Pathogen identification: ring-stage trophozoites in RBC → *Plasmodium* spp. Disease: *Plasmodium* → Malaria Vector: Female *Anopheles* mosquito (breeds in stagnant water, bites at dusk/night)

  5. 5

    Substitution

    Ring trophozoites → *Plasmodium* (confirmed) Periodic fever + chills → Malaria (confirmed) Female mosquito + stagnant water → *Anopheles* (confirmed)

  6. 6

    Calculation

    No numerical calculation. Logical identification: - Disease = Malaria - Causative agent = *Plasmodium* (species: *P. vivax*, *P. falciparum*, *P. malariae*, *P. ovale*) - Vector = Female *Anopheles* mosquito

  7. 7

    Final answer

    Disease: **Malaria** Causative agent: ***Plasmodium*** (protozoan parasite) Vector: **Female *Anopheles* mosquito**

  8. 8

    Common trap

    Writing "*Anopheles*" as the causative agent — this is the vector, not the pathogen. The causative agent is always the organism that multiplies inside the host and produces the disease symptoms. *Anopheles* merely delivers *Plasmodium* into the bloodstream.

  9. 9

    Similar NEET-style question

    "A child develops high fever, enlarged spleen, and headache after visiting a rural area. Which organism is the causative agent, and what is its mode of transmission?" (Answer: *Plasmodium*; transmitted by female *Anopheles* mosquito bite) ---

Before solving, remember these

Key Fact

Common diseases

Bacterial: typhoid (Salmonella typhi — Widal test), pneumonia (Streptococcus pneumoniae). Viral: common cold (rhinovirus). Protozoan: malaria (Plasmodium — Anopheles vector), amoebiasis (E. histolytica), kala-azar (Leishmania). Fungal: ringworm. Helminthic: ascariasis, filariasis (Wuchereria, mosquito vector — elephantiasis).

-- NCERT Class 12 Biology, Ch. 7, p. 148

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

AIDS confirmation vs screening

Category: Similar Terms

ELISA = screening (cheap, sensitive); Western blot = confirmation. CD4+ T cell count tracks disease progression.

When it triggers

Question on which test confirms HIV vs which monitors progression.

How to avoid

ELISA first (screening); Western blot confirms; CD4+ count = monitoring marker (<200/µL = AIDS).

Trap

Active vs passive immunity

Category: Similar Terms

Active: own immune response (vaccination, infection). Passive: pre-formed antibodies received (colostrum, antiserum injection).

When it triggers

Question on immunity type from vaccination, antiserum, mother's milk.

How to avoid

Active = body produces; passive = body receives. Vaccination → active. Mother's milk → passive (IgA).

Past Year Questions

29 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2024

Given below are two statements: Statement I : Bt toxins are insect group specific and coded by a gene cry IAc. Statement II : Bt toxin exists as inactive protoxin in B. thuringiensis. However, after ingestion by the insect the inactive protoxin gets converted into active form due to acidic pH of the insect gut. In the light of the above statements, choose the correct answer from the options given below:

1Both Statement I and Statement II are true
2Both Statement I and Statement II are false
3Statement I is true but Statement II is false
4Statement I is false but Statement II is true
NTA Answer: Option 3(final)
NEET 2024

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R: Assertion A : Breast-feeding during initial period of infant growth is recommended by doctors for bringing a healthy baby. Reason R : Colostrum contains several antibodies absolutely essential to develop resistance for the new born baby. In the light of the above statements, choose the most appropriate answer from the options given below:

1Both A and R are correct and R is the correct explanation of A
2Both A and R are correct but R is NOT the correct explanation of A
3A is correct but R is not correct
4A is not correct but R is correct
NTA Answer: Option 1(final)
NEET 2023

Which one of the following is NOT an advantage of inbreeding?

