AIPMT 1994 Biology Question Paper with Answer and Solution

(C) The genus $Ustilago$ belongs to the class $Basidiomycetes$ and is known for causing smut diseases in various plants,particularly cereals.
These fungi are called 'smuts' because they produce large quantities of dark-colored,powdery teliospores (resting spores) that replace the host tissues.
This accumulation of black,soot-like spores gives the infected plant parts a charred or 'smutty' appearance.
Therefore,the correct reason is that they develop a black mass of spores.

(C) Nitrogen fixation is the process of converting atmospheric nitrogen into ammonia,which is essential for plant growth.
$Nostoc$,$Azotobacter$,and $Anabaena$ are well-known nitrogen-fixing organisms.
$Nostoc$ and $Anabaena$ are cyanobacteria (blue-green algae) that possess specialized cells called heterocysts for nitrogen fixation.
$Azotobacter$ is a free-living soil bacterium that also fixes nitrogen.
$Spirogyra$ is a filamentous green alga that performs photosynthesis but lacks the ability to fix atmospheric nitrogen.
Therefore,the correct answer is $Spirogyra$.

(B) Pteridophytes are the first terrestrial plants to possess vascular tissues ($xylem$ and $phloem$).
They reproduce by producing spores,which are formed in sporangia.
Unlike Bryophytes,where the sporophyte is dependent on the gametophyte,in Pteridophytes,the sporophyte is the dominant,independent phase.
Therefore,the production of spores is a characteristic feature of Pteridophytes.

(B) In $Chlorophyceae$ (green algae),sexual reproduction shows considerable variation in the type and formation of sex cells.
It may be isogamous,anisogamous,or oogamous.
$1$. Isogamous: Fusion of morphologically similar gametes (e.g.,$Ulothrix$).
$2$. Anisogamous: Fusion of morphologically dissimilar gametes (e.g.,$Eudorina$).
$3$. Oogamous: Fusion of a large non-motile female gamete and a small motile male gamete (e.g.,$Volvox$,$Spirogyra$ is an exception as it is isogamous but non-motile).
Therefore,all three types of sexual reproduction are observed in $Chlorophyceae$.

(C) In $Pinus$,the seed is winged to facilitate wind dispersal.
This wing is not a part of the seed coat (testa) itself.
Instead,the wing is derived from the thin layer of tissue that peels off from the upper surface of the ovuliferous scale.
Therefore,the correct answer is the surface of the ovuliferous scale.

(A) The phylum $Platyhelminthes$ consists of flatworms.
$Schistosoma$ (blood fluke) belongs to the class $Trematoda$ within the phylum $Platyhelminthes$.
$Trypanosoma$ is a protozoan belonging to the phylum $Protozoa$ (or $Sarcomastigophora$).
$Plasmodium$ is a protozoan belonging to the phylum $Protozoa$ (or $Apicomplexa$).
$Wuchereria$ is a roundworm belonging to the phylum $Aschelminthes$ (or $Nematoda$).
Therefore,the correct option is $A$.

(C) In a closed circulatory system,blood is pumped through vessels of varying diameters (arteries,veins,and capillaries).
Among the given options:
$1$. Snails (Mollusca) typically have an open circulatory system.
$2$. Cockroaches (Arthropoda) have an open circulatory system.
$3$. Cuttlefish (Cephalopoda,Mollusca) possess a closed circulatory system,which is an exception within the phylum Mollusca.
Therefore,the correct answer is $C$.

(B) The phylum $Cnidaria$ (also known as $Coelenterata$) is characterized by the presence of specialized cells called $Cnidoblasts$ or $Cnidocytes$.
These cells contain stinging capsules known as $nematocysts$, which are used for anchorage, defense, and capturing prey.
$Flame$ $cells$ are characteristic of Phylum $Platyhelminthes$ (excretion).
$Polymorphism$ is seen in some $Cnidarians$ but is not the defining characteristic of the entire phylum.
$Hermaphroditism$ is found in various phyla and is not a unique feature of $Cnidaria$.

(B) The water vascular system,also known as the ambulacral system,is a unique characteristic feature of the phylum $Echinodermata$.
This system consists of a network of water-filled canals that function in locomotion,capture and transport of food,and respiration.
Among the given options,$Starfish$ $(Asterias)$ belongs to the phylum $Echinodermata$.
Therefore,the water vascular system is found in $Starfish$.

(D) $1$. Tapeworms $(Taenia)$ are endoparasites that live in the intestine of humans.
$2$. Mosquitoes are ectoparasites that feed on the blood of vertebrates.
$3$. Leeches $(Hirudinaria)$ are ectoparasites that feed on the blood of various animals.
$4$. Sea Anemones $(Adamsia)$ are marine cnidarians that are free-living and predatory,not parasitic. Therefore,the Sea Anemone is the non-parasitic organism.

