NEET 2018 Biology Question Paper with Answer and Solution

(A) Osteoporosis is a condition characterized by a decrease in bone mass and increased fragility of bones.
$1$. Estrogen is crucial for maintaining bone density in women; a decline in estrogen levels after menopause leads to increased bone resorption.
$2$. Parathyroid hormone $(PTH)$ regulates calcium levels in the blood. Excess $PTH$ stimulates osteoclasts to break down bone tissue to release calcium into the bloodstream,which can lead to bone loss.
Therefore,both estrogen and parathyroid hormone play a significant role in the development of osteoporosis.

(B) Hormones are classified based on their chemical nature into peptide,steroid,iodothyronines,and amino acid derivatives.
$1$. $Estriol$ and $Estradiol$ are steroid hormones derived from cholesterol.
$2$. $Ecdysone$ is a steroid hormone found in insects.
$3$. $Epinephrine$ (also known as adrenaline) is an amino acid derivative,specifically synthesized from the amino acid $Tyrosine$.
Therefore,the correct option is $B$.

(D) The $Limbic$ $system$ is a complex structure in the brain involved in the regulation of sexual behavior,expression of emotional reactions (e.g.,excitement,pleasure,rage,and fear),and motivation. It does not control voluntary movement; voluntary movement is primarily controlled by the motor cortex and the cerebellum. Therefore,the pairing in option $D$ is incorrect. All other options correctly describe the functions of the respective brain structures.

(B) The human eye contains a transparent,crystalline lens.
This lens is held in its position by suspensory ligaments.
These ligaments are attached to the ciliary body,which is an extension of the choroid.
The ciliary body contains ciliary muscles that control the shape of the lens by adjusting the tension on these ligaments,thereby facilitating accommodation for near and far vision.

(B) The $Parietal$ cells (also known as $Oxyntic$ cells) present in the gastric glands secrete $Intrinsic$ $Factor$ ($Castle's$ $Intrinsic$ $Factor$).
This factor is essential for the absorption of $Vitamin$ $B_{12}$ in the ileum of the small intestine.
$Vitamin$ $B_{12}$ is a crucial co-factor required for the maturation of red blood cells $(RBCs)$ in the bone marrow.
Therefore,by facilitating the absorption of $Vitamin$ $B_{12}$,$Parietal$ cells indirectly support the process of erythropoiesis.

(A) The plasma proteins play specific roles in the human body:
$1$. Fibrinogen: These are proteins needed for clotting or coagulation of blood. Thus, $(a)$ matches with $(ii)$.
$2$. Globulin: These are primarily involved in the defence mechanisms of the body (e.g., immunoglobulins/antibodies). Thus, $(b)$ matches with $(iii)$.
$3$. Albumin: These proteins help in maintaining the osmotic balance of the blood. Thus, $(c)$ matches with $(i)$.
Therefore, the correct matching is $a-ii, b-iii, c-i$.

(D) Occupational respiratory disorders are conditions caused by the inhalation of harmful substances (such as dust, fumes, or gases) present in the workplace environment.
$Silicosis$ is a classic example of an occupational respiratory disorder caused by the inhalation of silica dust, which leads to inflammation and fibrosis of the lung tissue.
$Emphysema$ is primarily caused by cigarette smoking.
$Anthracis$ refers to a bacterial infection caused by $Bacillus$ \text{ anthracis}.
$Botulism$ is a rare but serious illness caused by a toxin that attacks the body's nerves.

(B) During skeletal muscle contraction,the binding of $Ca^{2+}$ ions to the $Troponin$ complex is a critical step.
In a relaxed state,the active sites on the actin filament are masked by the $Tropomyosin$ protein.
When $Ca^{2+}$ ions are released from the sarcoplasmic reticulum,they bind to $Troponin$.
This binding causes a conformational change in the $Troponin-Tropomyosin$ complex,which shifts the $Tropomyosin$ away from the active sites on the actin filament.
This exposure allows the myosin heads to bind to the actin,forming cross-bridges and initiating muscle contraction.

(C) Nissl bodies (also known as Nissl substance or chromatophilic substance) are large granular bodies found in neurons.
They are primarily composed of rough endoplasmic reticulum $(RER)$ and free ribosomes.
These structures are the sites of protein synthesis within the nerve cell,which is essential for the maintenance and repair of the neuron.

(C) The correct answer is $C$.
$1$. Glycolysis requires $NAD^+$ to act as an electron acceptor to form $NADH + H^+$.
$2$. The enzymes of the $TCA$ cycle (Krebs cycle) are located in the mitochondrial matrix.
$3$. Oxidative phosphorylation (the electron transport system) takes place in the inner mitochondrial membrane,not the outer membrane.
$4$. Glycolysis occurs in the cytosol of the cell.

(A) Polytene chromosomes are giant chromosomes found in the salivary glands of Drosophila (fruit fly) larvae and some other dipteran insects,not in the oocytes of amphibians.
Lampbrush chromosomes are observed in the diplotene stage of meiotic prophase-$I$ in the oocytes of many vertebrates,including amphibians.
Submetacentric chromosomes have a centromere slightly away from the center,resulting in unequal arms,which gives them an $L$-shape during anaphase.
Allosomes are the chromosomes that determine the sex of an organism,commonly known as sex chromosomes.
Therefore,the incorrect match is Polytene chromosomes - Oocytes of amphibians.

