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B1 ILTS — 08-30-2026 · Zoology · Error notes

Human Health and Disease

Zoology · 9 questions · scored 139 / 180

Every question flagged on this paper, worked through in full: what was given, what was asked, the concept, the formula, the steps written out, an animated diagram, and the shortcut that gets there faster. The weak areas for the chapter are set out at the end.

9Questions flagged
5Attempted, wrong
4Left blank
139Marks scored

Contents

Q143Q147Q151Q155Q160Q163Q167Q169Q176

Dark = attempted and missed · amber = left blank

Q 143Attempted · wrongPrimary and secondary immune response

A person is exposed to antigen Y for the first time on Day 1. He is again exposed to the same antigen on Day 24. Simultaneously, he gets initial exposure to antigen X. Select the correct option that correctly depicts the antibody concentration in his blood plasma.

Her answerthe graph with two sharp equal peaks
Correct answeranti-Y showing a small primary then a large secondary peak, anti-X only a small primary
1  Given
  • Antigen Y: first exposure Day 1, second exposure Day 24.
  • Antigen X: first exposure Day 24 only.
  • Antibody concentration plotted against time.
2  Asked

Which graph correctly shows the two antibody responses.

3  Concept

The first encounter with an antigen gives a primary response — small, slow, with a lag while lymphocytes are recruited. A second encounter gives a secondary response — much larger and much faster, because memory cells already exist.

So anti-Y must show a small early peak and a large later peak, while anti-X, meeting its antigen for the first time on Day 24, shows only a small response.

4  Formula or rule
first exposure → PRIMARY (small, slow)  ·  second exposure → SECONDARY (large, fast)
5  Baby steps
  1. Anti-Y, Day 1. First exposure → a small primary peak.
  2. Anti-Y, Day 24. Second exposure → memory cells respond → a much larger and faster peak.
  3. Anti-X, Day 24. First exposure → only a small primary response.
  4. So the correct graph has anti-Y with two peaks, the second much bigger, and anti-X with a single small peak.
6  Diagram
Primary and secondary antibody responsedaysantibodyanti-Y (secondary: big, fast)anti-X (primary: small)day 1day 24SECOND exposure to the same antigen → memory cells →a much larger and faster responsea FIRST exposure always gives a small, slow primary response
7  Shortcuts
Check the relative heights before anything else. The secondary response is several times larger than the primary — a graph showing two peaks of similar size is wrong on sight.

Then check which curve belongs to which antigen. The antigen seen twice must be the one with two peaks; the antigen seen once can only have one. The options are built by swapping these labels.
Q 147Attempted · wrongDrugs and their effects

Select the correct statements from the following.
(i) Cocaine decreases the activity of the central nervous system.
(ii) Opioid drugs typically produce a sense of euphoria and increased energy.
(iii) Morphine is used for the treatment of severe pain associated with surgery.
(iv) Datura contains drugs that cause hallucinations.

Her answer(i) and (iv)
Correct answer(iii) and (iv)
1  Given
  • Four statements about drugs of abuse and their effects.
2  Asked

Which statements are correct.

3  Concept

Sort each drug by which way it pushes the nervous system.

Cocaine is a STIMULANT — it increases CNS activity, producing euphoria and excitement. Statement (i) says the opposite.
Opioids are DEPRESSANTS — they slow the CNS. They do produce euphoria, but not “increased energy”, so (ii) is wrong.
Morphine is a powerful analgesic, used exactly as (iii) describes.
Datura is a source of hallucinogens, so (iv) is correct.

4  Formula or rule
stimulant: cocaine  ·  depressant: opioids  ·  hallucinogen: Datura, LSD  ·  cardiovascular: cannabinoids
5  Baby steps
  1. (i) Cocaine is a stimulant, not a depressant. Incorrect.
  2. (ii) Opioids depress the CNS — euphoria yes, increased energy no. Incorrect.
  3. (iii) Morphine is a strong painkiller used post-operatively. Correct.
  4. (iv) Datura contains hallucinogenic compounds. Correct.
  5. Answer: (iii) and (iv).
6  Diagram
Drugs: which way do they push the nervous system?CocaineSTIMULANT — increases CNS activityOpioids (morphine, heroin)DEPRESSANT — suppresses CNS, kills painCannabinoidsaffect the cardiovascular systemDatura, LSDHALLUCINOGENSCocaine is a STIMULANT — any statement saying it decreasesCNS activity is false. Morphine, an opioid, is a painkiller.
7  Shortcuts
Fix the four categories once and every drug question becomes a lookup:

Stimulant — cocaine (coke, crack), from Erythroxylum coca
Depressant / painkiller — opioids: morphine, heroin, from the poppy
Hallucinogen — Datura, LSD, from Atropa belladonna
Cardiovascular effects — cannabinoids, from Cannabis sativa

Cocaine and opioids are the pair most often swapped, and they push in opposite directions.
Q 151Attempted · wrongMatching diagnostic tests

Select the correct match.