(C) Radial symmetry is a type of body plan where an organism can be divided into identical halves by any plane passing through the central axis. This type of symmetry is commonly found in organisms that are sessile (attached to a substrate) or free-floating,such as Cnidarians (e.g.,Hydra,Jellyfish) and adult Echinoderms. $A$ sessile or benthic lifestyle allows the organism to interact with its environment from all directions,making radial symmetry an evolutionary advantage for such animals.

(C) The body cavity that is derived from the blastocoel during embryonic development is called a $Pseudocoelom$.
In organisms like $Aschelminthes$ (roundworms),the mesoderm is present as scattered pouches between the ectoderm and endoderm,and the body cavity is not lined by mesoderm,which is why it is termed a false body cavity or $Pseudocoelom$.

(D) The phylum $Chordata$ is characterized by the presence of a notochord,a dorsal hollow nerve cord,and paired pharyngeal gill slits at some stage of their life cycle. The notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Therefore,the presence of a notochord is the defining feature of all chordates.

(A) Vertebrates are a subphylum of Chordata characterized by the presence of a vertebral column.
All vertebrates possess a cranium (brain box) that protects the brain,which is why they are also known as Craniata.
Option $A$ is correct because the presence of a cranium is a defining feature of all vertebrates.
Options $B$,$C$,and $D$ are not universal characteristics; for example,cyclostomes lack jaws and paired appendages,and many vertebrates do not have a distinct neck or a body covered by an exoskeleton.

(C) $1$. Vascular tissue (xylem and phloem) is present in Pteridophytes,Gymnosperms,and Angiosperms.
$2$. Seed production is a characteristic of Gymnosperms and Angiosperms.
$3$. $A$ taproot system is a characteristic feature of Dicots (a group within Angiosperms) and Gymnosperms.
$4$. Monocots typically possess a fibrous root system.
$5$. Therefore,plants that possess vascular tissue,produce seeds,and have a taproot system are Gymnosperms and Dicots.

(C) Hypanthodium is a specialized type of inflorescence. In this type,the receptacle (thalamus) becomes fleshy and forms a cup-shaped cavity with a small opening at the top. The flowers are borne on the inner surface of this cavity. This is commonly observed in the genus $Ficus$ (e.g.,Banyan,Peepal).

(B) The Casparian strips are characteristic features of the endodermis in the roots of vascular plants.
These are bands of suberin-impregnated cell wall material that prevent the apoplastic movement of water and solutes into the vascular cylinder.
Therefore,the correct option is $B$.

(D) The procambium is a primary meristematic tissue derived from the apical meristem.
It differentiates into the primary vascular tissues,which include primary xylem and primary phloem.
Additionally,it gives rise to the vascular cambium,which is responsible for secondary growth in dicotyledonous plants.
Therefore,the procambium gives rise to primary vascular tissues and the vascular cambium.

(A) As secondary growth proceeds in a tree,the vascular cambium produces secondary xylem towards the inner side.
Over time,the older secondary xylem near the center of the stem becomes non-functional and is filled with tannins,resins,and oils,forming the heartwood.
The peripheral,functional part of the secondary xylem is called sapwood.
As the tree ages,the amount of heartwood increases because more secondary xylem is converted into heartwood,while the sapwood layer remains relatively constant in thickness to maintain water conduction.

(A) The epithelial cells described as thin,flat,and tile-like are known as $Squamous$ $Epithelium$.
These cells are found in the walls of blood vessels and air sacs of lungs,and they also form the inner lining of the cheek (buccal cavity).
Therefore,the correct option is $A$.

(B) Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus.
These organelles are rich in almost all types of hydrolytic enzymes (hydrolases like lipases,proteases,and carbohydrases) optimally active at the acidic $pH$.
These enzymes are capable of digesting carbohydrates,proteins,lipids,and nucleic acids,which is why lysosomes are often referred to as the 'suicide bags' of the cell.

(D) The $Golgi$ $apparatus$ is an organelle composed of many flat, disc-shaped sacs or cisternae of $0.5 \mu m$ to $1.0 \mu m$ diameter.
These are stacked parallel to each other.
Varied numbers of cisternae are present in a $Golgi$ complex.
The $Golgi$ cisternae are concentrically arranged near the nucleus with distinct convex $cis$ or the forming face and concave $trans$ or the maturing face.

(D) Mitochondrial cristae are the inner membrane folds of the mitochondria.
These cristae significantly increase the surface area of the inner mitochondrial membrane.
The inner mitochondrial membrane contains the components of the Electron Transport System $(ETS)$ and $ATP$ synthase.
These components facilitate various oxidation-reduction (redox) reactions,which are essential for the process of oxidative phosphorylation to generate $ATP$.
Therefore,the cristae are the specific sites for these oxidation-reduction reactions.

