NEET 2026 Biology Question Paper with Answer and Solution

(D) . $2,4-D$ is a synthetic auxin used as a herbicide $(III)$.
$B$. $GA_3$ (Gibberellic acid) is used in the brewing industry to speed up the malting process $(I)$.
$C$. Kinetin is a cytokinin that promotes nutrient mobilisation $(IV)$.
$D$. $ABA$ (Abscisic acid) stimulates stomatal closure during water stress $(II)$.
Therefore,the correct match is $A-III, B-I, C-IV, D-II$.

(C) In racemose inflorescence,the main axis continues to grow indefinitely,and flowers are borne in an acropetal succession,meaning older flowers are at the base and younger flowers are towards the apex (tip).

(A) The alpha-helix is a common motif in the secondary structure of proteins.
It is stabilized by hydrogen bonding between the carbonyl oxygen of one amino acid and the amino hydrogen of another amino acid located further along the polypeptide chain.

(B) In the Calvin cycle,the enzyme RuBisCO (RuBP carboxylase-oxygenase) catalyzes the carboxylation step.
This enzyme facilitates the fixation of atmospheric $CO_2$ into a $5$-carbon sugar called Ribulose $1,5$-bisphosphate (RuBP).

(D) . $G_1$ phase $(II)$ - The cell is metabolically active and continuously grows but does not replicate its $DNA$.
$B$. $S$ phase $(III)$ - $DNA$ synthesis occurs,and the amount of $DNA$ per cell doubles.
$C$. $G_2$ phase $(IV)$ - Proteins are synthesized while cell growth continues in preparation for mitosis.
$D$. $M$ phase $(I)$ - Actual cell division (mitosis or meiosis) occurs.
Therefore,the correct matching is $A-II, B-III, C-IV, D-I$.

(D) The Respiratory Quotient $(RQ)$ is defined as the ratio of the volume of $CO_2$ evolved to the volume of $O_2$ consumed during respiration.
$RQ = \frac{\text{Volume of } CO_2 \text{ evolved}}{\text{Volume of } O_2 \text{ consumed}}$
From the given balanced chemical equation: $2(C_5H_9O_5) + 145O_2 \rightarrow 102CO_2 + 98H_2O + \text{energy}$.
The volume of $CO_2$ evolved is $102$ units and the volume of $O_2$ consumed is $145$ units.
$RQ = \frac{102}{145} \approx 0.703$.
Since $0.703$ lies between $0.5$ and $0.95$,the correct option is $D$.

(C) During the elongation phase of plant growth,cells undergo significant enlargement,increased vacuolation,and new cell wall deposition. As the vacuole grows in size,the cytoplasm is pushed towards the periphery,causing the nucleus to become peripheral and less conspicuous. Therefore,having large,conspicuous nuclei is not a characteristic of cells in the elongation phase.

(B) . Conjunctive tissue is the parenchymatous tissue present between the xylem and phloem bundles in roots $(III)$.
$B$. Casparian strips are the water-impermeable bands of suberin found in the endodermal cells $(IV)$.
$C$. Subsidiary cells are specialized epidermal cells that surround the guard cells of the stomata $(I)$.
$D$. Starch sheath refers to the endodermis of the stem,which is rich in starch grains $(II)$.
Therefore,the correct matching is $A-III, B-IV, C-I, D-II$.

(C) Root hairs are unicellular extensions of the epidermal cells (epiblema) found in the region of maturation of the root. They are responsible for the absorption of water and minerals from the soil.

(C) The floral formula of the Solanaceae family is characterized by being actinomorphic $(\oplus)$,bisexual,having a calyx with $5$ fused sepals $(K_{(5)})$,a corolla with $5$ fused petals $(C_{(5)})$,an androecium with $5$ stamens $(A_5)$,and a gynoecium with $2$ fused carpels $(G_{(2)})$.
Thus,the correct floral formula is $\oplus \text{ K}_{(5)} \text{ C}_{(5)} \text{ A}_5 \text{ G}_{(2)}$.

(D) $R.H. Whittaker$ $(1969)$ proposed the Five Kingdom Classification based on the following five main criteria:
$1$. Cell structure (prokaryotic vs. eukaryotic)
$2$. Body organization (unicellular vs. multicellular)
$3$. Mode of nutrition (autotrophic vs. heterotrophic)
$4$. Reproduction
$5$. Phylogenetic relationships
Presence of flagellum was not a primary criterion used in this classification system.
Therefore,the correct criteria are $(A)$,$(B)$,$(D)$,and $(E)$.
Thus,option $(4)$ is correct.

(D) Plants follow different pathways in response to the environment or phases of life to form different kinds of structures. This ability is called plasticity.
Heterophylly,which is the development of different leaf forms in response to environmental changes like moisture or light intensity in aquatic and terrestrial plants (e.g.,buttercup),is a classic example of plasticity in plants.
Therefore,option $(4)$ is correct.

(D) Analysis of statements:
$(A)$ Amino acids are substituted methanes where four substituent groups (amino,carboxyl,hydrogen,and $R$-group) occupy the four valency positions of the $\alpha$-carbon. This statement is correct.
$(B)$ Serine is a polar,uncharged (neutral) amino acid,not an aromatic one. This statement is incorrect.
$(C)$ Valine possesses a non-polar,hydrophobic side chain and is classified as a neutral amino acid. This statement is correct.
$(D)$ Lysine contains an extra amino group in its side chain,which makes it a basic amino acid,not acidic. This statement is incorrect.
Therefore,statements $A$ and $C$ are correct. The correct option is $(4)$.