(D) Human dentition is characterized by three main features:
$1$. $Thecodont$: The teeth are embedded in the sockets of the jaw bone.
$2$. $Diphyodont$: Two sets of teeth are formed during the life of an individual,a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth.
$3$. $Heterodont$: An adult human has different types of teeth,namely incisors $(I)$,canines $(C)$,premolars $(PM)$,and molars $(M)$,which serve different functions.

(A) The rough endoplasmic reticulum $(RER)$ is primarily involved in the synthesis,folding,and modification of proteins destined for secretion or for use in membranes.
$1$. Protein folding occurs in the lumen of the $RER$ with the help of chaperone proteins.
$2$. Cleavage of the signal peptide occurs as the nascent polypeptide enters the $RER$ lumen.
$3$. Protein glycosylation (specifically $N$-linked glycosylation) begins in the $RER$.
$4$. Phospholipid synthesis primarily occurs in the smooth endoplasmic reticulum $(SER)$,not the $RER$. Therefore,phospholipid synthesis is the event that does not occur in the $RER$.

(B) In protein synthesis,a single $mRNA$ molecule can be translated by multiple ribosomes simultaneously.
This structure,where several ribosomes are attached to a single $mRNA$ strand,is known as a $Polysome$ or $Polyribosome$.
This mechanism allows the cell to produce multiple copies of the same polypeptide chain efficiently from a single $mRNA$ template.

(B) Ciliates,such as $Paramecium$,are unique among protozoans because they possess two types of nuclei: a large macronucleus and a small micronucleus.
The macronucleus controls vegetative functions,while the micronucleus is involved in reproduction and genetic exchange.
Other protozoans like amoeboids,flagellates,and sporozoans do not exhibit this specific nuclear dimorphism.

(C) The digestive tract of birds $(Aves)$ has additional chambers,the crop and the gizzard.
$1$. The crop is a specialized pouch used for the storage of food.
$2$. The gizzard is a thick-walled,muscular organ used for grinding food,which compensates for the lack of teeth in birds.
Therefore,the correct group is $Aves$.

(D) Homeotherms (or endotherms) are animals that can maintain a constant body temperature regardless of the environmental temperature. Birds $(Aves)$ and mammals $(Mammalia)$ are homeotherms.
$Psittacula$ (Parrot) is a bird.
$Macropus$ (Kangaroo) is a mammal.
$Camelus$ (Camel) is a mammal.
$Chelone$ (Green sea turtle) belongs to the class $Reptilia$. Reptiles are poikilotherms (ectotherms),meaning they cannot maintain a constant body temperature and their body temperature fluctuates with the environment.
Therefore,$Chelone$ is not a homeotherm.

(D) In male cockroaches,the $9th$ abdominal segment bears a pair of short,thread-like anal styles (caudal styles).
These structures are absent in female cockroaches.
Anal cerci are present in both male and female cockroaches.
The $7th$ sternum is boat-shaped in females,not males.
Therefore,the presence of caudal styles is the diagnostic feature used to distinguish a male cockroach from a female.

(B) Metamorphosis is a biological process by which an animal physically develops after birth or hatching,involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.
$A$. Starfish undergo indirect development involving a larval stage (e.g.,bipinnaria larva),which is a form of metamorphosis.
$B$. Earthworms exhibit direct development. They hatch from cocoons as miniature versions of the adult,meaning they do not undergo a larval stage or metamorphosis.
$C$. Moths undergo complete metamorphosis,which includes four stages: egg,larva (caterpillar),pupa,and adult.
$D$. Tunicates (Urochordates) undergo retrogressive metamorphosis,where the free-swimming larva possesses a notochord,which is lost in the sessile adult form.
Therefore,the correct answer is $B$.

(C) Diatoms are microscopic,photosynthetic organisms belonging to the kingdom $Protista$ (class $Bacillariophyceae$).
They are found in both fresh water and marine environments.
In the oceans,they are the primary source of food for many aquatic organisms and are responsible for a significant portion of global photosynthesis.
Due to their massive abundance and photosynthetic activity,they are famously known as the 'chief producers' in the oceans.

(A) Asthma is a respiratory disorder characterized by difficulty in breathing due to inflammation of the bronchi and bronchioles.
Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased.
Thus,asthma involves inflammation of bronchioles,and emphysema involves a decreased respiratory surface.

(B) The correct matches are as follows:
$1$. $(a)$ Tricuspid valve: This valve is located between the right atrium and the right ventricle, preventing the backflow of blood into the atrium during ventricular systole.
$2$. $(b)$ Bicuspid valve (Mitral valve): This valve is located between the left atrium and the left ventricle.
$3$. $(c)$ Semilunar valve: These valves are located at the openings of the right ventricle into the pulmonary artery and the left ventricle into the aorta, preventing backflow into the ventricles.
Therefore, the correct matching is: $(a-iii, b-i, c-ii)$.