(D) The inner membrane of the mitochondrion forms a number of infoldings called $Cristae$ towards the matrix.
These infoldings increase the surface area of the inner membrane,which is essential for the attachment of enzymes involved in the electron transport chain and $ATP$ synthesis.
Therefore,the correct option is $D$.

(D) nephron consists of two major parts: the renal corpuscle and the renal tubule.
$1$. The renal corpuscle includes the Glomerulus and Bowman's capsule.
$2$. The renal tubule consists of the Proximal Convoluted Tubule $(PCT)$,Loop of Henle,and Distal Convoluted Tubule $(DCT)$.
$3$. The collecting duct is not considered a part of the nephron itself,as multiple nephrons drain their filtrate into a single collecting duct.

(B) Animals that excrete nitrogenous waste in the form of uric acid are called uricotelic animals.
Uric acid is excreted in the form of a pellet or paste with a minimum loss of water.
This is an adaptation for water conservation.
Birds,reptiles (like lizards and snakes),and land snails are examples of uricotelic organisms.
Therefore,birds and lizards excrete uric acid as their primary nitrogenous waste.

(B) If the kidneys fail to reabsorb water,it leads to excessive loss of water from the body through urine (polyuria).
This results in a decrease in the volume of blood plasma and an increase in the osmotic pressure of the blood.
Due to the high osmotic pressure in the blood,water moves out of the body tissues into the blood vessels via osmosis to maintain equilibrium.
As a result,the body tissues lose water and consequently shrink or shrivel.

(A) The pectoral girdle (shoulder girdle) consists of two bones: the clavicle (collar bone) and the scapula (shoulder blade).
The scapula is a large,triangular,flat bone situated in the dorsal part of the thorax between the second and the seventh ribs.
It contains a depression called the glenoid cavity,which articulates with the head of the humerus to form the shoulder joint.
Sternum is part of the axial skeleton.
Coxal bone and acetabulum are parts of the pelvic girdle.

(A) Muscle contraction is initiated by the release of calcium ions $(Ca^{2+})$ from the sarcoplasmic reticulum into the sarcoplasm.
These $Ca^{2+}$ ions bind to the troponin complex on the actin filaments,which causes a conformational change that exposes the myosin-binding sites on the actin.
This allows the myosin heads to bind to actin,forming cross-bridges and leading to muscle contraction via the sliding filament mechanism.

(B) The respiratory rhythm center is a specialized center primarily responsible for the regulation of respiration. It is located in the medulla region of the hindbrain. This center is primarily responsible for the regulation of respiratory rhythm.

(A) The blood group $O$ is determined by the genotype $ii$.
For a child to have blood group $O$ $(ii)$,both parents must contribute an $i$ allele.
Parents with blood group $AB$ have the genotype $I^A I^B$.
Since they do not possess the $i$ allele,they cannot produce a child with blood group $O$ $(ii)$.
Therefore,parents with blood group $AB$ cannot have a child with blood group $O$.

(C) Living organisms are primarily composed of carbon,hydrogen,oxygen,and nitrogen.
These four elements constitute approximately $99\%$ of the total mass of the living system.
Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,and Nitrogen $(N)$ are the fundamental building blocks of biological macromolecules like proteins,nucleic acids,carbohydrates,and lipids.
Therefore,the correct option is $CHON$.

(B) During $Metaphase$, chromosomes are highly condensed and align at the equatorial plate of the cell. This stage provides the clearest view of the chromosome structure, allowing for the accurate observation of their number, size, and morphology (shape). Therefore, $Metaphase$ is considered the best stage for karyotyping and chromosomal analysis.

(D) Meiosis is a specialized type of cell division that reduces the chromosome number by half,creating four haploid cells.
Its significance for evolution lies in the process of genetic recombination (crossing over) that occurs during Prophase-$I$.
This process shuffles the genetic material between homologous chromosomes,leading to variations in the offspring.
These variations are the raw material for natural selection and evolution.
While options $B$ and $C$ describe outcomes of meiosis,they do not directly explain the significance regarding evolution as effectively as genetic recombination does.

(B) Abscisic acid $(ABA)$ is a plant growth inhibitor that plays a crucial role in the closure of stomata during water stress conditions.
When a plant experiences water stress,$ABA$ is synthesized in the leaves,which triggers the efflux of potassium ions $(K^+)$ from the guard cells.
This loss of ions leads to a decrease in the turgor pressure of the guard cells,causing them to become flaccid and resulting in the closure of the stomatal pore.
Therefore,$ABA$ acts as a stress hormone to prevent water loss through transpiration.

(B) $Potometer$ is an apparatus used to measure the rate of water uptake by a cut shoot,which is directly proportional to the rate of transpiration.
$Auxanometer$ is used to measure the growth in length of a plant.
$Porometer$ is used to measure the size of stomatal apertures.
$Tensiometer$ is used to measure soil water tension.
Therefore,the correct instrument for measuring the rate of transpiration is the $Potometer$.

