NEET 2020 Biology Question Paper with Answer and Solution

$(B)$ The anatomical features described are characteristic of a $Monocotyledonous$ stem:
$1$. Scattered vascular bundles: In monocot stems, vascular bundles are scattered throughout the ground tissue.
$2$. Bundle sheath: Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.
$3$. Ground tissue: The ground tissue is large, conspicuous, and parenchymatous.
$4$. Conjoint and closed vascular bundles: The bundles are conjoint (xylem and phloem together) and closed (no cambium present, so secondary growth does not occur).
$5$. Phloem parenchyma: Phloem parenchyma is typically absent in monocot stems.
Therefore, the correct option is $B$.

(C) Diuresis refers to an increased production of urine. Aldosterone is a mineralocorticoid hormone secreted by the adrenal cortex. It acts on the distal convoluted tubules and collecting ducts of the kidney to stimulate the reabsorption of $Na^+$ and water. By increasing the reabsorption of water back into the blood,aldosterone reduces the volume of urine produced,thereby preventing diuresis.

(D) In a standard $ECG$,the $P$-wave represents the electrical excitation or depolarisation of the atria (auricles),which leads to the contraction of both the atria.
The $QRS$ complex represents the depolarisation of the ventricles,which initiates the ventricular contraction.
The $T$-wave represents the return of the ventricles from an excited to a normal state,i.e.,repolarisation of the ventricles.

(B) In the light reaction of photosynthesis,electrons are excited in $PS-II$ and are captured by the primary electron acceptor. From there,they are passed to an electron transport system consisting of cytochromes. Plastoquinone $(PQ)$ acts as a mobile electron carrier that facilitates the transfer of electrons from $PS-II$ to the $Cytb_{6}f$ complex. This movement of electrons is coupled with the pumping of protons into the lumen,creating a proton gradient.

(A) The enzyme nitrogenase catalyzes the biological nitrogen fixation process in the root nodules of leguminous plants. The chemical reaction is represented as: $N_2 + 8e^- + 8H^+ + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16Pi$. As shown in the equation,the products of this reaction are ammonia $(NH_3)$ and hydrogen $(H_2)$.

(C) The correct matching is as follows:
$(a)$ Zygotene: Synapsis occurs,where homologous chromosomes pair up $(iv)$.
$(b)$ Pachytene: Crossing over occurs between non-sister chromatids of homologous chromosomes $(iii)$.
$(c)$ Diplotene: The dissolution of the synaptonemal complex occurs,and chiasmata become visible $(ii)$.
$(d)$ Diakinesis: The final stage of prophase-$I$ where terminalization of chiasmata occurs $(i)$.
Therefore,the correct sequence is $(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)$.

(B) $6-15$ pairs of gill slits are a characteristic feature of Cyclostomes $(ii)$.
$(b)$ Heterocercal caudal fin is a characteristic feature of Chondrichthyes $(iii)$.
$(c)$ Air Bladder is present in Osteichthyes $(iv)$ to regulate buoyancy.
$(d)$ Poison sting is found in Trygon $(i)$,which belongs to Chondrichthyes.
Therefore,the correct matching is $(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)$.

(D) The Golgi apparatus (or Golgi bodies) is the primary site for the modification,packaging,and sorting of proteins and lipids.
In eukaryotic cells,proteins synthesized in the rough endoplasmic reticulum and lipids synthesized in the smooth endoplasmic reticulum are transported to the Golgi apparatus.
Within the Golgi cisternae,these molecules undergo glycosylation,where carbohydrates are added to them to form glycoproteins and glycolipids.
Therefore,the Golgi apparatus is the important site for the formation of glycoproteins and glycolipids.

(B) The correct matching is as follows:
$(a)$ Inhibitor of catalytic activity: $(ii)$ Malonate (it acts as a competitive inhibitor of succinate dehydrogenase).
$(b)$ Possess peptide bonds: $(iv)$ Collagen (it is a protein, and proteins are polymers of amino acids linked by peptide bonds).
$(c)$ Cell wall material in fungi: $(iii)$ Chitin (it is a complex polysaccharide forming the fungal cell wall).
$(d)$ Secondary metabolite: $(i)$ Ricin (it is a toxic secondary metabolite produced by plants).
Therefore, the correct sequence is $(a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)$.

(C) The animals belonging to the phylum $Platyhelminthes$ (flatworms) exhibit bilateral symmetry,where the body can be divided into two identical left and right halves in only one plane.
They are also acoelomate,meaning they lack a body cavity (coelom) between the body wall and the digestive tract.
$Annelida$ are coelomates,$Ctenophora$ exhibit radial symmetry,and $Aschelminthes$ are pseudocoelomates.

(C) Floridean starch is the stored food material found in Rhodophyceae (red algae).
Its chemical structure is very similar to amylopectin and glycogen,as it is a branched polysaccharide composed of glucose units linked by $\alpha-1,4$ and $\alpha-1,6$ glycosidic bonds.

(D) The $G_{1}$ phase,also known as the first gap phase,is the interval between mitosis and the initiation of $DNA$ replication. During this phase,the cell is metabolically active and continuously grows in size,but it does not replicate its $DNA$.

