Weak areas from this paper
Assertion–reason, in both directions recurring
Q15, Q28, Q63, Q66 — 4 of the 14 wrong answers, 20 marks swing. Q15 flipped both verdicts. Q28 and Q66 accepted a false reason because its words were familiar. Q63 rejected a reason that is the actual mechanism. The same pattern appears in the Physics (Q15, Q44), Chemistry (Q54, Q72, Q80) and HHD notes.
Fix to drill. In the margin, before reading any option: write A: T/F — reason, then R: T/F — reason, then say the sentence 'A because R' aloud. Only then look at the options. Ten assertion–reason items a day from past papers until this is automatic.
Right content, wrong arrangement recurring
Q11, Q53, Q72 — every name was known, but the order was not. Q53 swapped the middle rows (B/C) of a match question this time, not the usual C/D.
Fix to drill. For any sequence, write the fixed ends first (first/last, oldest/newest), or write a date or shape beside each item. For match questions, solve every row in the margin before reading List-II, and check all four rows, not only C and D.
Hardy–Weinberg and selection are the weakest block new
Q47, Q48, Q53, Q54, Q55 — Section D scored 7 / 12, the lowest on the paper. The mistakes are term-picking (p² for 2pq; B = p² + q²), definitions (stabilising vs disruptive) and reading curve shapes.
Fix to drill. Always write the whole row p² · 2pq · q² with numbers and labels. For ABO, draw the 3 × 3 p/q/r grid. For selection: stabilising = middle, directional = one side, disruptive = both ends.
Planted word and label swaps watch
Q3, Q12, Q20, Q44 — Q12 accepted 'on land'; Q20 swapped homologous and analogous; Q44 chose the true modern fact over what the theory claims; Q3 went the other way and rejected an unchanged NCERT line.
Fix to drill. Read each statement to the full stop and underline the one word most likely to be swapped. If you cannot find one, the statement is true.
Three blanks, all one-liners attempt rate
Q30, Q55, Q61 are each answerable in under 30 seconds (seed eater; medium wings → stabilising; fish-like reptile). That is 12 marks left on the table. The blank rate has dropped a lot compared with earlier ILTS papers.
The seventeen at a glance
| Q | Status | Marked | Key | Sub-topic | Error family |
|---|---|---|---|---|---|
| Q3 | wrong | C | A | Origin of Life and the Early Earth | Over-suspicion in statement questions |
| Q11 | wrong | C | D | Origin of Life and the Early Earth | Right content, wrong arrangement |
| Q12 | wrong | B | A | Evidences for Evolution | Planted word missed |
| Q15 | wrong | D | C | Evidences for Evolution | Assertion–reason instability |
| Q20 | wrong | B | A | Evidences for Evolution | Label swap (homologous ↔ analogous) |
| Q28 | wrong | A | C | Evidences for Evolution | Assertion–reason instability |
| Q30 | blank | — | A | Adaptive Radiation and the Theories | Blank — one-line recall |
| Q44 | wrong | C | B | Adaptive Radiation and the Theories | Multi-statement — planted clause |
| Q47 | wrong | D | B | Hardy–Weinberg and Natural Selection | Hardy–Weinberg term slip |
| Q48 | wrong | B | C | Hardy–Weinberg and Natural Selection | Hardy–Weinberg term slip |
| Q53 | wrong | B | A | Hardy–Weinberg and Natural Selection | Right content, wrong arrangement |
| Q54 | wrong | A | D | Hardy–Weinberg and Natural Selection | Definition swap |
| Q55 | blank | — | B | Hardy–Weinberg and Natural Selection | Blank — application of a definition |
| Q61 | blank | — | A | A Brief Account of Evolution | Blank — word order in a description |
| Q63 | wrong | B | A | A Brief Account of Evolution | Assertion–reason instability |
| Q66 | wrong | A | C | A Brief Account of Evolution | Assertion–reason instability |
| Q72 | wrong | C | D | Origin and Evolution of Man | Right content, wrong arrangement |
Question by question
Origin of Life and the Early Earth
Q3Attempted · wrong Over-suspicion in statement questions
Given below are two statements.
Statement I: The UV rays from the sun broke up water into hydrogen and oxygen, and the lighter H2 escaped from the early earth.
Statement II: In the early atmosphere, oxygen combined with ammonia and methane to form water, CO2 and others.
Choose the most appropriate answer.
Statement I: The UV rays from the sun broke up water into hydrogen and oxygen, and the lighter H2 escaped from the early earth.
Statement II: In the early atmosphere, oxygen combined with ammonia and methane to form water, CO2 and others.
Choose the most appropriate answer.