(B) Photosynthesis is the process by which green plants,algae,and certain bacteria convert light energy into chemical energy.
While terrestrial plants are visible,the vast majority of photosynthesis on Earth occurs in aquatic environments.
Marine algae (phytoplankton) are responsible for approximately $85-90\%$ (or $9/10$) of the total global photosynthesis.
Therefore,the correct option is $B$.

(B) Photophosphorylation is the process of synthesizing $ATP$ from $ADP$ and inorganic phosphate in the presence of light.
In non-cyclic photophosphorylation,both $PS-I$ and $PS-II$ are involved,leading to the production of $ATP$,$NADPH$,and the release of $O_2$.
In cyclic photophosphorylation,only $PS-I$ is involved,and it results in the production of $ATP$ only,without the release of $O_2$ or the formation of $NADPH$.
Therefore,the common product produced in both processes is $ATP$.

(A) The $C_4$ cycle,also known as the $C_4$ photosynthetic pathway or the Hatch-Slack pathway,was discovered by $M$.$D$. Hatch and $C$.$R$. Slack in $1966$.
This pathway is an adaptation found in certain plants to minimize photorespiration and increase photosynthetic efficiency in hot and dry environments.

(C) In the light-harvesting complex of photosynthesis,the reaction center is composed of a special pair of chlorophyll-$a$ molecules.
In Photosystem-$I$ $(PS-I)$,the reaction center is known as $P_{700}$ because it absorbs light at a wavelength of $700 \ nm$.
In Photosystem-$II$ $(PS-II)$,the reaction center is known as $P_{680}$ because it absorbs light at a wavelength of $680 \ nm$.
Among the given options,$P_{700}$ is the pigment that acts as the reaction center for $PS-I$.

(A) The energy yield from the oxidation of respiratory substrates depends on their chemical structure and the amount of hydrogen atoms available for oxidation.
Fats (lipids) are highly reduced molecules compared to carbohydrates (like starch) or proteins.
Upon complete oxidation,$1 \ g$ of fat yields approximately $9 \ kcal$ of energy,whereas $1 \ g$ of carbohydrates or proteins yields approximately $4 \ kcal$ of energy.
Therefore,fats yield the maximum energy per unit mass through the process of $\beta$-oxidation and the subsequent entry of acetyl-$CoA$ into the Krebs cycle.

(B) Cyanide is a potent inhibitor of the electron transport chain $(ETC)$,specifically binding to cytochrome c oxidase (Complex $IV$).
This inhibition prevents the final step of aerobic respiration,where oxygen is reduced to water.
As a result,the proton gradient across the inner mitochondrial membrane cannot be maintained,and $ATP$ synthesis stops.
Since $ATP$ is essential for vital cellular processes,including the active transport of ions via the $Na^+ - K^+$ pump,the cessation of $ATP$ production leads to cell death and toxicity.

(B) The amount of $ATP$ produced depends on the energy content of the respiratory substrate.
Glucose $(C_6H_{12}O_6)$ is a standard carbohydrate that yields approximately $36$ to $38$ $ATP$ molecules per molecule through aerobic respiration.
However,fatty acids (lipids) and certain amino acids have a higher energy density per gram compared to carbohydrates.
Among the given options,glucose is the primary respiratory substrate.
However,if we consider the energy yield per gram,lipids provide more energy than glucose.
Since the question asks for the substrate yielding the maximum $ATP$ and glucose is the standard reference,but glycogen is a polymer of glucose that can be broken down into glucose units,the question implies a comparison of energy substrates.
Actually,$1$ gram of fat yields $9.4$ $kcal$ while $1$ gram of carbohydrate yields $4.1$ $kcal$.
Given the options,glucose is the most efficient direct substrate for cellular respiration.

(D) In yeast, fermentation is an anaerobic process where glucose is incompletely oxidized in the absence of oxygen.
This process is catalyzed by enzymes like pyruvic acid decarboxylase and alcohol dehydrogenase.
The chemical reaction is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
Thus, the end products of fermentation in yeast are ethyl alcohol $(C_2H_5OH)$ and carbon dioxide $(CO_2)$.

(B) The process of breaking down glucose into two molecules of pyruvic acid is known as glycolysis.
This process occurs in the cytoplasm of the cell and is the first step in cellular respiration for both aerobic and anaerobic organisms.
It does not require oxygen and is common to all living cells.

(B) Auxin transport in plants is primarily polar. In the stem,auxin is transported from the shoot apex towards the base,which is known as basipetal transport. In the root,it is transported from the root tip towards the base,which is also basipetal. However,in certain contexts like the vascular tissue,it can show complex patterns. Given the standard physiological context of auxin movement in the stem and root tips,it is characterized as basipetal transport.