Her answerPap smear test – Breast cancer
Correct answerELISA – HIV
1  Given
  • Widal test – Tuberculosis (as offered).
  • Pap smear test – Breast cancer (as offered).
  • ELISA – HIV (as offered).
  • Mantoux test – Typhoid (as offered).
2  Asked

Which pairing is correct.

3  Concept

Only one of the four options pairs a test with the disease it actually detects. The correct associations are:

Widal → typhoid  ·  Mantoux → tuberculosis  ·  Pap smear → cervical cancer  ·  ELISA → HIV

Notice that the options have swapped Widal and Mantoux, and moved Pap smear from cervical to breast cancer.

4  Formula or rule
Widal → typhoid · Mantoux → TB · Pap smear → cervical cancer · ELISA → HIV
5  Baby steps
  1. Widal – Tuberculosis: wrong. Widal detects typhoid.
  2. Pap smear – Breast cancer: wrong. Pap smear screens for cervical cancer.
  3. ELISA – HIV: correct. ELISA detects antibodies against HIV.
  4. Mantoux – Typhoid: wrong. Mantoux tests for tuberculosis.
6  Diagram
Diagnostic tests — match them onceWidal testtyphoidPap smearcervical cancerELISAHIV / AIDSMantoux testtuberculosisthese four are the whole set, and options are built byshuffling the right-hand column — learn them as fixed pairs
7  Shortcuts
Learn these four as fixed pairs, because the options are built purely by shuffling the right-hand column. Two mnemonics help:

Widal and typhoid both carry a d; Mantoux and Mycobacterium both start with M.

Pap smear is cervical, never breast — breast cancer screening is mammography. That single substitution is the most frequently used distractor in this topic.
Q 155Left blankHIV and macrophages

Which of the following cells in the human body acts like a HIV factory?

Correct answer (left blank)Macrophage
1  Given
  • HIV enters the body and first infects macrophages.
  • Inside them, reverse transcriptase makes viral DNA, which integrates into the host genome.
  • New viral particles are then produced continuously.
2  Asked

Which cell acts as the HIV factory.

3  Concept

After entering the body, HIV infects macrophages. Reverse transcriptase produces viral DNA from the viral RNA, that DNA integrates into the host cell's DNA, and the infected macrophage then keeps producing virus particles — behaving, as NCERT puts it, like an HIV factory.

The virus subsequently also enters and destroys helper T lymphocytes, whose progressive loss causes the immunodeficiency.

4  Formula or rule
HIV → macrophage (the FACTORY) → helper T cells (progressively DESTROYED)
5  Baby steps
  1. HIV enters the body via body fluids and infects macrophages.
  2. Reverse transcriptase makes viral DNA, which becomes part of the host genome.
  3. The infected macrophage continuously produces new virus particles — the factory.
  4. Released virus then attacks helper T lymphocytes, which decline in number.
  5. Macrophage.
6  Diagram
Where lymphocytes are made, and where they meet antigenPRIMARY organsbone marrow · thymuslymphocytes are PRODUCEDand mature hereSECONDARY organsspleen · lymph nodestonsils · Peyer's patcheslymphocytes MEET antigensIn the SECONDARY organs, lymphocytes interact with ANTIGENSand then proliferate into effector cells.Made in primary, activated in secondary — that is the whole split.
7  Shortcuts
Two cells, two roles — and the question asks about the first:

Macrophage = the factory where virus is made
Helper T lymphocyte = the target that is progressively destroyed

It is the fall in helper T cells that defines AIDS, but it is the macrophage that manufactures. The word factory in the stem points to production, not destruction.
Q 160Left blankSecondary lymphoid organs

Secondary lymphoid organs provide the sites for interaction of ___(A)___ with the ___(B)___, then ___(A)___ proliferate to become effector cells. Fill the blanks with correct option.

Correct answer (left blank)(A) – Lymphocytes, (B) – antigens
1  Given
  • Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches, appendix.
  • The same term (A) appears twice in the sentence — whatever fills it must both interact and proliferate.
2  Asked

What fills blanks (A) and (B).

3  Concept

Lymphocytes are produced and matured in the primary lymphoid organs (bone marrow and thymus). They then migrate to the secondary lymphoid organs, where they meet antigens, become activated, and proliferate into effector cells.

So (A) is lymphocytes and (B) is antigens.