(B) The correct matching is based on standard respiratory volumes:
$(a)$ Tidal volume $(TV)$: The volume of air inspired or expired during a normal respiration is approximately $500\,mL$ $(iii)$.
$(b)$ Inspiratory Reserve volume $(IRV)$: Additional volume of air, a person can inspire by a forcible inspiration, is $2500-3000\,mL$ $(i)$.
$(c)$ Expiratory Reserve volume $(ERV)$: Additional volume of air, a person can expire by a forcible expiration, is $1000-1100\,mL$ $(iv)$.
$(d)$ Residual volume $(RV)$: Volume of air remaining in the lungs even after a forcible expiration, is $1100-1200\,mL$ $(ii)$.
Thus, the correct sequence is $a-iii, b-i, c-iv, d-ii$.

$(A)$ Glycosuria is the presence of glucose in the urine, which is a common symptom of diabetes mellitus. Thus, $a-iv$.
$(b)$ Gout is caused by the accumulation of uric acid crystals in the joints, leading to inflammation and pain. Thus, $b-i$.
$(c)$ Renal calculi are stones or masses of crystallised salts (like oxalates) formed within the kidney. Thus, $c-ii$.
$(d)$ Glomerular nephritis is the inflammation of the glomeruli of the kidney. Thus, $d-iii$.
Therefore, the correct matching is $a-iv, b-i, c-ii, d-iii$.

(D) The correct matching is as follows:
$(a)$ Ultrafiltration occurs in the Malpighian corpuscle (glomerulus + Bowman's capsule),which is $(iv)$.
$(b)$ Concentration of urine is primarily performed by the Henle's loop through the counter-current mechanism,which is $(i)$.
$(c)$ Transport of urine from the kidneys to the urinary bladder is carried out by the ureter,which is $(ii)$.
$(d)$ Storage of urine occurs in the urinary bladder,which is $(iii)$.
Therefore,the correct sequence is $a-iv, b-i, c-ii, d-iii$.

(D) In dicot stems,secondary growth occurs due to the activity of the vascular cambium.
During secondary growth,the cells of the vascular cambium divide periclinally to produce secondary xylem towards the inner side and secondary phloem towards the outer side.
$A$ - Axillary meristems are responsible for the formation of branches or flowers.
$B$ - Apical meristems are responsible for primary growth (increase in length).
$C$ - Phellogen (cork cambium) is responsible for the formation of periderm (cork and secondary cortex).
$D$ - Vascular cambium is the correct answer as it is responsible for secondary vascular tissues.

(B) Pneumatophores are specialized root structures found in plants that grow in saline,swampy,or waterlogged areas,such as mangroves.
These roots grow vertically upward (negatively geotropic) out of the soil or water to facilitate gaseous exchange,as the soil in these environments is often oxygen-deficient.
Plants that grow in such saline,marshy areas are known as halophytes (e.g.,$Rhizophora$ and $Avicennia$).
Therefore,pneumatophores are characteristic of halophytes.

(B) Secondary growth is the increase in thickness or girth of the plant body and is caused by the activity of lateral meristems (vascular cambium and cork cambium).
Monocots,such as grasses,typically lack secondary growth because they do not possess a functional vascular cambium.
In contrast,gymnosperms (like Cycads and Conifers) and dicotyledonous angiosperms (like deciduous trees) exhibit significant secondary growth to support their perennial habit.
Therefore,grasses are the plants among the options that exhibit little or no secondary growth.

(D) Casparian strips are water-impermeable deposits of suberin found in the radial and tangential walls of the endodermal cells of roots.
These strips play a crucial role in regulating the flow of water and solutes into the vascular cylinder by forcing water to move through the symplastic pathway rather than the apoplastic pathway.
Therefore,the correct location for Casparian strips is the endodermis.

(B) Sweet potato $(Ipomoea \text{ } batatas)$ is a modified adventitious root.
These roots become swollen and fleshy to store food, primarily in the form of starch.
Unlike tap roots, which develop from the radicle, adventitious roots arise from parts of the plant other than the radicle, such as the stem or leaves.
Other examples of modified adventitious roots include $Cassava$ and $Dahlia$.

(D) $1$. $Cycas$ has an unbranched stem, but $Cedrus$ has a branched stem. Thus, option $A$ is incorrect.
$2$. Both $Selaginella$ and $Salvinia$ are heterosporous. Thus, option $B$ is incorrect.
$3$. Horsetails (Equisetum) are pteridophytes, not gymnosperms. Thus, option $C$ is incorrect.
$4$. Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. Thus, option $D$ is correct.

(A) Winged pollen grains are a characteristic feature of $Pinus$ (a gymnosperm).
These wings are formed by the expansion of the exine (outer layer of the pollen wall) and help in the dispersal of pollen grains by wind (anemophily).
$Cycas$,Mustard,and Mango do not possess winged pollen grains.

(D) In $Agaricus$ (a member of Basidiomycetes),the sexual spores are called basidiospores.
These spores are produced exogenously on club-shaped structures called basidia.
Following karyogamy and meiosis within the basidium,the resulting nuclei migrate into outgrowths called sterigmata to form basidiospores externally.
In contrast,$Saccharomyces$ and $Neurospora$ are Ascomycetes,where spores (ascospores) are produced endogenously within an ascus.
$Alternaria$ belongs to Deuteromycetes and does not produce sexual spores.