(C) Pellagra is a deficiency disease caused by a lack of $Vitamin B_3$ (Niacin or Nicotinamide).
Symptoms of Pellagra are often described by the '$4Ds$': Dermatitis (thick,pigmented skin),Diarrhea,Dementia (irritability,confusion),and Death.
Swollen lips (cheilosis) and glossitis are also common clinical features associated with this deficiency.
Therefore,the correct pair is Nicotinamide - Pellagra.

(C) The regulation of the digestive system is mediated by gastrointestinal hormones:
$1$. Gastrin stimulates the secretion of $HCl$ and pepsinogen in the stomach.
$2$. Enterogastrone (also known as Gastric Inhibitory Peptide or $GIP$) inhibits gastric secretion and motility.
$3$. Cholecystokinin $(CCK)$ stimulates the release of bile from the gallbladder and pancreatic enzymes from the pancreas.
$4$. Pancreozymin stimulates the secretion of pancreatic enzymes.
Therefore,the correct sequence of hormones involved in the inhibition of gastric secretion and the regulation of gastric,pancreatic,and bile secretions is Gastrin,Enterogastrone,Cholecystokinin,and Pancreozymin.

(A) Vitamin $D$ is essential for the absorption of calcium from the gastrointestinal tract.
In the absence of vitamin $D$,the body cannot effectively absorb calcium from the diet,even if calcium intake is sufficient.
This leads to a deficiency of calcium in the blood and tissues,which can cause conditions like rickets in children and osteomalacia in adults.

(D) Rennin (also known as chymosin) is a proteolytic enzyme found in the gastric juice of infants.
It acts on the milk protein casein.
In the presence of calcium ions,it converts soluble casein into insoluble calcium paracaseinate (curdling of milk).
This reaction occurs in the acidic environment of the stomach,typically at a $pH$ range of $1-3$.

(D) Color blindness is an $X$-linked recessive disorder. Let the allele for normal vision be $X^C$ and the allele for color blindness be $X^c$.
The genotype of a color-blind woman is $X^cX^c$.
The genotype of a man with normal vision is $X^CY$.
When these two individuals cross:
Parents: $X^cX^c$ (female) $\times$ $X^CY$ (male)
Gametes: $X^c$ and $X^c$ (from mother); $X^C$ and $Y$ (from father)
Offspring genotypes:
$X^CX^c$ (Carrier daughter, normal vision)
$X^CX^c$ (Carrier daughter, normal vision)
$X^cY$ (Color-blind son)
$X^cY$ (Color-blind son)
Therefore, all sons will be color-blind, and all daughters will be carriers with normal vision.

(A) Tautomeric shifts are spontaneous changes in the molecular structure of nitrogenous bases in $DNA$.
These shifts involve the migration of a hydrogen atom,which changes the base from its standard keto form to an imino or enol form.
These alternative valence states allow for rare,incorrect base pairing (e.g.,$A$ pairing with $C$ instead of $T$),which can lead to mutations during $DNA$ replication.

(D) Let $T$ be the allele for tallness and $t$ for dwarfness. Let $G$ be the allele for green pods and $g$ for yellow pods.
The cross is between a pure tall green plant $(TTGG)$ and a dwarf yellow plant $(ttgg)$.
The $F_1$ generation will be $TtGg$ (tall and green).
In the $F_2$ generation,the phenotypic ratio for a dihybrid cross is $9:3:3:1$.
The distribution is as follows:
- Tall and Green: $9$
- Tall and Yellow: $3$
- Dwarf and Green: $3$
- Dwarf and Yellow: $1$
Therefore,out of $16$ offspring,only $1$ plant will be dwarf with yellow pods $(ttgg)$.

(B) In a dihybrid cross,the $F_1$ generation produces $AaBb$ individuals. When $AaBb$ is self-crossed to produce the $F_2$ generation,the phenotypic ratio follows Mendel's Law of Independent Assortment.
For a dihybrid cross involving two traits,the phenotypic ratio of the $F_2$ generation is $9 : 3 : 3 : 1$.
This ratio represents the four possible phenotypes: both dominant,one dominant and one recessive,one recessive and one dominant,and both recessive.

(D) In protein synthesis,the process of translation begins with an initiation codon.
For both prokaryotes and eukaryotes,the codon $AUG$ serves as the initiation codon.
$AUG$ codes for the amino acid Methionine.
Therefore,the correct option is $D$.

(B) The genetic code is a triplet code,meaning each codon consists of $3$ nucleotides. There are $4$ types of nitrogenous bases $(A, U, G, C)$. The total number of possible codons is calculated as $4^3 = 4 \times 4 \times 4 = 64$. Out of these $64$ codons,$61$ codons code for amino acids,while $3$ codons $(UAA, UAG, UGA)$ are stop codons (nonsense codons) that do not code for any amino acid. Therefore,the number of codons that code for amino acids is $61$.

