AIPMT 2001 Biology Question Paper with Answer and Solution

(B) $Leghaemoglobin$ is a red-colored pigment found in the root nodules of leguminous plants,such as $Soybean$.
This pigment acts as an oxygen scavenger,which maintains a low concentration of molecular oxygen within the root nodules.
This low oxygen environment is essential because the enzyme $Nitrogenase$,which is responsible for nitrogen fixation by the symbiotic bacteria $Rhizobium$,is highly sensitive to oxygen and gets inactivated in its presence.

(B) Fertile soil generally has a $pH$ range that is slightly acidic to neutral,typically between $6$ and $7$.
This range is optimal for the availability of essential plant nutrients,microbial activity,and root growth.
Soils that are too acidic or too alkaline can hinder the uptake of minerals by plants.

(A) The primary difference between Gram-positive and Gram-negative bacteria is the composition and structure of their cell wall.
Gram-positive bacteria possess a thick layer of peptidoglycan (murein) in their cell wall,which retains the crystal violet stain.
Gram-negative bacteria have a much thinner layer of peptidoglycan and an additional outer membrane containing lipopolysaccharides $(LPS)$,which prevents the retention of the crystal violet stain.

(B) Photolithotrophs are organisms that use light (photo) as their energy source and inorganic compounds (litho) as their electron donor (source of $H$ or electrons).
Therefore,they obtain energy from radiation and $H$ from inorganic compounds.

(A) Cyanobacteria are photosynthetic prokaryotes that perform oxygenic photosynthesis,meaning they release $O_2$ as a byproduct.
Many species of Cyanobacteria (e.g.,Nostoc,Anabaena) are capable of nitrogen fixation,a process catalyzed by the enzyme nitrogenase.
Since they perform oxygenic photosynthesis and possess the nitrogenase enzyme for nitrogen fixation,they are characterized as oxygenic with nitrogenase.

(A) Cauliflower mosaic virus $(CaMV)$ is a member of the family $Caulimoviridae$.
Unlike most plant viruses which contain $RNA$ as their genetic material,$CaMV$ contains double-stranded $DNA$ $(dsDNA)$ as its genetic material.
Therefore,the correct option is $A$.

(D) Archaebacteria are considered the oldest living organisms because they possess unique cell wall structures (lacking peptidoglycan) that allow them to survive in extreme environmental conditions,such as high temperatures,high salinity,and acidic environments. They are believed to be the ancestors of modern bacteria and eukaryotes. Therefore,they are often referred to as the 'oldest living organisms'.

(A) Fungal pathogens often use specialized structures like adhesive pads or appressoria to attach to the host surface.
To penetrate the host cell wall,the fungus exerts mechanical pressure through the growth of the infection peg and simultaneously secretes cell wall-degrading enzymes (such as cellulases,pectinases,and proteases).
These enzymes soften the host cell wall,making it easier for the mechanical pressure to force the penetration peg into the host tissue.
Therefore,the process involves both mechanical pressure and enzymatic action.

(A) Decomposers are organisms that break down dead or decaying organic matter. In the biological classification system,$Monera$ (specifically certain bacteria) and $Fungi$ are the primary decomposers in the ecosystem. $Fungi$ are heterotrophic organisms that absorb nutrients from dead organic matter,while many bacteria in the kingdom $Monera$ act as saprophytes,playing a crucial role in nutrient cycling.

(A) The primary classification of plants into $Gymnosperms$ and $Angiosperms$ is based on the nature of the ovules.
In $Angiosperms$,the ovules are enclosed within the ovary,which later develops into a fruit.
In $Gymnosperms$,the ovules are naked,meaning they are not enclosed by any ovary wall or fruit.
Although $Cycas$ exhibits two cotyledons (a characteristic often associated with dicotyledonous angiosperms),it is classified as a $Gymnosperm$ because its ovules are exposed and not protected by an ovary wall.

(D) The presence of a post-anal tail is one of the fundamental diagnostic characteristics of the Phylum $Chordata$.
Among the given options, the $Earthworm$ (Annelida), $Scorpion$ (Arthropoda), and $Lower$ invertebrates do not possess a post-anal tail.
A $Snake$ is a member of the Class $Reptilia$, which belongs to the Phylum $Chordata$.
Therefore, the $Snake$ possesses a post-anal tail during its life cycle.