4  Formula or rule
PRIMARY organs: lymphocytes are made  ·  SECONDARY organs: lymphocytes meet ANTIGENS and proliferate
5  Baby steps
  1. Identify (A) from its second appearance: whatever proliferates into effector cells must be lymphocytes.
  2. Lymphocytes interact with antigens in the secondary organs, so (B) = antigens.
  3. The interaction activates them and they divide into effector cells.
  4. (A) – Lymphocytes, (B) – antigens.
6  Diagram
Where lymphocytes are made, and where they meet antigenPRIMARY organsbone marrow · thymuslymphocytes are PRODUCEDand mature hereSECONDARY organsspleen · lymph nodestonsils · Peyer's patcheslymphocytes MEET antigensIn the SECONDARY organs, lymphocytes interact with ANTIGENSand then proliferate into effector cells.Made in primary, activated in secondary — that is the whole split.
7  Shortcuts
Use the repeated blank. (A) appears twice, so it must make sense in both places — only lymphocytes both interact and proliferate into effector cells. Antigens and antibodies do neither.

The primary / secondary split in one line: primary organs make lymphocytes (bone marrow, thymus); secondary organs activate them (spleen, lymph nodes, tonsils, Peyer's patches, appendix).
Q 163Left blankCancer and contact inhibition

Assertion (A): Cancer cells divide continuously, giving rise to masses of cells.
Reason (R): Tumor formation is due to contact inhibition of neoplastic cells.

Correct answer (left blank)(A) is true but (R) is false
1  Given
  • Assertion about continuous division of cancer cells.
  • Reason attributing tumour formation to contact inhibition.
2  Asked

The truth of each statement.

3  Concept

Contact inhibition is the property of normal cells that makes them stop dividing when they touch neighbouring cells. It is a brake.

Cancer cells have LOST contact inhibition, which is precisely why they keep dividing and pile up into a tumour. The reason states the opposite of the truth — it credits tumour formation to the very mechanism that prevents it.

4  Formula or rule
normal cells: contact inhibition PRESENT → growth stops
cancer cells: contact inhibition LOST → uncontrolled growth
5  Baby steps
  1. Assertion. Cancer cells do divide continuously and form masses. True.
  2. Reason. Tumours form because contact inhibition has been lost, not because it is present. False.
  3. (A) is true but (R) is false.
6  Diagram
Contact inhibition, and its lossNORMAL cellsstop dividing on contactCANCER cellspile up — contact inhibition LOSTTumours form because contact inhibition is lost, not becauseit is present. A statement crediting tumour formation TO contactinhibition has the logic exactly backwards.
7  Shortcuts
Watch for a statement that names the right mechanism with the wrong sign. Contact inhibition is genuinely central to this topic — the error is one missing word, loss of.

Test it by asking what the property does: contact inhibition stops growth. A statement saying it causes a tumour therefore has the logic inverted, and that check needs no recall at all.
Q 167Attempted · wrongDiseases eradicated by vaccination

Which of the following diseases has been completely eradicated by the use of vaccines?

Her answerHepatitis
Correct answerSmallpox
1  Given
  • Smallpox, ringworms, malaria and hepatitis are offered.
2  Asked

Which disease has been completely eradicated by vaccination.

3  Concept

Smallpox is the only human disease ever completely eradicated worldwide, declared so by the WHO in 1980 after a global vaccination campaign. That singular status is what the question is testing.

Hepatitis has an effective vaccine but the disease still circulates widely — a vaccine existing is not the same as eradication.

4  Formula or rule
smallpox = the ONLY human disease eradicated (WHO, 1980)
5  Baby steps
  1. Ringworms: a fungal infection, with no vaccine at all.
  2. Malaria: caused by a protozoan; still endemic across large parts of the world.
  3. Hepatitis: an effective vaccine exists (especially for Hepatitis B), but the disease is far from eradicated.
  4. Smallpox: eradicated worldwide, declared by the WHO in 1980. Correct.
6  Diagram
Diagnostic tests — match them onceWidal testtyphoidPap smearcervical cancerELISAHIV / AIDSMantoux testtuberculosisthese four are the whole set, and options are built byshuffling the right-hand column — learn them as fixed pairs
7  Shortcuts
Distinguish “has a vaccine” from “has been eradicated”. Many diseases have vaccines; only one human disease has ever been wiped out.

Two facts worth holding: smallpox was eradicated in 1980, and polio is the disease closest to eradication now but is not there yet. If polio appears as an option alongside smallpox, smallpox is still the answer.
Q 169Left blankLarvivorous fish and disease control

Which of the following diseases cannot be controlled through the use of the larvivorous fish Gambusia?

Correct answer (left blank)Typhoid
1  Given
  • Gambusia is a larvivorous fish that eats mosquito larvae in water bodies.
  • Malaria, filariasis and dengue are all mosquito-borne.
  • Typhoid is water-borne, spread by contaminated food and water.
2  Asked

Which disease Gambusia cannot help control.

