AIPMT 2006 Biology Question Paper with Answer and Solution

(C) The ornithine cycle (also known as the urea cycle) occurs in the liver.
It is a metabolic pathway that converts toxic ammonia $(NH_3)$ and carbon dioxide $(CO_2)$ into urea.
Therefore,the cycle effectively removes $NH_3$ and $CO_2$ from the blood to synthesize urea,which is then excreted by the kidneys.

(C) $Mucor$ is a filamentous fungus commonly known as black mould,found in humus-rich soil,decaying fruits,and vegetables.
For optimal growth,$Mucor$ requires:
$1$. $A$ moderate temperature,typically around $25^{\circ}C$ to $30^{\circ}C$ $(A)$.
$2$. High relative humidity,typically around $90-95\%$ $(D)$.
$3$. $A$ moist and shady environment $(E)$.
It does not grow well at low temperatures $(5^{\circ}C)$ or in very dry conditions ($5\%$ humidity),and it prefers dark or shady areas over brightly illuminated ones.
Therefore,the correct conditions are $A, D,$ and $E$.

(C) $Sphagnum$ is a genus of mosses commonly known as peat moss.
It has a remarkable capacity to hold and retain water for long periods due to its hygroscopic nature.
Because of this property,it is used as a packing material for transporting live plants and flowers to distant places,as it keeps them moist and prevents them from drying out during transit.

(A) : Conifers belong to gymnosperms. They are seed-bearing plants in which the sporophylls are aggregated to form cones,and the seeds develop in an exposed state over the surface of megasporophylls.
Vascular tissue in conifers consists of tracheids and sieve cells.
The female gametophyte forms archegonia,provides nourishment to the developing embryo,and later transforms into food-laden tissue or endosperm inside the seed.
This endosperm is formed before fertilization,so it is haploid $(n)$ in nature.
It provides nourishment for the growth of seedlings at the time of seed germination.
Grass is an angiospermic plant,and in angiosperms,the endosperm is produced after fertilization (typically through double fertilization).

(B) In mosses (Bryophytes),the plant body is a gametophyte,which is independent and photosynthetic.
The sporophyte is dependent on the gametophyte for its nutrition and anchorage.
It is attached to the gametophyte and derives nutrients from it,making it partially parasitic or dependent on the gametophyte for survival.
Therefore,the correct statement is that the sporophyte is partially parasitic on the gametophyte.

(C) : $Ctenophora$ is a small phylum of exclusively marine,invertebrate animals. $Ctenoplana$ and $Beroe$ are examples of $Ctenophora$. They exhibit biradial symmetry,which is a combination of radial and bilateral symmetries. They lack the specialized stinging cells known as cnidoblasts or nematocysts,which are characteristic of the phylum $Cnidaria$ (coelenterates). Although one species,$Haeckelia$ $rubra$,can incorporate stinging cells from its jellyfish prey for defense,it is not a general characteristic of the phylum.

(C) : Centipede,cockroach,and crab all belong to the phylum $Arthropoda$,which is characterized by the presence of jointed legs and a chitinous exoskeleton.
Arthropods possess a bilaterally symmetrical and metamerically segmented body with a haemocoel and an open blood vascular system.

(D) : Migration is the seasonal movement of complete populations of animals to a more favourable environment.
It is common in mammals (e.g.,porpoises),fish (e.g.,eels and salmon),and some insects,but is most marked in birds.
The arctic tern,for example,migrates annually from its breeding ground in the Arctic circle to the Antarctic.
Salmon usually migrate from marine to fresh water to spawn.
The siberian crane breeds in arctic Russia in Yakutia and western Siberia and is a long-distance migrant.
Salamander is an amphibian with a slender body,short legs,and a long tail.
Outside the breeding season,they are seldom seen as they spend most of their time underground and do not perform annual long-distance migrations.

(D) The correct answer is $D$.
Metameric segmentation,or metamerism,refers to the linear repetition of body parts along the longitudinal axis of an animal.
This phenomenon is a characteristic feature of the phyla $Annelida$,$Arthropoda$,and $Chordata$.
In $Annelida$,segmentation is clearly visible both externally and internally.
In $Arthropoda$,the body is segmented,although the segments are often fused to form tagmata.
In $Chordata$,metamerism is prominent in the embryonic stage and persists in adult internal structures such as vertebrae,ribs,and nerves.

(D) : Mollusca includes those animals which have soft bodies,usually furnished with a shell. The body is often divided into a head,with eyes or tentacles,a muscular foot,and a visceral mass housing the organs. $Loligo$ (squid or sea arrow),$Teredo$ (shipworm),and $Octopus$ are some of their examples.
In option $A$,$Spongilla$ and $Euplectella$ belong to Porifera,but $Pennatula$ (the sea pen or sea feather) belongs to Coelenterata (Cnidaria).
In option $B$,$Physalia$ and $Aurelia$ belong to Cnidaria,but $Bonellia$ belongs to Phylum Annelida.
In option $C$,$Planaria$ and $Schistosoma$ belong to Platyhelminthes,but $Enterobius$ (pinworm) belongs to Aschelminthes.

(B) is the correct answer.
$Protista$ is the kingdom of unicellular eukaryotes.
The group includes heterotrophs,autotrophs,and some organisms that can vary their nutritional mode depending upon environmental conditions.
$Protists$ occur in freshwater,saltwater,soil,and as symbionts within other organisms.
$Trypanosoma$,$Noctiluca$,$Monocystis$,and $Giardia$ are all unicellular protists.

(D) The correct answer is $D$.
$1$. Pentamerous actinomorphic flowers: The floral parts are in multiples of five,and the flower exhibits radial symmetry.
$2$. Bicarpellary ovary: The gynoecium consists of two carpels.
$3$. Oblique septa: $A$ diagnostic feature of the family $Solanaceae$ is the presence of an obliquely placed septum in the ovary,which makes the ovary appear bilocular.
$4$. Fruit: The fruits are typically capsules or berries.
These features are characteristic of the family $Solanaceae$ (e.g.,$Solanum$ $tuberosum$,$Datura$).