(A) The correct answer is $A$.
$Polysiphonia$ is a red alga (Rhodophyceae).
Red algae are characterized by the complete absence of flagellated stages in their life cycle; they produce non-motile gametes.
Therefore,the statement 'Uniflagellate gametes - $Polysiphonia$' is incorrect.
$Chlorella$ is a well-known unicellular green alga.
$Marchantia$ is a liverwort that reproduces asexually via gemmae produced in gemma cups.
Brown algae (Phaeophyceae) typically produce biflagellate zoospores that are pear-shaped and have two laterally attached unequal flagella.

$(A)$ The correct matches are as follows:
$(a)$ Herbarium $(iii)$: It is a storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
$(b)$ Key $(iv)$: It is a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities. It contains a list of characters and their alternates called couplets.
$(c)$ Museum $(i)$: These are generally set up in educational institutes such as schools and colleges. Museums have collections of preserved plant and animal specimens for study and reference.
$(d)$ Catalogue $(ii)$: It is a list that enumerates methodically all the species found in an area with brief descriptions aiding identification.
Therefore, the correct sequence is $a-iii, b-iv, c-i, d-ii$.

(C) Plants absorb iron primarily in the form of ferric ions $(Fe^{3+})$.
Although iron can exist in both ferrous $(Fe^{2+})$ and ferric $(Fe^{3+})$ states in the soil,the uptake mechanism in most plants is specifically adapted to absorb the ferric form.

(C) $Potassium$ $(K^+)$ is the most abundant cation in the cell and plays a crucial role in maintaining the turgor pressure of cells.
It regulates the opening and closing of stomata by changing the osmotic potential of guard cells.
It is also involved in protein synthesis, activation of enzymes, and maintenance of the anion-cation balance in cells.

(D) $NAD^+$ (Nicotinamide Adenine Dinucleotide) acts as a coenzyme in cellular respiration.
Its primary role is to accept high-energy electrons and hydrogen ions during metabolic pathways such as glycolysis,the link reaction,and the Krebs cycle.
By accepting these electrons,it gets reduced to $NADH$.
This $NADH$ then transports these electrons to the electron transport system $(ETS)$ located in the inner mitochondrial membrane,where they are used to generate $ATP$.
Therefore,$NAD^+$ functions as an electron carrier.

(A) Photosynthesis is classified into two types: oxygenic and anoxygenic.
Oxygenic photosynthesis occurs in organisms that use $H_2O$ as an electron donor, releasing $O_2$ as a byproduct. This is characteristic of cyanobacteria (e.g., $Nostoc$), algae (e.g., $Chara$), and higher plants (e.g., $Cycas$).
Anoxygenic photosynthesis occurs in organisms that use other compounds like $H_2S$ as an electron donor instead of $H_2O$. Consequently, they do not produce $O_2$. $Green\,sulphur\,bacteria$ are examples of organisms that perform anoxygenic photosynthesis.
Therefore, the correct answer is $Green\,sulphur\,bacteria$.

(D) The Golgi complex (or Golgi apparatus) is a membrane-bound organelle found in eukaryotic cells.
Its primary functions include the modification,sorting,and packaging of proteins and lipids synthesized in the endoplasmic reticulum.
These processed molecules are packaged into secretory vesicles,which then transport them to their final destinations,such as the plasma membrane,lysosomes,or the extracellular space.
Therefore,the formation of secretory vesicles is a key function of the Golgi complex.

(B) Stomatal movement is primarily regulated by environmental factors such as light,temperature,and the concentration of $CO_2$ inside the leaf.
Light triggers the opening of stomata by promoting the accumulation of potassium ions $(K^+)$ in guard cells,which lowers the water potential and causes water to enter the cells via osmosis.
$CO_2$ concentration acts as a feedback mechanism; high internal $CO_2$ levels typically induce stomatal closure to prevent excessive water loss while maintaining gas exchange efficiency.
Temperature influences the rate of transpiration and the metabolic activity of guard cells.
However,the concentration of $O_2$ does not have a direct regulatory effect on the opening or closing of stomata.

(B) In most dicotyledonous plants,the guard cells of the stomata are kidney-shaped or bean-shaped.
However,in monocotyledonous plants like grasses,the guard cells are dumb-bell shaped.
The outer walls of these guard cells are thin,while the inner walls are highly thickened,which helps in the opening and closing of the stomata.

(A) The nucleolus is a spherical structure present in the nucleoplasm of the nucleus.
It is not a membrane-bound structure,meaning it lacks a limiting membrane.
Its primary function is the active synthesis of ribosomal $RNA$ $(rRNA)$.
Cells that are actively involved in protein synthesis contain larger and more numerous nucleoli.
Spindle formation is a function of the centrosome/microtubules,not the nucleolus.
Therefore,the statement that it is a site for active ribosomal $RNA$ synthesis is correct.

(A) The light reaction of photosynthesis produces $ATP$,$NADPH$,and $Oxygen$ as end products.
$NADH$ is primarily produced during cellular respiration (e.g.,glycolysis and the Krebs cycle),not during the light-dependent reactions of photosynthesis.

