AIPMT 2005 Biology Question Paper with Answer and Solution

(C) Barophilic prokaryotes,also known as piezophiles,are microorganisms that thrive at high hydrostatic pressures.
These organisms are typically found in deep-sea environments,such as deep marine sediments or ocean trenches,where the pressure is significantly higher than at the surface.
They have specialized cellular structures and enzymes that allow them to function optimally under extreme pressure conditions.

(C) $1$. Most plant viruses contain single-stranded $RNA$ as their genetic material.
$2$. Most animal viruses contain either $DNA$ or $RNA$ (often double-stranded $DNA$ or single-stranded $RNA$).
$3$. $TMV$ (Tobacco Mosaic Virus) is a well-known plant virus that contains a single-stranded $RNA$ molecule,not double-stranded $RNA$. Therefore,statement $C$ is false.
$4$. $T_4$ bacteriophage is a virus that infects bacteria and contains a double-stranded $DNA$ molecule.

(C) $Frankia$ is a filamentous soil bacterium that forms symbiotic nitrogen-fixing root nodules in actinorhizal plants.
$1$. $Frankia$ is capable of inducing root nodules on many plant species (actinorhizal plants).
$2$. It is known that $Frankia$ can fix nitrogen in the free-living state,although the rate is often lower than in symbiosis.
$3$. The statement in option $C$ is incorrect because $Frankia$ $DOES$ form specialized structures called vesicles. These vesicles provide an anaerobic environment for the enzyme nitrogenase,protecting it from oxygen using a chemical barrier composed of triterpene hopanoids.
$4$. Like $Rhizobium$,$Frankia$ infects host plants via root hair deformation and triggers cortical cell division to form nodules.
Therefore,the incorrect statement is $C$.

(A) Auxospores are specialized cells formed by diatoms to restore their original size after repeated cell divisions,as the cell wall size decreases with each division.
Hormocysts are thick-walled,resting structures formed by some cyanobacteria (blue-green algae) under unfavorable conditions to survive and propagate when conditions become favorable again.
Therefore,auxospores are associated with diatoms and hormocysts are associated with cyanobacteria.

(A) Trichocysts are small,thread-like organelles found in the cytoplasm of certain protists,such as $Paramecium$.
They are primarily involved in the mechanism of defence against predators and for capturing prey.
When stimulated,they discharge a long,thread-like filament that can entangle or deter other organisms.

(C) $Paramecium$ is a ciliate protozoan that exhibits nuclear dimorphism.
It possesses two types of nuclei: a large,kidney-shaped macronucleus and one or more small,spherical micronuclei.
The macronucleus is polyploid and controls the metabolic and trophic (nutritional) activities of the cell.
The micronucleus is diploid and is primarily responsible for genetic recombination and reproduction during conjugation.

(B) lichen is a symbiotic association between an alga (phycobiont) and a fungus (mycobiont).
In this association,the algal component is responsible for photosynthesis,providing food for the fungus.
The fungal component provides protection,anchorage,and absorption of water and minerals for the alga.
Therefore,the fungus acts as the protective and structural partner in this relationship.

(D) The characteristic features mentioned are:
$1$. Top-shaped multiciliate male gametes (antherozoids).
$2$. Mature seeds containing an embryo with two cotyledons.
These features are characteristic of the group $Cycads$ (e.g.,$Cycas$).
$Cycas$ is a gymnosperm that produces large,top-shaped,multiciliate male gametes and seeds that contain an embryo with two cotyledons.

(A) The correct matches are as follows:
$(A)$ Peritrichous flagellation: $Escherichia \text{ } coli$ $(L)$. Bacteria with flagella distributed over the entire surface are called peritrichous.
$(B)$ Living fossil: $Ginkgo$ $(J)$. $Ginkgo \text{ } biloba$ is a classic example of a living fossil.
$(C)$ Rhizophore: $Selaginella$ $(M)$. $Selaginella$ possesses a specialized root-bearing organ called a rhizophore.
$(D)$ Smallest flowering plant: $Wolffia$ $(N)$. It is a genus of tiny aquatic plants known as watermeal.
$(E)$ Largest perennial alga: $Macrocystis$ $(K)$. It is a giant kelp that can grow to massive lengths.
Therefore, the correct sequence is $A-L, B-J, C-M, D-N, E-K$.

(A) Animals in the phylum $Cnidaria$ (such as jellyfish,sea anemones,and corals) exhibit radial symmetry.
This means that their body parts are arranged around a central axis,and any plane passing through this central axis divides the body into two identical halves.

(A) Annelids are coelomate animals,meaning they possess a true body cavity (coelom) lined by mesoderm. In contrast,Platyhelminths (flatworms) are acoelomate,meaning they lack a body cavity entirely. Therefore,the absence of a body cavity is the key feature that distinguishes Platyhelminths from Annelids.

(D) The statement 'Animals belonging to phylum Porifera are exclusively marine' is incorrect. While most sponges (Porifera) are marine,there are several freshwater species,such as those belonging to the family Spongillidae (e.g.,$Spongilla$). Therefore,they are not exclusively marine.

