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NEET (UG) · revision cheat sheet · neetlogic.in

Zoology

15 chapters · 42 topics · ~180 marks · 29 solved previous-year questions

Class 11

1. Animal Kingdom

Basis of classification: NEET tests the coelom hierarchy by its exceptions: acoelomates (Platyhelminthes) have no body cavity at all, pseudocoelomates (Aschelminthes) have one not lined by mesoderm, and among true coelomates, protostomes (mouth develops from the blastopore) are separated from deuterostomes (anus develops from the blastopore, mouth forms later) by that one embryonic detail alone.
Non-chordates: Porifera to Echinodermata: The exception NEET checks most across these nine phyla is Echinodermata: its adults are radially symmetrical even though its larvae are bilaterally symmetrical, and it is the one phylum with no excretory system at all, relying instead on its unique water-vascular system for locomotion.
Chordates: Pisces to Mammalia: Chondrichthyes (sharks, rays) have neither an operculum nor an air bladder, unlike bony fish, so they must swim continuously to avoid sinking; higher up the tree, reptiles and birds have a single occipital condyle where mammals have two, a numeric detail NEET likes to hide inside an option.

While trying to find out the characteristics of a newly found animal, a researcher did the histology of the adult animal and observed a cavity with the presence of mesodermal tissue towards the body wall, but no mesodermal tissue was observed towards the alimentary canal. What could be the possible coelom of that animal?

Ans: Pseudocoelomate·Mesoderm lining the body wall but not the gut marks a false coelom — a pseudocoelomate, as in Aschelminthes. A true coelom has mesoderm on both sides.

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Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): All vertebrates are chordates but all chordates are not vertebrates. Reason (R): The members of subphylum Vertebrata possess a notochord during the embryonic period; the notochord is replaced by a cartilaginous or bony vertebral column in adults. In the light of the above statements, choose the correct answer from the options given below:

Ans: Both (A) and (R) are true and (R) is the correct explanation of (A)·Vertebrata is a subphylum of Chordata, so every vertebrate is a chordate but tunicates and cephalochordates are chordates that never form a vertebral column (A true). Vertebrates keep the notochord only as embryos, replacing it with a vertebral column (R true), which is exactly what separates them from the other chordates.

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2. Structural Organisation in Animals

Animal tissues: The classic trap is cardiac muscle: it is striated exactly like skeletal muscle, but involuntary, which breaks the shortcut that striated automatically means voluntary. NEET separately swaps tendon (connects muscle to bone) with ligament (connects bone to bone) as the other easily-confused pair in this tissue list.
Frog: morphology and anatomy: A frog breathes through three different surfaces depending on where it is — lungs in air, moist skin (cutaneous respiration) while submerged or hibernating, and the buccal lining — but fertilisation stays external, in water, which is what NEET checks against the male's nuptial pad and vocal sac (mate-attracting features, not internal-fertilisation ones).

Frogs respire in water by the skin and buccal cavity, and on land by the skin, buccal cavity and lungs. Choose the correct answer from the following:

Ans: The statement is false for water but true for land·In water the frog breathes only through its skin (cutaneous respiration); on land it uses the skin, the buccal cavity and the lungs. So the statement is false for water but true for land.

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In the frog, the renal portal system is a special venous connection that acts to link:

Ans: Kidney and lower part of the body·The frog's renal portal system carries venous blood from the hind limbs and lower body to the kidneys before it returns to the heart.

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3. Biomolecules

Carbohydrates, lipids, amino acids and proteins: NEET's favourite trap here is two different "most abundant" claims: protein is the most abundant biomolecule inside a living cell, but cellulose, a structural polysaccharide, is the most abundant organic compound in the entire biosphere — mixing up "in a cell" with "in nature" is exactly how this gets tested.
Nucleic acids: The base-pairing fact NEET checks most is the hydrogen-bond count: A pairs with T (U in RNA) through two hydrogen bonds, G pairs with C through three — the extra bond is why GC-rich DNA is harder to melt, and swapping the two numbers is the standard wrong option.
Enzymes: mechanism, factors, classification: Enzyme pH optima are not universal: pepsin works best in the stomach's strongly acidic pH while trypsin needs the small intestine's alkaline pH, so "neutral is optimal" is the wrong default to bring to a question naming a specific enzyme. Separately, a competitive inhibitor such as malonate on succinic dehydrogenase can be out-competed by raising substrate concentration; a non-competitive one, which doesn't bind the active site, cannot.

