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Inheritance, and Health and Disease

Two chapters, nine questions

Every biology question flagged on this paper, rebuilt in full. Each one carries what was given, what was asked, the concept behind it, the rule, the steps written out, a table justifying the right option and ruling out each of the others, the fastest route through, and an animated figure wherever seeing the thing settles the answer.

9Questions reviewed
5Attempted, wrong
3Left blank
1Attempted, correct

The shape of this paper

Nine questions were flagged: five attempted and missed, three left blank, and one attempted and answered correctly. That last one is kept in because its distractor is worth locking in permanently.

What is striking is how the two chapters differ. In Human Health and Disease every single question was attempted — and every single one was missed. In Principles of Inheritance and Variation the attempt rate was lower but the accuracy when attempting was much better. That is the reverse of the pattern in the physics paper, where attempting was the weak point rather than precision.

And in all five wrong answers the underlying biology recalled was accurate. What failed was the match between what was recalled and what was actually asked.

Contents

Principles of Inheritance and Variation5 questions · 1 wrong · 3 blank · 1 correct
Q1Q17Q27Q37Q38
Human Health and Disease4 questions · 4 wrong · 0 blank
Q61Q64Q77Q88
Red = attempted and missed · Amber = left blank · Green = attempted and correct

Principles of Inheritance and Variation

1 wrong · 3 blank

Five questions, and a clear divide inside them. The two that were missed were missed on reading rather than on genetics; the three left blank are all standard bookwork with a one-line answer.

Q 1Attempted · correctPedigree disorders · phenylketonuria
Answered correctlyKept in the set because the distractor is worth locking in permanently — a broad palm with a single crease belongs to a different disorder entirely, and it recurs as a distractor across the whole chapter.

Which of the following is not a clinical manifestation of phenylketonuria?

  1. Excretion of phenyl pyruvic acid through urine
  2. Mental retardation
  3. Reduction in hair and skin pigmentation
  4. Correct — and chosenA broad palm with a characteristic crease
Given
  • Phenylketonuria (PKU), an inborn error of metabolism.
  • It is autosomal recessive.
  • Four candidate clinical features.
Asked

Which feature does not belong to PKU.

Concept to use

PKU is one missing enzyme and nothing more: phenylalanine hydroxylase. Without it, phenylalanine cannot be converted to tyrosine. Everything that goes wrong afterwards is downstream of that single blocked arrow — so the test for any candidate symptom is simply can I trace it back to that one step?

Diagram
PhenylalanineTyrosinephenylalanine hydroxylaseenzyme missingphenylpyruvic acidbuilds up → urine, brainmelanin runs short→ pale hair and skinOne blocked step explains all three real symptoms: acid in the urine,damage to the developing brain, and loss of pigment. A palm creaseis not on this pathway at all — it belongs to Down's syndrome.
AnimatedOne blocked enzyme step, and every real symptom hanging off it.
Formula to usePhe —X→ Tyr so Phe piles up and Tyr runs short
Baby steps
  1. Phenylalanine accumulates and is shunted down a side road into phenylpyruvic acid, which spills into the urine. That covers option A.
  2. The same accumulation is toxic to the developing brain, giving mental retardation. That covers option B.
  3. Tyrosine is the raw material for melanin. With tyrosine short, melanin is short, so hair and skin lose pigment. That covers option C.
  4. A broad palm with a single transverse crease has nothing to do with amino acid chemistry. It is a morphological feature, and it belongs to Down's syndrome. Option D is the odd one out.
Answer
A broad palm with a characteristic crease
Why this option and not the others
OptionVerdictReason
AkeepPhenylpyruvic acid in the urine is the diagnostic sign that gives the disorder its name — “phenyl-keton-uria” is literally phenyl ketone in the urine.
BkeepAccumulated phenylalanine damages the developing nervous system. This is why PKU is screened for at birth — a low-Phe diet started early prevents it.
CkeepMelanin is made from tyrosine, and tyrosine is exactly what the blocked step fails to produce. Pale hair and skin follow directly.
Drule outThis is the simian crease of Down's syndrome, a chromosomal disorder. It is the correct answer because it does not belong here.
Shortcut
Sort the four features into two piles: biochemical (something in the blood or urine, something the body cannot build) and morphological (the shape of a body part). Single-gene metabolic disorders like PKU produce biochemical signs; chromosomal disorders like Down's and Turner's produce morphological ones. The odd feature out will almost always be the one from the wrong pile.
Q 17Left blankAutosomal recessive cross

If both parents are carriers of phenylketonuria, what are the chances of pregnancy resulting in an affected child?