(D) Reverse transcriptase is an enzyme that catalyzes the synthesis of $DNA$ from an $RNA$ template.
Since it uses $RNA$ as a template to synthesize a complementary $DNA$ $(cDNA)$ strand,it is classified as an $RNA$-dependent $DNA$ polymerase.
This enzyme is commonly found in retroviruses,such as $HIV$,allowing them to integrate their genetic material into the host genome.

(A) In the $lac$ operon of $Escherichia$ $coli$,the $i$ gene codes for a repressor protein that binds to the operator region and prevents transcription.
When lactose is present in the medium,it enters the cell and is converted into its isomer,allolactose.
Allolactose acts as an inducer by binding to the repressor protein,which changes the shape of the repressor so that it can no longer bind to the operator.
This allows $RNA$ polymerase to transcribe the structural genes,thus lactose (or its isomer allolactose) acts as the inducer for the $lac$ operon.

(A) During transcription,the $RNA$ polymerase enzyme synthesizes $RNA$ using the template strand of $DNA$ in the $3' \rightarrow 5'$ direction.
According to the principle of complementarity,$Adenine$ $(A)$ pairs with $Uracil$ $(U)$ in $RNA$,$Thymine$ $(T)$ pairs with $Adenine$ $(A)$,$Cytosine$ $(C)$ pairs with $Guanine$ $(G)$,and $Guanine$ $(G)$ pairs with $Cytosine$ $(C)$.
Given template strand: $3'-C-T-G-A-T-A-G-C-5'$.
Complementary $RNA$ sequence: $5'-G-A-C-U-A-U-C-G-3'$.
Therefore,the correct sequence is $5'-GACUAUCG-3'$.

(D) During $DNA$ replication,the enzyme $Helicase$ is responsible for unwinding the $DNA$ double helix by breaking the hydrogen bonds between the nitrogenous bases. This process creates the replication fork,allowing the replication machinery to access the template strands. While $DNA$ Gyrase (a type of Topoisomerase) relieves the supercoiling strain ahead of the fork,the actual opening of the helix is performed by $Helicase$.

(A) Protein synthesis,also known as translation,involves three main stages: $Initiation$,$Elongation$,and $Termination$.
Transcription is the process of synthesizing $RNA$ from a $DNA$ template,which occurs in the nucleus before translation.
Therefore,transcription is not a stage of protein synthesis itself,but rather a precursor process.

(A) In nucleic acids, the pyrimidine bases are Cytosine $(C)$, Thymine $(T)$, and Uracil $(U)$. Purine bases are Adenine $(A)$ and Guanine $(G)$.
We need to count the number of pyrimidines $(C, T, U)$ in each sequence:
$A$: $GATCAATGC$ $\rightarrow$ $T, C, T, C$ (Total $4$ pyrimidines).
$B$: $GCUAGACAA$ $\rightarrow$ $C, U, C$ (Total $3$ pyrimidines).
$C$: $UAGCGGUAA$ $\rightarrow$ $U, C, C$ (Total $3$ pyrimidines).
$D$: $TGCCTAACG$ $\rightarrow$ $T, C, C, T, C$ (Total $5$ pyrimidines).
Therefore, the sequence containing exactly four pyrimidine bases is $GATCAATGC$.

(B) In the context of evolutionary biology and natural selection,traits that provide a survival or reproductive advantage tend to increase in frequency within a population over generations. These traits are typically expressed as dominant traits in the phenotype,allowing them to be selected for by environmental pressures. Therefore,when traits are dominant,they are more likely to be expressed and passed on,leading to an increase in their frequency.

(D) Lamarckism,or the theory of inheritance of acquired characters,suggests that organisms acquire traits during their lifetime through use or disuse of organs and pass these to their offspring.
$A$,$B$,and $C$ are examples that Lamarck used to support his theory (e.g.,snakes losing limbs due to disuse,aquatic birds developing webs due to constant use).
$D$ (the darkening of white-winged moths in industrial areas,known as industrial melanism) is an example of natural selection,which supports Darwinism,not Lamarckism. It is a change in population frequency due to environmental pressure,not the inheritance of an acquired trait.

(B) Human evolution is characterized by several key adaptations.
$1$. $A$ is correct: The development of a precision grip allowed for the creation and use of complex tools.
$2$. $B$ is incorrect: Human evolution involved a transition from a diet of tough,fibrous plant material to a more varied diet,but the shift was not specifically from 'hard nuts' to 'soft food' as a primary evolutionary driver; rather,it involved the use of fire and cooking,which softened food. However,in the context of evolutionary biology questions,the option describing a shift from 'hard nut-based diet' to 'soft food' is often considered a distractor or scientifically inaccurate compared to the other evolutionary milestones.
$3$. $C$ is correct: The expansion of the brain,particularly the cerebral cortex,facilitated complex language and social structures.
$4$. $D$ is correct: The loss of the tail is a characteristic trait of the hominoid lineage (apes and humans).