Match List I with List II.

List I	List II
A. Adenosine	I. Nitrogen base
B. Adenylic acid	II. Nucleotide
C. Adenine	III. Nucleoside
D. Alanine	IV. Amino acid

Choose the option with all correct matches:

Ans: A-III, B-II, C-I, D-IV·Adenosine is a nucleoside (III), adenylic acid a nucleotide (II), adenine a nitrogen base (I) and alanine an amino acid (IV).

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Which one of the following enzymes contains 'haem' as the prosthetic group?

Ans: Catalase·Catalase contains haem as its prosthetic group. Carbonic anhydrase and carboxypeptidase use zinc; RuBisCO needs

M g^{2 +}

; succinate dehydrogenase uses FAD.

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4. Breathing and Exchange of Gases

Respiratory organs and mechanism of breathing: Quiet breathing is not two mirrored active steps: inspiration is active (the diaphragm contracts and flattens, intercostals lift the ribs, thoracic volume rises), but normal expiration is passive, driven by elastic recoil once those muscles relax. Only forced expiration calls in the internal intercostals and abdominal muscles — the detail NEET's active-or-passive options hinge on.
Exchange and transport of gases: The percentages NEET likes to swap: of the CO2 carried in blood, about 70% travels as bicarbonate and only 20-25% as carbaminohaemoglobin, the reverse of how most students remember it. For O2, the Bohr effect — more CO2, more H+, lower pH, higher temperature in the tissues — shifts the dissociation curve right, making haemoglobin release more oxygen exactly where it's needed.
Regulation and disorders: Breathing rate is regulated mainly by CO2 and H+ levels sensed by the medulla's chemosensitive area, not by how much O2 is available — the opposite of the intuitive "we breathe because we need oxygen." Among disorders, emphysema is alveolar-wall damage that shrinks the gas-exchange surface (usually from chronic smoking), while asthma is inflammation of the bronchi and bronchioles causing wheezing, not alveolar damage.

Match List I with List II.

List I	List II
A. Emphysema	I. Rapid spasms in muscle due to low $C a^{++}$ in body fluid
B. Angina pectoris	II. Damaged alveolar walls and decreased respiratory surface
C. Glomerulonephritis	III. Acute chest pain when not enough oxygen is reaching the heart muscle
D. Tetany	IV. Inflammation of the glomeruli of the kidney

Choose the correct answer from the options given below:

Ans: A-II, B-III, C-IV, D-I·Emphysema: damaged alveolar walls and reduced respiratory surface (II). Angina pectoris: acute chest pain from an under-supplied heart muscle (III). Glomerulonephritis: inflammation of the glomeruli (IV). Tetany: rapid muscle spasms from low

C a^{2 +}

(I).

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Which of the following factors are favourable for the formation of oxyhaemoglobin in the alveoli?

Ans: High

p O_{2}

and lesser

H^{+}

concentration·In the alveoli, high

p O_{2}

, low

p C O_{2}

, lower

H^{+}

concentration and lower temperature all favour binding of oxygen to haemoglobin.

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5. Body Fluids and Circulation

Blood, blood groups and lymph: Rh incompatibility is a second-pregnancy problem, not a first one: an Rh-negative mother is not sensitised until her first Rh-positive baby's blood mixes with hers at delivery, so it is the second Rh-positive pregnancy onward that risks erythroblastosis foetalis, once anti-Rh antibodies already exist to cross the placenta — a timing detail NEET tests directly.
Human heart, cardiac cycle and ECG: The SA node generates about 70-75 impulses a minute on its own, faster than any other part of the conduction system, which is exactly why it — not the AV node — is the pacemaker that sets heart rate. On an ECG, the P wave is atrial depolarisation and the T wave is ventricular repolarisation, but atrial repolarisation never gets a wave of its own because it is buried inside the much larger QRS complex.
Double circulation and disorders: Double circulation exists because a four-chambered heart keeps oxygenated and deoxygenated blood from mixing — blood crosses the heart twice per cycle, once via the pulmonary route and once via the systemic route. NEET's disorder questions hinge on the exact numbers: normal blood pressure is around 120/80 mmHg, and a sustained reading at or above 140/90 mmHg marks hypertension.