(D) : Pineapple is a $Sorosis$ type of fruit that develops from a spike or spadix inflorescence. In this type of inflorescence,the flowers fuse by their succulent tepals,and the axis bearing the flowers becomes fleshy or woody,thus forming a compact mass. These are known as composite or multiple fruits. In pineapple,the fleshy axis,bracts,fused perianth,and pericarp are edible.

(A) The correct answer is $A$. In $Litchi$,the edible part is the fleshy $aril$.
An $aril$ is a specialized outgrowth that develops from the base of the ovule and covers the seed. It is a fleshy,succulent structure that is sweet and edible.
In $Litchi$,the pericarp (fruit wall) is leathery,while the $aril$ surrounds the seed and serves as the edible portion. Other examples of plants with an $aril$ include $Asphodelus$,$Trianthema$,and $Ulmus$.

(A) $Xylem$ is the principal water-conducting tissue of the plant. It consists of four types of cells: tracheids,vessels,xylem fibres,and xylem parenchyma.
$Xylem$ vessels are hollow,elongated cells with open ends and pitted walls. Cell walls are lignified. At maturity,the nucleus is absent in vessels.
The constituent cells of the phloem are sieve elements (sieve cells,sieve tubes),companion cells,phloem fibres,and phloem parenchyma cells.
Sieve tube members are long,slender,tube-like cells joined end-to-end to form long tubular channels called sieve tubes. Sieve tube members possess specialized sieve areas on the end walls called sieve plates. Young sieve tube members have abundant cytoplasm,but there is no nucleus. The nucleus disintegrates during their development.
Therefore,the common feature between mature vessel elements and mature sieve tube elements is the absence of a nucleus (enucleate condition).

(C) : Areolar tissue is a loose connective tissue comprised of a semifluid ground substance containing several kinds of loosely arranged fibres. Its function is to attach the skin (integument) to the underlying tissues,to fill the spaces between various organs and thus hold them in place,and to surround and support the blood vessels. Tendons connect muscles with bone,while ligaments connect bone with bone.

(D) : Mast cells are granulated wandering cells found in connective tissue.
Their granules contain histamine,which acts as a vasodilator.
It is responsible for symptoms like a running nose,sneezing,and itching,and it can also cause the narrowing of airways in the lungs.
Haemoglobin and myoglobin are respiratory pigments present in the blood and muscles,respectively.

(A) Earthworms possess excretory organs known as $nephridia$.
When water is abundantly available,they excrete ammonia as their primary nitrogenous waste,making them $ammonotelic$.
However,in terrestrial environments where water may be limited,they can excrete urea,making them $ureotelic$.
Therefore,the correct statement is that they are $ammonotelic$ when plenty of water is available.

(C) : The outer membrane of the mitochondrion is smooth,freely permeable to most small molecules,contains fewer enzymes,and is poor in proteins. It has porin proteins which form channels for the passage of molecules. It allows the uptake of substrates and the release of $ATP$. The inner membrane is semipermeable and regulates the passage of materials into and out of the mitochondrion. It is rich in enzymes and carrier proteins (permeases). It is usually produced into numerous infolds called cristae (singular: crista). It bears minute,regularly spaced,lollipop-shaped particles known as oxysomes. The inner membrane contains the electron carrier molecules of the electron transport chain,not the outer membrane.

(B) The correct answer is $B$.
Cilia are fine,hair-like,vibratile cytoplasmic processes found on certain cell types.
Their movement either propels the organism or moves the surrounding medium past a fixed cell.
Cilia are enclosed by a unit membrane,which is an extension of the plasma membrane.
Within the membrane is a fluid matrix containing a supporting axial shaft called the axoneme.
The axoneme typically shows a $9+2$ arrangement,where nine doublets of microtubules are arranged in a ring around two central singlet microtubules.
These microtubules are composed of globular units of the protein tubulin.
The arms of the $A$ microtubules contain the protein dynein,which acts as an $ATPase$ enzyme to catalyze the hydrolysis of $ATP$ to $ADP$,providing energy for ciliary movement.
Statement $B$ is incorrect because the beating of cilia is primarily driven by the sliding of microtubule doublets powered by dynein-mediated $ATP$ hydrolysis,not by $Ca^{2+}$ fluxes across the membrane.

(B) : Microscopes are used for studying cellular structures. They are used to magnify small objects. In electron microscopes,a high-energy beam of electrons is focused through electromagnetic lenses. It can magnify very small details with high resolving power. The increased resolution results from the shorter wavelength of the electron beam.

(C) $P$-proteins (Phloem proteins) are components found in large amounts in phloem sieve tubes. The main function of these bodies is to seal off the sieve tube element or sieve cell by bringing about the blockage of the sieve plate. These bodies perform this function when the sieve element is injured. These bodies and callose together block the pores of sieve tube elements. $P$-protein bodies and callose form blocking plugs. These bodies remain along the walls of sieve tube elements. $P$-protein bodies are assigned some role in the translocation of food material in the sieve tubes,but this is not universally accepted.

(A) : Sulphur is an essential nutrient for the growth and development of plants. It is a key component of sulphur-containing amino acids like cystine,cysteine,and methionine,which are vital for protein synthesis.
Oilseed crops,particularly those belonging to the family $Brassicaceae$ (e.g.,mustard,rapeseed),have a high requirement for sulphur because they synthesize sulphur-rich oils.
Plants absorb sulphur from the soil primarily as sulphate ions $(SO_4^{2-})$.
It is a structural component of ferredoxin and certain lipids in chloroplasts.
The characteristic pungent odour of mustard and cabbage is due to the presence of sulphur-containing oils.
Application of $40 \ kg/ha$ of sulphur in oilseed-based cropping systems significantly enhances seed yield,oil content,and protein quality.