- Both Statement I and Statement II are correct ✓ key
- Both Statement I and Statement II are incorrect
- Statement I is correct but Statement II is incorrect her answer
- Statement I is incorrect but Statement II is correct
- Given
- Statement I: UV rays split water into H₂ and O₂; the lighter H₂ escaped.
- Statement II: O₂ combined with NH₃ and CH₄ to form water, CO₂ and others.
- Asked
- Which statements are correct.
- Concept
- Both lines are lifted word for word from the NCERT account of the early earth. After the UV split water, the lighter hydrogen escaped; the oxygen that remained reacted with the ammonia and methane of the reducing atmosphere. Only later did the ozone layer form and the oceans fill.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- UV + H₂O → H₂↑ + O₂ ; O₂ + NH₃ / CH₄ → H₂O, CO₂, …
- Baby steps
- Read Statement I against NCERT: matches exactly → true.
- Read Statement II: 'oxygen combined with ammonia and methane to form water, CO₂ and others' → matches exactly → true.
- Nothing was changed in either line, so both are correct.
- Answer
- (A) Both Statement I and Statement II are correct
- Why not the others
A · keep Both lines are NCERT sentences, unchanged. B · rule out Neither statement has a false word in it. C · rule out Statement II is not false — the oxygen left over did react with NH₃ and CH₄. D · rule out Statement I is the standard first step of the story. - Shortcut
- In a statement pair, underline the one word most likely to have been swapped (a gas, a direction, a number). If you cannot find a swapped word in a statement, it is true. Do not invent a trap.
- Where it went wrong
- Marked (C): Statement I is correct but Statement II is incorrect.
Statement II was rejected even though it is an NCERT line. The likely reason is that 'oxygen in the early atmosphere' sounds wrong — we are taught the early atmosphere had no free oxygen. But this oxygen is exactly the short-lived oxygen that UV had just released, and NCERT says it immediately combined with NH₃ and CH₄. Being suspicious of every statement costs marks as surely as trusting every one.
Q11Attempted · wrong Right content, wrong arrangement
Arrange the following in the probable sequence of their origin.
A. Chemoautotrophs
B. Oxygenic photoautotrophs
C. Anaerobic heterotrophs
D. Anoxygenic photoautotrophs
Choose the correct answer from the options given below.
A. Chemoautotrophs
B. Oxygenic photoautotrophs
C. Anaerobic heterotrophs
D. Anoxygenic photoautotrophs
Choose the correct answer from the options given below.
- B, A, D, C
- A, C, D, B
- D, C, B, A her answer
- C, A, D, B ✓ key
- Given
- A. Chemoautotrophs
- B. Oxygenic photoautotrophs
- C. Anaerobic heterotrophs
- D. Anoxygenic photoautotrophs
- Asked
- The probable order in which these forms of life originated.
- Concept
- Two rules settle the order. Heterotrophs came first — the first life fed on the ready-made organic 'soup' of chemical evolution and needed no machinery to make food. Oxygen-releasing forms came last — the early atmosphere had no free O₂, so the organisms that produce it must follow all the others. Between those ends, making food from chemicals (chemoautotrophy) is simpler than making it from light, and light-using forms first worked without releasing oxygen.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- heterotroph → chemoautotroph → anoxygenic photoautotroph → oxygenic photoautotroph
- Baby steps
- First: anaerobic heterotrophs (C) — no O₂ available, food from the soup.
- Next: chemoautotrophs (A) — make food using energy from chemical reactions.
- Then: anoxygenic photoautotrophs (D) — use light, release no oxygen.
- Last: oxygenic photoautotrophs (B) — release O₂ and change the atmosphere.
- Order: C, A, D, B.
- Answer
- (D) C, A, D, B
- Why not the others
A · rule out Puts oxygenic forms (B) first — impossible in an oxygen-free atmosphere. B · rule out Chemoautotrophs before heterotrophs: the first two are swapped. C · rule out D, C, B, A starts with a photosynthesiser and ends with chemoautotrophs — almost the reverse. D · keep Heterotroph first, oxygen-releaser last, with the two intermediates in between. - Shortcut
- Fix the two ends first: C must be first and B must be last. Only one option begins with C and ends with B.
- Where it went wrong
- Marked (C): D, C, B, A.
The chosen order D, C, B, A starts with a light-using form and puts the oxygen producer third. The single check 'oxygenic must be LAST' would have ruled it out instantly. This is the right-content-wrong-arrangement family: all four names are familiar, and the error is purely in the ordering.
Evidences for Evolution
Q12Attempted · wrong Planted word missed
Select the correct statement.
- The geological history of the earth closely correlates with its biological history. ✓ key
- The first non-cellular forms of life originated three billion years back on land. her answer
- Alfred Wallace asserted that evolution is driven by use and disuse of organs.