(D) In a cockroach,the nervous system consists of a series of fused,segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side. The head holds only a small proportion of the nervous system (supra-oesophageal ganglia,which act as the brain),while the rest of the nervous system is situated along the ventral part of its body. Therefore,if the head is removed,the cockroach can still survive for a few days because the major part of its nervous system remains intact in the body.

(C) The enzyme enterokinase is secreted by the intestinal mucosa. It acts on the inactive enzyme trypsinogen,which is secreted by the pancreas,and converts it into its active form,trypsin. This activation is a crucial step in the protein digestion process in the small intestine.

(D) The correct matches are as follows:
$(a)$ Organ of Corti is located on the basilar membrane $(iv)$.
$(b)$ Cochlea is the coiled part of the labyrinth $(ii)$.
$(c)$ Eustachian tube connects the middle ear and the pharynx $(i)$.
$(d)$ Stapes is the ear ossicle attached to the oval window $(iii)$.
Therefore,the correct sequence is $(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)$.

(D) The correct answer is $D$.
In the alveoli,conditions are favourable for the formation of oxyhaemoglobin,which include high $pO_2$,low $pCO_2$,low $H^+$ concentration,and lower temperature.
Conversely,in the tissues,low $pO_2$,high $pCO_2$,high $H^+$ concentration,and higher temperature favour the dissociation of oxygen from oxyhaemoglobin.
Therefore,a higher $H^+$ concentration in the alveoli would actually inhibit the formation of oxyhaemoglobin,making statement $D$ incorrect.

(B) Glucocorticoids,such as cortisol,are hormones produced by the adrenal cortex. They stimulate the process of gluconeogenesis,which is the synthesis of glucose from non-carbohydrate sources like amino acids and glycerol. This helps in maintaining blood glucose levels. Insulin is hypoglycemic (lowers blood glucose),while glucagon is hyperglycemic (raises blood glucose).

(D) Amino acids are classified based on the number of amino and carboxyl groups in their structure.
$1$. Valine is a neutral,non-polar amino acid.
$2$. Tyrosine is a polar,aromatic amino acid.
$3$. Glutamic acid is an acidic amino acid because it contains an extra carboxyl group.
$4$. Lysine is a basic amino acid because it contains an extra amino group in its side chain.
Therefore,the correct answer is Lysine.

(D) Secondary metabolites like nicotine,strychnine,and caffeine are chemical compounds produced by plants that are not directly involved in growth,development,or reproduction. Instead,these compounds serve as a chemical defence mechanism against herbivores,insects,and pathogens,protecting the plant from being consumed or infected.

(D) Diabetes Mellitus is a metabolic disorder characterized by high blood glucose levels (Hyperglycaemia).
When blood glucose levels exceed the renal threshold,glucose is excreted in the urine,a condition known as Glycosuria.
Additionally,due to the inability of cells to utilize glucose,the body breaks down fats,leading to the accumulation of ketone bodies in the blood and their subsequent excretion in urine,known as Ketonuria.
Therefore,the presence of Ketonuria and Glycosuria in urine is indicative of Diabetes Mellitus.

(A) Statement $(a)$ is incorrect because in $Urochordata$ (Tunicata),the notochord is present only in the larval tail.
Statement $(b)$ is correct because in $Vertebrata$,the notochord is replaced by a cartilaginous or bony vertebral column in the adult.
Statement $(c)$ is correct as a dorsal,hollow central nervous system is a fundamental characteristic of chordates.
Statement $(d)$ is incorrect because $Chordata$ is divided into $3$ subphyla: $Urochordata$ (or $Tunicata$),$Cephalochordata$,and $Vertebrata$. $Hemichordata$ is a separate phylum.
Therefore,statements $(b)$ and $(c)$ are true.

(D) The proximal convoluted tubule $(PCT)$ of the nephron is lined by simple cuboidal epithelium. This epithelium possesses a prominent brush border of microvilli,which significantly increases the surface area for the reabsorption of water,electrolytes,and nutrients from the filtrate.

(C) Viroids were discovered by $T.O. Diener$ in $1971$. They are infectious agents that are smaller than viruses. Structurally,they consist of a low molecular weight free $RNA$ molecule and lack the protein coat that is found in viruses. Therefore,they are essentially 'naked' $RNA$ particles.

(C) In photorespiration, the $RuBisCo$ enzyme acts as an oxygenase. It catalyzes the reaction between $RuBP$ ($5-C$ compound) and $O_2$. This reaction results in the formation of one molecule of $3-phosphoglycerate$ ($3-C$ compound) and one molecule of $phosphoglycolate$ ($2-C$ compound).

(B) The correct matching is as follows:
$(a)$ Eosinophils: $(iii)$ Release histaminase and destructive enzymes,which help in resisting infections and allergic reactions.
$(b)$ Basophils: $(iv)$ Release granules containing histamine,serotonin,and heparin,which are involved in inflammatory reactions.
$(c)$ Neutrophils: $(ii)$ Phagocytosis,as they are the most abundant phagocytic cells that destroy foreign organisms.
$(d)$ Lymphocytes: $(i)$ Immune response,as they are responsible for the specific immune response of the body.
Therefore,the correct sequence is $(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)$.