Cardiac activities of the heart are regulated by: A. Nodal tissue B. A special neural centre in the medulla oblongata C. Adrenal medullary hormones D. Adrenal cortical hormones Choose the correct answer from the options given below:

Ans: A, B and C only·The heart is myogenic — its rhythm comes from nodal tissue (A) — but is modulated by a neural centre in the medulla through the autonomic system (B) and by adrenaline and noradrenaline from the adrenal medulla (C). Adrenal cortical hormones do not regulate cardiac activity.

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Following are the stages of the pathway for conduction of an action potential through the heart: A. AV bundle · B. Purkinje fibres · C. AV node · D. Bundle branches · E. SA node Choose the correct sequence of the pathway from the options given below:

Ans: E-C-A-D-B·The impulse starts at the SA node, reaches the AV node, passes down the AV bundle, splits into the bundle branches and spreads through the Purkinje fibres: E, C, A, D, B.

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6. Excretory Products and their Elimination

Human excretory system and nephron: Not all nephrons are equal: about 85% are cortical nephrons with short loops of Henle, but the remaining 15%, the juxtamedullary ones, have loops that dive deep into the medulla — and it is specifically those long loops that build the gradient letting humans excrete hypertonic urine, a proportion-and-function pairing NEET tests together.
Urine formation and its regulation: The huge gap between GFR (about 125 mL/minute, 180 L/day filtered) and actual urine output (1-1.5 L/day) exists because roughly 99% of the filtrate is reabsorbed — most of it "obligatory" reabsorption in the PCT that happens regardless of hydration, while the small remainder in the DCT and collecting duct is "facultative," switched on by ADH only when the body needs to conserve water.
Disorders and dialysis: Haemodialysis works by diffusion down a gradient, not filtration under pressure: the dialysing fluid is deliberately kept similar to normal blood plasma but without nitrogenous wastes, so urea and other wastes diffuse out while useful ions and glucose are left largely undisturbed — the fluid's exact composition, not just "it removes urea," is what NEET options probe.

Choose the correct statement regarding the juxtamedullary nephron:

Ans: The loop of Henle of a juxtamedullary nephron runs deep into the medulla.·Juxtamedullary nephrons have their renal corpuscles close to the cortex–medulla junction and long loops of Henle that run deep into the medulla, which lets them concentrate urine. Cortical nephrons are far more numerous.

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Given below are two statements: Statement I: In the nephron, the descending limb of the loop of Henle is impermeable to water and permeable to electrolytes. Statement II: The proximal convoluted tubule is lined by simple columnar brush-border epithelium and increases the surface area for reabsorption. In the light of the above statements, choose the correct answer from the options given below:

Ans: Both Statement I and Statement II are false·The descending limb of the loop of Henle is permeable to water but nearly impermeable to electrolytes — the reverse of Statement I. The PCT is lined by simple cuboidal brush-border epithelium, not columnar — Statement II is also false.

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7. Locomotion and Movement

Skeletal muscle and mechanism of contraction: The sliding filament model's classic trap is which band changes: during contraction the A band (myosin's length) stays constant while the I band and H zone shrink as actin slides inward — the filaments don't shorten, the sarcomere does. ATP is needed not just for the power stroke but to detach the myosin head from actin afterward, which is why its absence after death causes rigor mortis.
Skeletal system and joints: The skeleton's numbers are exact and tested as-is: 206 bones total, split into 80 in the axial skeleton (skull, vertebral column, ribs, sternum) and 126 in the appendicular skeleton (limbs and girdles). Among joints, NEET likes naming the less obvious synovial types by example — the saddle joint between the thumb's carpal and metacarpal, not just the familiar hinge and ball-and-socket.
Disorders: The muscular-disorder pair NEET likes to swap is myasthenia gravis (autoimmune — antibodies attack acetylcholine receptors at the neuromuscular junction, causing fatigue) against muscular dystrophy (genetic, progressive degeneration of skeletal muscle, no immune component at all). Tetany is a different mechanism again — spasms from low blood Ca2+, not muscle wasting.