(B) During the $Meiosis-I$ process,specifically in the $Prophase-I$ stage,homologous chromosomes undergo pairing (synapsis) during the $Zygotene$ phase.
In the subsequent phase,$Pachytene$,crossing over occurs.
In the $Diplotene$ phase,the synaptonemal complex dissolves,and the paired homologous chromosomes begin to separate from each other,except at the sites of crossovers,which are known as $Chiasmata$.
Therefore,the separation of paired homologous chromosomes begins in the $Diplotene$ stage.

(A) Sugars (carbohydrates) are polyhydroxy aldehydes or polyhydroxy ketones.
This means they contain multiple hydroxyl $(-OH)$ groups and a single carbonyl $(C=O)$ group (either an aldehyde or a ketone group).
Therefore,the two functional groups characteristic of sugars are carbonyl and hydroxyl.

(B) An organism that does not possess a true nucleus (nucleus with nuclear membrane) and double membrane-bounded organelles is called a prokaryote.
Kingdom Monera consists of prokaryotes,such as bacteria (e.g.,$Mycobacterium$) and cyanobacteria (e.g.,$Nostoc$ and $Oscillatoria$).
In contrast,$Saccharomyces$ (yeast) belongs to the Kingdom Fungi. It possesses a true nucleus and membrane-bound organelles,making it a eukaryote.

(B) The amnion is one of the four extra-embryonic membranes found in amniotes,including mammals.
It is formed by the folding of the somatopleure,which consists of the somatic layer of the extra-embryonic mesoderm and the overlying ectoderm.
Therefore,the amnion is derived from the ectoderm and the mesoderm.

(C) The placenta acts as an endocrine tissue and produces several hormones essential for maintaining pregnancy.
These hormones include Human Chorionic Gonadotropin $(hCG)$,Human Placental Lactogen $(hPL)$,progestogens (progesterone),and estrogens.
$hCG$ stimulates the corpus luteum to secrete progesterone until the placenta takes over this function.
$hPL$ is involved in growth of the fetus and metabolic changes in the mother.
Progesterone is essential for maintaining the endometrium,and estrogens are necessary for the development of the fetus and maternal tissues.

(D) $SAHELI$ is a non-steroidal oral contraceptive pill developed by the $CDRI$ (Central Drug Research Institute) in Lucknow,India.
It contains a compound called $Centchroman$.
Unlike hormonal pills that prevent ovulation,$SAHELI$ works by blocking estrogen receptors in the uterus.
By blocking these receptors,it prevents the implantation of the fertilized egg (blastocyst) in the uterine wall,thereby acting as an effective contraceptive.
It is taken once a week,making it a popular choice for birth control.

(C) $Spermiogenesis$ is the process of transformation of non-motile spermatids into mature,motile spermatozoa.
$Spermiation$ is the process by which mature spermatozoa are released from the $Sertoli$ cells into the lumen (cavity) of the seminiferous tubules.
Therefore,$Spermiogenesis$ involves the formation of spermatozoa,and $Spermiation$ involves the release of these spermatozoa.

(A) woman has two $X$ chromosomes $(XX)$. If one of her $X$ chromosomes carries an $X$-linked condition,she can pass this specific chromosome to any of her offspring.
During meiosis,the woman produces eggs,each containing one $X$ chromosome. Half of her eggs will carry the $X$ chromosome with the condition,and the other half will carry the normal $X$ chromosome.
When these eggs are fertilized by sperm from a male $(XY)$:
$1$. If an egg with the affected $X$ chromosome is fertilized by a $Y$-bearing sperm,the resulting offspring will be a son $(XY)$ who inherits the condition.
$2$. If an egg with the affected $X$ chromosome is fertilized by an $X$-bearing sperm,the resulting offspring will be a daughter $(XX)$ who inherits the condition.
Therefore,the $X$-linked condition can be inherited by both sons and daughters.

(B) Hugo de Vries proposed the Mutation Theory of evolution.
He believed that evolution is a discontinuous process caused by large,sudden,and heritable changes in the genetic material,which he termed as mutations.
He specifically used the term $Saltation$ to describe these single-step large mutations that lead to speciation.
Therefore,according to Hugo de Vries,the mechanism of evolution is $Saltation$.

(C) An operon is a functional unit of $DNA$ in bacteria and phages,consisting of a cluster of genes under the control of a single promoter.
An operon typically includes:
$1$. Structural genes: These code for the proteins or enzymes required for a metabolic pathway.
$2$. $A$ promoter: The site where $RNA$ polymerase binds to initiate transcription.
$3$. An operator: $A$ segment of $DNA$ that acts as a switch,where a repressor protein binds to prevent transcription.
Enhancers are regulatory $DNA$ sequences that increase the rate of transcription,but they are primarily associated with eukaryotic gene regulation,not prokaryotic operons.

(A) The coding strand of a gene has the same sequence as the $mRNA$ except that $Thymine$ $(T)$ in $DNA$ is replaced by $Uracil$ $(U)$ in $RNA$.
Given coding strand sequence: $AGGTATCGCAT$.
Replacing $T$ with $U$ gives the $mRNA$ sequence: $AGGUAUCGCAU$.
Therefore,the correct option is $A$.