(A) Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed both before and after fertilization.
$Pinus$ is a gymnosperm.
$Wolffia$ is an angiosperm,where ovules are enclosed within an ovary.
$Funaria$ is a bryophyte,which does not produce seeds or ovules.
$Selaginella$ is a pteridophyte,which does not produce seeds or ovules.
Therefore,option $(1)$ is correct.

(A-II, B-IV, C-I, D-III) The correct matches for placentation types are:
$1$. Marginal placentation: Found in Pea $(A-II)$.
$2$. Axile placentation: Found in Lemon $(B-IV)$.
$3$. Parietal placentation: Found in Mustard $(C-I)$.
$4$. Basal placentation: Found in Marigold $(D-III)$.
Therefore,the correct sequence is $A-II, B-IV, C-I, D-III$.

(A) The nucleolus is a non-membrane bound sub-organelle present inside the nucleus. It is the primary site for the transcription and processing of ribosomal $RNA$ $(rRNA)$ and the assembly of ribosomal subunits.

(B) Bulliform cells are large,bubble-shaped epidermal cells present in the leaves of many grasses.
When water is abundant,they become turgid,causing the leaf to expand.
During water stress,they lose turgidity,causing the leaf to roll inward to minimize the surface area exposed to the atmosphere,thereby reducing transpiration and water loss.

(A) According to the rules of binomial nomenclature:
$1$. The first word represents the $Genus$ (starting with a capital letter).
$2$. The second word represents the specific epithet (starting with a small letter).
$3$. Biological names are generally derived from Latin or are Latinized.
$4$. When handwritten,both words are separately underlined,and when printed,they are in italics.
Therefore,statement $(1)$ is incorrect because it incorrectly states that the first word is the specific epithet and the second is the genus.

(D) Statement $A$ is incorrect because the water-splitting complex is associated with $PS-II$,not $PS-I$.
Statement $B$ is incorrect because $C_4$ plants use the $C_4$ pathway (Hatch-Slack pathway) as the primary biosynthetic pathway,although they also contain the $C_3$ cycle.
Statement $D$ is incorrect because $C_4$ plants,not $C_3$ plants,exhibit 'Kranz' anatomy.
Statements $C$ and $E$ are correct.
Thus,the incorrect statements are $A, B,$ and $D$. However,based on the provided options,the most appropriate choice identifying the incorrect statements is $(4)$ $A$ and $D$.

(A) The correct matches are as follows:
$1$. Trypsin is a protein that acts as an enzyme $(A-III)$.
$2$. Morphine is a secondary metabolite classified as an alkaloid $(B-IV)$.
$3$. Concanavalin $A$ is a secondary metabolite classified as a lectin $(C-II)$.
$4$. Collagen is the most abundant protein in the animal world and forms the intercellular ground substance $(D-I)$.
Therefore,the correct matching is $A-III, B-IV, C-II, D-I$.

(B, C, E) . Incorrect: Lipids are hydrophobic and generally water-insoluble.
$B$. Correct: Proteins are polymers of amino acids linked by peptide bonds,hence they are polypeptides.
$C$. Correct: Polysaccharides are complex carbohydrates formed by long chains of monosaccharide units.
$D$. Incorrect: Adenine and guanine are purines,not pyrimidines.
$E$. Correct: Most enzymes are proteinaceous in nature,with the exception of some $RNA$ molecules known as ribozymes.
Therefore,the correct statements are $B, C,$ and $E$.

(B) For the synthesis of one molecule of glucose $(C_6H_{12}O_6)$ via the Calvin cycle,$6$ turns are required.
Each turn fixes one $CO_2$ molecule,consuming $3$ $ATP$ and $2$ $NADPH$.
Therefore,for $6$ $CO_2$ molecules,the total requirement is:
$6 \times 3 = 18$ $ATP$
$6 \times 2 = 12$ $NADPH$
Thus,$18$ $ATP$ and $12$ $NADPH$ molecules are required to produce one molecule of glucose.

(D) $1$. Glycolysis occurs in the cytoplasm $(A-III)$.
$2$. Electron Transport System $(ETS)$ is located in the inner mitochondrial membrane $(B-I)$.
$3$. Protons accumulate in the intermembrane space of mitochondria during oxidative phosphorylation $(C-IV)$.
$4$. The Krebs' cycle occurs in the mitochondrial matrix $(D-II)$.
Therefore,the correct matching is $A-III, B-I, C-IV, D-II$.

(D) . Molluscs generally use gills (branchial) for respiration $(A-II)$.
$B$. Reptiles rely on pulmonary respiration $(B-I)$.
$C$. Adult amphibians use both lungs (pulmonary) and skin (cutaneous) $(C-IV)$.
$D$. Amoeba,being unicellular,relies on diffusion across the cell membrane,which is a form of cellular respiration $(D-III)$.
Therefore,the correct matching is $A-II, B-I, C-IV, D-III$. Note: Based on the provided options,option $(4)$ is the closest intended answer,though the scientific match for Molluscs is Branchial $(II)$.