(C) Photorespiration is a wasteful process that occurs in $C_3$ plants. The oxygen-consuming reactions occur in two main locations:
$1$. In the $Stroma$ of chloroplasts,the enzyme $RuBisCO$ acts as an oxygenase,where $O_2$ is consumed during the oxygenation of $RuBP$.
$2$. In the $Peroxisomes$,the enzyme $Glycolate$ oxidase consumes $O_2$ to convert glycolate into glyoxylate.
Therefore,the correct answer is $C$.

(A) : In the light reaction of photosynthesis,two types of photosystems are involved. $PS-I$ consists of a large amount of chlorophyll-$a$ and a very small quantity of chlorophyll-$b$. These pigments absorb light energy and transfer it to the reaction centre,$P_{700}$.
After absorbing an adequate amount of light energy,an electron gets excited from the $P_{700}$ molecule and moves to an iron-sulphur protein complex,designated as $A$ $(Fe-S)$.
It gets reduced after accepting electrons. It later transfers these electrons to ferredoxin and gets oxidized again.

(D) The total energy released from the complete oxidation of one mole of glucose is $686 \ kcal$.
The energy stored in one mole of $ATP$ (high-energy phosphate bond) is $12 \ kcal$.
To find the maximum number of $ATP$ molecules that can be generated,we divide the total energy released by the energy required to synthesize one mole of $ATP$.
Number of $ATP$ molecules = $\frac{686 \ kcal}{12 \ kcal/ATP} = 57.16 \ ATP$ molecules.
Therefore,the maximum number of $ATP$ molecules that can be generated is $57$.

(B) The correct answer is $(b)$.
Germination is the process by which a dormant embryo in a seed resumes active growth to form a seedling.
The initial step in the germination process is the uptake of water and rehydration of seed tissues through imbibition.
Upon imbibition,the embryo releases gibberellins,which signal the aleurone layer to synthesize and secrete hydrolytic enzymes,most notably $\alpha$-amylase.
$\alpha$-amylase hydrolyzes the starch stored in the endosperm into simple sugars like glucose.
These sugars are essential as a respiratory substrate for energy production and as a source of carbon skeletons for the synthesis of new molecules required for growth.

(A) The correct answer is $A$.
Premature yellowing of leaves (chlorosis) in pulse crops is often caused by a deficiency of nitrogen,as nitrogen is a critical component of chlorophyll,proteins,and nucleic acids.
Cytokinins are plant hormones that delay leaf senescence (aging) and promote cell division.
By applying a combination of cytokinins and nitrogenous fertilizers,the plant can maintain chlorophyll levels,delay senescence,and improve overall growth and seed yield.
While iron and magnesium are involved in chlorophyll synthesis,nitrogen deficiency is the most common cause of widespread chlorosis in pulse crops,making the combination of nitrogen and cytokinins the most effective treatment for maximizing yield.

(C) : Pruning is the process of cutting shoot tips to promote the lateral growth of branches.
Removal of shoot tips involves the removal of apical buds.
In the shoot tips,auxins are produced,which are growth-promoting phytohormones.
They cause apical dominance by promoting the growth of apical buds and suppressing the growth of axillary buds.
When the auxins produced in the shoot tips are removed by decapitation,it results in lateral growth,and plants thus show a bushy appearance.
This occurs because of the removal of the source of auxin that was inhibiting the lateral buds.

(A) The correct answer is $A$ (stratification).
$1$. Stratification is the process of exposing seeds to low temperatures under moist conditions to break seed dormancy and promote germination. This mimics natural winter conditions.
$2$. Scarification involves the physical or chemical degradation of the seed coat to allow water and oxygen to enter,which helps in breaking physical dormancy.
$3$. Vernalization is the induction of flowering in plants by exposure to prolonged cold,typically applied to young plants rather than seeds.
$4$. Chelation is a chemical process used to make micronutrients more available to plants in the soil.
Therefore,the specific treatment of seeds under moist,cold conditions to break dormancy is known as stratification.

(C) The presence of large,immature,and nucleated erythrocytes (megaloblasts) indicates a deficiency in $DNA$ synthesis required for $RBC$ maturation.
Folic acid (Vitamin $B_9$) and Cobalamine (Vitamin $B_{12}$) are essential cofactors for $DNA$ synthesis and the maturation of $RBCs$ in the bone marrow.
$A$ deficiency in these vitamins leads to megaloblastic anaemia,where $RBCs$ fail to mature properly and remain large and nucleated.
Therefore,supplementing the diet with Folic acid and Cobalamine is the correct treatment to alleviate these symptoms.

(C) The correct answer is $C$.
When systemic arterial blood flows through capillaries,carbon dioxide diffuses from the tissues into the blood.
Some carbon dioxide is dissolved in the blood plasma.
Some carbon dioxide reacts with haemoglobin to form carbaminohaemoglobin.
The remaining and majority of carbon dioxide is converted into bicarbonate ions $(HCO_3^-)$ and hydrogen ions $(H^+)$ within the red blood cells.
Thus,most carbon dioxide is transported through the blood in the form of bicarbonate ions.

(D) : The circulatory system of insects is open,whereby blood (haemolymph) flows freely through the body cavity (haemocoel). Insects possess a tracheal system for respiration,where oxygen is delivered directly to tissues via tubes called tracheae,bypassing the blood. Haemolymph does not contain an oxygen-carrying pigment like $Hb$ (haemoglobin); therefore,it does not assist in the transport of oxygen.

(C) : At high altitudes,the composition of air remains almost the same as at sea level,but the density (barometric pressure) of air gradually decreases,due to which arterial $pO_2$ is also decreased (hypoxemia).
High altitudes present complex conditions to which the human body has to acclimatize.
The number of red blood cells per unit volume of blood is likely to be higher in a person living at high altitudes.
This is in response to the air being less dense at high altitude.
More red blood cells are needed to trap $O_2$ from rarefied air having low $pO_2$ (partial pressure of oxygen).

(C) The correct answer is $C$.
$Periplaneta$ (cockroach) possesses an open circulatory system,meaning the blood does not flow exclusively within blood vessels but circulates through a body cavity known as the haemocoel.
In contrast,vertebrates,annelids (such as $Pheretima$ and $Hirudinaria$),and cephalopods (such as $Octopus$) possess a closed circulatory system,where blood is confined within a network of vessels including arteries,veins,and capillaries.