(A) The menstrual cycle consists of different phases:
$1$. The Proliferative Phase is also known as the Follicular phase,where the endometrium regenerates under the influence of estrogen. Thus,$(a)$ matches with $(ii)$.
$2$. The Secretory Phase is also known as the Luteal phase,where the corpus luteum secretes progesterone to maintain the endometrium. Thus,$(b)$ matches with $(iii)$.
$3$. Menstruation is the phase characterized by the breakdown of the endometrial lining due to the decline in progesterone levels. Thus,$(c)$ matches with $(i)$.
Therefore,the correct matching is $a-ii, b-iii, c-i$.

(B) Elephantiasis, also known as $Filariasis$, is caused by the filarial worms $Wuchereria$ $bancrofti$ and $Wuchereria$ $malayi$.
These pathogens are transmitted to healthy individuals through the bite of female $Culex$ mosquitoes.
The parasites primarily reside in the lymphatic vessels, where they cause chronic inflammation and obstruction, leading to the characteristic swelling of the lower limbs and other body parts.

(A) Divergent evolution occurs when species with a common ancestor evolve different traits to adapt to different environments,resulting in homologous organs.
Homologous organs are those that have the same structural origin and developmental pattern but may perform different functions.
$A$. The eye of an octopus (a mollusc) and the eye of a mammal (bat or man) are examples of convergent evolution,not divergent evolution. They perform similar functions but have different evolutionary origins.
$B$. The forelimbs of man,bat,and cheetah are classic examples of homologous organs,showing divergent evolution.
$C$. The brains of vertebrates like bats,humans,and cheetahs share a common structural plan,indicating divergent evolution.
$D$. The hearts of vertebrates like bats,humans,and cheetahs share a common structural plan,indicating divergent evolution.
Therefore,the incorrect option regarding divergent evolution is the eye of an octopus,bat,and man.

(B) The similarity in the bone structure of the forelimbs of many vertebrates (such as whales,bats,cheetahs,and humans) indicates that they share a common ancestry.
These structures perform different functions in different animals (e.g.,swimming,flying,running,grasping) but share the same anatomical origin and basic structural plan.
Such structures are called homologous organs,and the phenomenon is known as homology.
Homology is based on divergent evolution,where organisms with a common ancestor evolve different traits to adapt to different environments.

(C) An autoimmune disease occurs when the immune system mistakenly attacks healthy cells in the body.
$A$. Vitiligo is an autoimmune condition where the immune system destroys melanocytes.
$B$. Psoriasis is an autoimmune disease that causes skin cells to multiply up to $10$ times faster than normal.
$C$. Alzheimer's disease is a progressive neurodegenerative disorder characterized by the accumulation of amyloid plaques and tau tangles in the brain; it is not classified as an autoimmune disease.
$D$. Rheumatoid arthritis is an autoimmune disorder in which the immune system attacks the joints,causing inflammation.
Therefore,the correct answer is $C$.

(D) The inheritance of $ABO$ blood groups in humans is governed by the gene $I$.
$1$. Dominance: The alleles $I^A$ and $I^B$ are dominant over the allele $i$.
$2$. Co-dominance: When both $I^A$ and $I^B$ are present together,they both express themselves equally,resulting in blood group $AB$.
$3$. Multiple Allelism: The gene $I$ exists in three allelic forms $(I^A, I^B, i)$,which is a classic example of multiple alleles.
Therefore,the characteristics represented are dominance,co-dominance,and multiple alleles,which correspond to $(a), (b),$ and $(c)$.

(C) The conversion of milk into curd is carried out by Lactic Acid Bacteria $(LAB)$ such as Lactobacillus.
These bacteria grow in milk and convert it into curd.
During this process,$LAB$ significantly increases the nutritional quality of curd by increasing the amount of Vitamin $B_{12}$.
Therefore,the correct option is $C$.

(A) The correct matches are as follows:
$(a)$ Eutrophication refers to the natural or artificial enrichment of water bodies with nutrients (like nitrogen and phosphorus),which leads to excessive growth of algae. Thus,$(a)-(iii)$.
$(b)$ Sanitary landfills are a method of solid waste disposal where waste is buried in a prepared area. Thus,$(b)-(iv)$.
$(c)$ Snow blindness is caused by the inflammation of the cornea due to high doses of $UV-B$ radiation,which is reflected by snow. Thus,$(c)-(i)$.
$(d)$ Jhum cultivation,also known as slash-and-burn agriculture,is a major cause of deforestation in many regions. Thus,$(d)-(ii)$.
Therefore,the correct sequence is $a-iii, b-iv, c-i, d-ii$.

(C) Amensalism is a type of population interaction where one species is harmed while the other remains unaffected.
Antibiotics are chemical substances produced by some microorganisms (like fungi or bacteria) that inhibit or kill the growth of other microorganisms.
For example,the mold $Penicillium$ produces penicillin,which inhibits the growth of bacteria.
In this interaction,the bacteria are harmed,while the $Penicillium$ mold is not significantly affected by the presence of the bacteria,making it a classic example of amensalism.

(A) Ex-situ conservation involves the conservation of organisms outside their natural habitats.
$1$. 'Ex-situ' methods include botanical gardens,zoological parks,wildlife safari parks,seed banks,and cryopreservation.
$2$. 'In-situ' conservation involves protecting the entire ecosystem and its biodiversity within its natural habitat.
$3$. Sacred groves are a form of 'In-situ' conservation where specific patches of forest are protected by local communities due to religious or cultural beliefs.
Therefore,sacred groves are not included in 'Ex-situ' conservation.