3  Concept

Gambusia works by eating mosquito larvae, so it can only control diseases whose transmission depends on mosquitoes.

Typhoid is caused by Salmonella typhi and spreads through contaminated food and water — no mosquito is involved at any stage, so removing mosquito larvae achieves nothing.

4  Formula or rule
Gambusia eats mosquito larvae → helps only against MOSQUITO-BORNE diseases
5  Baby steps
  1. Malaria — spread by female Anopheles. Mosquito-borne, so Gambusia helps.
  2. Filariasis — spread by Culex. Mosquito-borne, so Gambusia helps.
  3. Dengue — spread by Aedes. Mosquito-borne, so Gambusia helps.
  4. Typhoid — spread through contaminated food and water. No mosquito stage, so Gambusia is irrelevant. Correct answer.
6  Diagram
Why malarial fever recursmosquito biteSPOROZOITES injectedliver, then RBCsparasite multipliesRBCs RUPTUREhaemozoin releasedthe CYCLE repeats → recurrent feverHaemozoin is a toxin RELEASED when infected red cells burst.It is NOT injected by the mosquito — the mosquito deliverssporozoites. Recurrence follows the synchronised rupture cycle.
7  Shortcuts
Ask what the control method targets, then ask which disease does not use that route. Gambusia targets mosquito larvae, so the odd one out is whichever disease is not mosquito-borne.

Sort the chapter's diseases by vector once:
Mosquito — malaria (Anopheles), filariasis (Culex), dengue and chikungunya (Aedes)
Food and water — typhoid, amoebiasis, ascariasis
Air — pneumonia, common cold
Q 176Attempted · wrongWhy malarial fever recurs

Assertion (A): Malaria patients experience recurrent fever.
Reason (R): Haemozoin is injected into humans through a mosquito bite.

Her answerBoth true, and (R) is the correct explanation
Correct answer(A) is true but (R) is false
1  Given
  • Assertion about recurrent fever in malaria.
  • Reason about how haemozoin enters the body.
2  Asked

The truth of each statement.

3  Concept

The assertion is true. The recurring fever follows the synchronised rupture of infected red blood cells, which releases the toxin haemozoin.

The reason is false. The mosquito injects sporozoites, not haemozoin. Haemozoin is a by-product formed inside the human red blood cells and released when they burst — it is produced in the body, not delivered by the bite.

4  Formula or rule
mosquito injects SPOROZOITES → liver → RBCs → RBCs rupture → HAEMOZOIN released → fever
5  Baby steps
  1. Assertion. Malarial fever recurs at regular intervals. True.
  2. Reason. What the mosquito injects is sporozoites. Haemozoin is a toxin generated inside human red cells as the parasite digests haemoglobin. False.
  3. The fever recurs because the parasites multiply and rupture the red cells in synchronised waves, releasing haemozoin each time.
  4. (A) is true but (R) is false.
6  Diagram
Why malarial fever recursmosquito biteSPOROZOITES injectedliver, then RBCsparasite multipliesRBCs RUPTUREhaemozoin releasedthe CYCLE repeats → recurrent feverHaemozoin is a toxin RELEASED when infected red cells burst.It is NOT injected by the mosquito — the mosquito deliverssporozoites. Recurrence follows the synchronised rupture cycle.
7  Shortcuts
Follow the malaria life cycle in order and every question in this topic falls out:

female Anopheles bites → sporozoites injected → liver cells → RBCs → parasites multiply → RBCs rupture → haemozoin released → fever

Haemozoin is released, never injected. Any statement using the word “injected” with haemozoin is false, and that one word decides the question.

Weak areas — Human Health and Disease

Zoology was the strongest subject at 139, and the pattern reflects that: only nine questions flagged, and five of the nine were attempted rather than skipped. The errors are mostly single facts rather than reasoning failures, which is the easiest kind to fix.

Three are pure recall, and all three sit in short closed lists:

ListContentsQuestions
Diagnostic testsWidal → typhoid · Mantoux → TB · Pap smear → cervical cancer · ELISA → HIV151
Drug categoriescocaine = stimulant · opioids = depressant · Datura, LSD = hallucinogen · cannabinoids = cardiovascular147
Disease vectorsmosquito: malaria, filariasis, dengue · food and water: typhoid, amoebiasis169

Two are inverted mechanisms, and both have the same shape — the right concept named with the sign reversed:

Q143 is the one genuine reasoning question, and it turns on relative heights: a secondary response is several times larger and faster than a primary one, so any graph showing two similar peaks is wrong before the labels are even read.

The most efficient revision here is to write out the three lists above once. They answer five of the nine questions between them and require no derivation at all.