  1. 0%
  2. Correct25%
  3. 50%
  4. 100%
Given
  • PKU is autosomal recessive.
  • Both parents are carriers, i.e. heterozygous, Aa.
  • Neither parent is affected.
Asked

The probability that a child is affected.

Concept to use

Two words do all the work. Carrier means heterozygous — one normal allele, one faulty one, and no symptoms because the normal allele is dominant. Recessive means the disorder appears only when both alleles are faulty. So the question is asking how often two heterozygotes produce a homozygous recessive child.

Diagram
gametes from one parentAaAaAAAaAaaagametesfrom the otherOne box in four is aa — the affected child.
AnimatedAa × Aa: the 1 : 2 : 1 square, with the affected box picked out.
Formula to useAa × Aa → 1 AA : 2 Aa : 1 aa affected = aa = 1/4
Baby steps
  1. Write both parents as Aa (carrier = heterozygous).
  2. Each parent makes two kinds of gamete in equal numbers: A and a.
  3. The Punnett square gives AA, Aa, Aa, aa — the classic 1 : 2 : 1.
  4. Only aa is affected, and it is one box out of four.
  5. Probability = 1/4 = 25%.
Answer
25%
Why this option and not the others
OptionVerdictReason
0%rule outThis would only hold if the disorder were dominant, or if one parent carried no faulty allele at all. Two carriers each have one to give.
25%keepOne box in four is aa. This is the fixed answer for every carrier × carrier autosomal recessive cross.
50%rule out50% is the chance of a child being a carrier (Aa), not of being affected. Reading the wrong row of the same square gives this.
100%rule outThis would need both parents to be affected (aa × aa). Carriers are not affected.
Shortcut
“Both parents are carriers” is a fixed phrase with a fixed answer set. Learn the trio and never draw the square again: 25% affected, 50% carriers, 75% look normal, and 2 out of the 3 normal-looking children are carriers. The last figure is the one examiners like to ask for as a follow-up.
Q 27Attempted · wrongX-linked recessive · who receives the gene

A woman who carries the gene for haemophilia can transmit the recessive gene to

  1. Her answersons only
  2. daughters only
  3. Correctboth daughters and sons
  4. all sons and few daughters
Given
  • Haemophilia is X-linked recessive.
  • The woman is a carrier: XHXh.
  • She is not affected herself.
Asked

To whom she can transmit the recessive gene.

Concept to use

A mother contributes an X to every one of her children, sons and daughters alike — it is the father who decides the sex by contributing X or Y. She has two X chromosomes and passes one at random, so each child, whatever its sex, has a 50% chance of receiving the X carrying h. What differs between sons and daughters is not whether they can receive the gene, but what happens afterwards.

Diagram
gametes from one parentXᴇYXᴇXʰXᴇXᴇXᴇYXᴇXʰXʰYgametesfrom the otherBoth lower boxes carry h — one is a daughter, one is a son.
AnimatedMother's Xʰ reaches a daughter and a son alike.
Formula to useXHXh × XHY → XHXH, XHXh, XHY, XhY
Baby steps
  1. Mother's gametes: XH and Xh, in equal numbers.
  2. Father's gametes: XH and Y, in equal numbers.
  3. The four combinations are XHXH (normal daughter), XHXh (carrier daughter — she received h), XHY (normal son), XhY (haemophilic son — he received h).
  4. Both a daughter and a son received the recessive gene. So it can be transmitted to both.
  5. What differs is the outcome: the son has no second X to mask it and is affected; the daughter has a normal X from her father and is a carrier.
Answer
Both daughters and sons
Why this option and not the others
OptionVerdictReason
sons onlyrule outTrue for who is affected, false for who receives the gene. Daughters receive it just as often — they simply do not show it.
daughters onlyrule outThere is no mechanism that would send a mother's X to her daughters preferentially. Every child gets one maternal X.
both daughters and sonskeepEach child, regardless of sex, has a 50% chance of inheriting the X that carries h.
all sons and few daughtersrule out“All sons” is wrong on its own — half the sons receive XH and are entirely normal.
Shortcut
Read the verb before choosing. “Transmit the gene”, “carry” and “pass on” are about inheritance, and the answer includes daughters. “Suffer from”, “be affected by” and “express” are about the phenotype, and the answer is sons. Same cross, two different questions.
Where it went wrong
“Sons only” is the answer to the question that was not asked. The genetics behind the choice was correct — sons are indeed the ones who suffer haemophilia — but the stem says transmit the recessive gene, not express it. A daughter who receives Xh has received the gene perfectly well; she just has a spare copy that hides it. This is a reading error rather than a knowledge gap, and it is worth flagging because the same transmit-versus-express distinction reappears in colour blindness, Duchenne muscular dystrophy and every other X-linked recessive question.
Q 37Left blankMutagens · UV radiation

Select the correct option w.r.t. UV radiation.