(D) : Angiotensinogen is an $\alpha$-globulin protein produced and secreted by the liver cells.
Renin,which is secreted by the juxtaglomerular $(JG)$ cells,acts as an enzyme to convert the plasma protein angiotensinogen into angiotensin-$I$.
Angiotensin-$II$ (formed from angiotensin-$I$) stimulates the adrenal cortex to produce aldosterone.
Aldosterone acts on the distal convoluted tubules and collecting ducts to increase the reabsorption of $Na^+$ and water,which subsequently increases blood volume and blood pressure.

(C) The correct answer is $C$.
Myosin is a motor protein that functions as a contractile protein in skeletal muscle.
It possesses ATPase activity,meaning it can hydrolyze $ATP$ to release energy required for muscle contraction.
The myosin molecule consists of a tail and a globular head; the head contains binding sites for actin and $ATP$.
Troponin and tropomyosin are regulatory proteins associated with the thin filament (actin),while $\alpha$-actinin is a structural protein that anchors actin filaments to the $Z$-line.

(B) The correct answer is $B$.
Bowman's glands,also known as olfactory glands,are branched tubuloalveolar glands located in the mucous membrane of the olfactory region of the nasal cavity.
These glands produce mucus that serves to moisten the olfactory epithelium and dissolve odor-containing gases,which is essential for the sense of smell.

(A) The correct answer is $A$.
Neurotransmitters are chemical messengers that transmit,amplify,and modulate signals between a neuron and another cell.
Common neurotransmitters include:
$(1)$ Amino acids (e.g.,Glutamic acid,$GABA$,Aspartic acid,Glycine).
$(2)$ Peptides (e.g.,Vasopressin,Somatostatin).
$(3)$ Monoamines (e.g.,Norepinephrine,Dopamine,Serotonin) and Acetylcholine.
Cortisone is a glucocorticoid steroid hormone secreted by the adrenal cortex. It plays a role in metabolism and immune suppression,but it does not function as a neurotransmitter.

(D) : Adrenaline is the hormone secreted by the adrenal medulla. It prepares the body to face special conditions created by physical stress.
These conditions require more energy,which is provided by increasing heart rate,blood pressure,respiratory rate,blood glucose levels,and blood supply to the heart,skeletal muscles,and brain through the dilation of their small arteries.
It also increases oxidative metabolism and stimulates the breakdown of liver and muscle glycogen (glycogenolysis) to provide glucose for cellular respiration.

(D) The posterior pituitary,also known as the $Neurohypophysis$,is not a gland in the traditional sense because it does not synthesize hormones itself. Instead,it is a structure under the direct regulation of the $Hypothalamus$. The axons of the neurons originating in the $Hypothalamus$ transport the hormones $Vasopressin$ $(ADH)$ and $Oxytocin$ to the posterior pituitary. These hormones are stored and accumulated in the posterior pituitary and are released into the bloodstream as needed. Therefore,the posterior pituitary lobe serves as the accumulation and release centre for these neurohormones.

(B) The adrenal cortex produces glucocorticoids, which are involved in carbohydrate metabolism.
Cortisol is the primary glucocorticoid in humans and plays a crucial role in regulating glucose metabolism by stimulating gluconeogenesis, lipolysis, and proteolysis.
It helps maintain blood glucose levels during stress.
Therefore, the correct answer is $cortisol$.

(D) The correct answer is $D$.
Secondary messengers are low-molecular-weight,diffusible molecules used to relay signals within a cell.
They are synthesized or released by specific enzymatic reactions,usually as a result of an external signal received by a transmembrane receptor.
$cAMP$,$cGMP$,and $Ca^{2+}$ act as secondary messengers and are located within the cytoplasm.
Sodium $(Na^+)$ is an essential mineral ion involved in maintaining membrane potential and nerve impulse conduction,but it does not function as a secondary messenger in hormone signaling pathways.

(C) : The endocrine system and the nervous system work together to maintain homeostasis. The nervous system regulates the endocrine system through the hypothalamus,which acts as a bridge between the two systems. For example,the hypothalamus secretes releasing hormones that stimulate the pituitary gland to release tropic hormones,which in turn regulate other endocrine glands. Conversely,hormones produced by endocrine glands can influence neural activity,affecting behavior,mood,and physiological processes. Thus,both systems regulate each other.

(C) The development of fruits without fertilization is known as parthenocarpy,and such fruits are called parthenocarpic fruits.
Parthenocarpic fruits are typically seedless.
In horticultural practices,parthenocarpy can be artificially induced by applying plant growth regulators,specifically auxins and gibberellins,to the stigma or ovaries of the flowers.
These hormones mimic the signals usually provided by developing seeds,stimulating the ovary to grow into a fruit even in the absence of fertilization.
Therefore,treating the plants with low concentrations of gibberellic acid and auxins is a standard method to produce parthenocarpic tomato fruits.

(C) The correct answer is $C$. In monocotyledonous seeds such as cereal grains (e.g.,maize,wheat),the embryo consists of a single cotyledon,which is shield-shaped and is known as the $scutellum$.
$1$. The $scutellum$ is situated towards one side of the embryonic axis and functions to absorb nutrients from the endosperm and transfer them to the developing embryo.
$2$. The $coleoptile$ is a protective sheath that covers the plumule (shoot apex).
$3$. The $coleorhiza$ is a protective sheath that covers the radicle (root apex).
$4$. Therefore,the single cotyledon in cereal grains is specifically termed the $scutellum$.

(C) : Mad cow disease is the common term for Bovine Spongiform Encephalopathy $(BSE)$,a progressive neurological disorder of cattle.
It is caused by prions.
Symptoms include an excitable or nervous temperament to external stimuli such as touch to the skin.
$A$ prion (short for proteinaceous infectious particle) is a unique type of infectious agent,as it is made only of protein.
Prions are abnormally structured forms of a host protein,which are able to convert normal molecules of the protein into the abnormal structure.