(D) Ribosomes are non-membrane bound cell organelles found in both prokaryotic and eukaryotic cells.
In prokaryotes,they are $70S$ ribosomes,whereas in eukaryotes,they can be $80S$ (cytosol) or $70S$ (organelles like mitochondria and chloroplasts).
Lysosomes,centrosomes,and mitochondria are membrane-bound organelles.

(D) The correct sequence for the Renin-Angiotensin mechanism is as follows:
$1$. Fall in Glomerular filtration rate $(GFR)$ $(C)$.
$2$. Renin converts Angiotensinogen into Angiotensin $I$,which is then converted into Angiotensin $II$ $(E)$.
$3$. Vasoconstriction by Angiotensin $II$ and release of Aldosterone $(D)$.
$4$. Reabsorption of $Na^+$ and water from the distal parts of the tubule due to Aldosterone $(B)$.
$5$. Increase in blood pressure and $GFR$ $(A)$.
Thus,the correct order is $C, E, D, B, A$.

(C) The correct sequence of respiration in humans is:
$1$. Pulmonary ventilation $(C)$
$2$. Diffusion across alveolar membrane $(B)$
$3$. Transport of gases by blood $(E)$
$4$. Diffusion between blood and tissues $(A)$
$5$. Cellular respiration $(D)$
Thus,the correct sequence is $C, B, E, A, D$.

(D) Lyases are enzymes that catalyze the removal of groups from substrates by mechanisms other than hydrolysis,leaving double bonds.
The reaction shown represents the formation of a double bond by the elimination of a group $(X-Y)$,which is a characteristic feature of the Lyases enzyme class.
Therefore,the correct enzyme class is Lyases.

(B) The correct matching is as follows:
$(A)$ Tetany is caused by low levels of $Ca^{++}$ in body fluids,leading to wild contractions $(III)$.
$(B)$ Arthritis is the inflammation of joints $(I)$.
$(C)$ Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction $(II)$.
$(D)$ Muscular dystrophy is the progressive degeneration of skeletal muscles $(IV)$.
Thus,the correct matching is $A-III, B-I, C-II, D-IV$.

(C) Statement $A$ is correct: The membrane of human $RBCs$ consists of approximately $52\%$ protein and $40\%$ lipids.
Statement $B$ is correct: The phospholipids are arranged in a bilayer with the polar heads towards the outer sides and hydrophobic tails towards the inner part.
Statement $C$ is incorrect: Mesosomes are specialized membranous structures formed by the extensions of the plasma membrane into the cell in prokaryotes,not eukaryotes.
Statement $D$ is correct: The hydrophobic tails of the lipid molecules are directed towards the inner side,ensuring they are protected from the aqueous environment.
Statement $E$ is correct: Glycocalyx is a sugar coat present on the outer surface of the plasma membrane.
Therefore,statements $A, B, D,$ and $E$ are correct. Since the provided options do not contain this combination,and based on standard examination patterns where $C$ is explicitly false,the intended answer is $A, B, D$ and $E$. Given the options,$(3)$ is the most appropriate choice as it contains the correct statements $A, B,$ and $D$.

(D) Statement $A$ is incorrect because the endomembrane system consists of the endoplasmic reticulum,Golgi complex,lysosomes,and vacuoles; mitochondria are not part of it.
Statement $B$ is correct because rough endoplasmic reticulum $(RER)$ has ribosomes attached to its surface.
Statement $C$ is correct because both mitochondria and plastids are semi-autonomous organelles containing circular $DNA$.
Statement $D$ is correct because the cytoskeleton is an elaborate network of proteinaceous filaments consisting of microtubules,microfilaments,and intermediate filaments.
Statement $E$ is incorrect because mitochondria are double-membrane bound structures.
Thus,statements $B, C,$ and $D$ are correct.

(C) The Juxta Glomerular Apparatus $(JGA)$ is a complex regulatory structure found in the kidney.
It is formed by cellular modifications in the Distal Convoluted Tubule $(DCT)$ and the Afferent Arteriole at the point of their contact.
This apparatus plays a crucial role in the regulation of the Glomerular Filtration Rate $(GFR)$ and blood pressure.

(D) Statement $A$ is correct: The hepatic portal system is a special venous connection between the intestine and the liver.
Statement $B$ is incorrect: Frogs have $10$ pairs of cranial nerves,not $12$.
Statement $C$ is correct: In female frogs,the ureters and oviducts open separately into the cloaca.
Statement $D$ is incorrect: The hind-brain consists of the cerebellum and medulla oblongata; the optic lobes are part of the mid-brain.
Statement $E$ is correct: The sinus venosus is a triangular chamber that joins the right atrium of the heart.
Therefore,statements $A, C,$ and $E$ are correct.

(A) The correct matches are as follows:
$A$. Cortisol: It is a glucocorticoid that produces anti-inflammatory reactions and suppresses the immune response $(II)$.
$B$. Aldosterone: It is a mineralocorticoid that acts mainly at the renal tubules and stimulates the reabsorption of $Na^+$ and water and excretion of $K^+$ and phosphate ions $(III)$.
$C$. Cholecystokinin $(CCK)$: It acts on both the pancreas and the gallbladder and stimulates the secretion of pancreatic enzymes and bile juice $(IV)$.
$D$. Progesterone: It supports pregnancy and also stimulates the formation of alveoli (sac-like structures which store milk) in mammary glands $(I)$.
Therefore,the correct matching is $A-II, B-III, C-IV, D-I$.