(C) The class $Mammalia$ is characterized by the presence of $12$ pairs of cranial nerves,not $10$ pairs.
$10$ pairs of cranial nerves are typically found in classes $Amphibia$,$Reptilia$,$Aves$,and $Pisces$.
$Thecodont$ dentition,alveolar lungs,and the presence of $7$ cervical vertebrae (in most mammals) are characteristic features of mammals.

(A) The stem is divided into nodes and internodes.
Nodes are the regions of the stem where leaves are born.
Internodes are the portions between two nodes.
Therefore,leaves are always situated on the nodes.

(C) In a woody dicotyledonous tree,secondary growth occurs in the stem and root,leading to the formation of secondary tissues (secondary xylem and phloem).
However,parts like flowers,fruits,and leaves do not undergo secondary growth and are composed primarily of primary tissues throughout their lifespan.
Therefore,these organs remain in the primary state of development.

(A) An ectophloic siphonostele is a type of stele where the phloem is restricted to the outer side of the xylem,surrounding it completely.
This arrangement is characteristic of certain pteridophytes.
Examples include $Osmunda$ and $Equisetum$.

(B) The villi are small,finger-like projections found in the inner lining of the small intestine.
Their primary function is to increase the surface area available for the absorption of digested food nutrients.
By increasing the surface area,they ensure that the maximum amount of nutrients is absorbed into the bloodstream efficiently.
Therefore,the correct option is $(b)$.

(B) $G-6-P$ dehydrogenase (Glucose$-6-$phosphate dehydrogenase) is an enzyme that plays a crucial role in the pentose phosphate pathway within cells.
In $RBCs$ (Red Blood Cells),this enzyme is essential for producing $NADPH$,which helps maintain the levels of reduced glutathione.
Reduced glutathione protects $RBCs$ from oxidative damage caused by reactive oxygen species.
When $G-6-P$ dehydrogenase is deficient,$RBCs$ become susceptible to oxidative stress,leading to their premature destruction,a process known as haemolysis.

(B) The correct answer is $(b)$.
According to the fluid mosaic model, while lipids and proteins exhibit lateral diffusion (moving within the plane of the membrane), proteins do not undergo flip-flop movements (transverse diffusion) across the lipid bilayer due to their large size and polar nature.
Option $(a)$ is correct because proteins can move laterally within the lipid bilayer.
Option $(c)$ is correct because certain proteins are restricted to specific domains (e.g., lipid rafts or specific cell surfaces) to perform localized functions.
Option $(d)$ is correct because integral proteins can be completely embedded within the lipid bilayer (non-transmembrane proteins).

(D) The $Golgi$ $apparatus$ is the primary organelle responsible for the modification, sorting, and packaging of proteins synthesized by the $Endoplasmic$ $reticulum$.
After proteins are synthesized in the $Rough$ $Endoplasmic$ $reticulum$ $(RER)$, they are transported to the $Golgi$ $apparatus$ in vesicles.
Within the $Golgi$ $apparatus$, these proteins undergo modifications such as glycosylation and are then sorted and routed to their specific destinations, such as the plasma membrane, lysosomes, or for secretion outside the cell.

(C) The correct answer is $(c)$. During cell division,spindle fibres attach to the kinetochore located on the centromere of the chromosomes.
As the spindle fibres shorten,they pull the chromosomes towards the opposite poles.
This movement results in the chromosomes appearing $'V'$,$'L'$,$'J'$,or $'I'$ shaped depending on the position of the centromere.

(C) Carbohydrates are primarily produced through the process of photosynthesis.
Photosynthesis is performed by organisms that contain chlorophyll or other photosynthetic pigments,such as green plants,algae,and certain bacteria (e.g.,cyanobacteria).
Fungi and viruses are heterotrophic or parasitic and cannot synthesize their own carbohydrates via photosynthesis.
Therefore,the correct group of organisms that produce carbohydrates is some bacteria (photosynthetic bacteria),algae,and green plant cells.

(C) Glycine is considered the simplest amino acid because its side chain ($R$-group) is a single hydrogen atom $(H)$.
It has the chemical formula $NH_2-CH_2-COOH$.
Due to the presence of a hydrogen atom instead of a larger functional group,it is the only achiral amino acid among the $20$ standard amino acids.

(C) The catalytic efficiency of an enzyme is often represented by the $k_{cat}/K_m$ ratio,also known as the specificity constant.
While $K_m$ (Michaelis constant) reflects the affinity of the enzyme for its substrate,it is a key parameter used to compare the efficiency of different enzymes.
$A$ lower $K_m$ value generally indicates a higher affinity of the enzyme for the substrate,which is a primary factor in determining catalytic efficiency under physiological conditions.

(B) Competitive inhibition occurs when the substrate and the inhibitor molecule resemble each other in structure. Due to this structural similarity,both compete for the same active site on the enzyme. If the inhibitor binds to the active site,the enzyme-substrate complex cannot be formed,thus inhibiting the reaction. This type of inhibition can be overcome by increasing the concentration of the substrate,which outcompetes the inhibitor for the active site.