1It exposes harmful recessive genes but are eliminated by selection.
2Elimination of less desirable genes and accumulation of superior genes takes place due to it.
3It decreases the productivity of inbred population, after continuous inbreeding.
4It decreases homozygosity.
NTA Answer: Option 3(final)
NEET 2022

Given below are two statements: Statement I: Autoimmune disorder is a condition where body defense mechanism recognizes its own cells as foreign bodies. Statement II: Rheumatoid arthritis is a condition where body does not attack self cells. In the light of the above statements, choose the most appropriate answer from the options given below:

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 4(final)
NEET 2022

Select the incorrect statement with respect to acquired immunity.

1Acquired immunity is non-specific type of defense present at the time of birth.
2Primary response is produced when our body encounters a pathogen for the first time.
3Anamnestic response is elicited on subsequent encounters with the same pathogen.
4Anamnestic response is due to memory of first encounter.
NTA Answer: Option 1(final)
NEET 2020

Match the following columns and select the correct option. 107. ÁŸêŸ Sà ÷Ê ∑§Ê Á◊‹ÊŸ ∑§⁄U ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – Column - I Column - II Sà ÷ - I Sà ÷ - II (a) Bt cotton (i) Gene therapy (a) ’Ë≈UË ∑§¬Ê‚ (i) ¡ËŸ ÁøÁ∑§à‚Ê (b) Adenosine (ii) Cellular defence (b) ∞«UËŸÊ ‚ËŸ Á«U∞◊ËŸ ¡ (ii) ∑§Ê Á‡Ê∑§Ëÿ ‚È⁄UˇÊÊ deaminase ∑§Ë ∑§◊Ë deficiency (c) •Ê⁄U.∞Ÿ.∞.•Ê߸ (iii) HIV ‚ ∑˝§◊áÊ ∑§Ê ¬ÃÊ (c) RNAi (iii) Detection of HIV ‹ªÊŸÊ infection (d) ¬Ë.‚Ë.•Ê⁄U. (iv) ’ÒÁ‚‹‚ (d) PCR (iv) Bacillus ÕÈÁ⁄ UÁ¡ÁŸÁ‚‚ thuringiensis (a) (b) (c) (d) (a) (b) (c) (d)

1(i) (ii) (iii) (iv) (1) (i) (ii) (iii) (iv)
2(iv) (i) (ii) (iii) (2) (iv) (i) (ii) (iii)
3(iii) (ii) (i) (iv) (3) (iii) (ii) (i) (iv)
4(ii) (iii) (iv) (i) (4) (ii) (iii) (iv) (i)
NTA Answer: Option 2(final)
NEET 2020

ÁŸêŸ ◊ ∑§ÊÒŸ flÊÁ„Ã◊‹ ©¬øÊ⁄U ∑ § Á‹∞ •flÊÿflËÿ •Ê¬ ∑§ 120. Which of the following is put into Anaerobic sludge digester for further sewage treatment ? ‚ ¬ÊÁøòÊ ◊ «UÊ‹Ê ¡ÊÃÊ „Ò?

1Activated sludge (1) ‚ Á∑˝§ÿËà •Ê¬ ∑§
2Primary sludge (2) ¬˝ÊÕÁ◊∑§ •Ê¬ ∑§
3Floating debris (3) ÃÒ⁄Uà „È∞ ∑ͧ«∏ -∑§⁄U∑§≈U
4Effluents of primary treatment (4) ¬˝ÊÕÁ◊∑§ ©¬øÊ⁄U ∑ § ’Á„—dÊfl
NTA Answer: Option 1(final)
NEET 2020

Which of the following statements about inclusion 128. • ÃÁfl¸c≈U ∑§ÊÿÊ ∑ § Áfl ÿ ◊ ÁŸêŸÁ‹Áπà ◊ ‚ ∑§ÊÒŸ ‚Ê ∑§ÕŸ bodies is incorrect ? ª‹Ã „Ò?