(C) Male frogs can be distinguished from female frogs by the presence of specific secondary sexual characteristics.
$1$. Vocal sacs $(B)$: These are present in male frogs and help in producing loud croaking sounds to attract females.
$2$. Copulatory (nuptial) pads $(D)$: These are present on the first digit of the forelimbs in male frogs and are used to grip the female during the process of amplexus (mating).
Therefore,the correct combination is $B$ and $D$.

(D) The differential $WBC$ count percentages are as follows:
Eosinophils: $2-3\%$ of $8000 = 160-240/cu.mm$.
Lymphocytes: $20-25\%$ of $8000 = 1600-2000/cu.mm$.
Therefore,option $D$ matches these calculated values.

(B) The bird described is the penguin.
*Aptenodytes* is the genus for penguins.
Penguins are flightless birds whose forelimbs are modified into paddle-like structures called flippers,which are highly adapted for swimming in aquatic environments.

(B) Statement $A$ is correct: Platyhelminthes have an incomplete digestive system.
Statement $B$ is incorrect: Adult Echinoderms exhibit radial symmetry,while their larvae exhibit bilateral symmetry.
Statement $C$ is correct: Aschelminthes are pseudocoelomates.
Statement $D$ is correct: In class Chondrichthyes,the notochord is persistent throughout life.
Statement $E$ is incorrect: Reptiles are poikilothermic (cold-blooded) animals and cannot maintain a constant body temperature.
Therefore,the incorrect statements are $B$ and $E$.

(C) The characters described are:
$1$. Endoskeleton is cartilaginous.
$2$. Ectoparasitic nature with a circular,suctorial mouth.
$3$. Absence of paired fins and scales.
$4$. Presence of $6-15$ pairs of gill slits for respiration.
These features are diagnostic of the class $Cyclostomata$. Among the given options,$Petromyzon$ (lamprey) belongs to this class. $Scoliodon$ is a cartilaginous fish (Chondrichthyes),$Exocoetus$ is a bony fish (Osteichthyes),and $Branchiostoma$ is a cephalochordate.

(D) The correct statements are $A, B, D,$ and $E$.
Statement $A$ is correct: $A$ motor neuron transmits a signal from the $CNS$ to the sarcolemma.
Statement $B$ is correct: The neural signal triggers an action potential,leading to the release of $Ca^{++}$ ions into the sarcoplasm.
Statement $C$ is incorrect: $Ca^{++}$ binds to troponin on the actin filament,which exposes the active sites on actin,thereby facilitating (not inactivating) the formation of cross-bridges.
Statement $D$ is correct: The exposed active sites on actin bind to the myosin head to form a cross-bridge.
Statement $E$ is correct: The myosin heads pull the actin filaments towards the center of the '$A$' band,causing the sarcomere to shorten.
Therefore,the correct sequence of events leads to the conclusion that $A, B, D,$ and $E$ are correct.

(B) Statement $A$ is incorrect because the human skull is dicondylic,not monocondylic.
Statement $B$ is correct because the joints between adjacent vertebrae are cartilaginous joints (specifically,symphysis joints).
Statement $C$ is correct because all mammals,including humans,have exactly $7$ cervical vertebrae.
Statement $D$ is incorrect because all ribs are bicephalic,meaning they have two articulation surfaces (head and tubercle) for attachment to the vertebrae.
Statement $E$ is correct because the occipital condyles of the skull articulate with the atlas $(C1)$ vertebra to form the atlanto-occipital joint.
Therefore,the correct statements are $B, C,$ and $E$.

(C) Statement $A$ is incorrect because Erythroblastosis foetalis occurs when the mother is $Rh^{-ve}$ and the foetus is $Rh^{+ve}$.
Statement $E$ is incorrect because anti-$Rh$ antibodies (anti-$D$) are administered to the mother immediately after the delivery of the first $Rh^{+ve}$ child to prevent sensitization in subsequent pregnancies.

(D) Class $Osteichthyes$ consists of bony fishes.
Examples include $Exocoetus$ (Flying fish),$Pterophyllum$ (Angel fish),and $Betta$ (Fighting fish).
Sawfish $(Pristis)$ and Dogfish $(Scoliodon)$ belong to class $Chondrichthyes$ (cartilaginous fishes).
Devil fish (Octopus),Cuttlefish $(Sepia)$,and Starfish $(Asterias)$ are not true fishes; they belong to phyla $Mollusca$ and $Echinodermata$ respectively.
Hagfish $(Myxine)$ belongs to class $Cyclostomata$.

(B) In a chemical synapse,the neurotransmitters are released from the synaptic vesicles of the pre-synaptic neuron into the synaptic cleft.
These neurotransmitters then bind to specific receptor proteins located on the membrane of the post-synaptic neuron (post-synaptic membrane) to generate an action potential.