(A) The cell cycle consists of two main phases: Interphase and $M$ phase (Mitosis).
Interphase is further divided into $G_1$,$S$,and $G_2$ phases.
During the $S$ phase (Synthesis phase),the replication of $DNA$ takes place.
Along with $DNA$ replication,the synthesis of histone proteins occurs in the nucleus to facilitate the packaging of the newly formed $DNA$ into chromatin.
Therefore,both $DNA$ and histone proteins are synthesized during the $S$ phase.

(A) potometer is an apparatus used to measure the rate of transpiration in a leafy shoot. It operates on the principle that the amount of water absorbed by the plant is approximately equal to the amount of water lost through transpiration. By measuring the movement of an air bubble in the capillary tube,we can calculate the volume of water lost by the plant over a specific period.

(A) $Cu$ (Copper) acts as a component of plastocyanin,which is involved in electron transport between $PS II$ and $PS I$,and in cytochrome oxidase for mitochondrial respiration.
$Mn$ (Manganese) is essential for the photolysis of water in photosynthesis and acts as an activator for many enzymes involved in respiration and photosynthesis.
$Fe$ (Iron) is a crucial component of cytochromes and ferredoxin,which are vital for electron transfer in both photosynthetic and mitochondrial electron transport chains.
Therefore,the group $Cu, Mn, Fe$ is most critical for these processes.

(A) The correct answer is $A$.
In plants,water and dissolved inorganic minerals are absorbed by the roots from the soil.
These materials are transported upward from the roots to the leaves and other parts of the plant through the $Xylem$ tissue.
$Phloem$ is primarily responsible for the translocation of organic food (sugars) synthesized during photosynthesis.

(B) Photosynthetically active radiation $(PAR)$ is the spectral range of solar radiation from $400$ to $700 \,nm$ that photosynthetic organisms are able to use in the process of photosynthesis.
This range corresponds to the visible light spectrum,which is essential for the excitation of chlorophyll molecules to initiate the light-dependent reactions.

(D) In ${C_3}$ plants,the synthesis of one molecule of glucose $(C_6H_{12}O_6)$ requires $18$ $ATP$ and $12$ $NADPH$ molecules.
In ${C_4}$ plants,an additional $C_4$ cycle (Hatch-Slack pathway) operates to concentrate $CO_2$ around the enzyme $RuBisCO$.
This process requires $2$ additional $ATP$ molecules per $CO_2$ molecule fixed to regenerate phosphoenolpyruvate $(PEP)$.
Since $6$ molecules of $CO_2$ are required to produce one molecule of hexose sugar,the total additional $ATP$ required is $6 \times 2 = 12$ $ATP$ molecules.
Therefore,${C_4}$ plants require a total of $30$ $ATP$ $(18 + 12)$ to produce one molecule of glucose.

(A) The chemiosmotic theory,proposed by Peter Mitchell,explains how $ATP$ is synthesized in chloroplasts and mitochondria.
It states that the energy for $ATP$ synthesis is derived from a proton gradient ($H^+$ gradient) across the membrane (thylakoid membrane in chloroplasts and inner mitochondrial membrane in mitochondria).
As protons move down their electrochemical gradient through the $ATP$ synthase enzyme,the energy released is used to phosphorylate $ADP$ into $ATP$.

(B) In the complete oxidation of glucose, the majority of $ATP$ molecules are produced during the $Electron \text{ } Transport \text{ } Chain$ $(ETC)$ via oxidative phosphorylation.
During glycolysis and the $Kreb's \text{ } cycle$, only a small amount of $ATP$ (or $GTP$) is produced through substrate-level phosphorylation.
However, the reduced coenzymes ($NADH$ and $FADH_2$) generated in the earlier stages donate electrons to the $ETC$, which drives the synthesis of a large number of $ATP$ molecules through the $ATP \text{ } synthase$ complex.

(D) Brunner's glands are located in the submucosa of the duodenum.
These glands secrete an alkaline mucus that helps protect the duodenal wall from acidic chyme.
Additionally,the cells of the duodenal mucosa secrete hormones such as $Secretin$ and $Cholecystokinin$ $(CCK)$ in response to the presence of chyme.
Therefore,the correct option is $D$.

(D) Enzymes,vitamins,and hormones are all essential biological molecules that play a critical role in the regulation of metabolic processes within living organisms.
Enzymes act as biological catalysts that speed up biochemical reactions.
Hormones act as chemical messengers that coordinate various physiological activities.
Vitamins act as co-factors or co-enzymes necessary for the proper functioning of enzymes.
Therefore,they are collectively involved in the regulation of metabolism.

(A) Beri-beri is a nutritional disorder caused by the deficiency of thiamine (vitamin $B_1$). This is statement $2$.
It is commonly found in populations where the staple diet consists of polished rice,as the milling process removes the outer layer of the rice grain which contains thiamine. This is statement $4$.
The clinical symptoms of beri-beri include neuritis (nerve inflammation),muscle wasting,paralysis,oedema (swelling),mental confusion,and cardiovascular complications leading to heart failure. This is statement $5$.
Statement $1$ describes a disease prevalent in sub-Saharan Africa (often associated with other conditions),and statement $3$ describes protein-energy malnutrition (like Kwashiorkor or Marasmus),not beri-beri.
Therefore,the correct group of statements is $2, 4,$ and $5$.