(B) Inspiration is the process by which atmospheric air is drawn in.
$(1)$ During inspiration,the diaphragm contracts,which increases the thoracic volume in the antero-posterior axis.
$(2)$ The external inter-costal muscles contract,lifting up the ribs and the sternum,which increases the thoracic volume in the dorso-ventral axis.
$(3)$ An increase in thoracic volume leads to an increase in pulmonary volume.
$(4)$ According to Boyle's Law,an increase in pulmonary volume causes a decrease in intra-pulmonary pressure to less than atmospheric pressure,forcing air from outside into the lungs.
Therefore,events $(a)$ and $(b)$ are correct.

(C) Collagen is the most abundant protein in the animal kingdom. It is a structural protein that provides strength and support to various tissues,including skin,tendons,ligaments,and bones.

(A) Chlorella is a unicellular green alga. Spirulina is a unicellular cyanobacterium (often referred to as blue-green algae). Both are widely used as food supplements due to their high protein content. In contrast,Laminaria and Sargassum are multicellular brown algae,Gelidium and Gracilaria are multicellular red algae,and while Volvox is a colonial green alga,Anabaena is a filamentous cyanobacterium.

(D) The incorrect statement is that sapwood is the innermost secondary xylem. In reality,heartwood is the innermost,non-functional region of the secondary xylem,while sapwood is the peripheral,functional region. Sapwood is lighter in colour and is involved in the conduction of water and minerals,whereas heartwood is darker due to the deposition of organic compounds like tannins,resins,and oils,and provides only mechanical support.

(B) Cells that do not divide further exit the $G_{1}$ phase to enter an inactive stage called the quiescent stage $(G_{0})$ of the cell cycle.
In this stage,cells remain metabolically active but no longer proliferate unless called upon to do so depending on the requirement of the organism.

(D) The correct statement is that the ileum is a highly coiled part of the small intestine.
- The vermiform appendix arises from the caecum,not the duodenum.
- The ileum opens into the large intestine,specifically the caecum,not the small intestine.
- The serosa is the outermost layer of the alimentary canal,not the innermost (the innermost is the mucosa).

(D) The correct matches are as follows:
$(a)$ Pituitary gland: Deficiency of antidiuretic hormone $(ADH)$ leads to Diabetes insipidus $(iii)$.
$(b)$ Thyroid gland: Hyperthyroidism leads to Grave's disease $(i)$.
$(c)$ Adrenal gland: Hyposecretion of glucocorticoids leads to Addison's disease $(iv)$.
$(d)$ Pancreas: Deficiency of insulin leads to Diabetes mellitus $(ii)$.
Therefore, the correct sequence is $(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)$.

(C) In the citric acid cycle (Krebs cycle),substrate-level phosphorylation occurs during the conversion of succinyl-CoA to succinate.
This reaction is catalyzed by the enzyme succinyl-CoA synthetase.
During this step,one molecule of $GDP$ (or $ADP$) is phosphorylated to form $GTP$ (or $ATP$).
Therefore,there is exactly one substrate-level phosphorylation per turn of the citric acid cycle.

(D) The correct matching is as follows:
$(a)$ Iron: Required for chlorophyll biosynthesis $(iii)$.
$(b)$ Zinc: Required for $IAA$ (Indole$-3-$acetic acid) biosynthesis $(iv)$.
$(c)$ Boron: Essential for pollen germination $(ii)$.
$(d)$ Manganese: Essential for the photolysis of water during photosynthesis $(i)$.
Therefore,the correct sequence is $(a-iii, b-iv, c-ii, d-i)$,which corresponds to option $(D)$.

(C) The correct matching is as follows:
$(a)$ Gregarious,polyphagous pest: $(iv)$ $Locusta$ (Locusts are known for their swarming behavior and feeding on various crops).
$(b)$ Adult with radial symmetry and larva with bilateral symmetry: $(i)$ $Asterias$ (Echinoderms like starfish exhibit radial symmetry in adults but bilateral symmetry in larvae).
$(c)$ Book lungs: $(ii)$ $Scorpion$ (Scorpions are arachnids that use book lungs for respiration).
$(d)$ Bioluminescence: $(iii)$ $Ctenoplana$ (Ctenophores are well-known for the property of bioluminescence).
Therefore,the correct sequence is $(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)$,which corresponds to option $(C)$.

(B) In the family $Asteraceae$ (Compositae),the inflorescence is a capitulum or head.
Ray florets are typically pistillate (female) or neutral and zygomorphic.
The ovary in ray florets is inferior,meaning the other floral parts (sepals,petals,and stamens) are situated above the level of the ovary.

(B) In monocotyledonous plants,the primary root is short-lived and is replaced by a large number of roots. These roots originate from the base of the stem and constitute the fibrous root system,as seen in wheat and grass.

(B) The growth rate is not uniform throughout the life cycle of an organism.
$1$. $Lag$ phase: This is the initial phase where growth is slow as the cells are preparing for division.
$2$. $Log$ phase (Exponential phase): During this phase,the growth rate is maximum because the cells divide rapidly and exponentially.
$3$. $Stationary$ phase: Growth slows down and eventually stops due to limited resources.
$4$. $Senescence$: This is the phase of decline or aging.
Therefore,the process of growth is maximum during the $Log$ phase.