- Fitness, according to Lamarck, refers ultimately and only to reproductive fitness.
- Given
- Four statements, one correct.
- Asked
- The correct statement.
- Concept
- Each wrong option changes one word in a real NCERT fact: it gives a theory to the wrong scientist, or moves an event to the wrong place.
- Formula / rule
- one planted word (or name) per wrong option
- Baby steps
- A: 'geological history of earth closely correlates with biological history' — NCERT line → correct.
- B: first non-cellular life (3 bya) — but NCERT never says 'on land'; early life arose in water.
- C: use and disuse is Lamarck's idea, not Wallace's.
- D: 'fitness = reproductive fitness' is Darwin's idea, not Lamarck's.
- Answer
- (A) The geological history of the earth closely correlates with its biological history
- Why not the others
A · keep NCERT sentence, unchanged. B · rule out 'on land' is the planted error — early life arose in water. C · rule out Attribution error: Lamarck, not Wallace. D · rule out Attribution error: Darwin, not Lamarck. - Shortcut
- When three options carry a scientist's name, check the name first — two of them are almost always swapped attributions.
- Where it went wrong
- Marked (B): The first non-cellular forms of life originated three billion years back on land.
Option B was picked because '3 billion years' is correct, so the rest of the sentence was taken on trust. The last two words, 'on land', are the planted error. Read statements to the full stop.
Q15Attempted · wrong Assertion–reason instability
Given below are two statements: one labelled Assertion (A) and the other labelled Reason (R).
Assertion (A): All vertebrate embryos, including humans, develop a row of vestigial gill slits just behind the head.
Reason (R): Embryos pass through the adult stages of other animals during development.
Choose the correct answer.
Assertion (A): All vertebrate embryos, including humans, develop a row of vestigial gill slits just behind the head.
Reason (R): Embryos pass through the adult stages of other animals during development.
Choose the correct answer.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true but R is NOT the correct explanation of A
- A is true but R is false ✓ key
- A is false but R is true her answer
- Given
- A: all vertebrate embryos, including humans, develop a row of vestigial gill slits behind the head.
- R: embryos pass through the adult stages of other animals.
- Asked
- Truth of A and R, and the link.
- Concept
- Assertion A is Ernst Haeckel's embryological observation, which NCERT reports as a fact: the gill slits appear in all vertebrate embryos but are functional only in fish. Reason R is Haeckel's interpretation — and it is exactly what Karl Ernst von Baer disproved: embryos never pass through the adult stages of other animals.
- Three-step defence
Step Verdict One-line reason 1 · Is A true? TRUE Haeckel's gill-slit observation is in NCERT. 2 · Is R true? FALSE Von Baer: embryos never pass through adult stages of other animals. 3 · 'A because R'? NOT ASKED Only asked when both are true. - Formula / rule
- observation (true) ≠ interpretation (disproved by von Baer)
- Baby steps
- A alone: NCERT states the gill-slit observation → TRUE.
- R alone: von Baer showed embryos never pass through other animals' adult stages → FALSE.
- One statement false → the link question is not asked.
- A true, R false.
- Answer
- (C) A is true but R is false
- Why not the others
A · rule out R is false, so R cannot explain anything. B · rule out R is false, so 'both true' fails. C · keep A is the observation; R is the disproved claim. D · rule out This reverses both verdicts. - Shortcut
- In embryology questions, separate the observation (true) from Haeckel's explanation (rejected). Whenever 'pass through adult stages' appears, it is the false part.
- Where it went wrong
- Marked (D): A is false but R is true.
Both verdicts were flipped: A was called false and R true. That is the same double reversal seen in the Coordination paper (Q54). It happens when the pair is judged as one unit. Writing a separate T/F beside A and beside R before reading the options prevents it.
Q20Attempted · wrong Label swap (homologous ↔ analogous)
The wings of a bird and the wings of an insect are
- analogous structures and represent convergent evolution ✓ key
- homologous structures and represent divergent evolution her answer
- homologous structures and represent convergent evolution
- phylogenetic structures and represent divergent evolution
- Given
- Wings of a bird and wings of an insect.
- Asked
- Their type and the kind of evolution they show.
- Concept
- Homologous organs share one basic plan but do different jobs, and arise by divergent evolution. Analogous organs do the same job but are built differently, and arise by convergent evolution. A bird's wing is a modified bony forelimb; an insect's wing is a thin fold of cuticle with no bones at all. Same job (flight), different plan → analogous → convergent.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- homologous ⇔ divergent · analogous ⇔ convergent
- Baby steps
- Same function? Yes — both are used to fly.
- Same structure and origin? No — bones versus cuticle.
- Same job, different plan → analogous.