  1. It can produce sexual recombinations
  2. CorrectIt can cause mutations
  3. It will not produce any variations in the progeny
  4. It is one of the chemical mutagens
Given
  • Ultraviolet radiation as an agent acting on DNA.
Asked

The correct statement about UV radiation.

Concept to use

UV is a physical mutagen. Absorbed by DNA, it fuses two adjacent thymine bases on the same strand into a thymine dimer. The strand kinks, replication machinery misreads it, and a permanent change in base sequence results. That is the definition of a mutation.

Diagram
ATTATAGCCGATUV photonT–T dimerUV is a PHYSICAL mutagen. It fuses two neighbouring thymines into adimer, the strand kinks, and replication copies it wrongly.That is a mutation — not a recombination, and not a chemical mutagen.
AnimatedUV fuses two neighbouring thymines; the copy that follows is wrong.
Formula to useUV photon → adjacent T–T fuse → dimer → misreplication → mutation
Baby steps
  1. UV is electromagnetic radiation, not a substance, so it is classed as a physical mutagen alongside X-rays and gamma rays.
  2. Chemical mutagens are molecules — mustard gas, nitrous acid, base analogues like 5-bromouracil.
  3. The damage UV does is a thymine dimer, which alters the base sequence when copied.
  4. An altered base sequence is a mutation, so option B is correct.
  5. Recombination is a quite separate process — crossing over during meiosis — and UV plays no part in it.
Answer
It can cause mutations
Why this option and not the others
OptionVerdictReason
produces sexual recombinationsrule outRecombination happens by crossing over in meiosis. It reshuffles existing alleles; it does not create new ones, and radiation is not involved.
can cause mutationskeepThymine dimers change the base sequence permanently. This is the textbook example of a physical mutagen.
no variations in the progenyrule outA mutation in a germ cell is inherited, so it is precisely a source of variation in the progeny.
one of the chemical mutagensrule outUV is radiation, not a chemical. It is a physical mutagen — this option is right about the mutagen part and wrong about the category.
Shortcut
Two options here can be dismissed without any biology at all. Option C flatly contradicts option B, so one of the two must be the answer — and a chapter on variation is not going to conclude that a famous mutagen produces no variation. Option D then fails on a single word, chemical. That leaves B standing after about ten seconds of reading.
Q 38Left blankX-linked recessive · expression

The recessive genes located on X-chromosome in humans are always

  1. expressed in females
  2. Correctexpressed in males
  3. lethal
  4. sub-lethal
Given
  • A recessive gene sitting on the X chromosome.
  • Human sex determination: females XX, males XY.
Asked

In whom such a gene is always expressed.

Concept to use

A male has only one X and a Y that carries no matching gene — he is hemizygous. There is no second copy to mask anything, so whatever is on his single X shows up in the phenotype, dominant or recessive alike. A female has two X chromosomes, so a recessive allele on one can be covered by a normal allele on the other; she expresses it only when both copies are faulty.

Diagram
FEMALE XXXXone normal copy can maskthe recessive one → carrierMALE XYXYnothing to mask it — the single Xis ALWAYS expressedno matching gene hereA male has only ONE X, so he is hemizygous: whatever is on it shows up,dominant or recessive. This is why X-linked disorders hit males hardest.
AnimatedTwo X chromosomes can hide a recessive allele. One cannot.
Formula to usemale XhY → expressed · female XHXh → hidden
Baby steps
  1. Count the copies. Male: one X. Female: two X.
  2. A recessive allele needs a partner allele to hide behind. In the male there is no partner — the Y does not carry the corresponding gene.
  3. So in males the recessive X-linked gene is always expressed.
  4. In females it is expressed only in the homozygous recessive case, which is far rarer — which is why haemophilia and red-green colour blindness are so much commoner in men.
Answer
Expressed in males
Why this option and not the others
OptionVerdictReason
expressed in femalesrule outA female has a second X that can carry the normal allele and mask the recessive one. She expresses it only when both X chromosomes carry it.
expressed in maleskeepHemizygosity: one X, no partner allele, nothing to mask it. The word always in the stem is exactly right for males and wrong for everyone else.
lethalrule outMost X-linked recessive genes are not lethal at all — colour blindness is the obvious counterexample.
sub-lethalrule outSame objection. Severity varies enormously from one X-linked gene to another; there is no general rule.
Shortcut
Absolute words like always usually mark a wrong option — but not here, and it is worth knowing why. The claim is true because it rests on chromosome counting rather than on biology that might vary: a male simply has nowhere to hide a recessive X allele. When an absolute word is backed by a structural fact rather than a tendency, it survives.