(D) During prolonged fasting,the body lacks a sufficient supply of carbohydrates for energy.
To meet its energy requirements,the body begins to break down stored fats through a process called lipolysis.
This leads to the production of fatty acids,which are then converted into ketone bodies (such as acetoacetate,beta-hydroxybutyrate,and acetone) in the liver.
When the concentration of these ketone bodies in the blood exceeds the renal threshold,they are excreted in the urine,a condition known as ketonuria.

(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) The glomerular filtration is driven by the net filtration pressure $(NFP)$.
$1$. Glomerular hydrostatic pressure $(GHP)$ is approximately $60\, mm\, Hg$.
$2$. Blood colloidal osmotic pressure $(BCOP)$ is approximately $32\, mm\, Hg$.
$3$. Capsular hydrostatic pressure $(CHP)$ is approximately $18\, mm\, Hg$.
The net filtration pressure is calculated as: $NFP = GHP - (BCOP + CHP) = 60 - (32 + 18) = 60 - 50 = 10\, mm\, Hg$.
However,in many standard textbook contexts,the effective filtration pressure is often cited as approximately $10-20\, mm\, Hg$. Given the options provided,$20\, mm\, Hg$ is the closest standard value used in physiological calculations for the net pressure gradient.

(B) The pectoral girdle in mammals consists of two bones: the clavicle and the scapula.
Each scapula is a large,triangular,flat bone situated in the dorsal part of the thorax between the second and the seventh ribs.
The dorsal,flat,triangular body of the scapula has a slightly elevated ridge called the spine which projects as a flat,expanded process called the acromion process.
The clavicle articulates with this acromion process.

(B) The correct match is $B$.
$1$. $A$ gliding joint allows for sliding or gliding movements between the articular surfaces of bones.
$2$. The zygapophyses (articular processes) of successive vertebrae are connected by gliding joints,which permit limited movement between the vertebrae.
$3$. Hinge joints are found in the elbow and knee,not between vertebrae.
$4$. Skull bones are joined by fibrous joints (sutures),and phalanges are connected by hinge joints.

(A) The abducens nerve is the $VI$ cranial nerve,which is a motor nerve. It specifically innervates the lateral rectus muscle of the eye. Therefore,an injury to this nerve will impair the lateral movement of the eyeball.

(D) . Neurons are the specialized cells of the nervous system.
Neurons in the central nervous system lack the ability to divide or regenerate once they have reached maturity. Therefore,if they are damaged or die,they are not replaced by new cells,unlike skin cells,liver cells,or osteocytes,which possess varying degrees of regenerative capacity.

(C) Parkinson's disease is a neurodegenerative disorder characterized by tremors,bradykinesia,and progressive rigidity of limbs.
It is caused by the degeneration of dopaminergic neurons in the substantia nigra region of the brain.
These neurons are responsible for movement control and utilize the neurotransmitter dopamine to transmit signals.
Therefore,the correct option is $C$.

(D) The autonomous nervous system $(ANS)$ regulates and coordinates involuntary activities within the body.
$ANS$ controls functions such as heart rate,homeostasis,body temperature,breathing,gut peristalsis,and the secretion of glands.
Among the given options,peristalsis of the intestines is a classic example of an involuntary process controlled by the $ANS$.
Knee-jerk response is a somatic reflex,while pupillary reflex and swallowing involve complex neural pathways including cranial nerves.

(D) The correct answer is $D$.
Blood coagulation is a complex process involving a cascade of clotting factors.
When tissue is damaged or platelets are activated,they release $Thromboplastin$.
$Thromboplastin$ acts as a catalyst in the conversion of inactive $Prothrombin$ into active $Thrombin$ in the presence of $Ca^{2+}$ ions.
Therefore,if $Thromboplastin$ is introduced directly into the bloodstream,it initiates the clotting cascade at that specific site,leading to blood coagulation.

(C) Nucleotides are the fundamental building blocks or monomeric units of nucleic acids ($DNA$ and $RNA$).
Each nucleotide consists of three distinct components:
$1$. $A$ nitrogenous base (Purines or Pyrimidines).
$2$. $A$ pentose sugar (Ribose or Deoxyribose).
$3$. $A$ phosphate group (derived from phosphoric acid).
Therefore,the correct composition is Base-sugar-phosphate.

(B) The correct answer is $B$. Protein synthesis occurs on ribosomes. In an animal cell,ribosomes are found in the cytoplasm (either free or attached to the endoplasmic reticulum) and within the mitochondria. Mitochondria are semi-autonomous organelles that possess their own $DNA$,$RNA$,and $70S$ ribosomes,allowing them to synthesize a portion of their required proteins independently.

(C) The simplest amino acid is $Glycine$.
In $Glycine$,the $R$-group (side chain) is a single hydrogen atom $(-H)$.
The general structure of an amino acid is $H_2N-CH(R)-COOH$.
For $Glycine$,$R = H$,resulting in the formula $H_2N-CH_2-COOH$.
It is the only achiral amino acid because it does not have a chiral carbon atom.