(A) The standard respiratory volumes are as follows:
$A$. $ERV$ (Expiratory Reserve Volume) is the additional volume of air that can be expired by a forcible expiration,which is $1000-1100 \text{ mL}$ $(III)$.
$B$. $RV$ (Residual Volume) is the volume of air remaining in the lungs even after a forcible expiration,which is $1100-1200 \text{ mL}$ $(IV)$.
$C$. $IRV$ (Inspiratory Reserve Volume) is the additional volume of air that can be inspired by a forcible inspiration,which is $2500-3000 \text{ mL}$ $(I)$.
$D$. $TV$ (Tidal Volume) is the volume of air inspired or expired during a normal respiration,which is $500 \text{ mL}$ $(II)$.
Thus,the correct matching is $A-III, B-IV, C-I, D-II$.

(A) . Genetically modified organism: Bt cotton $(II)$
$B$. $DNA$ polymerase: Thermus aquaticus $(III)$
$C$. Ti plasmid: Agrobacterium tumefaciens $(I)$
$D$. pBR322: Escherichia coli $(IV)$
Therefore,the correct matching is $A-II, B-III, C-I, D-IV$.

(A) Bioprospecting is the systematic search for genes,compounds,and other products of economic value in biological resources.
It involves the exploration of biodiversity at molecular,genetic,and species levels to discover new resources that can be used for commercial,pharmaceutical,or industrial purposes.

(A) In honeybees,the sex-determination system is known as haplodiploidy.
Females are diploid $(2n)$,produced from the union of a sperm and an egg (fertilized eggs).
Males are haploid $(n)$,produced from unfertilized eggs through a process called parthenogenesis.
Since males are haploid,they cannot undergo meiosis to produce gametes; instead,they produce sperms by mitosis.
Therefore,statements $A, B, C,$ and $E$ are correct,while statement $D$ is incorrect.

(B) The sixth mass extinction is primarily driven by human activities.
Its rate is estimated to be $100$ to $1000$ times faster than the natural background rate observed in pre-human times.
Therefore,option $(2)$ is the correct answer.

(D) The process of microsporogenesis occurs in the following sequence:
$1$. The primary sporogenous tissue $(B)$ undergoes mitotic divisions to form pollen mother cells $(D)$.
$2$. Each pollen mother cell $(D)$ undergoes meiosis to form a group of four haploid cells known as microspore tetrads $(A)$.
$3$. These microspores separate and mature into pollen grains $(C)$.
Therefore,the correct sequence is $B \rightarrow D \rightarrow A \rightarrow C$.

(A) Statement $A$ is true: Restriction endonucleases are known as molecular scissors.
Statement $B$ is true: They were discovered in $E. coli$ as a mechanism to restrict bacteriophage growth.
Statement $C$ is false: Restriction enzymes do not always cut at the exact center of palindromic sites; they often create staggered cuts.
Statement $D$ is false: Restriction endonucleases cut $DNA$ at specific internal positions,whereas exonucleases remove nucleotides from the ends.
Statement $E$ is true: They recognize specific palindromic sequences.
Therefore,statements $C$ and $D$ are not true.

(D) The lac operon consists of three structural genes: $z$,$y$,and $a$.
The $z$ gene codes for the enzyme $\beta$-galactosidase,which is responsible for the hydrolysis of lactose into glucose and galactose.
The $y$ gene codes for permease,and the $a$ gene codes for transacetylase.

(D) The process of somatic hybridization involves the following steps:
$1$. Isolation of single cells from two different plant varieties $(D)$.
$2$. Digestion of cell walls using enzymes like cellulase and pectinase $(A)$.
$3$. Isolation of naked protoplasts $(B)$.
$4$. Fusion of protoplasts to obtain hybrid protoplasts $(C)$.
$5$. Growing of hybrid protoplasts to regenerate a new plant $(E)$.
Therefore,the correct sequence is $D, A, B, C, E$.

(B) In angiosperms,the primary endosperm nucleus $(PEN)$ is formed by the fusion of two polar nuclei (each $n$) and one male gamete $(n)$,resulting in a $3n$ (triploid) structure.
Therefore,the primary endosperm cell is triploid.

(D) . Decomposition is the process of breaking down complex organic matter into simpler inorganic substances $(III)$.
$B$. Detritus refers to the dead remains of plants and animals,including fecal matter $(IV)$.
$C$. Mineralisation is the process of releasing inorganic nutrients into the soil through the activity of microbes $(II)$.
$D$. Humification is the process of accumulation of dark-coloured amorphous colloidal substances known as humus $(I)$.
Therefore,the correct matching is $A-III, B-IV, C-II, D-I$.

(C) The term "The Evil Quartet" is used to describe the four major causes of biodiversity loss:
$1$. Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction.
$2$. Over-exploitation: Humans have over-exploited many species (e.g.,Steller's sea cow,passenger pigeon).
$3$. Alien species invasions: When alien species are introduced unintentionally or deliberately,they often become invasive and cause the decline or extinction of indigenous species.
$4$. Co-extinctions: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct.
Therefore,option $(3)$ correctly lists all four components.