Match List I with List II.

List I	List II
A. Fibrous joints	I. Adjacent vertebrae, limited movement
B. Cartilaginous joints	II. Humerus and pectoral girdle, rotational movement
C. Hinge joints	III. Skull, don't allow any movement
D. Ball and socket joints	IV. Knee, help in locomotion

Choose the correct answer from the options given below:

Ans: A-III, B-I, C-IV, D-II·Fibrous joints in the skull allow no movement (III); cartilaginous joints between vertebrae allow limited movement (I); the knee is a hinge joint (IV); the shoulder (humerus–pectoral girdle) is a ball-and-socket joint allowing rotation (II).

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8. Neural Control and Coordination

Neuron, nerve impulse and synapse: Chemical synapses transmit in one direction only, since neurotransmitter is released solely from pre-synaptic vesicles and received solely by post-synaptic receptors, while the much rarer electrical synapse allows current to pass either way. The resting potential itself (about -70 mV, inside negative) is maintained by the Na+-K+ pump moving 3 Na+ out for every 2 K+ in, a ratio that's easy to invert in an option.
Central nervous system: NEET separates "initiates movement" from "coordinates movement": the cerebrum's motor areas initiate voluntary movement, so damage there causes paralysis, while the cerebellum only fine-tunes posture, balance and precision, so damage to it produces jerky, uncoordinated movement, not paralysis — the give-away in assertion-reason questions on this topic.
Reflex action: The specific trap is timing: a spinal reflex arc completes its receptor-to-effector loop through the spinal cord alone, so the hand is already withdrawn before the pain signal has finished travelling up to the brain for conscious perception. The sensation of pain is felt after the reflex action, not before or during it — exactly the sequence NEET's reflex-arc questions check.

Given below are two statements: Statement I: The cerebral hemispheres are connected by a nerve tract known as the corpus callosum. Statement II: The brain stem consists of the medulla oblongata, pons and cerebrum. In the light of the above statements, choose the most appropriate answer from the options given below:

Ans: Statement I is correct but Statement II is incorrect.·The corpus callosum is the tract joining the two cerebral hemispheres (Statement I true). The brain stem is the midbrain, pons and medulla — not the cerebrum — so Statement II is false.

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Match List I with List II.

List I	List II
A. Pons	I. Provides additional space for neurons, regulates posture and balance
B. Hypothalamus	II. Controls respiration and gastric secretions
C. Medulla	III. Connects different regions of the brain
D. Cerebellum	IV. Neurosecretory cells

Choose the correct answer from the options given below:

Ans: A-III, B-IV, C-II, D-I·The pons connects different regions of the brain (III); the hypothalamus carries neurosecretory cells (IV); the medulla controls respiration and gastric secretions (II); the cerebellum regulates posture and balance (I).

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9. Chemical Coordination and Integration

Endocrine glands and their hormones: The posterior pituitary does not make the hormones it releases: oxytocin and ADH are synthesised by the hypothalamus and only stored and released from the posterior lobe, while the anterior pituitary genuinely synthesises its own hormones (GH, TSH, ACTH, FSH, LH, prolactin). A second pairing worth keeping straight: PTH raises blood Ca2+ while calcitonin, from the thyroid, lowers it — opposite jobs on the same ion, from different glands.
Mechanism of hormone action: Where a hormone acts depends on its chemistry: lipophilic steroid and thyroid hormones cross the plasma membrane and bind intracellular or nuclear receptors, directly switching gene transcription on or off, while water-soluble peptide hormones cannot cross the membrane and instead bind surface receptors, triggering a second-messenger cascade such as cAMP inside the cell — NEET options often assign the wrong mechanism to the wrong hormone class.
Disorders: The same underlying problem, hypothyroidism, gets two different names depending on when it strikes: cretinism if present from childhood (stunted growth, mental retardation), myxoedema if it develops in an adult (low metabolic rate, puffiness) — a naming-by-age distinction NEET tests directly rather than asking about the hormone deficiency in the abstract.