(A) In $Pteridophytes$,the sporophytes bear sporangia that are subtended by leaf-like appendages called sporophylls. In some cases,such as in $Equisetum$,these sporophylls may form distinct compact structures called strobili or cones. Therefore,the correct answer is $Equisetum$.

(A) The correct matches are as follows:
$(a)$ Floating Ribs: These are the $11^{th}$ and $12^{th}$ pairs of ribs that do not connect with the sternum, hence $(iv)$.
$(b)$ Acromion: It is a bony process on the scapula that articulates with the clavicle, hence $(iii)$.
$(c)$ Scapula: It is a large triangular bone situated in the dorsal part of the thorax between the second and seventh ribs, hence $(i)$.
$(d)$ Glenoid cavity: It is a depression in the scapula that articulates with the head of the humerus, hence $(ii)$.
Therefore, the correct sequence is $(a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)$.

(A) In a perigynous flower,the gynoecium is situated in the center and other parts of the flower are located at the rim of the thalamus almost at the same level. The ovary is said to be half inferior. Examples of perigynous flowers include Plum,Rose,and Peach. Therefore,the correct option is Plum.

(D) The synaptonemal complex is a protein structure that forms between homologous chromosomes during meiosis $I$.
$1$. During $Zygotene$,the synaptonemal complex forms,facilitating the pairing of homologous chromosomes (synapsis).
$2$. During $Pachytene$,crossing over occurs between non-sister chromatids.
$3$. During $Diplotene$,the synaptonemal complex dissolves,and the homologous chromosomes begin to separate from each other except at the sites of crossovers,known as chiasmata.

(A) $1$. $Inulin$ is a polysaccharide (a polymer of fructose) and therefore contains glycosidic bonds between its monosaccharide units.
$2$. $Insulin$ is a protein (a hormone) composed of amino acids linked together by peptide bonds.
$3$. Therefore,$Inulin$ contains glycosidic bonds and $Insulin$ contains peptide bonds.

(C) Gibberellins are a group of plant growth regulators that promote stem elongation. When sprayed on sugarcane crops,they increase the length of the stem,which can increase the yield by as much as $20$ tonnes per acre.

(C) Inclusion bodies are non-membrane-bound structures found in prokaryotic cells that serve as storage sites for reserve materials like glycogen granules,phosphate granules,and cyanophycean granules. They lie free in the cytoplasm. They are not involved in the ingestion of food particles; therefore,statement $C$ is incorrect.

(C) The process described is known as guttation. Guttation occurs due to the development of positive hydrostatic pressure in the roots,known as root pressure. When transpiration is low (at night or early morning),water accumulates in the xylem,creating a positive pressure that pushes water out through specialized pores called hydathodes located at the tips of grass blades.

(B) Seed dormancy is a state in which seeds are prevented from germinating even under favorable environmental conditions. This state is maintained by various growth inhibitors.
$1$. Abscisic acid $(ABA)$,phenolic acids,and para-ascorbic acid are well-known growth inhibitors that promote seed dormancy.
$2$. Gibberellic acid $(GA)$ is a plant growth promoter that acts antagonistically to $ABA$. It helps in breaking seed dormancy and promotes germination.
Therefore,Gibberellic acid is not an inhibitory substance; rather,it is a stimulatory substance for seed germination.

(C) $Diabetes$ $Mellitus$ is a metabolic disorder characterized by high blood glucose levels $(Hyperglycemia)$.
When blood glucose levels exceed the renal threshold,glucose is excreted in the urine,a condition known as $Glycosuria$.
Additionally,due to the inability of cells to utilize glucose,the body breaks down fats for energy,leading to the production of ketone bodies,which are also excreted in the urine,a condition known as $Ketonuria$.
Therefore,the presence of $Glycosuria$ and $Ketonuria$ in the urine is a diagnostic indicator of $Diabetes$ $Mellitus$.

(D) Viroids are infectious agents that are smaller than viruses.
They consist of a short strand of circular,single-stranded $RNA$ without a protein coat (capsid).
Because they lack a protein coat,they are distinct from viruses.
Therefore,the correct statement is that they have free $RNA$ without a protein coat.

(C) Cyanobacteria are photosynthetic autotrophs. Some species of Cyanobacteria,such as $Nostoc$ and $Anabaena$,possess specialized cells called heterocysts. These heterocysts are responsible for fixing atmospheric nitrogen into ammonia,which is essential for the organism's survival in nitrogen-deficient environments. Therefore,the statement that they lack heterocysts is incorrect.

(D) The correct statement is that functional insulin has $A$ and $B$ chains linked together by disulfide bonds,not hydrogen bonds.
Proinsulin consists of $A$,$B$,and $C$ peptides.
During maturation,the $C-peptide$ is removed to form functional insulin.
Therefore,the statement claiming that chains are linked by hydrogen bonds is incorrect.

(B) The embryological support for evolution,which was proposed by Ernst Haeckel (based on the observation of certain features during embryonic development),was disapproved by Karl Ernst von Baer. He noted that embryos never pass through the adult stages of other animals; rather,they share common embryonic features that diverge as development progresses.