- Analogous organs arise by convergent evolution.
- Answer
- (A) analogous structures and represent convergent evolution
- Why not the others
A · keep Correct pairing of both halves. B · rule out Bird and insect wings share no common plan — not homologous. C · rule out Mismatched pair: homologous never goes with convergent. D · rule out 'Phylogenetic structures' is not an NCERT category. - Shortcut
- The two words are welded together: analogous–convergent and homologous–divergent. Any option pairing across them (like option C) is dead on sight, and you then only need to decide which pair fits.
- Where it went wrong
- Marked (B): homologous structures and represent divergent evolution.
The chosen option was 'homologous, divergent'. It is internally consistent, so the swap happened at the first step: deciding whether the two wings share a plan. They don't. Birds are vertebrates and insects are arthropods, so nothing in their wings is inherited from a common ancestor.
Q28Attempted · wrong Assertion–reason instability
Given below are two statements: one labelled Assertion (A) and the other labelled Reason (R).
Assertion (A): Resistance of microbes to antibiotics is an example of evolution by anthropogenic action.
Reason (R): Such evolution takes millions of years before it can be detected.
Choose the correct answer.
Assertion (A): Resistance of microbes to antibiotics is an example of evolution by anthropogenic action.
Reason (R): Such evolution takes millions of years before it can be detected.
Choose the correct answer.
- Both A and R are true and R is the correct explanation of A her answer
- Both A and R are true but R is NOT the correct explanation of A
- A is true but R is false ✓ key
- A is false but R is true
- Given
- A: antibiotic resistance in microbes is evolution by anthropogenic action.
- R: such evolution takes millions of years to become detectable.
- Asked
- Truth of A and R, and the link.
- Concept
- NCERT uses herbicide, pesticide and antibiotic resistance as examples of evolution driven by human action. The whole point of those examples is speed: resistant varieties appear within months or years, not over geological time.
- Three-step defence
Step Verdict One-line reason 1 · Is A true? TRUE Antibiotic resistance is NCERT's anthropogenic example. 2 · Is R true? FALSE It appears in months or years, not millions of years. 3 · 'A because R'? NOT ASKED Only asked when both are true. - Formula / rule
- anthropogenic evolution → months or years
- Baby steps
- A alone: NCERT example → TRUE.
- R alone: 'millions of years' contradicts the months-or-years point → FALSE.
- A true, R false.
- Answer
- (C) A is true but R is false
- Why not the others
A · rule out R is false. B · rule out R is false. C · keep Correct verdicts. D · rule out A is an NCERT example, so it is true. - Shortcut
- If R contains a number or timescale, check that number first — it is the most common place for the planted error.
- Where it went wrong
- Marked (A): Both A and R are true and R is the correct explanation of A.
Option A ('both true, R explains') accepted 'millions of years'. The sentence sounds like general evolution, which is slow, and that familiar idea carried R through without being checked. Judge R on its own before thinking about any link.
Adaptive Radiation and the Theories
Q30Left blank Blank — one-line recall
The ancestor of Darwin's finches was probably a
- seed eater ✓ key
- insect eater
- fruit eater
- cactus eater
- Given
- Darwin's finches of the Galapagos Islands.
- Asked
- The feeding habit of their probable ancestor.
- Concept
- NCERT describes Darwin's finches as the classic case of adaptive radiation. From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- seed eater (ancestor) → insect eaters, vegetarian finches, …
- Baby steps
- The question asks for the ancestor, not the descendants.
- NCERT: 'from the original seed-eating features'.
- Ancestor = seed eater.
- Answer
- (A) seed eater
- Why not the others
A · keep NCERT: the original features were seed-eating. B · rule out Insect eating is a derived beak type. C · rule out Not named for the ancestor. D · rule out Not in the NCERT account. - Shortcut
- Radiation diagrams always start from one plain ancestor. For the finches, that ancestor eats seeds.
Q44Attempted · wrong Multi-statement — planted clause
The theory of special creation has three connotations. Identify them.
A. All living organisms (species) that we see today were created as such.
B. The diversity was always the same since creation and will be the same in future.
C. The earth is about 4000 years old.
D. The earth is several billion years old.
Choose the correct answer from the options given below.
A. All living organisms (species) that we see today were created as such.
B. The diversity was always the same since creation and will be the same in future.
C. The earth is about 4000 years old.
D. The earth is several billion years old.
Choose the correct answer from the options given below.
- A and D only
- A, B and C only ✓ key
- A, B and D only her answer
- B, C and D only
- Given
- A. All species were created as they are today.
- B. Diversity has always been the same and will stay the same.
- C. The earth is about 4000 years old.
- D. The earth is several billion years old.