Which of the following hormones released from the pituitary is actually synthesised in the hypothalamus?

Ans: Anti-diuretic hormone (ADH)·ADH (vasopressin) and oxytocin are synthesised by hypothalamic neurons and only stored and released by the posterior pituitary. LH, FSH and ACTH are made in the anterior pituitary itself.

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Consider the following statements regarding the functions of adrenal medullary hormones: (A) They cause pupillary constriction. (B) They are hyperglycaemic hormones. (C) They cause piloerection. (D) They increase the strength of heart contraction. Choose the correct answer from the options given below:

Ans: B, C and D only·Adrenaline and noradrenaline raise blood glucose (B), cause piloerection (C) and increase the force of heart contraction (D). They dilate the pupils, so A is wrong. Hence B, C and D.

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Class 12

10. Human Reproduction

Male and female reproductive systems: The testis packs two different jobs into two different cell types: Sertoli cells, inside the seminiferous tubules, nurse the developing sperm, while Leydig (interstitial) cells, in the spaces between tubules, secrete testosterone. On the female side, fertilisation normally happens in the ampulla of the fallopian tube, not the uterus itself — NEET regularly offers the isthmus or the uterus as decoy locations.
Gametogenesis and menstrual cycle: FSH acts on Sertoli cells to drive spermatogenesis, which then release inhibin as feedback to lower FSH; LH — called ICSH in males — acts on Leydig cells to trigger testosterone synthesis. In the menstrual cycle it is specifically the LH surge around day 14 that triggers ovulation, not the rising FSH that matured the follicle beforehand — a sequencing swap NEET tests directly.
Fertilisation, implantation, pregnancy, parturition, lactation: Early pregnancy runs on hCG: it is what keeps the corpus luteum from degenerating, and it is what a pregnancy test actually detects, buying time until the placenta itself takes over progesterone production later on. Parturition is one of the syllabus's rare genuine positive-feedback loops — signals from the fully developed foetus trigger mild contractions, which release oxytocin, which strengthens contractions further — the opposite of the negative feedback most hormone regulation in this chapter runs on.

Match List I with List II.

List I	List II
A. Head	I. Enzymes
B. Middle piece	II. Sperm motility
C. Acrosome	III. Energy
D. Tail	IV. Genetic material

Choose the correct answer from the options given below:

Ans: A-IV, B-III, C-I, D-II·The sperm head carries the genetic material in its nucleus (IV); the middle piece has mitochondria that supply energy (III); the acrosome holds enzymes for penetrating the egg (I); the tail gives motility (II).

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Twins are born to a family that lives next door to you. The twins are a boy and a girl. Which of the following must be true?

Ans: They are fraternal twins.·Twins of different sexes must have come from two separate zygotes — they are dizygotic (fraternal) twins, genetically no more alike than ordinary siblings.

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11. Reproductive Health

Population and birth control methods: Among all these methods, only barrier methods (condoms, diaphragms) double as protection against sexually transmitted infections — IUDs and hormonal pills prevent pregnancy but offer no protection against infection, which is the distinction NEET's "which method also prevents STDs" questions are built around. Oral contraceptive pills themselves work mainly by inhibiting ovulation, through their effect on the pituitary's FSH-LH balance.
MTP, STDs and infertility; ART: NCERT is specific that most STDs are curable if caught early — hepatitis-B, genital herpes and HIV are the three named exceptions, which is how NEET phrases a "which of these is NOT curable" question. In ART, embryos up to the 8-celled stage are transferred into the fallopian tube (ZIFT); only later embryos, past 8 cells, go into the uterus (IUT) — the cell-count cutoff, not just the destination, is what these questions check.

What are the potential drawbacks in the adoption of the IVF method? A. High fatality risk to the mother B. Expensive instruments and reagents C. Husband/wife necessary for being donors D. Less adoption of orphans E. Not available in India F. Possibility that the early embryo does not survive Choose the correct answer from the options given below:

Ans: B, D, F only·IVF is expensive (B), needs sophisticated instruments, may reduce the adoption of orphans (D), and the early embryo transferred may fail to survive (F). It carries no high fatality risk to the mother, the gametes need not come from husband and wife, and it is available in India. Hence B, D and F.