(C) $Clostridium$ is a genus of Gram-positive bacteria. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped.
Foodborne disease caused by $C. botulinum$ is referred to as botulism (a muscle-paralyzing disease).
It is caused by the ingestion of a neurotoxin (botulin) produced by the microorganism in the food.
Botulin blocks nerve function,leading to respiratory and musculoskeletal paralysis.
Symptoms of botulism include weakness,fatigue,and dizziness,followed by blurred vision and progressive difficulty in speaking and swallowing.
Weakening of the respiratory muscles is also observed,and death may occur due to respiratory failure.

(A) All the organisms mentioned ($Trypanosoma$,$Noctiluca$,$Monocystis$,and $Giardia$) belong to the Kingdom $Protista$.
$Trypanosoma$ is a flagellated protozoan.
$Noctiluca$ is a dinoflagellate.
$Monocystis$ is a sporozoan.
$Giardia$ is a flagellated protozoan.
While they have different modes of locomotion or life cycles,the common characteristic among all these organisms is that they are all unicellular eukaryotic organisms classified under the Kingdom $Protista$.

(A) Slime molds are saprophytic protists. Under suitable conditions,they form an aggregation called $Plasmodium$ which may grow and spread over several feet. This $Plasmodium$ is the vegetative,thalloid body of the slime mold. During unfavorable conditions,the $Plasmodium$ differentiates and forms fruiting bodies bearing spores at their tips.

(B) The correct answer is $B$.
Curing is a process performed to enhance the flavor and aroma of tea leaves.
This process is also commonly used for tobacco leaves.
After harvesting,the leaves are dried in the shade and subjected to the action of specific bacteria.
The curing of tea leaves is primarily facilitated by the bacterium $Micrococcus$ $candidans$.
$Micrococcus$ is a Gram-positive,aerobic bacterium belonging to the family $Micrococcaceae$.

(D) : $A$ living fossil is a term for any living species (or clade) of organism that closely resembles species otherwise known only from fossils and has no close living relatives. These species have survived major extinction events and generally retain low taxonomic diversity.
Some examples of living fossils in animals include the coelacanth,coral (polyp),Crocodylia (crocodiles,gavials,and alligators),horseshoe crab $(Limulus \ polyphemus)$,monotremes (platypus and echidna),and the purple frog $(Nasikabatrachus \ sahyadrensis)$.
$Archaeopteryx$ is the earliest and most primitive known bird to date. It lived in the Jurassic Period around $150-155$ million years ago. It possessed feathers and wings but also had teeth and a skeleton similar to a small carnivorous dinosaur; therefore,it exhibited both bird and theropod dinosaur features. $Archaeopteryx$ is a powerful piece of evidence showing that birds evolved from dinosaurs and is considered an extinct transitional fossil,not a living fossil.

(A) The scutellum is the tissue in a grass,wheat,or maize seed that lies between the embryo and the endosperm. It is a modified cotyledon,specialized for the digestion and absorption of the endosperm nutrients for the developing embryo.

(C) : In maize,the male inflorescence occupies the terminal position on the main axis,whereas the female inflorescence (ear or cob) is borne on modified lateral branches in the axils of leaves.
The ear-producing branch has short internodes and bears a female spike at its apex.
Each spikelet has a pair of small membranous glumes and two florets.
The feathery,long,filamentous threads protruding from the cob are the styles of the female florets.
These styles emerge out of the cob to expose the stigma,which facilitates wind pollination.

(C) typical mature embryo sac of an angiosperm (including dicots) is $7$-celled and $8$-nucleate.
The arrangement of these $8$ nuclei is as follows:
$1$. Three nuclei are present at the micropylar end,forming the egg apparatus (one egg cell and two synergids).
$2$. Two nuclei are present in the central cell,known as polar nuclei.
$3$. Three nuclei are present at the chalazal end,known as antipodal cells.
Therefore,the arrangement is $3 + 2 + 3$ (three at the top,two in the center,and three at the bottom).

(B) $(b) :$ Sertoli cells are located within the germinal epithelium of the seminiferous tubules.
These cells provide nourishment to the developing spermatozoa.
They facilitate the process of spermatogenesis by supporting the differentiation of spermatogonia into mature sperms.
These cells are primarily regulated by the Follicle Stimulating Hormone $(FSH)$,which is secreted by the anterior pituitary gland.

(A) The menstrual cycle consists of three phases: the proliferative phase,the secretory phase,and the menstrual phase.
During the secretory phase,the corpus luteum secretes large amounts of progesterone,which is essential for the maintenance of the endometrium.
If fertilization does not occur,the corpus luteum degenerates.
This degeneration leads to a sharp decrease in the levels of progesterone.
The withdrawal of progesterone causes the breakdown of the endometrial lining and its blood vessels,which leads to menstruation.

(D) The correct answer is $D$. $A$ test cross is performed to determine the unknown genotype of an organism showing a dominant phenotype.
In a typical test cross, an organism with a dominant phenotype is crossed with an individual that is homozygous recessive for the trait being investigated.
By analyzing the phenotypic ratio of the resulting progeny, the genotype of the parent organism can be determined.
For example, if an organism with a dominant trait (genotype $Tt$) is crossed with a homozygous recessive individual $(tt)$, the offspring will reveal whether the parent was homozygous dominant $(TT)$ or heterozygous $(Tt)$.

(C) : $A$ congenital disorder is a medical condition that is present at birth. Congenital disorders can be a result of genetic abnormalities,the intrauterine environment,or unknown factors.
Sickle cell anaemia is a group of genetic disorders caused by sickle haemoglobin $(HbS)$. $HbS$ molecules tend to clump together,making red blood cells sticky,stiff,and more fragile,causing them to form into a curved,sickle shape.
Huntington's chorea is an inherited disorder characterized by degenerative changes in the basal ganglia structures,which ultimately result in a severely shrunken brain and enlarged ventricles,abnormal body movements called chorea,and loss of memory.
Both are genetic in origin and present from birth,hence they are classified as congenital disorders.