- Asked
- The three connotations of the theory of special creation.
- Concept
- Special creation has three connotations in NCERT: species were created as such; diversity has always been the same since creation and will be in future; and the earth is about 4000 years old. Statement D is the modern scientific view that challenged special creation in the nineteenth century.
- Formula / rule
- special creation: created as such · diversity fixed · earth ≈ 4000 years old
- Baby steps
- A: NCERT connotation → yes.
- B: NCERT connotation → yes.
- C: NCERT connotation (4000 years) → yes.
- D: billions of years is the opposing, modern view → no.
- Answer: A, B and C.
- Answer
- (B) A, B and C only
- Why not the others
A · rule out Drops B and C, and keeps the modern view D. B · keep All three NCERT connotations, and nothing else. C · rule out Swaps C (4000 years) for D (billions) — the opposite claim. D · rule out Drops A and keeps D. - Shortcut
- C and D contradict each other, so exactly one of them belongs. Ask: which age would a theory of recent creation claim? The young one.
- Where it went wrong
- Marked (C): A, B and D only.
Statement D was picked over C. D is scientifically true, and that is the trap: the question asks what the theory claims, not what is true. Special creation's own claim was an earth about 4000 years old.
Hardy–Weinberg and Natural Selection
Q47Attempted · wrong Hardy–Weinberg term slip
In a population in Hardy–Weinberg equilibrium, 1 in 100 individuals is affected by a recessive disorder. The frequency of carriers is
- 0.09
- 0.18 ✓ key
- 0.01
- 0.81 her answer
- Given
- Population in Hardy–Weinberg equilibrium.
- 1 in 100 individuals has the recessive disorder → q² = 0.01.
- Asked
- The frequency of carriers.
- Concept
- In a population in equilibrium, p² + 2pq + q² = 1. Affected individuals are the recessive homozygotes (q²). Carriers are heterozygotes — they carry one recessive allele but are not affected — so their frequency is 2pq.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- p² + 2pq + q² = 1 ; p + q = 1 ; carriers = 2pq
- Baby steps
- q² = 1/100 = 0.01.
- q = √0.01 = 0.1.
- p = 1 − 0.1 = 0.9.
- 2pq = 2 × 0.9 × 0.1 = 0.18.
- Answer
- (B) 0.18
- Why not the others
A · rule out 0.09 = pq — forgot the 2. B · keep 2pq, the heterozygotes. C · rule out 0.01 = q², the affected individuals. D · rule out 0.81 = p², the normal homozygotes. - Shortcut
- Write the whole row every time: p² = 0.81 · 2pq = 0.18 · q² = 0.01. Check that it adds to 1, then pick the term the question names. Carrier = heterozygote = 2pq.
- Where it went wrong
- Marked (D): 0.81.
0.81 is p², the frequency of homozygous normal individuals. Every step up to p = 0.9 was probably correct, and then the wrong term was chosen at the last step. Writing the full row with a label on each term prevents this.
Q48Attempted · wrong Hardy–Weinberg term slip
In a population, the frequencies of the alleles IA, IB and i of the ABO blood group system are p, q and r. Assuming Hardy–Weinberg equilibrium, which statement is correct?
- Frequency of blood group A individuals is p²
- Frequency of blood group B individuals is p² + q² her answer
- Frequency of blood group O individuals is r² ✓ key
- Frequency of blood group AB individuals is pq
- Given
- Alleles Iᴬ, Iᴮ, i with frequencies p, q, r.
- Population in equilibrium: (p + q + r)² = 1.
- Asked
- Which blood-group frequency is correct.
- Concept
- Expand (p + q + r)² and group the terms by phenotype. Iᴬ and Iᴮ are both dominant over i, so groups A and B each include a heterozygote with i. Only group O is a single genotype (ii).
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- A = p² + 2pr · B = q² + 2qr · AB = 2pq · O = r²
- Baby steps
- O needs two i alleles → r².
- A = IᴬIᴬ + Iᴬi = p² + 2pr (not just p²).
- B = IᴮIᴮ + Iᴮi = q² + 2qr (p never appears in B).
- AB = 2pq (the 2 is required).
- Answer
- (C) Frequency of blood group O individuals is r²
- Why not the others
A · rule out Misses the Iᴬi heterozygotes (2pr). B · rule out p² belongs to group A; group B is q² + 2qr. C · keep ii is the only O genotype → r². D · rule out AB is 2pq — the factor 2 is missing. - Shortcut
- Only one group has a single genotype, so only one frequency can be a plain square: O = r². Choose that option without expanding anything.
- Where it went wrong
- Marked (B): Frequency of blood group B individuals is p² + q².