(D) The $centromere$ is a specialized $DNA$ sequence of a chromosome that links a pair of sister chromatids. During cell division, the $kinetochore$ (a protein complex) assembles on the $centromere$. Spindle fibers attach to the $kinetochore$, which is essential for the movement of chromosomes towards the opposite poles during $anaphase$ of mitosis and meiosis.

(B) The process of retting involves the separation of fibres from the plant stem by the action of microorganisms.
In this process,bacteria decompose the pectin present in the plant tissues to liberate the fibres.
This process is primarily carried out by $Clostridium$ $butyricum$,which is a type of butyric acid bacterium.

(C) Predation escape mechanisms are adaptations that help animals avoid being eaten by predators.
$A$. Colour change in chameleon is a form of camouflage (crypsis) used to blend into the environment.
$B$. Puffer fish swallow air or water to increase their body size,making them difficult for predators to swallow.
$C$. Poison fangs in snakes are primarily used for hunting prey or defense,but they are not a direct mechanism for escaping predation in the same sense as camouflage or mimicry.
$D$. Melanism in moths (industrial melanism) is an example of camouflage against soot-covered backgrounds,which helps them escape predation.
Therefore,$C$ is the least appropriate example of an innate escape mechanism from predation compared to the others.

(A) Vegetative propagation by leaves occurs when adventitious buds develop on the leaf margins or surfaces.
In $Bryophyllum$,the leaf margins possess notches where epiphyllous buds (adventitious buds) develop. When these leaves fall on moist soil,these buds grow into new plantlets.
Similarly,$Kalanchoe$ also reproduces vegetatively through leaf buds.
Therefore,the correct pair is $Bryophyllum$ and $Kalanchoe$.

(A) Adventive embryony is a form of apomixis where the embryo develops directly from diploid sporophytic cells,such as the $Nucellus$ or $Integuments$,without undergoing fertilization.
These cells protrude into the embryo sac and develop into embryos.
This process is common in plants like $Citrus$ and $Mango$.

(C) In $Campylotropous$ ovules,the body of the ovule is curved,and the embryo sac becomes horse-shoe shaped due to the curvature of the nucellus. This is a characteristic feature of the family $Leguminosae$ and $Cruciferae$.

(D) The pollen tube enters the embryo sac through the synergids. Specifically,the pollen tube enters the embryo sac through the degenerated synergid. The filiform apparatus present in the synergids guides the entry of the pollen tube into the embryo sac.

(B) The grey crescent is a specialized region of the cytoplasm that appears in the fertilized egg of an amphibian,such as a frog.
It forms in the equatorial zone of the egg,specifically on the side geometrically opposite to the point where the sperm enters the ovum.
This region is crucial for the initiation of gastrulation and the establishment of the dorsal-ventral axis of the embryo.

(A) Cytoplasmic male sterility $(CMS)$ is a condition in plants where a plant is unable to produce functional pollen.
This trait is inherited maternally because the genes responsible for $CMS$ are located in the mitochondrial genome.
Unlike nuclear genes which follow Mendelian inheritance,mitochondrial genes are passed from the mother to the offspring through the cytoplasm of the egg cell.
Therefore,the correct location for these genes is the mitochondrial genome.

(B) Down's syndrome is a genetic disorder caused by the presence of an extra copy of chromosome $21$ (trisomy $21$).
This results in a total chromosome count of $46 + 1 = 47$ chromosomes.
Therefore,the correct option is $B$.

(C) Haemophilia is a sex-linked recessive disorder.
It is caused by a mutation in the genes located on the $X$ chromosome.
In human males,there is only one $X$ chromosome $(XY)$. If the $X$ chromosome carries the recessive mutant gene,the male will express the disease because there is no corresponding allele on the $Y$ chromosome to mask its effect.
In contrast,human females have two $X$ chromosomes $(XX)$. For a female to express the disease,she must be homozygous for the recessive allele $(X^hX^h)$. If she has only one recessive allele $(X^hX)$,she remains a carrier and does not show the disease phenotype.
Therefore,the disease is much more common in males than in females.

(A) $Cystic \text{ fibrosis}$, $Thalassaemia$, and $Haemophilia$ are genetic disorders caused by mutations in genes, making them hereditary diseases.
$Cretinism$ is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormone (hypothyroidism) during pregnancy or early infancy. It is not caused by a genetic mutation passed through inheritance but rather by hormonal deficiency.

(D) $1$. The parents are phenotypically normal,but they have affected children. This indicates that the disease is recessive.
$2$. The disease affects only the sons ($3$ out of $5$) and none of the daughters are affected.
$3$. In $X$-linked recessive inheritance,a carrier mother $(X^CX)$ can pass the trait to her sons $(X^CY)$,while the father is unaffected $(XY)$.
$4$. Since the trait appears in males and skips generations (parents are unaffected),it is characteristic of $X$-linked recessive inheritance.