Human Health and Disease

4 wrong · 0 blank

Four questions, all four attempted, all four missed. Every one of them turns on a single word — small against large, mechanical against biological, arm against stem, T against lymphocyte in general.

Q 61Attempted · wrongAmoebiasis · statement set

Identify the correct statements related to amoebiasis.
A) Pathogen is a protozoan that lives in the small intestine of human.
B) Pathogen is transmitted through contaminated food and water.
C) Typical symptom is excess mucus and blood clots in the stools.
D) Houseflies act as biological vectors for the pathogen.

  1. A, B, C, D
  2. A, C, D
  3. CorrectB, C
  4. Her answerB, C, D
Given
  • Amoebiasis (amoebic dysentery), caused by Entamoeba histolytica.
  • Four statements about its site, transmission, symptoms and vector.
Asked

Which statements are correct.

Concept to use

Two of these four statements are planted with a single wrong word each, and both wrong words are ones that sound plausible. The parasite lives in the large intestine, not the small one — which is why the symptoms are dysenteric. And the housefly is a mechanical carrier, not a biological vector: it carries cysts on its body from faeces to food, but the parasite neither develops nor multiplies inside it.

Diagram
infected personfaeces with cystshouseflyMECHANICAL carrierfood and watercysts depositedLARGE intestinenot the small oneA MECHANICAL carrier just carries dirt on its feet — the parasitedoes not develop or multiply inside the fly. That is what makes itmechanical rather than BIOLOGICAL.
AnimatedThe route from faeces to colon — and where the fly fits in.
Formula to usebiological vector: parasite DEVELOPS inside it · mechanical carrier: it just gives the parasite a lift
Baby steps
  1. A. Entamoeba histolytica lives in the large intestine (colon). Statement A says small intestine. Incorrect.
  2. B. Transmission is by cysts in contaminated food and water. Correct.
  3. C. The classic symptoms are constipation, abdominal pain and cramps, with stools containing excess mucus and blood clots. Correct.
  4. D. Houseflies transfer cysts from faeces to food on their bodies. The parasite does not develop in them, so they are mechanical carriers, not biological vectors. Incorrect.
  5. Only B and C stand.
Answer
B and C
Why this option and not the others
OptionVerdictReason
A, B, C, Drule outFails on both A and D.
A, C, Drule outFails on A and D, and drops B which is correct.
B, CkeepThe only combination that keeps both true statements and rejects both planted ones.
B, C, Drule outCorrectly rejects A but keeps D. The housefly is mechanical, not biological.
Shortcut
In statement sets, go hunting for the one word that could be swapped rather than reading each statement as a whole. Here the two swappable words are “small” (should be large) and “biological” (should be mechanical). Once both are spotted, the option list collapses to one survivor.
Where it went wrong
Statement D was accepted. NCERT is unusually consistent on this point: houseflies are always described as mechanical carriers, and the phrase appears in the same form for typhoid and amoebiasis both. A biological vector is one inside which the parasite develops or multiplies — the female Anopheles for malaria, Aedes for dengue. A fly that simply walks from faeces to food with cysts stuck to its legs does none of that. Note also that statement A was correctly rejected, so the small-versus-large intestine point was secure; the mark turned entirely on the vector word.
Q 64Attempted · wrongAntibody structure

A typical antibody is a 'Y' shaped molecule. The stem of 'Y' consists of

  1. one light chain
  2. Her answerone heavy chain and one light chain
  3. two light chains
  4. Correcttwo heavy chains
Given
  • A typical antibody, H₂L₂.
  • Four polypeptide chains in all: two heavy (long) and two light (short).
  • The molecule is Y-shaped.
Asked

Which chains make up the stem of the Y.