(C) $Chlorocruorin$ is a respiratory pigment found in the blood of certain marine polychaete worms,which belong to the phylum $Annelida$.
It is a green-colored iron-containing protein that functions similarly to hemoglobin in transporting oxygen.
Among the given options,$Annelids$ is the correct group where this pigment is observed.

(C) Tetradynamous condition refers to the presence of $6$ stamens,where $4$ are long (inner) and $2$ are short (outer).
This specific arrangement of stamens is a characteristic feature of the family $Brassicaceae$ (formerly known as $Cruciferae$).

(B) banana is a berry fruit. In a banana,the outer thick skin is the epicarp. The edible portion consists of the fleshy mesocarp and the less developed endocarp,which surrounds the seeds (though seeds are often vestigial in commercial varieties). Therefore,the correct answer is $B$.

(B) In $Tomato$ $(Solanum \text{ } lycopersicum)$, the edible part is the pericarp and placenta. In $Maize$ $(Zea \text{ } mays)$, the edible part is the endosperm and cotyledon. In $Guava$ $(Psidium \text{ } guajava)$, the edible part is the pericarp and placenta. In $Date \text{ } palm$ $(Phoenix \text{ } dactylifera)$, the edible part is the fleshy pericarp. Therefore, the correct match is $Maize - \text{Cotyledon}$ (specifically the scutellum, which is a single cotyledon).

(B) The roots of the soybean plant $(Glycine \ max)$ are known to contain oxidizing agents,specifically peroxidase enzymes,which play a role in various metabolic processes within the plant. These enzymes are involved in the oxidation of phenolic compounds and are essential for the plant's defense mechanisms and growth regulation.

(D) The family $Solanaceae$ is characterized by a bicarpellary,syncarpous ovary. The ovary is placed obliquely at a $45^{\circ}$ angle,which is a diagnostic feature of this family. Among the given options,$Solanum$ (e.g.,$Solanum \ melongena$ or brinjal) belongs to the family $Solanaceae$. Therefore,the correct answer is $Solanum$.

(C) The potato tuber is a modified underground stem.
On the surface of the potato tuber,there are several small depressions known as 'eyes'.
These 'eyes' represent the nodes of the stem.
Each 'eye' consists of an axillary bud,which is capable of growing into a new shoot under favorable conditions.

(A) Phloem loading is the process of transporting sugars from source tissues (like leaves) into the sieve tube elements of the phloem.
This process increases the concentration of sucrose in the phloem,which leads to a decrease in water potential.
Consequently,water enters the phloem from the adjacent xylem by osmosis,creating a high pressure that drives the bulk flow of sap towards the sink tissues.

(A) The nasal septum is primarily composed of $Hyaline$ cartilage.
$Hyaline$ cartilage is the most abundant type of cartilage in the body and provides structural support while maintaining flexibility.
It is found in the nose,trachea,larynx,and at the ends of long bones.
Due to its composition,it plays a critical role in the structural integrity and repair of the nasal septum following an injury.

(A) Microtubules are cytoskeletal components made of tubulin protein. They are structural components of centrioles,cilia,flagella,and spindle fibers. Mitochondria are double-membrane-bound organelles involved in cellular respiration and do not contain microtubules.

(C) In $Hydra$,the digestive system is incomplete,meaning it has only one opening which acts as both the mouth and the anus. Therefore,undigested food is egested through the mouth. Nitrogenous waste products,such as ammonia,are primarily removed via simple diffusion through the general body surface (body wall) into the surrounding water.

(D) sarcomere is the functional unit of a striated muscle fiber.
It is defined as the segment of a myofibril located between two successive $Z$-lines (or $Z$-discs).
These $Z$-lines are dense protein structures that bisect the $I$-bands and serve as the anchor points for actin filaments.
Therefore,the correct option is $D$.

(B) According to the Sliding Filament Theory of muscle contraction:
$1$. During contraction,the thin filaments slide over the thick filaments,which pulls the $Z$-lines closer together,thereby shortening the sarcomere.
$2$. The $A$-band (Anisotropic band) contains myosin filaments and its length remains constant throughout the contraction process.
$3$. The $I$-band (Isotropic band) and the $H$-zone shorten as the actin filaments move deeper into the $A$-band.
$4$. Therefore,the statement that the length of the $A$-band remains constant is correct.