(D) Colour blindness is an $X$-linked recessive trait.
Let the allele for normal vision be $X^C$ and the allele for colour blindness be $X^c$.
The woman has normal vision but her father was colour blind,so her genotype is $X^CX^c$ (carrier).
The man is colour blind,so his genotype is $X^cY$.
When these two individuals marry,the cross is $X^CX^c \times X^cY$.
The possible genotypes for their children are:
$1$. $X^CX^c$ (Carrier daughter)
$2$. $X^cX^c$ (Colour blind daughter)
$3$. $X^CY$ (Normal vision son)
$4$. $X^cY$ (Colour blind son)
Since the question specifies the child is a boy,we look at the male offspring genotypes: $X^CY$ and $X^cY$.
Therefore,the boy has a $50\%$ chance of being colour blind and a $50\%$ chance of having normal vision.

(D) The $Z$ gene in the $lac$ operon codes for the enzyme $\beta$-galactosidase. This enzyme is responsible for the hydrolysis of the disaccharide lactose into its monomeric units,glucose and galactose. If the $Z$ gene is mutated,the cell cannot produce a functional $\beta$-galactosidase enzyme. Consequently,the cell is unable to break down lactose to utilize it as an energy source,preventing growth in a medium where lactose is the sole carbon source.

(D) To determine the different types of gametes produced by an organism with a heterozygous genotype (like $AaBb$),a test cross is performed. $A$ test cross involves crossing the individual with a homozygous recessive individual. In this case,the homozygous recessive genotype is $aabb$. By crossing $AaBb$ with $aabb$,the resulting offspring will reflect the gametes produced by the $AaBb$ parent,as the $aabb$ parent only contributes recessive alleles ($ab$ gametes).

(C) The correct answer is $C$.
Endonucleases are enzymes that cleave the phosphodiester bonds within a polynucleotide chain.
Unlike exonucleases,which remove nucleotides from the ends of the chain,endonucleases act on internal sites.
Restriction endonucleases are a specific type of endonuclease that recognize and cut $DNA$ at specific internal sequences.

(A) The correct answer is $A$.
Temin and Baltimore reported that the formation of $DNA$ on an $RNA$ template is possible.
This process is called reverse transcription or Teminism.
This reaction is catalyzed by the enzyme reverse transcriptase,which uses $RNA$ as a template to synthesize a complementary strand of $DNA$.

(B) According to the Hardy-Weinberg principle,for a population in genetic equilibrium,the genotype frequencies are given by the expansion of $(p + q)^2 = p^2 + 2pq + q^2 = 1$.
Here,$p$ is the frequency of the dominant allele $(A)$ and $q$ is the frequency of the recessive allele $(a)$.
Given: $p = 0.6$ and $q = 0.4$.
The frequency of heterozygotes $(Aa)$ is represented by $2pq$.
Substituting the values: $2 \times 0.6 \times 0.4 = 2 \times 0.24 = 0.48$.
Therefore,the frequency of heterozygotes in the population is $0.48$.

(D) Telomerase is a specialized enzyme that adds specific $DNA$ sequence repeats to the $3'$ end of $DNA$ strands in the telomere regions.
It is a ribonucleoprotein complex,meaning it consists of both a protein component (which acts as a reverse transcriptase) and an $RNA$ component (which serves as a template for the synthesis of telomeric $DNA$ repeats).

(D) Salivary gland chromosomes,also known as polytene chromosomes,are found in the salivary glands of dipteran larvae (e.g.,$Drosophila$).
These chromosomes are formed through a process called endoreduplication,where the $DNA$ undergoes multiple rounds of replication without cell division,resulting in thousands of chromatids aligned side-by-side.
This process creates distinct banding patterns (chromomeres) that are visible under a light microscope.
Because these banding patterns are constant and specific to certain gene loci,they are extremely useful for cytogenetic gene mapping.

(B) The theory of the African origin of modern man is supported by the study of $DNA$ variation,specifically mitochondrial $DNA$ $(mtDNA)$.
Populations that have inhabited a region for a longer period accumulate more genetic mutations over time due to the accumulation of random changes.
Studies have shown that there is greater genetic diversity (variation) in human populations in Africa compared to populations in other parts of the world,including Asia.
This higher level of genetic variation in Africa indicates that modern humans have been present in Africa for a longer duration,supporting the 'Out of Africa' hypothesis.

(C) $AIDS$ (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus $(HIV)$.
$HIV$ primarily targets and infects $T_4$ lymphocytes,also known as $CD4^+$ helper $T$ cells.
These cells are crucial for the immune system as they coordinate the immune response by activating other immune cells,including $B$ cells and cytotoxic $T$ cells.
By destroying these $T_4$ lymphocytes,$HIV$ severely weakens the body's immune system,making the individual susceptible to opportunistic infections.

(A) Valium is a type of benzodiazepine,which acts as a central nervous system depressant. It works by enhancing the effect of the neurotransmitter $GABA$ in the brain,which results in a calming,relaxing,and sedative effect,often leading to drowsiness.

(C) Induced mutagenesis is a technique used in plant breeding to create genetic variation.
Gamma rays,specifically those emitted from $Cobalt-60$,are the most commonly used ionizing radiations for inducing mutations in crop plants because they have high penetrating power and effectively cause $DNA$ damage leading to mutations.
Therefore,the correct option is $C$.