'B = p² + q²' mixes two homozygote terms from different groups. The expansion was probably not written out at all. A 3 × 3 grid of p, q, r (below) takes twenty seconds and makes every group visible.
Q53Attempted · wrong Right content, wrong arrangement
In each graph below, the dashed curve shows the population before selection and the solid curve shows it after selection.Match List-I with List-II.
Choose the correct answer.
| List-I | List-II | ||
|---|---|---|---|
| A | Stabilising selection | I | Graph I |
| B | Directional selection increasing the mean phenotype | II | Graph II |
| C | Directional selection decreasing the mean phenotype | III | Graph III |
| D | Disruptive selection | IV | Graph IV |
- A–II, B–I, C–IV, D–III ✓ key
- A–II, B–IV, C–I, D–III her answer
- A–IV, B–II, C–III, D–I
- A–III, B–I, C–IV, D–II
- Given
- Four graphs: dashed = before selection, solid = after.
- I: peak shifted right. II: peak narrower, same mean. III: two peaks. IV: peak shifted left.
- Asked
- Match each type of selection to its graph.
- Concept
- Read only the solid peak. Narrower and taller at the same mean → stabilising. Moved to one side → directional; the side tells you whether the mean increased (right) or decreased (left). Split into two peaks → disruptive.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- stabilising: narrow · directional: shifted · disruptive: split
- Baby steps
- A (stabilising) → II.
- B (directional, mean increases) → peak moves RIGHT → I.
- C (directional, mean decreases) → peak moves LEFT → IV.
- D (disruptive) → III.
- A–II, B–I, C–IV, D–III.
- Answer
- (A) A–II, B–I, C–IV, D–III
- Why not the others
A · keep Every row matches its graph. B · rule out B and C swapped — increase and decrease reversed. C · rule out A given the left shift; stabilising misplaced. D · rule out A given the two-peak graph (that is disruptive). - Shortcut
- A and D are fixed by shape alone (narrow; split). That leaves only the two directional graphs. 'Increase' means the peak moves towards larger values — to the right.
- Where it went wrong
- Marked (B): A–II, B–IV, C–I, D–III.
Rows A and D were right; B and C were swapped. This is a direction reversal inside a match question: the right-shifted and left-shifted graphs were exchanged. Note the swap was in the middle rows this time, not the usual C/D pair — so check every row, not just the last two.
Q54Attempted · wrong Definition swap
Which type of natural selection takes place when more individuals acquire peripheral character values at both ends of the distribution curve?
- Stabilising selection her answer
- Centripetal selection
- Directional selection
- Disruptive selection ✓ key
- Given
- More individuals acquire peripheral (extreme) character values at both ends of the distribution.
- Asked
- The type of selection.
- Concept
- NCERT's three definitions differ in where the individuals end up: at the mean (stabilising), at one side (directional), or at both ends (disruptive). 'Centripetal' is another name for stabilising selection.
- Formula / rule
- mean → stabilising · one side → directional · both ends → disruptive
- Baby steps
- The key phrase is 'both ends of the distribution curve'.
- Both ends → the curve splits into two peaks.
- That is disruptive selection.
- Answer
- (D) Disruptive selection
- Why not the others
A · rule out Stabilising favours the mean — the opposite of both ends. B · rule out Centripetal is stabilising under another name. C · rule out Directional favours one end, not both. D · keep Both ends → disruptive. - Shortcut
- 'Disrupt' = break apart. Both ends pulling away from the middle breaks the curve in two.
- Where it went wrong
- Marked (A): Stabilising selection.
Stabilising was chosen: the opposite definition. Stabilising and disruptive are exact mirror images (middle vs both ends), and under time pressure they get swapped. One anchor word each fixes it: stabilising = middle, disruptive = both ends.
Q55Left blank Blank — application of a definition
In a bird population with short, medium and long wings, short wings hinder flight and long wings reduce manoeuvrability. Which type of selection is most likely to operate, and which birds survive best?
- Directional selection; short-winged birds
- Stabilising selection; medium-winged birds ✓ key
- Disruptive selection; both short- and long-winged birds
- Directional selection; long-winged birds
- Given
- Short wings hinder flight.
- Long wings reduce manoeuvrability.
- Medium wings suffer neither problem.
- Asked
- Which selection operates, and which birds survive best.
- Concept
- Selection acts against both extremes here, so the individuals with the average value leave the most offspring. The peak narrows around the mean: stabilising selection.
- Formula / rule
- both extremes disadvantaged → stabilising → mean favoured
- Baby steps
- Short: disadvantaged. Long: disadvantaged.
- Medium: not disadvantaged → favoured.
- Favouring the mean = stabilising selection.
- Survivors: medium-winged birds.