(B) When moving from a dark environment to a bright one,the photoreceptor cells (rods and cones) in the retina require time to adjust to the sudden change in light intensity. This process is known as sensory adaptation. Specifically,the photopigments in the rods,which are highly sensitive to low light,are bleached by bright light,and the cones take over to provide vision in bright light. This adjustment period is a classic example of adaptation.

(C) The human cornea is the transparent anterior part of the eye.
It is unique because it is avascular, meaning it lacks blood vessels $(blood \text{ circulation is absent})$.
Oxygen is obtained directly from the atmosphere through the tear film.
Option $A$ is incorrect as the cornea is not a secretion.
Option $B$ is incorrect as the lacrimal gland is separate from the cornea.
Option $D$ describes the lens, not the cornea.

(C) Regeneration is the ability of an organism to regrow lost or damaged parts.
$1$. $Epimorphosis$ involves the replacement of a lost part through the proliferation of cells at the wound site,forming a blastema.
$2$. $Morphallaxis$ is a type of regeneration where the existing body parts are remodeled or transformed into new structures to restore the whole organism,often seen in $Hydra$ and $Planaria$.
Therefore,the process of transformation of one body part into another during regeneration is known as $Morphallaxis$.

(A) Inulin is a polysaccharide,specifically a fructan,which is stored in the roots or tubers of certain plants like Dahlia as a reserve food material. Pectin is a structural polysaccharide found in the primary cell walls of terrestrial plants. Both are considered stored substances or reserve materials in the context of plant physiology.

(A) The middle lamella is a layer that cements the cell walls of two adjoining plant cells together.
It is primarily composed of calcium pectate and magnesium pectate.
Calcium $(Ca^{2+})$ ions are essential for the formation of these pectate salts,which provide structural stability to the middle lamella.
Therefore,$Ca$ is the essential element for the middle lamella.

(B) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
They contain a heme group,which is a porphyrin ring with a central iron $(Fe)$ atom.
These proteins are essential for cellular respiration and photosynthesis.
Therefore,they are classified as $Fe$-containing porphyrin pigments.

(B) Cellulose is a polysaccharide consisting of a linear chain of several hundred to many thousands of $\beta(1\rightarrow4)$ linked $D$-glucose units.
It is the structural component of the primary cell wall of green plants,many forms of algae,and the oomycetes.
Because it is the main component of plant cell walls,which make up the vast majority of biomass on Earth,cellulose is considered the most abundant organic compound in the biosphere.

(D) The term 'constant of oil' refers to the specific physical and chemical properties of oils,such as the iodine value,which measures the degree of unsaturation. Erucic acid $(C_{22}H_{42}O_2)$ is a monounsaturated omega-$9$ fatty acid found in high concentrations in rapeseed and mustard oils. It is often used as a marker or constant in the analysis of these specific oils to determine their purity and composition.

(C) When water moves through a semi-permeable membrane due to osmosis,it exerts pressure against the cell wall,which is known as $Turgor \ Pressure \ (T.P.)$.
$Osmotic \ Pressure$ is the pressure required to prevent the movement of water,while $Turgor \ Pressure$ is the actual physical pressure exerted by the protoplast against the cell wall due to the entry of water.
Therefore,the force generated by the movement of water into the cell is $Turgor \ Pressure$.

(A) Sunken stomata are a characteristic adaptation of xerophytic plants to reduce the rate of transpiration.
Among the given options,$Nerium$ (Oleander) is a xerophytic plant that possesses sunken stomata located in pits to minimize water loss.
$Hydrilla$ is a submerged hydrophyte,while Mango and Guava are mesophytes.

(B) Glycolate is a product of photorespiration. In the presence of light,glycolate is produced in the chloroplasts. This glycolate is converted into glyoxylate in the peroxisomes,which leads to the production of $H_2O_2$. The metabolism of glycolate is associated with the reduction of $CO_2$ concentration within the guard cells. $A$ low concentration of $CO_2$ in the guard cells triggers the opening of stomata. Therefore,glycolate induces stomatal opening by lowering the internal $CO_2$ concentration.

(A) The aquatic fern $Azolla$ maintains a symbiotic relationship with the cyanobacterium $Anabaena$ $azollae$.
This cyanobacterium resides in the leaf cavities of $Azolla$ and is responsible for fixing atmospheric nitrogen.
Therefore,$Azolla$ is the aquatic fern associated with nitrogen fixation.