(A) Thomas Hunt Morgan provided the experimental verification of the chromosomal theory of inheritance. While Sutton and Boveri proposed the theory, it was Morgan who worked with $Drosophila$ $\text{melanogaster}$ (fruit flies) to demonstrate the linkage and recombination of genes on chromosomes, thereby providing the necessary experimental evidence.

(B) In both water hyacinth and water lily,the flowers emerge above the level of water. Therefore,they are not pollinated by water. Instead,pollination is carried out by insects or wind,which is a common feature in many aquatic plants.

(B) $Bt$ cotton is a genetically modified organism $(GMO)$ created by inserting the cry genes from the bacterium $Bacillus$ $thuringiensis$ into the cotton plant genome.
These genes encode for crystal $(Cry)$ proteins,which are toxic to specific groups of insects.
When insect pests,such as bollworms,feed on the tissues of the $Bt$ cotton plant,the protoxin is activated in their alkaline gut,leading to cell lysis and the death of the insect.
Therefore,$Bt$ cotton is specifically resistant to insect pests.

(C) The flippers of penguins (birds) and dolphins (mammals) are analogous organs.
These organs perform similar functions (swimming) but have different evolutionary origins and anatomical structures.
When different groups of organisms evolve similar traits due to adaptation to similar environmental pressures,it is known as convergent evolution.

(B) In $1953$,$S.L.$ Miller conducted a famous experiment to test the Oparin-Haldane hypothesis regarding the origin of life.
He created a simulated primitive atmosphere in a closed flask containing methane $(CH_{4})$,hydrogen $(H_{2})$,ammonia $(NH_{3})$,and water vapor $(H_{2}O)$.
He maintained the temperature at $800^{\circ}C$ and provided energy through electric discharges to simulate lightning.
As a result of this experiment,he observed the formation of simple amino acids,which are the building blocks of proteins.

(B) The restriction endonuclease $EcoRI$ recognizes the specific palindromic sequence $5^{\prime}-GAATTC-3^{\prime}$ and $3^{\prime}-CTTAAG-5^{\prime}$.
This sequence is read the same in both directions when the orientation of the strands is $5^{\prime}$ to $3^{\prime}$.

(C) The correct matches are as follows:
$(a)$ Clostridium butylicum produces Butyric Acid $(ii)$.
$(b)$ Trichoderma polysporum produces Cyclosporin-$A$ $(i)$,which is an immunosuppressive agent.
$(c)$ Monascus purpureus produces statins,which act as blood cholesterol lowering agents $(iv)$.
$(d)$ Aspergillus niger produces Citric Acid $(iii)$.
Therefore,the correct sequence is $(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)$.

(B) The process of ovulation is triggered by a sudden surge in the levels of Luteinizing Hormone $(LH)$,often referred to as the $LH$ surge. This surge is induced by a high concentration of Estrogen in the blood,which exerts positive feedback on the anterior pituitary gland. Therefore,a high concentration of Estrogen is the primary hormonal signal that leads to the release of the ovum from the Graafian follicle.

(B) The techniques where embryos are transferred into the female reproductive tract are $ZIFT$ (Zygote Intra Fallopian Transfer) and $IUT$ (Intra Uterine Transfer).
In $ZIFT$,the zygote or early embryos (up to $8$ blastomeres) are transferred into the fallopian tube.
In $IUT$,embryos with more than $8$ blastomeres are transferred into the uterus.
$GIFT$ (Gamete Intra Fallopian Transfer) involves the transfer of gametes (ova),not embryos,and $ICSI$ (Intra Cytoplasmic Sperm Injection) is a procedure to form an embryo,not a transfer technique for an already formed embryo.

(C) The life cycle of $Plasmodium$ begins when an infected female $Anopheles$ mosquito bites a human.
During this bite,the parasite in the form of $Sporozoites$ is injected into the human bloodstream through the mosquito's saliva.
$Sporozoites$ are the infectious stage of $Plasmodium$ for humans,which then travel to the liver to initiate the infection.

$(A)$ The correct matches are as follows:
$(a)$ Placenta produces hormones like Human Chorionic Gonadotropin $(hCG)$. Thus, $(a)-(ii)$.
$(b)$ Zona pellucida is the outer glycoprotein layer of the ovum. Thus, $(b)-(iii)$.
$(c)$ Bulbo-urethral glands secrete a fluid that helps in the lubrication of the penis. Thus, $(c)-(iv)$.
$(d)$ Leydig cells (interstitial cells) present in the testis produce male sex hormones called androgens. Thus, $(d)-(i)$.
Therefore, the correct sequence is $(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)$.

(D) $1$. Thalassemia is an autosomal recessive blood disorder.
$2$. Haemophilia is an $X$-linked recessive disorder.
$3$. Phenylketonuria is an autosomal recessive metabolic disorder.
$4$. Sickle cell anaemia is an autosomal recessive trait caused by a mutation in the gene located on chromosome $11$.

(B) In the structure of $DNA$,adenine $(A)$ is a purine that specifically pairs with thymine $(T)$,which is a pyrimidine.
This pairing is stabilized by two hydrogen $(H)$ bonds between the nitrogenous bases.
Therefore,the statement that adenine pairs with thymine through two $H$-bonds is correct.