(A) population is considered to be growing (expanding) when the number of pre-reproductive individuals is significantly higher than the number of reproductive and post-reproductive individuals.
This creates an age pyramid with a broad base,indicating a high birth rate and a large number of young individuals who will enter the reproductive age in the future.
Therefore,the correct condition for a growing population is that pre-reproductive individuals are more than the reproductive individuals.

(B) The drug commonly known as "Smack" is $Heroin$, which is chemically $Diacetylmorphine$.
It is a white, odorless, bitter crystalline compound.
It is obtained by the acetylation of $Morphine$, which is extracted from the $Latex$ of the poppy plant, $Papaver \text{ } somniferum$.

(B) The given data represents the biomass at different trophic levels:
Primary producer: $10\,g$
Primary consumer: $60\,g$
Secondary consumer: $120\,g$
In this case,the biomass increases as we move from the producer level to the consumer levels.
An ecological pyramid where the biomass increases at higher trophic levels is known as an inverted pyramid.
Therefore,this data represents an inverted pyramid of biomass,which is commonly observed in aquatic ecosystems.

(C) World Ozone Day is celebrated annually on $16th$ September.
This date was designated by the United Nations General Assembly to commemorate the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in $1987$.
The primary objective of this day is to raise awareness about the importance of the ozone layer and the need to protect it from ozone-depleting substances.

(D) In the stratosphere,chlorofluorocarbons $(CFCs)$ are broken down by ultraviolet $(UV)$ radiation,which releases chlorine atoms $(Cl)$.
These chlorine atoms act as catalysts in the degradation of ozone $(O_3)$ into molecular oxygen $(O_2)$.
The reaction mechanism is as follows:
$Cl + O_3 \rightarrow ClO + O_2$
$ClO + O \rightarrow Cl + O_2$
Thus,the chlorine atom is regenerated and continues to destroy more ozone molecules.

(C) Natality is defined as the birth rate within a population.
It refers to the number of births per unit of time per unit of population.
In contrast,mortality refers to the death rate,immigration refers to the number of individuals entering a habitat,and emigration refers to the number of individuals leaving a habitat.
Therefore,the correct option is $C$.

(B) $Niche$ refers to the specific functional role that an organism plays within its ecosystem. It encompasses how the organism interacts with both biotic and abiotic components of its environment,including its diet,reproductive habits,and how it utilizes resources. While a $Habitat$ refers to the physical place where an organism lives,a $Niche$ describes its 'profession' or functional status in the community.

(C) Primary pollutants are emitted directly from sources,such as $SO_2$,$CO$,and $CO_2$.
Secondary pollutants are formed in the atmosphere through chemical reactions between primary pollutants and other atmospheric components.
$O_3$ (Ozone) in the troposphere is a classic example of a secondary pollutant,formed by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight.

(A) The plant $Yucca$ exhibits a mutualistic relationship with a specific species of moth $(Tegeticula)$.
In this relationship,the moth deposits its eggs in the locule of the ovary of the $Yucca$ flower.
In exchange,the moth pollinates the $Yucca$ flower while moving around it.
The larvae of the moth hatch from the eggs as the seeds develop.
Neither the $Yucca$ plant nor the moth can complete their life cycles without each other,making this an obligate mutualism.

(C) Pollen grains are stored in liquid nitrogen to maintain their viability for long periods.
This process is known as cryopreservation.
The temperature of liquid nitrogen is $-196^oC$.
At this extremely low temperature,the metabolic activities of the pollen grains are suspended,allowing them to be stored for several years.

(D) Double fertilization is a characteristic feature of angiosperms.
It involves two distinct fusion events:
$1$. Syngamy: One male gamete fuses with the egg cell to form a diploid zygote $(2n)$.
$2$. Triple fusion: The second male gamete fuses with the two polar nuclei (or the secondary nucleus) to form a primary endosperm nucleus $(PEN)$,which is triploid $(3n)$.
Therefore,double fertilization is the combination of syngamy and triple fusion.

(D) Offsets are a type of vegetative propagule produced by certain aquatic plants like $Eichhornia$ (water hyacinth).
Vegetative propagation is a form of asexual reproduction where new plants are formed from vegetative parts of the parent plant.
Since asexual reproduction involves the formation of clones,it occurs through $Mitotic$ $divisions$ only,without the involvement of meiosis or gamete fusion.

(D) The correct statement is that the Punnett square was developed by a British geneticist, Reginald $C$. Punnett.
- Transduction was discovered by Joshua Lederberg and Norton Zinder in $1952$, not $S$. Altman.
- The term "linkage" was coined by Thomas Hunt Morgan, not Franklin Stahl.
- Spliceosomes are involved in $RNA$ splicing (post-transcriptional modification), not in translation.

(A) The exine of the pollen grain is composed of a highly resistant organic material called $Sporopollenin$.
$Sporopollenin$ is one of the most resistant organic materials known.
It can withstand high temperatures,strong acids,and alkali solutions.
No enzyme that degrades $Sporopollenin$ is known to date.
Due to this remarkable stability,pollen grains are well-preserved as fossils.