(B) The $Palaearctic$ and $Oriental$ realms are separated by the high mountain ranges of the $Himalayas$. These mountains act as a significant physical barrier that prevents the migration and intermingling of species between these two distinct biogeographical regions.

(C) Homologous organs are those organs that have the same basic structural design and developmental origin but perform different functions.
These organs indicate divergent evolution.
The flipper of a whale and the forelimbs of a horse are homologous because they share the same skeletal structure (humerus,radius,ulna,carpals,metacarpals,and phalanges) despite being adapted for swimming and running,respectively.
In contrast,wings of insects and bats,or grasshoppers and crows,are analogous organs because they perform the same function (flight) but have different evolutionary origins.

(C) The evolutionary history of the horse is well-documented in the fossil record.
$Eohippus$ (also known as $Hyracotherium$) is recognized as the earliest known ancestor of the modern horse.
It lived during the Eocene epoch,approximately $50$ million years ago.
It was a small,dog-sized animal with four toes on its front feet and three toes on its hind feet,adapted for browsing in forests.
Therefore,$Eohippus$ represents the oldest fossil in this evolutionary lineage.

(A) The $Mesozoic$ era is famously known as the $Age$ of $Reptiles$ or the $Golden$ $Age$ of $Dinosaurs$.
This era lasted approximately from $252$ to $66$ million years ago.
It is divided into three periods: $Triassic$,$Jurassic$,and $Cretaceous$.
During this time,reptiles were the dominant terrestrial vertebrates.

(B) Most of our modern cereal crops,such as wheat $(Triticum \ aestivum)$,are $allopolyploids$.
An $allopolyploid$ is an organism that contains two or more sets of chromosomes derived from different species.
These crops were developed through hybridization between different species followed by chromosome doubling,which allowed for the combination of desirable traits from multiple ancestors.

(C) Haploid plants can be produced through tissue culture techniques using pollen grains (microspores).
Since pollen grains are haploid $(n)$ cells formed by meiosis,culturing them on a suitable nutrient medium allows them to develop into haploid embryos and subsequently into haploid plants.
This technique is widely used in plant breeding to obtain homozygous lines rapidly.

(A) Organisms are classified based on their tolerance to salinity levels in their environment.
$1$. $Stenohaline$ organisms are those that can tolerate only a narrow range of salt concentrations.
$2$. $Euryhaline$ organisms are those that can tolerate a wide range of salt concentrations.
$3$. $Anadromous$ and $Catadromous$ refer to migratory patterns of fish between freshwater and marine environments.
Therefore,the correct term for organisms that tolerate a narrow range of salinity is $Stenohaline$.

(C) Tropical rain forests are characterized by high rainfall and high temperature throughout the year.
In India,these forests are primarily located in the Western Ghats (including Kerala) and the North-Eastern regions (including Assam).
Therefore,the correct option is $C$.

(C) The pyramid of energy is always upright in any ecosystem.
This is because, according to the $10\%$ law of energy transfer, energy is lost as heat at each trophic level as it moves from producers to consumers.
Consequently, the amount of energy available at higher trophic levels is always less than that at lower trophic levels.
Unlike the pyramid of biomass or the pyramid of numbers, which can be inverted in certain ecosystems (e.g., aquatic ecosystems for biomass or tree ecosystems for numbers), the pyramid of energy can never be inverted.

(B) The bulk of $CO_2$ fixation on Earth occurs in the oceans. Although terrestrial ecosystems like tropical rainforests are highly productive,the vast surface area of the oceans,combined with the photosynthetic activity of phytoplankton,accounts for approximately $40\%$ of the total global carbon fixation.

(B) The desert environment is characterized by extreme conditions that limit the survival of many organisms.
Key features include:
$1$. Low and erratic rainfall.
$2$. High solar radiation leading to high temperatures.
$3$. High rate of evaporation.
$4$. Low atmospheric humidity.
While high temperature and high evaporation are features,'Low atmospheric humidity' is a fundamental climatic characteristic that defines the aridity of the desert biome. However,in many standard biological contexts,all these factors contribute to the desert environment. Given the options,'Low atmospheric humidity' is a defining abiotic factor.

(A) In a pond ecosystem,the trophic levels are organized based on energy flow.
$1$. The first trophic level consists of producers,which are the $Phytoplankton$.
$2$. The second trophic level consists of primary consumers,which feed on the producers. In a pond,$Zooplankton$ act as the primary consumers.
$3$. Therefore,$Zooplankton$ represent the second trophic level,making them the second most important level in terms of energy transfer from producers to higher consumers.