Concept to use

The reason the light chains are called light is that they are short. Each one runs only along the outer edge of an arm and stops at the hinge. The heavy chains are long: each runs down an arm, through the hinge and all the way into the stem. So above the hinge you find both kinds of chain; below the hinge — the stem — you find heavy chains only, and there are two of them.

Diagram
the STEM — heavy chains onlylight chainlight chainheavyheavyH₂L₂ — four chains in all. The arms carry heavy AND light;the light chains stop at the hinge, so the stem is two heavy chains.
AnimatedLight chains stop at the hinge; heavy chains carry on into the stem.
Formula to useH₂L₂ · each ARM = 1 heavy + 1 light · the STEM = 2 heavy
Baby steps
  1. Count the chains: 2 heavy + 2 light = 4, written H₂L₂.
  2. Each arm of the Y is one heavy chain paired with one light chain.
  3. The light chains terminate at the hinge region, where the arms meet.
  4. The two heavy chains continue past the hinge and run down together to form the stem.
  5. The stem is therefore two heavy chains.
Answer
Two heavy chains
Why this option and not the others
OptionVerdictReason
one light chainrule outA single chain could not form a stem — the molecule is symmetrical, so whatever is in the stem comes in a pair.
one heavy + one lightrule outThis is the composition of an arm, not the stem. It is the right pair of chains described in the wrong place.
two light chainsrule outLight chains are too short to reach the stem — they stop at the hinge.
two heavy chainskeepOnly the heavy chains extend below the hinge, and both of them do.
Shortcut
Let the name do the work: light chains are light because they are short. Anything asking about the lower part of the molecule — the stem, the Fc region, the part that binds to cells — is heavy chain only. Anything about the tips, where the antigen binds, involves both.
Where it went wrong
“One heavy chain and one light chain” describes an arm of the Y. The chain composition was known correctly; what was misplaced was the location. The structural fact that fixes it is the hinge: the light chains end there and the heavy chains carry on. Sketching the Y once, with the light chains drawn visibly shorter, makes this impossible to get wrong again — which is why the figure above is drawn to that proportion.
Q 77Attempted · wrongVector control · matching measure to disease

Spraying of insecticides in ditches, drainage areas and swamps, etc. is one of the important measures to prevent

  1. Her answerascariasis
  2. amoebiasis
  3. Correctdengue fever
  4. typhoid fever
Given
  • A control measure: spraying insecticides in ditches, drainage areas and swamps.
  • Four candidate diseases.
Asked

Which disease this measure prevents.

Concept to use

Work backwards from the measure to the transmission route. Ditches, drains and swamps are places where water stands still, and standing water is where mosquitoes breed. Spraying insecticide there kills the larvae and breaks the mosquito life cycle. So the disease being prevented has to be a mosquito-borne one — and only one of the four is.

Diagram
stagnant water in ditches, drains and swampslarvalarvalarvalarvalarvalarvaINSECTICIDE SPRAYKilling the larvae in standing water breaks the MOSQUITO life cycle.So it prevents mosquito-borne disease — dengue, malaria, chikungunya.It does nothing for diseases spread by contaminated food or soil.
AnimatedWhat spraying stagnant water actually kills.
Formula to usecontrol measure → transmission route → disease
Baby steps
  1. Identify what the measure targets: standing water, therefore mosquito breeding sites.
  2. Ascariasis: Ascaris lumbricoides, transmitted by eggs in contaminated water, vegetables and soil. No insect involved.
  3. Amoebiasis: cysts in contaminated food and water, carried mechanically by houseflies. Houseflies do not breed in swamps and are not the target of larval spraying.
  4. Dengue: transmitted by Aedes aegypti, a mosquito that breeds in stagnant water. This is the match.
  5. Typhoid: Salmonella typhi, spread through contaminated food and water. Again no insect vector.
Answer
Dengue fever
Why this option and not the others
OptionVerdictReason
ascariasisrule outA soil-transmitted helminth. Its eggs reach humans through contaminated vegetables, water and soil — killing insects in a swamp does nothing to it.
amoebiasisrule outFood- and water-borne. A housefly may carry cysts, but flies are not what larval spraying in stagnant water targets.
dengue feverkeepAedes mosquitoes breed in standing water, so removing or treating that water is the standard control measure.
typhoid feverrule outBacterial and water-borne. Prevented by sanitation and safe drinking water, not by insecticide.
Shortcut
Sort every disease in this chapter by route once, and questions like this become one-step. Insect-borne: malaria, dengue, chikungunya, filariasis. Water- and food-borne: typhoid, amoebiasis, ascariasis, cholera. Air-borne: pneumonia, common cold. A control measure aimed at insects can only prevent a disease from the first list.
Where it went wrong
Ascariasis is transmitted through contaminated water, vegetables and soil — there is no insect anywhere in its life cycle, so no amount of spraying would touch it. The likely path to this answer is a general association of “ditches and drains” with dirt and worms rather than specifically with standing water. The word that matters in the stem is swamps: that is a breeding-site word, and breeding sites mean mosquitoes.
Q 88Attempted · wrongPrimary lymphoid organs