(A) $1$. Starch synthesis in pea is controlled by a single gene with two alleles ($B$ and $b$), which exhibits pleiotropy, not multiple alleles.
$2$. $T. H. Morgan$ is known for his work on linkage in Drosophila.
$3$. $XO$ type sex determination is observed in grasshoppers.
$4$. $ABO$ blood grouping in humans is an example of multiple alleles and co-dominance (for $I^A$ and $I^B$ alleles). However, the primary genetic principle for $ABO$ blood grouping is multiple alleles, and the pairing with co-dominance is technically correct but less specific than the error in option $A$. Since starch synthesis is clearly pleiotropy, option $A$ is the $wrongly$ matched pair.

(A) $1$. Francois Jacob and Jacques Monod proposed the $Lac\,operon$ model in $1961$ to explain gene regulation in $E. coli$.
$2$. Alec Jeffreys is known for developing $DNA$ fingerprinting,not for $Streptococcus\,pneumoniae$ (which was studied by Frederick Griffith).
$3$. Matthew Meselson and $F$. Stahl provided experimental evidence for the semi-conservative replication of $DNA$ in $E. coli$,not $Pisum\,sativum$ (which was studied by Gregor Mendel).
$4$. Alfred Hershey and Martha Chase conducted experiments with bacteriophages to prove that $DNA$ is the genetic material,not $TMV$ (Tobacco Mosaic Virus).

(B) Monocarpic plants are those that flower and fruit only once in their lifetime and then die.
Bamboo species (e.g.,$Bambusa$ $tulda$) are classic examples of monocarpic plants that exhibit a unique phenomenon of flowering only once in their lifetime,usually after $50-100$ years of vegetative growth,followed by the production of a large number of seeds and subsequent death.
Papaya,Mango,and Jackfruit are polycarpic plants,meaning they flower and produce fruits repeatedly throughout their lifespan.

(D) The experimental proof for the semiconservative replication of $DNA$ was first provided by Matthew Meselson and Franklin Stahl in $1958$.
They performed their experiments on the bacterium $Escherichia coli$ $(E. coli)$.
They grew $E. coli$ in a medium containing $^{15}N$ (a heavy isotope of nitrogen) for many generations, resulting in $DNA$ containing $^{15}N$.
Then, they transferred these bacteria to a medium containing $^{14}N$ (a normal isotope of nitrogen).
After one generation, the $DNA$ extracted had a hybrid density, and after two generations, it showed both light and hybrid $DNA$, which confirmed the semiconservative mode of $DNA$ replication.

(D) Retroviruses have the natural ability to infect host cells and integrate their genetic material into the host genome.
In biotechnology,disarmed retroviruses are used as vectors to deliver desired genes into animal cells,including human lymphocytes.
$pBR\,322$ is a plasmid vector used in bacteria.
$Ti\,plasmid$ is used for gene transfer in plants.
$\lambda$ phage is a bacteriophage used as a cloning vector in bacteria.
Therefore,the correct option is $D$.

(B) . $G. Mendel$ is known for the laws of inheritance,not transformation. Transformation was discovered by $F. Griffith$.
$B$. Ribozyme is an $RNA$ molecule that acts as an enzyme,which is a nucleic acid. This is the correct match.
$C$. $T.H. Morgan$ is known for linkage and recombination,not transduction. Transduction was discovered by $Zinder$ and $Lederberg$.
$D$. $F_2 \times$ Recessive parent is a test cross,not a dihybrid cross. $A$ dihybrid cross involves the study of two traits.

(D) Biopiracy is the term used to refer to the use of bioresources by multinational companies and other organizations without proper authorization from the countries and people concerned without compensatory payment.

(A) In $1997$, an American company named RiceTec Inc. was granted a patent by the $US$ Patent and Trademark Office for 'Basmati' rice lines and grains. This was highly controversial because Basmati rice has been grown in India and Pakistan for centuries and is a traditional variety. This act is considered an example of biopiracy, where multinational companies exploit biological resources and traditional knowledge of developing countries without proper authorization or compensation.

(D) The Indian government has established the Genetic Engineering Appraisal Committee $(GEAC)$ under the Ministry of Environment,Forest and Climate Change.
This organization is responsible for making decisions regarding the validity of research involving genetically modified organisms $(GMOs)$ and the safety of introducing them for public use.
While the Research Committee on Genetic Manipulation $(RCGM)$ monitors the safety of research activities,the final approval for commercial release and public use is granted by the $GEAC$.

(A) The Polymerase Chain Reaction $(PCR)$ is a technique used to amplify a specific $DNA$ segment.
It consists of three main steps performed in a cyclic manner:
$1$. Denaturation: The double-stranded $DNA$ is heated to a high temperature (usually around $94-98^{\circ}C$) to separate the two strands.
$2$. Annealing: The temperature is lowered (usually $50-65^{\circ}C$) to allow the primers to bind to the complementary sequences on the single-stranded $DNA$ templates.
$3$. Extension: The temperature is adjusted (usually $72^{\circ}C$) for the $DNA$ polymerase enzyme to synthesize the new $DNA$ strand by adding nucleotides to the primers.
Therefore,the correct order is Denaturation,Annealing,and Extension.