(A) In plants,the sporophyte generation is diploid $(2n)$ and the gametophyte generation is haploid $(n)$.
$(a)$ Pollen grains (male gametophyte,$n$) develop inside the anther (part of the sporophyte,$2n$). Thus,this represents two generations.
$(b)$ $A$ germinated pollen grain is a single generation (male gametophyte).
$(c)$ $A$ seed contains an embryo (new sporophyte) and endosperm/seed coat (parental sporophyte tissues). While it involves different generations,the question specifically refers to the gametophyte within the sporophyte structure.
$(d)$ The embryo sac (female gametophyte,$n$) develops inside the ovule (part of the sporophyte,$2n$). Thus,this represents two generations.
Therefore,$(a)$ and $(d)$ are the correct examples of one generation within another.

(D) The new breed of sheep,'Hisardale',was developed by crossing Bikaneri ewes and Marino rams. This method of mating animals of two different breeds is known as cross breeding. Cross breeding allows the desirable qualities of two different breeds to be combined into the progeny.

(D) Anthropogenic action refers to human-induced changes in the environment that drive evolution.
$(b)$ Herbicide-resistant weeds evolve due to the excessive use of herbicides.
$(c)$ Drug-resistant eukaryotes (like pathogens) evolve due to the overuse of medicines.
$(d)$ Man-created breeds of domesticated animals like dogs are the result of artificial selection by humans.
Darwin's Finches $(a)$ are an example of adaptive radiation driven by natural environmental factors,not anthropogenic action.
Therefore,$(b), (c),$ and $(d)$ are correct examples.

(B) Sexually transmitted diseases (STDs) are infections that are passed from one person to another through sexual contact.
$1$. Gonorrhoea is a bacterial infection caused by $Neisseria$ \text{ gonorrhoeae}.
$2$. Syphilis is a bacterial infection caused by $Treponema$ \text{ pallidum}.
$3$. Genital herpes is a viral infection caused by the Herpes Simplex Virus $(HSV)$.
Cancer, Malaria, and Filaria are not classified as sexually transmitted diseases. Therefore, the correct option is $B$.

(C) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion. It was signed in $1987$ and came into force in $1989$. These substances include chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances $(ODS)$.

(A) According to the estimates made by Robert May,the global species diversity is about $7$ million. While more than $1.5$ million species have been described so far,many more remain to be discovered and described.

(D) The length of $DNA$ is calculated by multiplying the distance between two consecutive base pairs by the total number of base pairs.
Given:
Distance between two base pairs = $0.34 \, nm = 0.34 \times 10^{-9} \, m$.
Total number of base pairs = $6.6 \times 10^{9} \, bp$.
Length of $DNA$ = $(\text{Distance between two base pairs}) \times (\text{Total number of base pairs})$.
Length of $DNA$ = $(0.34 \times 10^{-9} \, m) \times (6.6 \times 10^{9} \, bp)$.
Length of $DNA$ = $0.34 \times 6.6 \, m = 2.244 \, m$.
Therefore,the length of the $DNA$ is approximately $2.2 \, meters$.

(B) The correct matching is as follows:
$(a)$ $Bt$ cotton is produced using the bacterium $Bacillus$ $thuringiensis$ $(iv)$.
$(b)$ Adenosine deaminase $(ADA)$ deficiency is treated using Gene therapy $(i)$.
$(c)$ $RNAi$ ($RNA$ interference) is a method of cellular defence in eukaryotes $(ii)$.
$(d)$ $PCR$ (Polymerase Chain Reaction) is used for the detection of $HIV$ infection $(iii)$.
Therefore,the correct sequence is $(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)$.

(B) In a grassland ecosystem, the trophic levels are organized as follows:
$1$. First trophic level $(T_1)$: Producers (e.g., Grass) - $(c) - (iv)$
$2$. Second trophic level $(T_2)$: Primary consumers (e.g., Rabbit) - $(b) - (iii)$
$3$. Third trophic level $(T_3)$: Secondary consumers (e.g., Crow) - $(d) - (i)$
$4$. Fourth trophic level $(T_4)$: Tertiary consumers (e.g., Vulture) - $(a) - (ii)$
Therefore, the correct matching is $(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)$.
Thus, the correct option is $(B)$.

(C) The correct matches are as follows:
$(a)$ Typhoid is caused by the bacterium $Salmonella$ $typhi$ $(iii)$.
$(b)$ Pneumonia is caused by bacteria like $Streptococcus$ $pneumoniae$ or $Haemophilus$ $influenzae$ $(iv)$.
$(c)$ Filariasis (Elephantiasis) is caused by filarial worms like $Wuchereria$ $bancrofti$ or $Wuchereria$ $malayi$ $(i)$.
$(d)$ Malaria is caused by protozoan parasites of the genus $Plasmodium$ $(ii)$.
Therefore,the correct sequence is $(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)$.

(A) The secondary oocyte is arrested in $Metaphase-II$ of meiosis. The meiotic division of the secondary oocyte is completed only when a sperm enters the ovum during fertilization. This process results in the formation of a haploid ovum (ootid) and a second polar body.