(A) Colour blindness is a recessive sex-linked trait caused by a gene on the $X$ chromosome.
Let $X^c$ represent the allele for colour blindness and $X$ represent the normal allele.
$A$ colour blind woman has the genotype $X^c X^c$.
$A$ normal visioned man has the genotype $XY$.
When they reproduce,the cross is $X^c X^c \times XY$.
The possible genotypes for the offspring are $X^c X$ (carrier daughters) and $X^c Y$ (colour blind sons).
Since all sons receive their $X$ chromosome from their mother,and the mother is colour blind $(X^c X^c)$,all sons will inherit the $X^c$ allele.
Therefore,all sons will be colour blind.

(C) : Cri-du-chat syndrome, also known as $5p$ deletion syndrome (or $5p$ minus), is a rare genetic disorder.
Cri-du-chat syndrome is caused by a partial deletion of the short arm ($p$ arm) of chromosome number $5$.
The name of this syndrome is French for "cry of the cat," referring to the distinctive high-pitched cry of infants with this disorder.
The cry is caused by abnormal larynx development, which typically improves within a few weeks of birth.
Infants with cri-du-chat often have low birth weight and may experience respiratory or feeding difficulties.

(D) : Sickle cell anaemia is an autosomal hereditary disorder in which the erythrocytes become sickle-shaped. The disorder is caused by the formation of an abnormal haemoglobin called haemoglobin-$S$. As found out by Ingram $(1958)$,haemoglobin-$S$ differs from normal haemoglobin-$A$ in only one amino acid: the $6^{th}$ amino acid of the $\beta$-chain,glutamic acid,is replaced by valine.
Carriers of the sickle cell anaemia gene are protected against malaria because of this particular haemoglobin mutation. This explains why sickle cell anaemia is particularly common among people of African origin. The malarial parasite has a complex life cycle and spends part of it in red blood cells,feeding on haemoglobin. Both sickle-cell anaemia and thalassemia are more common in malaria-prone areas because these mutations convey some protection against the parasite. In a carrier,the presence of the malaria parasite causes the red blood cell to rupture,making the $Plasmodium$ unable to reproduce. Further,the polymerisation of $Hb$ affects the ability of the parasite to digest $Hb$. Therefore,in areas where malaria is a problem,people's chances of survival actually increase if they carry the sickle cell anaemia trait. Thus,sickle-cell anaemia acts as a potential saviour from malaria.

(A) In a dihybrid cross between a homozygous round yellow plant $(RRYY)$ and a homozygous wrinkled green plant $(rryy)$,the gametes produced by the parents are $RY$ and $ry$ respectively.
When these gametes fuse,the resulting $F_1$ generation genotype is $RrYy$.
Since round $(R)$ is dominant over wrinkled $(r)$ and yellow $(Y)$ is dominant over green $(y)$,the phenotype of the $F_1$ generation will be round seeds with yellow cotyledons.

(A) The number of different types of gametes produced by an organism can be calculated using the formula $2^n$,where $n$ represents the number of heterozygous gene pairs.
For the genotype $AABbCC$:
- $AA$ is homozygous.
- $Bb$ is heterozygous $(n=1)$.
- $CC$ is homozygous.
Thus,$n = 1$.
Number of gametes = $2^1 = 2$.
The two types of gametes produced are $ABC$ and $AbC$.

(A) The phenotype of an organism refers to its observable physical,morphological,or physiological characteristics.
It is determined by the interaction between the organism's genetic makeup $(genotype)$ and the environmental conditions in which it develops.
While the $genotype$ provides the potential for specific traits,the environment can influence how these traits are expressed.
Therefore,the phenotype is the result of the interaction between the $genotype$ and the environment.

(A) : Polygenic (or Quantitative) inheritance is a type of inheritance in which the expression of a trait is controlled by two or more genes. In this,each dominant allele contributes only a unit fraction of the trait,and the total phenotypic expression is the sum total of the additive or cumulative effect of all dominant alleles of the genes/polygenes.
Human skin colour is a classic example of polygenic inheritance,which is controlled by three pairs of polygenes,$A, B$,and $C$.
Negro (dark) skin colour is due to the presence of all six dominant contributing alleles $(AABBCC)$.
Very light (white) skin colour is due to the presence of all six recessive non-contributing alleles $(aabbcc)$.

(D) The correct answer is $D$.
In a $B$-form $DNA$ double helix,the structure consists of two antiparallel polynucleotide strands coiled around a common axis.
The distance between two adjacent base pairs is approximately $0.34 \ nm$ $(3.4 \ \mathring{A})$.
Since there are $10$ base pairs per turn of the helix,the length of one complete turn is $10 \times 0.34 \ nm = 3.4 \ nm$ $(34 \ \mathring{A})$.

(A) The correct answer is $A$.
In $1941$,George Beadle and Edward Tatum proposed the one gene-one enzyme hypothesis.
This hypothesis states that each gene is responsible for the synthesis of a specific enzyme that controls a particular metabolic step in an organism.
This work laid the foundation for biochemical genetics,for which they were awarded the Nobel Prize in $1958$.
Later,this theory was refined to the one gene-one polypeptide hypothesis,as many enzymes are composed of multiple polypeptide chains,and one gene typically codes for one polypeptide.

(D) $DNA$ is a type of nucleic acid that forms the genetic material in many organisms.
It consists of a long polymer of nucleotides.
It is a double helical molecule.
The two strands of $DNA$ run in opposite directions to one another,held together by hydrogen bonds.
One strand of $DNA$ has a $5' \rightarrow 3'$ direction,and the other strand has a $3' \rightarrow 5'$ direction.
This is why they are called antiparallel.
This orientation is determined by the presence of a free phosphate group at the $5'$ end and a free $OH$ group at the $3'$ end of the sugar-phosphate backbone.