- Answer
- (B) Stabilising selection; medium-winged birds
- Why not the others
A · rule out Directional would favour one end, but short wings are harmful. B · keep Both extremes lose, the mean wins. C · rule out Disruptive would favour the two extremes — the harmed groups. D · rule out Long wings are also harmful here. - Shortcut
- Ask which group has no disadvantage. If it is the middle group, the answer is stabilising.
A Brief Account of Evolution
Q61Left blank Blank — word order in a description
Choose the correct features of Ichthyosaurus.
a. Reptile-like fishes
b. Fish-like reptiles
c. Extinct
d. Extant
e. Aquatic
f. Terrestrial
Choose the correct answer from the options given below.
a. Reptile-like fishes
b. Fish-like reptiles
c. Extinct
d. Extant
e. Aquatic
f. Terrestrial
Choose the correct answer from the options given below.
- b, c and e ✓ key
- b, d and e
- a, d and f
- a, c and e
- Given
- Six descriptions: reptile-like fishes, fish-like reptiles, extinct, extant, aquatic, terrestrial.
- Asked
- The correct features of Ichthyosaurus.
- Concept
- NCERT: about 200 mya, some land reptiles went back into water and evolved into fish-like reptiles such as Ichthyosaurs. They were reptiles that took on a fish-like body — so they are reptiles, they lived in water, and like the other great reptiles of that era they are now extinct.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- Ichthyosaur = reptile (noun) + fish-like (adjective) + aquatic + extinct
- Baby steps
- The animal is a reptile → 'fish-like reptile' (b), not 'reptile-like fish' (a).
- It lived in water → aquatic (e).
- It no longer exists → extinct (c).
- b, c and e.
- Answer
- (A) b, c and e
- Why not the others
A · keep All three correct features. B · rule out 'Extant' means still living — Ichthyosaurs are extinct. C · rule out Wrong on all three: fish, living, terrestrial. D · rule out 'Reptile-like fish' makes it a fish. - Shortcut
- In 'X-like Y', the last word is what the animal is. Ichthyosaurus is a reptile, so pick the phrase ending in 'reptile'.
Q63Attempted · wrong Assertion–reason instability
Given below are two statements: one labelled Assertion (A) and the other labelled Reason (R).
Assertion (A): Reptiles could live on land independent of water for breeding, unlike amphibians.
Reason (R): Reptiles lay thick-shelled eggs which do not dry up in the sun.
Choose the correct answer.
Assertion (A): Reptiles could live on land independent of water for breeding, unlike amphibians.
Reason (R): Reptiles lay thick-shelled eggs which do not dry up in the sun.
Choose the correct answer.
- Both A and R are true and R is the correct explanation of A ✓ key
- Both A and R are true but R is NOT the correct explanation of A her answer
- A is true but R is false
- A is false but R is true
- Given
- A: reptiles could live on land independent of water for breeding, unlike amphibians.
- R: reptiles lay thick-shelled eggs which do not dry up in the sun.
- Asked
- Truth of A and R, and the link.
- Concept
- Amphibians must return to water to lay their eggs, because those eggs dry out on land. NCERT says reptiles lay thick-shelled eggs which do not dry up in the sun, unlike those of amphibians. The shelled egg is precisely what freed reptiles from water for breeding.
- Three-step defence
Step Verdict One-line reason 1 · Is A true? TRUE Reptiles breed on land; amphibians return to water. 2 · Is R true? TRUE Thick-shelled eggs do not dry up in the sun. 3 · 'A because R'? READS RIGHT R is the mechanism behind A. - Formula / rule
- shelled egg ⇒ no need for water to breed
- Baby steps
- A alone → TRUE.
- R alone → TRUE (NCERT line).
- 'Reptiles could breed away from water BECAUSE their eggs do not dry up' → reads as the actual mechanism.
- Both true, R explains A.
- Answer
- (A) Both A and R are true and R is the correct explanation of A
- Why not the others
A · keep R is the mechanism behind A. B · rule out Denies a link that is real. C · rule out R is an NCERT line, so it is true. D · rule out A is true. - Shortcut
- Use the 'because' test aloud: 'A, because R.' If the sentence states the real cause, pick option A. If it sounds like two unrelated facts, pick option B.
- Where it went wrong
- Marked (B): Both A and R are true but R is NOT the correct explanation of A.
Option B ('not the explanation') denied a real link. This is the same error as Q80 on the Coordination paper and the HHD pair about the placenta. When the reason is the mechanism, the link must be accepted.
Q66Attempted · wrong Assertion–reason instability
Given below are two statements: one labelled Assertion (A) and the other labelled Reason (R).
Assertion (A): Continental drift protected the pouched mammals of Australia.