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Which of the following is not a natural/traditional contraceptive method?

Ans: Vaults·Periodic abstinence, lactational amenorrhea and coitus interruptus are natural methods. Vaults are barrier devices placed over the cervix.

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12. Evolution

Origin of life and evidences of evolution: Miller and Urey's experiment specifically used a reducing atmosphere (CH4, NH3, H2, water vapour, no free O2) with an electric spark to generate amino acids — swap in an oxidising atmosphere and the option is wrong regardless of the rest of the setup. For evidence of evolution, the sharpest example pair is potato (a stem tuber) and sweet potato (a root tuber): same function, different origin, so they are analogous, not homologous.
Natural selection, Hardy–Weinberg, adaptive radiation: Adaptive radiation and convergent evolution get confused because NCERT covers them back to back: adaptive radiation is one ancestor diversifying into many forms in one place (Darwin's finches on the Galapagos), while convergent evolution is unrelated lineages converging on the same form under similar pressures in different places (the Australian marsupial wolf and the placental wolf). Hardy-Weinberg gets tested both as a calculation (given a recessive disorder's frequency, find the carrier frequency) and as a concept check on what disturbs the equilibrium — mutation, migration, drift, selection — so both are worth preparing.
Human evolution: Human evolution questions mostly come down to keeping the sequence and the brain-size numbers straight: Homo habilis (650-800 cc) was the first true tool user, Homo erectus (about 900 cc) hunted and definitely ate meat, and Neanderthal man (about 1400 cc) buried the dead and used hides — Neanderthal's brain size, close to modern humans' 1450 cc, is the number NEET most often tests students into underestimating.

Sweet potato and potato represent a certain type of evolution. Select the correct combination of terms to explain the evolution.

Ans: Analogy, convergent·Sweet potato (a root) and potato (a stem) look alike and store food but have different origins — analogous structures produced by convergent evolution.

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Given below are some stages of human evolution. Arrange them in the correct sequence (past to recent): A. Homo habilis · B. Homo sapiens · C. Homo neanderthalensis · D. Homo erectus Choose the correct sequence of human evolution from the options given below:

Ans: A-D-C-B·Chronological order: Homo habilis (~2 mya) → Homo erectus (~1.5 mya) → Neanderthal man (~100,000 years ago) → Homo sapiens. So A-D-C-B.

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13. Human Health and Disease

Common diseases: pathogens and life cycles: By parasitology's own definition, the mosquito, not the human, is Plasmodium's definitive host, because the sexual stage of the parasite's life cycle happens inside the mosquito; the human is only the intermediate host, where the asexual cycle runs. The recurring chills and high fever are timed to the synchronised rupture of infected RBCs releasing merozoites and toxic haemozoin — which is also why the fever's periodicity tracks the parasite's own reproductive cycle inside blood cells.
Immunity, vaccination, AIDS, cancer: Active immunity (from infection or vaccination) is slow to build but leaves lasting memory cells; passive immunity, like the antibodies a newborn gets through colostrum, acts immediately but fades, because the recipient's own immune system never produced those antibodies and keeps no memory of them. HIV's real target is the helper T cell specifically, and it is the resulting collapse in helper T cell count that cripples both antibody production and cytotoxic responses at once.
Drugs and alcohol abuse: Plant-source questions here are exact: Papaver somniferum gives opium and heroin, Erythroxylum coca gives cocaine, and Cannabis sativa alone yields marijuana, hashish, charas and ganja depending on which part of the same plant is used — mixing up the source plant is the standard wrong option. Anabolic steroid abuse is the counterintuitive one: external steroids suppress the body's own LH and testosterone production by negative feedback, causing reduced testicular size and gynaecomastia rather than the bigger physique one might assume.

Identify the statement that is not correct.

Ans: The antigen-binding site is located at the C-terminal region of antibody molecules.·Antigen-binding sites lie in the variable regions at the N-terminal ends of the heavy and light chains; the constant regions form the C-terminal end. Statement 3 is the incorrect one.