(D) The correct sequence for $DNA$ fingerprinting is as follows:
$1$. Isolation of $DNA$ and its digestion by restriction endonucleases $(A)$.
$2$. Separation of $DNA$ fragments by gel electrophoresis $(E)$.
$3$. Transferring (blotting) of separated $DNA$ fragments to synthetic membranes such as nitrocellulose or nylon $(C)$.
$4$. Hybridisation using a labelled $VNTR$ probe $(B)$.
$5$. Detection of hybridised $DNA$ fragments by autoradiography $(D)$.
Therefore,the correct sequence is $A \to E \to C \to B \to D$. Thus,option $(4)$ is correct.

(B) All statements provided are standard definitions related to the transcription unit in molecular biology.
$A$. $A$ transcription unit in $DNA$ is defined by three regions: promoter,structural gene,and terminator.
$B$. The promoter is located at the $5'$-end of the structural gene (upstream).
$C$. It provides a binding site for $RNA$ polymerase to initiate transcription.
$D$. By its position,the promoter determines which strand of $DNA$ acts as the template strand and which acts as the coding strand.
$E$. The terminator is located at the $3'$-end of the coding strand and signals the end of the transcription process.
Since all statements $A, B, C, D,$ and $E$ are correct,option $(2)$ is the correct answer.

(B) Pollination is classified into three main types:
$1$. Autogamy: This is self-pollination occurring within the same flower.
$2$. Geitonogamy: This is the transfer of pollen grains from the anther to the stigma of another flower on the same plant. Genetically,it is similar to autogamy since the pollen comes from the same plant.
$3$. Xenogamy: This is the transfer of pollen grains from the anther to the stigma of a different plant of the same species. This process brings genetically different types of pollen grains to the stigma.
Therefore,option $(2)$ is the correct answer.

(B) In situ conservation involves protecting species within their natural habitats.
Examples include National Parks,Wildlife Sanctuaries,Biosphere Reserves,and Sacred Groves.
Ex situ conservation involves protecting species outside their natural habitats,such as in Seed Banks,Botanical Gardens,and Wildlife Safari Parks.
Therefore,Sacred Groves is an in situ conservation method.
Thus,option $(2)$ is correct.

(C) The correct matches are as follows:
$A$. Productivity is defined as the rate of biomass production $(A-III)$.
$B$. Net primary productivity $(NPP)$ is the Gross primary productivity $(GPP)$ minus respiration losses $(R)$,i.e.,$NPP = GPP - R$ $(B-I)$.
$C$. Gross primary productivity is the rate of production of organic matter during photosynthesis $(C-IV)$.
$D$. Secondary productivity is the rate of formation of new organic matter by consumers $(D-II)$.
Therefore,the correct sequence is $A-III, B-I, C-IV, D-II$. Thus,option $(3)$ is correct.

(A, C, D, E) In eukaryotic cells,$DNA$ is wrapped around a histone octamer (composed of two molecules each of $H2A$,$H2B$,$H3$,and $H4$) to form a nucleosome.
Histones are positively charged basic proteins,as they are rich in the basic amino acids lysine and arginine.
Therefore,statements $A$,$C$,$D$,and $E$ are correct.
Statement $B$ is incorrect because histones are positively charged,not negatively charged.

(A, B, D) Statement $A$ is correct: Habitat loss and fragmentation are the most important causes driving animals and plants to extinction. The Amazon rainforest is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.
Statement $B$ is correct: Over-exploitation by humans has led to the extinction of species like Steller's sea cow and passenger pigeon.
Statement $C$ is incorrect: The introduction of the Nile perch into Lake Victoria in East Africa led to the extinction of an ecologically unique assemblage of more than $200$ species of cichlid fish in the lake.
Statement $D$ is correct: Water hyacinth $(Eichhornia \text{ } crassipes)$ is an alien species that became invasive and caused environmental damage.
Statement $E$ is incorrect: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct,a phenomenon known as co-extinction.
Therefore,statements $A, B,$ and $D$ are correct.

(C) Sickle-cell anaemia is an autosomal linked recessive trait that can be transmitted from parents to the offspring when both the partners are carriers for the gene.
This genetic disorder is caused by a point mutation in the gene coding for the beta-globin chain of haemoglobin.
Specifically,at the sixth position of the beta-globin chain,the amino acid Glutamic acid (Glu) is replaced by Valine (Val).
This substitution leads to the formation of abnormal haemoglobin molecules,which cause red blood cells to change their shape into a sickle-like structure under low oxygen tension.

(C) $1$. Incomplete Dominance in Antirrhinum sp. (snapdragon) results in an intermediate phenotype,matching $A-II$.
$2$. Co-dominance is exemplified by $ABO$ blood groups where both $A$ and $B$ alleles express themselves,matching $B-IV$.
$3$. Pleiotropy occurs where a single gene affects multiple traits,as seen in phenylketonuria,matching $C-III$.
$4$. Polygenic inheritance explains continuous traits like human skin colour,matching $D-I$.
Therefore,the correct matching is $A-II, B-IV, C-III, D-I$.

(B) The Polymerase Chain Reaction $(PCR)$ consists of three main steps performed in a cycle:
$1$. Denaturation: The reaction mixture is heated to $94-98^\circ C$ to separate the double-stranded $DNA$ into single strands.
$2$. Annealing: The mixture is cooled to $50-65^\circ C$,allowing the primers to bind to their complementary sequences on the single-stranded $DNA$ templates.
$3$. Extension: The temperature is raised to approximately $72^\circ C$,where the $Taq$ $DNA$ polymerase enzyme synthesizes new $DNA$ strands by adding nucleotides to the primers.
Thus,the correct sequence is Denaturation $\rightarrow$ Annealing $\rightarrow$ Extension.