(B) According to the $10\%$ law of energy transfer in an ecosystem,only about $10\%$ of the energy (or biomass) is transferred from one trophic level to the next.
$1$. Grass (Producer): $1$ tonne = $1000\,kg$.
$2$. Deer (Primary Consumer): $10\%$ of $1000\,kg = 100\,kg$.
$3$. Tiger (Secondary Consumer): $10\%$ of $100\,kg = 10\,kg$.
Therefore,the biomass of the tiger will be $10\,kg$.

(B) In a typical ecosystem, the food chain follows the $10\%$ law of energy transfer, where energy decreases at each trophic level.
Producers (plants) occupy the first trophic level and possess the highest biomass and population size to support all subsequent levels.
As we move up the trophic levels from primary consumers to tertiary consumers, the number of individuals and the available energy significantly decrease.
Therefore, producers have the largest population in a food chain.

(C) $DDT$ (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant.
It is not biodegradable,meaning it cannot be easily broken down by microorganisms in the environment.
Due to this property,it accumulates in the tissues of organisms and undergoes biomagnification through the food chain,causing long-term ecological damage.

(B) According to the $10\%$ law of energy transfer in an ecosystem,proposed by $Lindeman$ $(1942)$,only about $10\%$ of the energy available at one trophic level is transferred to the next trophic level.
This occurs because a large portion of the energy is lost as heat during metabolic activities,as dictated by the second law of thermodynamics.
Therefore,when energy is transferred from herbivores (primary consumers) to carnivores (secondary consumers),the average efficiency of energy transfer is $10\%$.

(A) Species diversity follows specific patterns based on geography and climate.
$1$. Latitudinal gradients: Species diversity is generally highest in the tropics (low latitudes) and decreases as we move towards the poles (high latitudes). Therefore,diversity increases as one moves from high latitudes to low latitudes.
$2$. Altitudinal gradients: Species diversity is generally higher at lower altitudes (near sea level) and decreases as we move to higher altitudes (mountains). Therefore,diversity increases as one moves from high altitudes to low altitudes.
Thus,species diversity increases as one moves from high altitude to low altitude and from high latitude to low latitude.

(D) The $Cheetah$ ($Acinonyx$ $jubatus$) was declared extinct in India in $1952$ due to habitat loss and over-hunting. Although recent efforts have been made to reintroduce them,historically,they are classified as extinct in the wild within the Indian subcontinent.

(C) The most significant cause driving animals and plants to extinction is habitat loss and fragmentation. As human populations grow,natural forests and ecosystems are cleared for agriculture,urbanization,and industrial development. This destroys the natural environment required for the survival of wildlife,leading to a rapid decline in biodiversity. While hunting and natural disasters also impact wildlife,habitat destruction is the primary and most widespread threat.

(B) $Ranthambore$ National Park is a famous wildlife sanctuary and national park located in the Sawai Madhopur district of Rajasthan,India. It is well-known for its population of Bengal tigers and is a significant site for biodiversity conservation in the region.

(A) Kaziranga National Park, located in the state of Assam, India, is world-famous for being the habitat of the one-horned rhinoceros $(Rhinoceros \text{ unicornis})$. It hosts two-thirds of the world's great one-horned rhinoceros population.

(A) Minamata disease is a neurological syndrome caused by severe mercury poisoning. It was first discovered in Minamata city,Japan,in $1956$. The disease was caused by the release of methylmercury in the industrial wastewater from the Chisso Corporation's chemical factory,which bioaccumulated in shellfish and fish in Minamata Bay and the Shiranui Sea. When local people consumed these contaminated fish,they developed the disease.

(A) In large and metropolitan cities,the primary source of air pollution is the combustion of fossil fuels in vehicles.
Automobile exhaust releases harmful gases such as $CO$,$NO_x$,$SO_2$,and particulate matter into the atmosphere.
These pollutants significantly degrade air quality in urban areas,making automobile exhaust the major contributor to metropolitan air pollution.

(B) The phenomenon of $DDT$ concentration increasing at each successive trophic level is known as $Biomagnification$.
In an aquatic food chain,$DDT$ enters the water and is absorbed by $Phytoplankton$ (producers).
As these are consumed by higher trophic levels,the concentration of $DDT$ increases because it is fat-soluble and cannot be metabolized or excreted.
Therefore,the highest concentration of $DDT$ is found in the top-level consumers,which in this list are the $Sea$ $birds$ $(Gulls)$.

(B) According to the World Health Organization $(WHO)$ and environmental standards,noise levels above $80 \, dB$ are considered harmful to human health.
Prolonged exposure to noise levels exceeding $80 \, dB$ can lead to hearing impairment,stress,and other physiological issues.
Therefore,$80 \, dB$ is the threshold level for noise pollution.