(B) The $Kyoto$ $Protocol$ is an international treaty that extended the $1992$ $United$ $Nations$ $Framework$ $Convention$ $on$ $Climate$ $Change$ $(UNFCCC)$ that commits state parties to reduce greenhouse gas emissions, based on the scientific consensus that global warming is occurring and that human-made $CO_2$ emissions are driving it.
Therefore, the pair $Kyoto$ $Protocol - \text{Climatic change}$ is correctly matched.

(C) Prolonged irrigation without proper drainage leads to the accumulation of salts in the soil. As water evaporates,the dissolved salts are left behind on the soil surface. This process increases the salt concentration in the soil,a condition known as soil salinity,which is detrimental to crop growth.

(B) The Earth's heat budget is balanced globally,but locally it varies by latitude.
In the tropical regions (between $0^\circ$ and $40^\circ$ North/South),there is a net surplus of heat because insolation exceeds terrestrial radiation.
In the polar regions,there is a net deficit of heat because terrestrial radiation exceeds insolation.
The transition point where the incoming solar radiation (insolation) is approximately equal to the outgoing terrestrial radiation occurs at approximately $40^\circ$ North and South latitudes.

(C) is the mismatched pair.
Prairies are temperate grasslands characterized by tall grasses and shrubs,not epiphytes.
Epiphytes are plants that grow on other plants,typically found in tropical rainforests where humidity is high.
$A$,$B$,and $D$ are correctly matched pairs representing typical vegetation or conditions of those biomes.

(A) The Earth's surface is covered by approximately $75\%$ water,of which $97.5\%$ is saline water found in oceans.
Only $2.5\%$ of the total water on Earth is freshwater.
Out of this $2.5\%$ freshwater,the majority (about $1.97\%$) is stored in the form of frozen ice caps and glaciers,primarily located in polar regions like Antarctica and Greenland.
Therefore,more than $70\%$ of the world's freshwater is contained in polar ice.

(D) The Biological Diversity Act of India was enacted by the Parliament in $2002$.
This act was established to provide for the conservation of biological diversity,sustainable use of its components,and fair and equitable sharing of the benefits arising out of the use of biological resources,knowledge,and for matters connected therewith or incidental thereto.

(C) is the correct answer.
Wildlife is protected in its natural habitat, which is known as $in-situ$ conservation.
However, when plants or animals are protected outside their natural habitats in areas such as zoos, botanical gardens, or seed banks, it is known as $ex-situ$ conservation.
Botanical gardens play a crucial role in $ex-situ$ conservation by preserving germ plasm of rare and threatened plant species.

(D) The Red Panda ($Ailurus$ $fulgens$) is currently classified as an $Endangered$ species by the $IUCN$ Red List of Threatened Species. This classification is due to a significant decline in their population caused by habitat loss,fragmentation,and poaching.

(D) Disinfection is the process of eliminating pathogenic microorganisms from water to make it safe for human consumption.
$A$,$B$,and $C$ (Chlorine,Ozone,and Chloramine) are widely used chemical disinfectants for treating drinking water.
$D$ (Phenyl) is a phenolic compound primarily used as a surface disinfectant or cleaner for floors and household surfaces,not for treating drinking water,as it is toxic and unsuitable for human consumption.

(A) Carbohydrates are primarily produced through the process of photosynthesis. Photosynthesis is carried out by organisms that contain chlorophyll or other photosynthetic pigments,such as green plants,algae,and certain bacteria (e.g.,cyanobacteria). Fungi and viruses lack the ability to perform photosynthesis and are therefore unable to produce carbohydrates independently.

(A) The resolution of a microscope is determined by the formula $d = \frac{0.61 \lambda}{NA}$,where $d$ is the limit of resolution,$\lambda$ is the wavelength of light used,and $NA$ is the numerical aperture of the objective lens.
To achieve the best resolution,the value of $d$ should be as small as possible.
Since $d$ is directly proportional to the wavelength $\lambda$,using light with the shortest wavelength will provide the highest resolution.
Among the visible spectrum,blue light has the shortest wavelength (approximately $450-495 \ nm$) compared to green,yellow,or red light.
Therefore,illuminating the object with blue light results in the best possible resolution.

(B) Predation is a biological interaction where one organism,the predator,kills and eats another organism,its prey. Animals have evolved various defensive mechanisms to avoid being eaten.
$A$. Puffer fish swallow air to increase their body size,making them difficult for predators to swallow.
$B$. Melanism in moths (like the peppered moth) is an example of industrial melanism,which is an adaptation for camouflage against soot-covered backgrounds,not a direct mechanism to escape predation through active defense or warning.
$C$. Poison fangs in snakes are defensive mechanisms used to deter or kill predators.
$D$. Colour change in chameleons is primarily used for camouflage to blend into the environment and avoid detection by predators.
Therefore,melanism is an evolutionary adaptation for camouflage,but it is not a direct behavioral or morphological mechanism to escape predation in the same sense as the others listed.

(B) . Vivipary is a condition where seeds germinate while still attached to the parent plant.
It is an undesirable character for annual crop plants because seeds that have already germinated cannot be stored under normal conditions for the next planting season,leading to loss of viability and difficulty in handling.