Reason (R): Placental mammals could not survive in Australia due to lack of competition with marsupials.
Choose the correct answer.
Assertion (A): Continental drift protected the pouched mammals of Australia.
Reason (R): Placental mammals could not survive in Australia due to lack of competition with marsupials.
Choose the correct answer.
- Both A and R are true and R is the correct explanation of A her answer
- Both A and R are true but R is NOT the correct explanation of A
- A is true but R is false ✓ key
- A is false but R is true
- Given
- A: continental drift protected the pouched mammals of Australia.
- R: placental mammals could not survive in Australia due to lack of competition with marsupials.
- Asked
- Truth of A and R, and the link.
- Concept
- NCERT: due to continental drift, the pouched mammals of Australia survived because of lack of competition from any other mammal. It is the marsupials that were spared competition. R turns this round and makes the placentals the ones lacking competition — and 'lack of competition' would help survival, not prevent it, so R is doubly wrong.
- Diagram
- Animated · the still frame carries the full message.
- Three-step defence
Step Verdict One-line reason 1 · Is A true? TRUE Isolation by drift protected Australian marsupials. 2 · Is R true? FALSE It was the marsupials that lacked competition, not the placentals. 3 · 'A because R'? NOT ASKED Only asked when both are true. - Formula / rule
- Australia isolated → marsupials faced no competition → marsupials survived
- Baby steps
- A alone → TRUE (NCERT idea).
- R alone: who lacked competition? The marsupials, not the placentals → FALSE.
- A true, R false.
- Answer
- (C) A is true but R is false
- Why not the others
A · rule out R is false. B · rule out R is false. C · keep Correct verdicts. D · rule out A is true. - Shortcut
- Ask 'who lacked competition?' and check that R names the right group. Lack of competition helps survival, so 'could not survive due to lack of competition' is self-contradictory.
- Where it went wrong
- Marked (A): Both A and R are true and R is the correct explanation of A.
Option A accepted R because its vocabulary — Australia, marsupials, competition — is all familiar. The roles inside it are reversed. Read R for WHO does WHAT, not for familiar words.
Origin and Evolution of Man
Q72Attempted · wrong Right content, wrong arrangement
The chronological order of human evolution from early to recent is
- Ramapithecus → Homo habilis → Australopithecus → Homo erectus
- Australopithecus → Homo habilis → Ramapithecus → Homo erectus
- Australopithecus → Ramapithecus → Homo habilis → Homo erectus her answer
- Ramapithecus → Australopithecus → Homo habilis → Homo erectus ✓ key
- Given
- Ramapithecus, Australopithecus, Homo habilis, Homo erectus.
- Asked
- Chronological order, early to recent.
- Concept
- NCERT dates: Dryopithecus and Ramapithecus about 15 mya; Australopithecines about 2 mya; then Homo habilis, the first human-like being; then Homo erectus about 1.5 mya.
- Diagram
- Animated · the still frame carries the full message.
- Formula / rule
- 15 mya → 2 mya → habilis → 1.5 mya
- Baby steps
- Ramapithecus ~15 mya — by far the oldest.
- Australopithecus ~2 mya.
- Homo habilis follows.
- Homo erectus ~1.5 mya.
- Ramapithecus → Australopithecus → H. habilis → H. erectus.
- Answer
- (D) Ramapithecus → Australopithecus → Homo habilis → Homo erectus
- Why not the others
A · rule out H. habilis placed before Australopithecus — middle pair swapped. B · rule out Ramapithecus placed third — 13 million years out of place. C · rule out First two swapped. D · keep Matches the NCERT dates. - Shortcut
- Write the date beside each name before reading the options: Rama 15, Austr 2, habilis, erectus 1.5. The order follows the numbers.
- Where it went wrong
- Marked (C): Australopithecus → Ramapithecus → Homo habilis → Homo erectus.
The chosen order starts with Australopithecus, swapping the first two. Both are 'pithecus' names, which makes them easy to exchange. The dates are 13 million years apart, so writing them down removes the confusion completely.
What to carry into the next paper
| Habit | Would have saved |
|---|---|
| Write T/F for A and for R, with a reason, before reading the options; then test 'A because R' aloud. | Q15, Q28, Q63, Q66 — 20 marks |
| For any sequence, fix the two ends first or write a date/shape beside every item. | Q11, Q53, Q72 — 15 marks |
| Write the full Hardy–Weinberg row (or the p/q/r grid) with labels before choosing a term. | Q47, Q48 — 10 marks |
| Selection anchors: middle / one side / both ends. Ask which group has no disadvantage. | Q54, Q55 — 9 marks |
| Read statements to the full stop; underline the swappable word; if none, it is true. | Q3, Q12, Q20, Q44 — 20 marks |