(A) is correct: Restriction endonucleases are known as molecular scissors that cut $DNA$ at specific sites.
$B$ is correct: During gel electrophoresis,$DNA$ fragments move through the agarose gel matrix and separate based on their size (molecular weight).
$C$ is incorrect: $DNA$ fragments are colorless and cannot be seen without staining.
$D$ is incorrect: $DNA$ fragments stained with ethidium bromide $(EtBr)$ require exposure to $UV$ light to fluoresce and be visualized; they are not visible under normal visible light.

(C) The mother is heterozygous for blood group '$A$',represented by the genotype $I^A i$.
The father is heterozygous for blood group '$B$',represented by the genotype $I^B i$.
Performing the genetic cross: $(I^A i) \times (I^B i)$.
The possible offspring genotypes are:
$1$. $I^A I^B$ (Blood group $AB$)
$2$. $I^A i$ (Blood group $A$)
$3$. $I^B i$ (Blood group $B$)
$4$. $ii$ (Blood group $O$)
Out of the four possible outcomes,only one results in blood group '$O$'.
Therefore,the probability of having a child with blood group '$O$' is $\frac{1}{4} = 25\%$.

(C) The cloning vector $pBR322$ contains two antibiotic resistance genes: one for ampicillin $(amp^R)$ and one for tetracycline $(tet^R)$.
In $pBR322$,the $BamHI$ restriction site is specifically located within the tetracycline resistance $(tet^R)$ gene.
When a foreign $DNA$ fragment is inserted at the $BamHI$ site,it disrupts the coding sequence of the $tet^R$ gene.
As a result,the bacteria containing this recombinant plasmid lose their ability to survive in the presence of tetracycline,a phenomenon known as insertional inactivation.

(C) Swiss cheese is ripened by the bacterium $Propionibacterium \text{ } sharmanii$.
During the fermentation process,this bacterium produces a large amount of $CO_2$ gas.
The release of this $CO_2$ gas trapped within the cheese curd is responsible for the formation of the characteristic large holes observed in Swiss cheese.

(A) Convergent evolution results in the development of analogous organs,which perform similar functions but have different evolutionary origins.
$(1)$ The forelimbs of whales and bats are homologous organs because they share a common ancestral structural plan (pentadactyl limb) but have adapted for different functions (swimming vs. flying). This is an example of divergent evolution.
$(2)$ Flippers of penguins and dolphins are analogous organs as they evolved independently for swimming.
$(3)$ Eyes of octopuses and mammals are analogous organs that evolved independently to perform the function of vision.
$(4)$ Wings of butterflies and birds are analogous organs that evolved independently for flight.
Therefore,the forelimbs of whales and bats represent divergent evolution,not convergent evolution.

(D) The pyramid of biomass in a sea ecosystem is generally inverted.
This occurs because the standing crop biomass of phytoplankton (producers) is much smaller than the biomass of zooplankton and small fish (primary consumers) and larger fish (secondary/top consumers) at any given time.
This happens because producers have a very high turnover rate,meaning they reproduce and are consumed very rapidly,resulting in a smaller standing biomass compared to the higher trophic levels.

(C) The correct statements are $B, D$,and $E$.
- $B$: Mutualism $(+,+)$: Both species benefit.
- $D$: Parasitism $(+,-)$: One species benefits and the other is harmed.
- $E$: Amensalism $(-,0)$: One species is harmed and the other is unaffected.
Statement $A$ is incorrect because in commensalism $(+,0)$,one species benefits and the other is unaffected.

(A) In male honeybees (drones),the cells are already haploid $(n)$.
Since they cannot undergo meiosis to produce gametes (as meiosis requires a diploid set of chromosomes for pairing),they produce gametes by mitosis.
Therefore,male honeybees produce sperm through mitotic division.

(C) The correct matches are:
$A$. Streptokinase: Used for removal of clots from blood vessels $(II)$.
$B$. Statins: Act as blood cholesterol-lowering agents $(III)$.
$C$. Lipases: Used in detergent formulations $(IV)$.
$D$. Cyclosporin $A$: Used as an immunosuppressive agent $(I)$.
Thus,the correct sequence is $A-II, B-III, C-IV, D-I$.

(A) The Verhulst-Pearl logistic growth equation describes population growth limited by environmental resources,represented by the carrying capacity $(K)$.
The equation is given by $\frac{dN}{dt} = rN \left( \frac{K-N}{K} \right)$.
Here,$N$ represents the population size at time $t$,$r$ is the intrinsic rate of natural increase,and $K$ is the carrying capacity of the environment.

(D) The structures surrounding the ovum from the outside to the inside are as follows:
$1$. Corona radiata (outermost layer consisting of follicular cells).
$2$. Zona pellucida (a glycoprotein layer).
$3$. Perivitelline space (the space between the zona pellucida and the plasma membrane).
$4$. Plasma membrane of the ovum (innermost boundary).
Therefore,the correct sequence from outer to inner is $C, A, B, D$.