(B) The statement 'Sticky ends can be joined by using $DNA$ ligases' is technically misleading in the context of standard textbook questions because while $DNA$ ligase joins the phosphodiester backbone,the term 'sticky ends' refers to the single-stranded overhangs created by restriction enzymes. However,in many competitive exam contexts,the statement that is often considered 'wrong' or 'incorrect' regarding the fundamental definition of restriction enzymes is that they 'inspect the length' of the sequence; they actually inspect the specific 'nucleotide sequence' (recognition site),not the length. Re-evaluating the provided options: Option $B$ is the most scientifically inaccurate because restriction enzymes recognize specific sequences,not lengths. If the question implies that sticky ends are joined by ligase,that is actually a correct biological process. Therefore,the statement 'Each restriction enzyme functions by inspecting the length of a $DNA$ sequence' is the incorrect statement.

(C) Gross primary productivity $(GPP)$ is the total amount of organic matter produced by producers through photosynthesis in an ecosystem per unit area over a time period.
Net primary productivity $(NPP)$ is the amount of biomass available for consumption by heterotrophs after accounting for the energy lost by producers during respiration $(R)$.
The relationship is defined by the equation: $NPP = GPP - R$.
Since respiration $(R)$ is always a positive value,$GPP$ must always be greater than $NPP$.

(C) The $Ori$ site (Origin of replication) is a specific sequence in the vector where replication starts. Any piece of $DNA$ linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked $DNA$.

(A) During the process of transcription,the enzyme $RNA$ polymerase is responsible for both the unwinding of the $DNA$ double helix and the synthesis of the $RNA$ strand. Unlike replication,where $DNA$ helicase is used to unwind the helix,transcription relies on the $RNA$ polymerase holoenzyme to initiate the separation of the $DNA$ strands at the promoter site.

(C) Snow-blindness is a condition caused by the inflammation of the cornea due to a high dose of $UV-B$ radiation. In the Antarctic region,the high reflection of $UV$ rays from the snow leads to an increased exposure of the eyes to these radiations,which causes the cornea to absorb high levels of $UV-B$,resulting in inflammation and temporary blindness.

(A) During sewage treatment,the sediment from the primary settling tank is called primary sludge. The sediment from the secondary treatment (biological treatment) is called activated sludge. $A$ small part of the activated sludge is pumped back into the aeration tank as inoculum,while the remaining major part of the activated sludge is pumped into large tanks called anaerobic sludge digesters. In these digesters,other kinds of bacteria,which grow anaerobically,digest the bacteria and the fungi in the sludge.

(D) The statement 'When $I^{A}$ and $I^{B}$ are present together,they express same type of sugar' is incorrect.
In the $ABO$ blood group system,the gene $I$ has three alleles: $I^{A}$,$I^{B}$,and $i$.
Alleles $I^{A}$ and $I^{B}$ produce different types of sugar polymers on the surface of red blood cells,while allele $i$ does not produce any sugar.
When both $I^{A}$ and $I^{B}$ are present together,they both express their own sugars simultaneously due to codominance,resulting in blood type $AB$. They do not express the same type of sugar.

(D) The process of translation involves the synthesis of a polypeptide chain from an $mRNA$ template. The first phase of this process is the 'charging' of $tRNA$,also known as the aminoacylation of $tRNA$. During this step,specific amino acids are linked to their cognate $tRNA$ molecules in the presence of $ATP$. This activation is essential for the subsequent steps of translation,such as the formation of peptide bonds.

(C) In gel electrophoresis,the separated $DNA$ fragments cannot be seen directly in visible light. To visualize them,the gel is stained with a fluorescent dye called Ethidium bromide $(EtBr)$. When this stained gel is exposed to $UV$ radiation,the $DNA$ fragments appear as bright orange-colored bands.

(A) The Amazon tropical rainforest,located in South America,is known as the 'Lungs of the Planet'. It possesses the greatest biodiversity on Earth. It is home to more than $40,000$ species of plants,$3,000$ species of fishes,$1,300$ species of birds,$427$ species of mammals,$427$ species of amphibians,$378$ species of reptiles,and more than $1,25,000$ invertebrates. Therefore,it exhibits the highest species diversity.

(D) Gregor Mendel selected $14$ true-breeding pea plant varieties.
These varieties were chosen as pairs that were similar in all aspects except for one character with contrasting traits.
These $14$ varieties represented $7$ pairs of contrasting traits (e.g.,tall/dwarf,violet/white flowers,etc.).

(D) The correct answer is $D$.
Active immunity is slow and takes time to give its full effective response because it involves the activation of the immune system and the production of antibodies by the host's body.
In contrast, passive immunity provides immediate relief as ready-made antibodies are introduced directly into the body.

(A) population is a group of individuals of the same species living in a specific geographical area at a given time. Attributes of a population include birth rate (natality),death rate (mortality),sex ratio,and age distribution. Species interaction refers to the interaction between two or more different species in a community,which is a property of a community,not a single population.

$(B)$ Ligases are enzymes that act as 'molecular glue' by catalyzing the formation of phosphodiester bonds between the $3'-OH$ end of one $DNA$ fragment and the $5'-phosphate$ end of another, thereby joining two $DNA$ molecules together. Exonucleases remove nucleotides from the ends of $DNA$, whereas endonucleases make cuts at specific positions within $DNA$. Polymerases are involved in the synthesis of $DNA$ strands, not in breaking them.