(C) Neomycin is a broad-spectrum antibiotic that was first isolated from a strain of $Streptomyces \, fradiae$.
It is effective against both Gram-positive and Gram-negative bacteria.
Its mechanism of action involves the selective inhibition of protein synthesis on the $70S$ (prokaryotic) ribosome.
Specifically, it inhibits the interaction between $mRNA$ and $tRNA$ during the translation process, thereby preventing the formation of the polypeptide chain.

(C) The correct answer is $C$.
$mRNA$ (messenger $RNA$) carries the genetic information from $DNA$ to the ribosomes,where protein synthesis occurs.
The sequence of nucleotides in $mRNA$ is organized into triplets called codons,each of which specifies a particular amino acid.
During translation,$tRNA$ molecules with complementary anticodons bring the corresponding amino acids to the $mRNA$ template,ensuring that the amino acids are linked in the order dictated by the $mRNA$ sequence.
$rRNA$ forms the structural and catalytic core of ribosomes,while $cDNA$ is complementary $DNA$ synthesized from an $RNA$ template,which is not directly involved in the translation process of protein synthesis.

(B) : Homologous organs and vestigial organs provide important evidence in favour of organic evolution (the process by which changes in the genetic composition of populations of organisms occur in response to environmental changes).
Homologous organs are those that share a common ancestral origin but may perform different functions,indicating divergent evolution.
Vestigial organs are anatomical structures that have lost their original ancestral function through evolution,such as the human appendix,which is a vestige of the larger herbivorous caecum found in primate ancestors.
These structures demonstrate evolutionary relationships and the gradual modification of biological forms over time.

(D) The correct answer is $D$.
In $1953$,Stanley Miller,a graduate student of Harold Urey at the University of Chicago,conducted a landmark experiment to test the Oparin-Haldane hypothesis.
He used an airtight apparatus to circulate a mixture of four gases: methane $(CH_4)$,ammonia $(NH_3)$,hydrogen $(H_2)$,and water vapour $(H_2O)$.
He subjected this mixture to electrical discharges from electrodes to simulate lightning and passed the mixture through a condenser to simulate rain.
After circulating the gases continuously for one week,he analyzed the chemical composition of the liquid collected.
He discovered the formation of several simple organic compounds,including amino acids such as alanine,glycine,and aspartic acid.
Glutamic acid was not among the amino acids synthesized in this specific experiment.

(B) The $Jurassic$ period of the $Mesozoic$ era is characterized by the dominance of gymnosperms (such as conifers,cycads,and ferns) and the appearance of the first birds (e.g.,$Archaeopteryx$).
Therefore,option $B$ is the correct answer.

(A) The correct answer is $A$. The praying mantis exhibits the phenomenon of camouflage,where it blends into its surroundings to match the background. This adaptation helps the insect to hide from predators and effectively hunt its prey.

(A) $AIDS$ (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus $(HIV)$.
$HIV$ is a retrovirus that specifically targets and destroys $CD4^+$ $T$-helper lymphocytes.
These cells are crucial for the immune system as they coordinate the immune response by activating $B$-lymphocytes to produce antibodies and stimulating cytotoxic $T$-cells.
By infecting and destroying $T$-helper cells,$HIV$ severely compromises the body's immune system,making the individual susceptible to opportunistic infections.

(C) : Borderline personality disorder $(BPD)$ is a serious mental illness characterized by pervasive instability in moods, interpersonal relationships, self-image, and behaviour.
This instability often disrupts family and work life, long-term planning, and the individual's sense of self-identity.
Originally thought to be at the "borderline" of psychosis, people with $BPD$ suffer from a disorder of emotion regulation.
Schizophrenia is a group of severe mental disorders characterized by disturbances of language and communication; thought disturbances that may involve distortion of reality, misperceptions, delusions and hallucinations; mood changes and withdrawn, regressive, or bizarre behaviour, lasting longer than six months.
$A$ mood disorder is a condition where the prevailing emotional mood is distorted or inappropriate to the circumstances.
Addiction is a state of dependence produced by the habitual taking of drugs, alcohol, etc.

(A) Antibodies are members of a class of proteins known as immunoglobulins.
Immunoglobulins are glycoproteins belonging to the immunoglobulin superfamily.
The terms antibody and immunoglobulin are often used interchangeably.
They are found in the blood,tissue fluids,and many secretions.
In structure,they are globulins (found in the $\gamma$-region of protein electrophoresis).
They are synthesized and secreted by plasma cells,which are derived from the $B$-cells of the immune system.

(A) : Hybridisation or heterosis or hybrid vigour is defined as the superiority of the hybrid over its parents. It has been commercially exploited in different commercial crops like maize,sorghum,and bajra. The main steps include: selection of parents,selfing of parents to create inbred lines,emasculation,bagging,crossing of desired and selected inbred parents,and finally seed setting and harvesting.

(A) : Monoculture describes agricultural systems that have very low genetic and species diversity.
Monoculture involves the replacement of a diverse ecosystem with a single species or crop variety.
Because of the lack of biodiversity,these crops are more susceptible to pests and diseases compared to those grown in a diverse crop environment.
Consequently,monoculture systems often require a larger amount of chemical pesticides and fertilizers to maintain productivity.

(A) The correct answer is $A$.
Meristem is a localized group of cells that are actively dividing and undifferentiated, eventually giving rise to permanent tissues.
Even if a plant is infected with a virus, the meristematic tissue remains free of the virus.
Therefore, the meristem can be excised and grown $in vitro$ to obtain virus-free plants.
Cultivation of axillary or apical shoot meristems is known as meristem culture, which is the standard technique for producing virus-free plants.

(B) $Triticale$ is the first man-made cereal crop,which has been produced by intergeneric hybridization between common wheat ($Triticum$ $aestivum$) and European rye ($Secale$ $cereale$) with a view to combine the desirable characters of these two parent plants.
$Triticale$ is typically hexaploid $(2n = 6x = 42)$ when tetraploid wheat is used,or octaploid $(2n = 8x = 56)$ when hexaploid wheat is used.
It is not suitable for bread-making due to its low gluten content,but it serves as an excellent forage crop.

