NEET 2025 — Zoology

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).

Adenosine is a nucleoside (III), adenylic acid a nucleotide (II), adenine a nitrogen base (I) and alanine an amino acid (IV).

Oogenesis begins in the foetal ovary, long before spermatogenesis starts at puberty (A true). In males meiosis I and II follow each other quickly; in females meiosis I halts before birth and meiosis II completes only at fertilisation (B true). The first polar body accompanies the secondary oocyte (C false); the LH surge triggers ovulation, not menstruation (D false). Hence A and B.

All living cyclostomes (lampreys and hagfishes) are ectoparasites on some fishes, attaching with their sucking mouths.

Packaging and delivering ER products is the Golgi's principal job (A true), and material does arrive in vesicles at the cis face and leave, modified, from the trans face (R true) — R describes how A is achieved.

The scutellum is the single cotyledon of a grass seed (II); groundnut is a non-albuminous seed (III); the epiblast is a rudimentary cotyledon in some monocot embryos (IV); perisperm is persistent nucellus (I).

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.

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.

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.

Independent assortment of two genes in a dihybrid cross gives the classical 9 : 3 : 3 : 1 phenotypic ratio in the $F_2($round yellow : round green : wrinkled yellow : wrinkled green).

Histones are rich in the basic amino acids lysine and arginine; their positive charge binds the negatively charged DNA.

The first menstruation, at puberty, is menarche; the cessation of cycles around age 50 is menopause.

The heart's atrial wall secretes ANF (III); the kidney secretes erythropoietin (I); the gut secretes secretin (IV); the adrenal cortex secretes aldosterone (II).

The protein part of a conjugated enzyme is the apoenzyme; with its cofactor it forms the active holoenzyme.

Productivity is the rate of biomass production per unit area per unit time, expressed in $\mathrm{g}{\mathrm{m}}^{-2}\mathrm{y}{\mathrm{r}}^{-1}$ or $(\mathrm{kcal}{\mathrm{m}}^{-2})\mathrm{y}{\mathrm{r}}^{-1}$.

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

The pedigree fits X-linked recessive inheritance (affected $F_0$ mother → all daughters carriers; carrier mother → affected son). The $F_2$ cross is carrier female $X^A{X}^a$ × affected male $X^{a}Y$: offspring $X^A{X}^a$ (carrier daughter), $X^a{X}^a$ (affected daughter), $X^{A}Y$ (normal son), $X^{a}Y$ (affected son), each 1/4. Probability of a disease-free carrier is 1/4.

Tapetal cells are multinucleate with dense cytoplasm (A true), and this polyploid, multinucleate state supports their role of nourishing the developing microspores (R true, and it explains A).

One meiosis of the megaspore mother cell gives four megaspores; the surviving one undergoes three mitotic divisions to form the 8-nucleate embryo sac. So 1 meiosis and 3 mitoses.

Pea (Fabaceae) has a zygomorphic papilionaceous flower. Petunia, Datura and chilli (Solanaceae) have actinomorphic flowers.

Thymus and bone marrow are the primary lymphoid organs where lymphocytes mature. They then migrate to the secondary lymphoid organs — spleen, lymph nodes, tonsils, Peyer's patches and appendix — to meet antigens. Hence C, D and E.

The official key marks both statements incorrect: the fig is a syconium (an inflorescence, not a true fruit) and the wasp inside it does not make it 'non-vegetarian'; and while fig and wasp are indeed mutualists, the statement as framed — the wasp completing its life cycle in a 'fruit' — was not accepted.

Spindle fibres attach to kinetochores and pull the sister chromatids apart to opposite poles during anaphase.

Gymnosperms bear naked seeds on megasporophylls; the ovules are not enclosed in an ovary, so there is no fruit.

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.

Insulin is a peptide hormone; taken by mouth it would be digested by gastric and pancreatic proteases before it could act, so it must be injected.

Salvinia is a pteridophyte (IV); Polytrichum a moss, i.e. bryophyte (III); Salvia an angiosperm (I); Ginkgo a gymnosperm (II).

George Gamow, a physicist, argued that a code for 20 amino acids using four bases must be a triplet code, since $4^3=64$ combinations suffice while $4^2=16$ do not.

The Evil Quartet names the causes of biodiversity loss (III); cryopreservation is an ex-situ method (I); Lantana camara is an invasive alien species (II); the dodo is the classic extinction (IV).

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.

The echinoderm water vascular system, with its tube feet, serves locomotion, capture and transport of food, and respiration — statements A and C. It plays no part in excretion or digestion.

Innate immunity is present from birth and is non-specific: physical, physiological, cellular and cytokine barriers. Acquired immunity is specific and develops after exposure.

Gemmae are green, multicellular buds formed in gemma cups on the thallus of liverworts such as Marchantia; they detach and grow into new plants — asexual reproduction.

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.

Energy from the sun flows one way through an ecosystem, from producers to consumers (I correct). Ecosystems obey the laws of thermodynamics; energy is lost as heat at every transfer, which is the second law at work (II incorrect).

RuBisCO catalyses the carboxylation of RuBP in the Calvin cycle. It is active in light, has a higher affinity for $\mathrm{C}{\mathrm{O}}_2$ than for ${\mathrm{O}}_2$, and has nothing to do with photolysis of water.

Gene cloning needs restriction enzymes to cut, DNA ligase to join and DNA polymerase for PCR. 'DNA mutase' and 'DNA recombinase' are not part of the toolkit. Hence C and D.

Auxins induce parthenocarpy (A); growth regulators can promote or inhibit growth (B); cells must dedifferentiate before they can redifferentiate (C). Abscisic acid is a growth inhibitor, and apical dominance suppresses lateral buds. Hence A, B and C.

In prokaryotes the rho $(\rho )$ factor binds the growing RNA and terminates transcription; the sigma $(\sigma )$ factor is needed for initiation.

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.

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

Lactobacillus (curd), Saccharomyces cerevisiae (bread, beverages) and Propionibacterium sharmanii (Swiss cheese) are household microbes. Aspergillus niger (citric acid) and Trichoderma polysporum (cyclosporin A) are industrial. Hence A and C.

Progesterone comes from the corpus luteum (IV); relaxin from the ovary (II); melanocyte-stimulating hormone from the pars intermedia (I); catecholamines from the adrenal medulla (III).

An insert in the lacZ gene destroys $\beta -$galactosidase, so recombinant colonies cannot turn the chromogenic substrate blue — recombinants are the white colonies. Statement I is wrong, Statement II is correct.

The Verhulst–Pearl logistic equation is $\frac{dN}{dt}=rN\left(\frac{K-N}{K}\right)$, growth slowing as the population $N$ approaches the carrying capacity $K$.