(B) Sexual deceit is a pollination strategy where a plant mimics the female of a specific insect species to attract the male of that species for pollination. The orchid 'Ophrys' employs this mechanism by mimicking the female bumblebee in both morphology and scent,thus deceiving the male bumblebee during its attempted copulation.

(C) The toxin proteins produced by $Bacillus$ $thuringiensis$ $(Bt)$ are encoded by specific $cry$ genes.
Specifically,the gene $cryIAc$ is used to control cotton bollworms.
The gene $cryIAb$ is used to control corn borers.
Therefore,the correct pair is $cryIAc$ and $cryIAb$.

(C) In sickle-cell anaemia,a point mutation in the beta globin gene changes the sixth codon from $GAG$ (coding for glutamic acid) to $GUG$ (coding for valine).
This substitution leads to the polymerization of haemoglobin under low oxygen tension,which causes the characteristic sickling of $RBC$s.

(C) $\alpha-1$-antitrypsin is a protein used to treat emphysema.
It is produced through transgenic animals (e.g.,transgenic sheep) as an example of biotechnological application in medicine.

(D) $1$. Nicotine acts as a stimulant that triggers the adrenal gland to release catecholamines (like adrenaline) into the blood circulation $(A-II)$.
$2$. Morphine is a potent opioid that acts as an effective sedative and painkiller $(B-III)$.
$3$. Heroin is a depressant that slows down body functions $(C-IV)$.
$4$. Cocaine is a stimulant that interferes with dopamine transport,causing a sense of euphoria and increased energy $(D-I)$.
Therefore,the correct matching is $A-II, B-III, C-IV, D-I$.

(C) The chronological order of the evolution of life forms is as follows:
$A$. About $65 \text{ mya}$: The dinosaurs suddenly disappeared from the earth $(II)$.
$B$. About $500 \text{ mya}$: Jawless fish probably evolved $(I)$.
$C$. About $350 \text{ mya}$: Seaweeds and few plants probably existed $(III)$.
$D$. About $320 \text{ mya}$: Invertebrates were formed and became active $(IV)$.
Therefore,the correct match is $A-II, B-I, C-III, D-IV$.

(C) Progestasert is a hormone-releasing $IUD$ $(A-III)$.
Multiload $375$ is a copper-releasing $IUD$ $(B-IV)$.
Diaphragm is a barrier method made of rubber used by females $(C-I)$.
Saheli is an oral contraceptive $(D-II)$.
Therefore,the correct sequence is $A-III, B-IV, C-I, D-II$.

(B) The life cycle of $Plasmodium$ follows these steps:
$1$. The female $Anopheles$ mosquito injects sporozoites into the human body through a bite $(E)$.
$2$. These sporozoites travel through the blood and reach the liver $(D)$.
$3$. In the liver,the parasites reproduce asexually,causing the liver cells to burst and releasing the parasites into the blood $(B)$.
$4$. The parasites then enter $RBCs$ and reproduce asexually,causing the $RBCs$ to burst $(A)$.
$5$. Finally,some parasites differentiate into gametocytes within the $RBCs$ $(C)$.
Thus,the correct sequence is $E, D, B, A, C$.

(B) The developmental stages of the human foetus are as follows:
$A$. The foetus movement starts and hair appears on the head occurs at $20$ weeks of pregnancy $(II)$.
$B$. The foetus develops limbs and digits by the end of $8$ weeks of pregnancy $(III)$.
$C$. The foetus develops external genital organs by $12$ weeks of pregnancy $(IV)$.
$D$. The foetus body is covered with fine hair,eyelids separate,and eyelashes are formed by $24$ weeks of pregnancy $(I)$.
Therefore,the correct matching is $A-II, B-III, C-IV, D-I$.

(D) $GIFT$ stands for Gamete Intra-Fallopian Transfer.
It is an assisted reproductive technology used for females who cannot produce an ovum but can provide a suitable environment for fertilization and embryonic development.
In this procedure,the ovum is collected from a donor and transferred into the fallopian tube of the recipient.

(B) is incorrect because spermatogonia initially undergo mitotic divisions to increase their population.
$B$ is incorrect because primary spermatocytes undergo meiosis $I$ to form secondary spermatocytes.
$C$ is correct because secondary spermatocytes undergo meiosis $II$ to produce haploid spermatids.
$D$ is incorrect because the transformation of spermatids into spermatozoa is a process of structural remodeling called spermiogenesis,not mitosis.
$E$ is correct because the process of transformation of spermatids into spermatozoa is known as spermiogenesis.
Therefore,the correct statements are $C$ and $E$.

(B) Grasshoppers exhibit $XO$ type of sex determination.
Females are homogametic $(XX)$ and males are heterogametic $(XO)$.
Therefore,males have one chromosome less than females.
If females have $24$ chromosomes $(22+XX)$,males have $23$ chromosomes $(22+XO)$.

(A) The correct evolutionary sequence of early humans is: $Ramapithecus \rightarrow Australopithecus \rightarrow Homo \ habilis \rightarrow Homo \ erectus \rightarrow Neanderthal \ man \rightarrow Homo \ sapiens$. Based on the given options,the sequence provided in option $A$ is the most accurate representation of the chronological appearance of these species.