Differentiation of immature cells into antigen-sensitive T-lymphocytes takes place

  1. only in bone marrow
  2. only in spleen
  3. Correctonly in thymus
  4. Her answerBoth bone marrow and thymus
Given
  • Immature lymphocytes differentiating into antigen-sensitive T-lymphocytes.
  • Primary lymphoid organs: bone marrow and thymus.
  • Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches, appendix.
Asked

Where T-lymphocytes differentiate.

Concept to use

Both bone marrow and thymus are primary lymphoid organs, and that is what makes the distractor tempting. But they divide the work between them. All lymphocytes are born in the bone marrow. From there, the ones destined to become B-cells stay and mature in the marrow, while the ones destined to become T-cells migrate to the thymus and mature there. The question names T-lymphocytes specifically.

Diagram
BONE MARROWall lymphocytesare BORN here(B-cells also mature here)THYMUSimmature cells becomeantigen-sensitiveT-lymphocytesThe T stands for thymus. Born in the marrow, SCHOOLED in the thymus.The question asks where they DIFFERENTIATE, not where they originate.
AnimatedBorn in the marrow, schooled in the thymus.
Formula to useB cells → Bone marrow T cells → Thymus
Baby steps
  1. Every lymphocyte originates in the bone marrow — that part is common to both.
  2. Immature cells that will become T-lymphocytes leave the marrow and travel to the thymus.
  3. In the thymus they acquire antigen receptors and become antigen-sensitive. That is the differentiation step the question asks about.
  4. The spleen is a secondary lymphoid organ — where mature lymphocytes meet antigens, not where they are made.
  5. So the answer is only in thymus.
Answer
Only in thymus
Why this option and not the others
OptionVerdictReason
only in bone marrowrule outThis is where B-lymphocytes mature, and where all lymphocytes originate — but not where T-cells become antigen-sensitive.
only in spleenrule outThe spleen is a secondary lymphoid organ. Mature lymphocytes go there to encounter antigen; they do not differentiate there.
only in thymuskeepThe T in T-lymphocyte stands for thymus. This is where immature cells acquire their receptors.
Both bone marrow and thymusrule outTrue for lymphocytes in general, but the stem specifies T-lymphocytes. Origin and differentiation are being merged here.
Shortcut
The letters are the mnemonic and they are exact: B for Bone marrow, T for Thymus. Whenever an option offers “both”, check whether the stem named a specific cell type — if it did, “both” is almost always the trap.
Where it went wrong
“Both bone marrow and thymus” is the correct answer to the more general question — where do immature lymphocytes differentiate into antigen-sensitive lymphocytes? — and NCERT does say exactly that about the two primary lymphoid organs together. The stem here narrows it to T-lymphocytes, and that one letter changes the answer. This is the same pattern as Q27 in this paper: the biology recalled was accurate, but it answered a slightly wider question than the one on the page.

What the nine have in common

Reading the paper as a whole

Every wrong answer was right about something else

QWhat was chosenWhat that answer is actually right about
27sons only Who is affected by haemophilia. The stem asked who can receive the gene.
88both bone marrow and thymus Where lymphocytes in general differentiate. The stem said T-lymphocytes.
64one heavy and one light chain The composition of an arm. The stem asked about the stem.
61B, C, D Correctly rejected the small-intestine trap. Only the vector word, mechanical against biological, was let through.
77ascariasis A genuine intestinal parasite — but one with no insect anywhere in its life cycle.

Not one of these five is a gap in knowledge. Every one is a mismatch between a correct fact and the precise question on the page. That is a different problem from not knowing the material, and it responds to a different fix.

The habit that would recover all five marks

Underline the noun and the verb in the stem before looking at the options. In every one of the five, the deciding word was sitting in the question and was not the word the answer was matched against:

Twenty marks turned on five words. This is much cheaper to fix than any amount of revision.

Two things to carry forward