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Neoplastic characteristics of cells refer to: A. A mass of proliferating cells B. Rapid growth of cells C. Invasion and damage to the surrounding tissue D. Those confined to their original location Choose the correct answer from the options given below:

Ans: A, B, C only·Neoplastic (malignant) cells form a proliferating mass (A), grow rapidly (B) and invade and damage surrounding tissue (C). Being confined to the original site describes a benign tumour. Hence A, B and C.

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14. Biotechnology: Principles and Processes

Tools of recombinant DNA technology: Recombinants are told apart from non-recombinants by insertional inactivation, not by size: in a vector like pBR322, foreign DNA inserted into the tetR gene knocks that gene out, so a recombinant colony loses tetracycline resistance while keeping ampicillin resistance — only replica plating onto both antibiotics catches the difference. Restriction enzymes cut only at specific palindromic sequences, such as EcoRI at GAATTC, which is why the same enzyme reliably cuts both vector and foreign DNA at matching ends.
Processes: cloning, PCR, bioreactors: PCR only survives cycle after cycle because Taq polymerase, isolated from Thermus aquaticus (a bacterium living in hot springs), survives the roughly 95°C denaturation step intact — an ordinary DNA polymerase would be destroyed at that temperature and need replacing every cycle, which is why the source organism itself, not just "a polymerase is used," is the specific fact NEET asks for.

Given below are two statements: Statement I: The DNA fragments extracted from gel electrophoresis can be used in the construction of recombinant DNA. Statement II: Smaller-size DNA fragments are observed near the anode while larger fragments are found near the wells in an agarose gel. In the light of the above statements, choose the most appropriate answer from the options given below:

Ans: Both Statement I and Statement II are correct·DNA bands cut from an agarose gel and eluted are used to build recombinant DNA (I correct). DNA is negative and moves towards the anode; smaller fragments travel farthest, so they lie nearer the anode while large ones stay near the wells (II correct).

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Polymerase chain reaction (PCR) amplifies DNA following the equation:

Ans:

2^{n}

·Each PCR cycle doubles the target, so after

n

cycles there are

2^{n}

copies — about a billion after 30 cycles.

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15. Biotechnology and its Applications

Applications in agriculture: Bt crops, RNAi: Bt cotton's toxin is made as an inactive protoxin and only becomes active once it meets the alkaline pH of an insect's gut — which is also why it is considered harmless if eaten by humans, whose acidic gut never activates it. RNAi-based nematode resistance uses the same silencing logic in reverse: a nematode-specific gene introduced into tobacco as both sense and antisense RNA forms double-stranded RNA that triggers interference, silencing the nematode's own mRNA when it feeds on the transgenic plant.
Applications in medicine: insulin, gene therapy, molecular diagnosis: Eli Lilly's recombinant insulin (Humulin) is made by synthesising the A and B chains separately in two E. coli strains and joining them with disulfide bonds afterward, skipping the C-peptide-containing proinsulin stage the human pancreas normally goes through and excises. Gene therapy's textbook case, ADA deficiency, is not a permanent cure: the corrected lymphocytes are not immortal, so the patient needs periodic fresh infusions unless the correction is made at the embryo stage instead.
Transgenic animals and ethical issues: NCERT's transgenic-animal examples are specific and get tested as specific facts: "Rosie," a transgenic cow, was engineered to produce human alpha-lactalbumin-enriched milk, and transgenic mice now carry out the safety testing for the polio vaccine that once required monkeys — knowing the named example, which animal and which product, is what separates a right answer from a vaguely-right-sounding one.

Silencing of specific mRNA is possible via RNAi because of:

Ans: Complementary dsRNA·RNAi silences a gene through a double-stranded RNA complementary to the target mRNA; the dsRNA is processed into fragments that bind the mRNA and block translation.

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Which of the following genetically engineered organisms was used by Eli Lilly to prepare human insulin?

Ans: Bacterium·Eli Lilly produced human insulin (Humulin) in 1983 by expressing the A and B chains in E. coli, a bacterium, and then joining them by disulphide bonds.

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