(A) Sexually transmitted diseases $(STDs)$ are infections that are transmitted through sexual contact.
$1$. Gonorrhoea is caused by the bacterium $Neisseria$ $gonorrhoeae$.
$2$. Syphilis is caused by the bacterium $Treponema$ $pallidum$.
$3$. Genital herpes is caused by the Herpes Simplex Virus $(HSV)$.
All three diseases listed in option $A$ are classic examples of $STDs$.
Malaria is a vector-borne disease,$AIDS$ is a viral disease (can be sexually transmitted but is not exclusively so),Filariasis is a helminthic disease,and Cancer is a non-communicable disease.

(A) The restriction enzyme $EcoRI$ is derived from $Escherichia \text{ } coli \text{ } RY13$.
It recognizes the specific palindromic base sequence $5'-GAATTC-3'$ and $3'-CTTAAG-5'$.
$A$ palindromic sequence in $DNA$ is a sequence of base pairs that reads the same on the two strands when the orientation of reading is kept the same (e.g., $5' \rightarrow 3'$ direction).
Therefore, the correct option is $A$.

(B) The $ori$ (Origin of replication) is a specific $DNA$ sequence in a vector where replication starts.
Any piece of $DNA$ linked to this sequence can be made to replicate within the host cells.
This sequence is also responsible for controlling the copy number of the linked $DNA$.
Therefore,if one wants to recover many copies of the target $DNA$,it should be cloned in a vector whose origin supports high copy number.

(A) Restriction enzymes are endonucleases that recognize specific $DNA$ sequences known as palindromic sequences and cut the $DNA$ at these sites.
Option $A$ is incorrect because restriction enzymes do not inspect the length of the $DNA$ sequence; rather,they recognize specific nucleotide sequences (recognition sites) regardless of the total length of the $DNA$ molecule.
Option $B$ is correct as they cut at palindromic sites.
Option $C$ is correct as they are fundamental tools in genetic engineering.
Option $D$ is correct as $DNA$ ligase is used to join the sticky ends produced by restriction enzymes.

(B) In gel electrophoresis,$DNA$ fragments are separated based on their size. Since $DNA$ is negatively charged,it moves towards the anode. These separated $DNA$ fragments are not visible under normal light. To visualize them,the gel is stained with a fluorescent dye called Ethidium Bromide $(EtBr)$. When this stained gel is exposed to $UV$ radiation,the $DNA$ fragments appear as bright orange-colored bands.

(A) The ovule is attached to the placenta by means of a stalk called the funicle. The point of attachment of the body of the ovule with the funicle is known as the hilum. Thus,the hilum represents the junction between the ovule and the funicle.

(A) $1$. Ligases are enzymes that catalyze the joining of two $DNA$ molecules by forming phosphodiester bonds. This is a correct statement.
$2$. Polymerases are enzymes that synthesize $DNA$ strands,not cut them.
$3$. Nucleases are enzymes that degrade $DNA$ by breaking phosphodiester bonds. Helicases are responsible for separating the $DNA$ double helix.
$4$. Exo-nucleases remove nucleotides from the ends of $DNA$ molecules,whereas Endo-nucleases cut $DNA$ at specific internal positions.

(B) In plants,the sporophyte generation is diploid $(2n)$ and the gametophyte generation is haploid $(n)$.
$(a)$ Pollen grains (gametophyte) are inside the anther (sporophyte). This represents two generations.
$(b)$ Germinated pollen grain is a single generation (gametophyte).
$(c)$ Seed (new sporophyte) is inside the fruit (parent sporophyte). This represents two generations.
$(d)$ Embryo sac (gametophyte) is inside the ovule (sporophyte). This represents two generations.
Therefore,$(a), (c),$ and $(d)$ consist of two generations,one within the other.

(D) The correct matches are as follows:
$(a)$ Bacillus thuringiensis produces $(iv)$ Cry proteins, which are used in insect-resistant crops.
$(b)$ Thermus aquaticus is the source of Taq $(iii)$ $DNA$ polymerase, which is essential for the Polymerase Chain Reaction $(PCR)$.
$(c)$ Agrobacterium tumefaciens acts as a $(i)$ cloning vector (specifically a natural genetic engineer) used to transfer genes into plants.
$(d)$ Salmonella typhimurium was used by Cohen and Boyer for the $(ii)$ construction of the first rDNA molecule in $1972$.
Thus, the correct sequence is $(a-iv, b-iii, c-i, d-ii)$, which corresponds to option $(D)$.

(C) population is a group of individuals of the same species living in a specific area at a specific time.
Key attributes of a population include:
$1$. Birth rate (Natality): The number of births per capita per unit time.
$2$. Death rate (Mortality): The number of deaths per capita per unit time.
$3$. Sex ratio: The ratio of males to females in a population.
$4$. Age distribution: The percentage of individuals of different ages in a population.
Species interaction refers to the interaction between two or more different species in a community,which is a community-level attribute,not a population-level attribute.
Therefore,the correct option is $C$.