(B) The correct answer is $B$. Golden rice is a transgenic variety of rice ($Oryza$ $sativa$) which is genetically engineered to produce $\beta$-carotene,a precursor of vitamin $A$.
When consumed,the human body converts $\beta$-carotene into vitamin $A$.
Therefore,the cultivation and consumption of golden rice are intended to help in the alleviation of vitamin $A$ deficiency in populations that rely heavily on rice as a staple food.

(D) : An ecological niche is the specific part of a habitat occupied by individuals of a species,which is defined by its range of tolerance,range of movement,microclimate,type of food and its availability,shelter,type of predator,and timing of activity.
An ecological niche is typically occupied by a single species.
Niche overlap occurs when two or more species share one or more limited resources for which they compete.
For example,both owls and cats may feed on shrews and mice,leading to a niche overlap because they utilize the same food resource,even if their broader habitats differ.

(A) : Ecological pyramids represent the trophic structure and trophic function of an ecosystem.
In an ecological pyramid,the first trophic level forms the base and successive trophic levels form the tiers that make up the apex.
Ecological pyramids are generally of three types: pyramid of number,pyramid of biomass,and pyramid of energy.
Pyramid of biomass is based on the dry weight of the organisms in a food chain present at any given time in an ecosystem.
Fresh weight is not used because it includes water content,which varies significantly and does not accurately represent the organic matter or energy content.
Therefore,fresh weight is not used for the construction of ecological pyramids.

(B) The correct answer is $B$.
An endangered species is a living organism that is at risk of extinction if its population continues to decline and its habitat is not protected.
$Bentinckia nicobarica$ is a critically endangered species of palm tree native to the Nicobar Islands.
The red panda $(Ailurus fulgens)$ is an endangered mammal species facing threats due to habitat loss and human encroachment.
Therefore,the pair consisting of $Bentinckia nicobarica$ (plant) and red panda (animal) represents endangered organisms in India.

(C) In situ conservation refers to the conservation of species within their natural habitats.
This approach involves the protection and management of important components of biological diversity through a network of protected areas,such as National Parks,Wildlife Sanctuaries,and Biosphere Reserves.
Botanical gardens,on the other hand,are examples of ex situ conservation,where species are maintained outside their natural habitats.

(C) : Kaziranga National Park in Assam is famous for the conservation of the one-horned rhinoceros. The other options are incorrectly matched: The Great Indian bustard is found in Desert National Park,the Asiatic Lion is found in Gir National Park,and the Wild ass is found in the Indian Wild Ass Sanctuary (Little Rann of Kutch).

(A) The Central Pollution Control Board $(CPCB)$ has established standards for the discharge of environmental pollutants.
For the discharge of industrial and municipal wastewater into natural surface water bodies,the prescribed limit for Biochemical Oxygen Demand $(BOD)$ is less than $30 \ ppm$ $(30 \ mg/L)$.
This measurement is typically taken over a period of $3$ days at a temperature of $27^{\circ}C$.

(D) Photochemical smog is a grey or yellow-brown opaque smog that creates an oxidizing environment.
It primarily contains secondary pollutants or photochemical oxidants.
Key components formed during its production include nitrogen dioxide $(NO_2)$,ozone $(O_3)$,and peroxyacyl nitrates $(PAN)$.
Carbon dioxide $(CO_2)$ is a greenhouse gas and a primary pollutant,but it is not a component of photochemical smog.
Therefore,the correct answer is $CO_2$.

(C) The correct answer is $C$.
The Montreal Protocol was signed in Montreal,Canada,by over $150$ countries at a convention in $1987$ to reduce the use of $CFCs$ (chlorofluorocarbons).
The primary aim of this protocol was to protect the ozone layer in the stratosphere by decreasing and eventually eliminating the use of ozone-depleting substances,such as $CFCs$.
It is widely regarded as one of the most successful international environmental treaties in modern history.

(B) The edible part of the litchi $(Litchi chinensis)$ is the fleshy,succulent outgrowth that develops from the base of the ovule,which is known as the aril.
Therefore,the correct option is $B$.

(A) In angiosperms,synergid cells are haploid $(n)$. Given that the number of chromosomes in synergid cells is $n = 8$.
The endosperm in angiosperms is formed by the fusion of two polar nuclei and one male gamete,resulting in a triploid $(3n)$ structure.
Therefore,the number of chromosomes in the endosperm cells = $3 \times n = 3 \times 8 = 24$.

(B) Cytoplasmic inheritance (also known as extranuclear or organellar inheritance) is the transmission of genes located in the cytoplasm,specifically within organelles like mitochondria or chloroplasts.
In most sexually reproducing organisms,the zygote receives the vast majority of its cytoplasm from the egg cell (ovum),while the sperm contributes little to no cytoplasm.
Therefore,traits governed by genes in the mitochondria or chloroplasts are almost exclusively inherited from the mother to all her offspring,regardless of their sex.
This results in a strong maternal effect observed in the progeny.

(A) The evolutionary history and relationship of a group of organisms is known as $Phylogeny$.
$Ontogeny$ refers to the developmental history of an individual organism.
$Paleontology$ is the study of fossils.
Therefore,the correct term for the evolutionary history of an organism is $Phylogeny$.

(A) Restriction endonucleases are enzymes that recognize specific palindromic nucleotide sequences in $DNA$ and cut the $DNA$ duplex at specific positions,usually within or near the recognition site. These are essential tools in recombinant $DNA$ technology,often referred to as 'molecular scissors'.

(C) The formula for exponential population growth is $\frac{dN}{dt} = rN$.
Here,$\frac{dN}{dt}$ represents the rate of change in population size over time.
$r$ represents the intrinsic rate of natural increase (biotic potential).
$N$ represents the current population size.

(D) Biodiversity hot spots are regions that are exceptionally rich in biodiversity and are under significant threat due to human activities.
In India,there are three recognized biodiversity hot spots: the Western Ghats and Sri Lanka,the Himalayas,and the Indo-Burma region.
Among the given options,the Western Ghats are a globally recognized biodiversity hot spot characterized by high levels of endemism and habitat loss due to developmental activities.