1These represent reserve material in (1) ÿ ∑§Ê Á‡Ê∑§ÊŒ˝√ÿ ◊ ÁŸÁøà ¬ŒÊÕ¸ ∑§Ê √ÿÄà ∑§⁄Uà „Ò – cytoplasm.
2ÿ Á∑§‚Ë Á¤ÊÀ‹Ë ‚ ÁÉÊ⁄ U Ÿ„Ë „Ê Ã – (2) They are not bound by any membrane.
3These are involved in ingestion of food (3) ÿ πÊl ∑§áÊÊ ∑ § • ê˝¸„áÊ ◊ ‡ÊÊÁ◊‹ „Ê Ã „Ò – particles.
4ÿ ∑§Ê Á‡Ê∑§ÊŒ˝√ÿ ◊ Sflà òÊ M§¬ ◊ „Ê Ã „Ò – (4) They lie free in the cytoplasm.
NTA Answer: Option 3(final)
NEET 2020

¬˝ÁÃ⁄UˇÊÊ ∑ § ‚ Œ÷¸ ◊ ª‹Ã ∑§ÕŸ ∑§Ê ¬„øÊÁŸ∞– 131. Identify the wrong statement with reference to immunity.

1÷˝ÍáÊ ◊ÊÃÊ ‚ ∑ȧ¿U ¬˝ÁÃ⁄UˇÊË ¬˝Êåà ∑§⁄UÃÊ „Ò, ÿ„ ÁŸÁc∑˝§ÿ (1) Foetus receives some antibodies from ¬˝ÁÃ⁄UˇÊÊ ∑§Ê ©ŒÊ„⁄UáÊ „Ò– mother, it is an example for passive
2¡’ ¬⁄U¬Ê Ë ∑§Ê ‡Ê⁄UË⁄U (¡ËÁflà •ÕflÊ ◊ÎÃ) ¬˝Á០∑ § immunity. ‚ ¬∑¸§ ◊ •ÊÃÊ „Ò •ÊÒ⁄U ©‚∑ § ‡Ê⁄UË⁄U ◊ ¬˝ÁÃ⁄UˇÊË ©à¬ÛÊ (2) When exposed to antigen (living or dead) „Ê Ã „Ò – ß‚ ““‚Á∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ”” ∑§„à „Ò – antibodies are produced in the host’s body. It is called “Active immunity”.
3¡’ ’Ÿ ’ŸÊ∞ ¬˝ÁÃ⁄UˇÊË ¬˝àÿˇÊ M§¬ ‚ ÁŒ∞ ¡Êà „Ò , ß‚ (3) When ready-made antibodies are directly ““ÁŸÁc∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ”” ∑§„à „Ò – given, it is called “Passive immunity”.
4‚Á∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ ¡ÀŒË „Ê ÃË „Ò •ÊÒ⁄U ¬Íáʸ ¬˝ÁÃÁ∑˝§ÿÊ Œ ÃË (4) Active immunity is quick and gives full „Ò– response.
NTA Answer: Option 4(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Diseases, immunity, AIDS, cancer, drugs, animal husbandry, microbes

RecallMedium

Common distractors

active vs passive immunity confusion

Vaccination triggers the body to produce its own antibodies (active immunity), but students interpret 'given externally' as passive. Passive immunity (antiserum, colostrum IgA from mother's milk) provides preformed antibodies with no immune response from the recipient. Questions that pair vaccination, antiserum, and colostrum expose students who cannot classify by mechanism rather than by route of administration.

vector vs causative agent confusion

Questions name both the vector (organism that transmits) and the causative agent (organism that causes disease) as answer options. Students who associate 'Anopheles = malaria' select Anopheles as the causative agent rather than recognising it as the vector; Plasmodium is the causative agent. The distinction -- vector transmits, causative agent infects -- is lost when both options are plausible from partial recall.

microbe product pair swap

Match-list questions pair 10 or more microbe names with industrial or household products. Students confuse Lactobacillus (lactic acid fermentation, curd) with Saccharomyces cerevisiae (ethanol, bread), or Aspergillus niger (citric acid) with Clostridium butylicum (butyric acid). Partial recall of one-to-one mappings produces swapped pairs, especially when two products share the same chemical class.

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