(B) The Pashmina wool is obtained from the Pashmina goat, scientifically known as $Capra \text{ } hircus$. This breed is native to the high-altitude regions of the Himalayas. It is highly prized for its extremely fine, soft, and warm undercoat, which is harvested to produce luxurious Pashmina shawls and garments. Therefore, the correct option is $B$.

(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.

(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 $B$.

(D) Vivipary is the phenomenon where seeds germinate while still attached to the parent plant. In annual cereal crops,if seeds germinate on the mother plant,they cannot be harvested,dried,and stored for the next season. This makes the seeds unsuitable for agricultural storage and future sowing,thereby negatively impacting the economic productivity and utility of the crop.

(A) Adventive embryony is a form of apomixis where the embryo arises directly from diploid sporophytic cells such as the nucellus or integuments,bypassing the process of fertilization. These cells protrude into the embryo sac and develop into embryos. This is commonly observed in species like Citrus and Mango.

(A) If fertilization does not occur,the $Corpus \ Luteum$ degenerates into a mass of fibrous tissue called $Corpus \ Albicans$.
As the $Corpus \ Luteum$ degenerates,it stops producing large amounts of progesterone and estrogen.
The rapid decline in the levels of these hormones,especially progesterone,leads to the disintegration of the endometrium,which causes menstruation.
While all options describe physiological changes,the primary event that triggers the end of the luteal phase is the degeneration of the $Corpus \ Luteum$.

(D) $1$. The parents are unaffected,but they have affected offspring,which indicates that the trait is recessive.
$2$. The disease appears only in sons ($5$ sons,$3$ affected) and not in daughters ($2$ daughters,$0$ affected).
$3$. This pattern of inheritance,where the trait skips a generation and affects primarily males,is characteristic of $X$-linked recessive inheritance.
$4$. In $X$-linked recessive inheritance,the mother is a carrier $(X^CX)$ and the father is unaffected $(XY)$. The sons inherit the $Y$ chromosome from the father and the $X$ chromosome from the mother. If the mother passes the affected $X$ chromosome to her son,he will express the disease.

(C) Color blindness is an $X$-linked recessive trait. Let $X^C$ be the allele for color blindness and $X$ be the allele for normal vision.
$1$. The woman's father was color-blind $(X^CY)$,so she must have inherited the $X^C$ allele from him. Since she has normal vision,her genotype is $XX^C$.
$2$. The man is color-blind,so his genotype is $X^CY$.
$3$. The cross is $XX^C \times X^CY$.
$4$. The possible genotypes for their children are: $XX^C$ (normal vision daughter),$X^CX^C$ (color-blind daughter),$XY$ (normal vision son),and $X^CY$ (color-blind son).
$5$. For any son,there is a $50\%$ chance of being color-blind and a $50\%$ chance of having normal vision. Therefore,the fourth boy can be either color-blind or have normal vision.

(C) Hemophilia is a sex-linked recessive disorder.
It is caused by a mutation in the genes located on the $X$ chromosome.
Since males have only one $X$ chromosome $(XY)$,a single recessive gene is sufficient to express the disease.
In contrast,females have two $X$ chromosomes $(XX)$,so they require two copies of the recessive gene to express the disease,making them less likely to be affected compared to males.

(D) To determine the genotype of an individual or the types of gametes produced,a test cross is performed.
In a test cross,the individual with an unknown genotype or the one whose gamete production is being analyzed is crossed with a homozygous recessive individual.
For the genotype $AaBb$,the homozygous recessive genotype is $aabb$.
By crossing $AaBb$ with $aabb$,the resulting offspring will reflect the types of gametes produced by the $AaBb$ parent,as the $aabb$ parent only contributes $ab$ gametes.

(D) Telomerase is a ribonucleoprotein enzyme that adds $DNA$ sequence repeats to the $3'$ end of $DNA$ strands in the telomere regions. It consists of a protein component $(TERT)$ and an $RNA$ component $(TERC)$ that serves as a template for the synthesis of telomeric $DNA$. Therefore,it is classified as a ribonucleoprotein.

(D) During the initiation of transcription in eukaryotes,the $RNA$ polymerase holoenzyme recognizes and binds to a specific promoter sequence located upstream of the gene.
This specific sequence is rich in $Adenine$ and $Thymine$ bases and is known as the $TATA$ box (or $Goldberg-Hogness$ box).
Binding of the $RNA$ polymerase to the $TATA$ box causes the $DNA$ double helix to unwind and bend,creating a characteristic saddle-like structure that facilitates the formation of the transcription initiation complex.

(C) The enzymes that cleave phosphodiester bonds in a polynucleotide chain are called nucleases.
Nucleases are classified into two types based on their site of action:
$1$. Exonucleases: These enzymes remove nucleotides from the ends (either $5'$ or $3'$) of the $DNA$ molecule.
$2$. Endonucleases: These enzymes make cuts at specific positions within the $DNA$ molecule,i.e.,they cleave internal phosphodiester bonds.
Therefore,the correct answer is $C$ (Endonuclease).