(B) In plants,metabolic activities produce various substances that are not required for further physiological processes. These are known as waste products or excretory products.
Inulin is a polysaccharide stored in the roots of plants like Dahlia. However,in the context of plant physiology,raphides are needle-like crystals of calcium oxalate that act as waste products or defensive structures.
In many biological contexts,both are categorized under plant excretory or waste products that the plant stores or deposits in specific tissues.

(A) Nitrogen fixation is the process of converting atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$.
This reaction is catalyzed by the enzyme complex known as nitrogenase.
Nitrogenase is a molybdenum-iron protein and is found exclusively in certain prokaryotes (diazotrophs).
Therefore,the correct option is $A$.

(A) Passive absorption of minerals is a process that does not require metabolic energy $(ATP)$.
Since it is a physical process (like diffusion or mass flow),it is not affected by metabolic inhibitors that block $ATP$ production.
However,passive absorption is influenced by physical factors such as temperature,which affects the kinetic energy of ions and the permeability of the membrane.

(A) $1$. $C_3$ plants are those that fix $CO_2$ into a $3$-carbon compound $(PGA)$. Maize is a $C_4$ plant,not a $C_3$ plant. Thus,the pair '$C_3$ - Maize' is incorrect.
$2$. $C_4$ plants exhibit Kranz anatomy,which is a correct association.
$3$. The Calvin cycle involves the formation of $3$-phosphoglyceric acid $(PGA)$ as the first stable product,which is correct.
$4$. The Hatch and Slack pathway is another name for the $C_4$ cycle. However,the pathway involves oxaloacetic acid $(OAA)$ as the first stable product,not acetic acid. Therefore,both options $A$ and $D$ contain incorrect information. Given the standard context of such questions,$C_3$ - Maize is a classic example of a mismatch.

(C) The red drop effect refers to the sharp decrease in the quantum yield of photosynthesis when the wavelength of light is increased beyond $680 \ nm$.
At wavelengths greater than $680 \ nm$,only $PS-I$ is functional,while $PS-II$ becomes inactive.
Since $PS-II$ is required for the photolysis of water and the production of $O_2$,its inactivity leads to a significant drop in the rate of photosynthesis,which is known as the red drop effect.

(A) Phytochrome is a proteinaceous pigment that acts as a photoreceptor in plants.
It exists in two interconvertible forms: $P_r$ (which absorbs red light) and $P_{fr}$ (which absorbs far-red light).
It plays a crucial role in light-dependent developmental processes such as photoperiodism,seed germination,and flowering.

(D) Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. Plants are classified based on their response to photoperiods into three categories: Long-day plants,Short-day plants,and Day-neutral plants.
$1$. Long-day plants $(LDP)$ flower when the day length exceeds a critical duration. Examples include Spinach ($Spinacia$ $oleracea$),Wheat,and Radish.
$2$. Short-day plants $(SDP)$ flower when the day length is shorter than a critical duration. Examples include Tobacco and Glycine max (Soybean).
$3$. Day-neutral plants flower regardless of the day length. An example is Mirabilis jalapa.
Therefore,Spinach is a long-day plant.

(A) Gibberellins are plant hormones that play a crucial role in breaking seed and bud dormancy. Specifically,$GA_3$ (Gibberellic acid) is widely used in agriculture to break the dormancy of potato tubers,thereby promoting their sprouting. $ABA$ (Abscisic acid) acts as an antagonist to gibberellins and promotes dormancy,while $IAA$ (Indole$-3-$acetic acid) is an auxin involved in cell elongation and root initiation.

(B) Auxins,such as $NAA$ (Naphthalene Acetic Acid),are known to inhibit leaf abscission by preventing the formation of the abscission layer at the base of the petiole. While ethylene promotes abscission,auxins act as antagonists to this process in young leaves and fruits,thereby delaying the shedding process.

(A) Abscisic acid $(ABA)$ is known as a stress hormone and a growth inhibitor in plants.
It plays a crucial role in promoting the process of senescence (aging) in leaves and other plant organs.
$ABA$ also promotes abscission of leaves,flowers,and fruits,and induces seed dormancy.
Therefore,$ABA$ is the hormone responsible for inducing senescence.

(A) The correct match is Vitamin $E - \text{Tocopherol}$.
Vitamin $D$ is $\text{Calciferol}$.
Vitamin $C$ is $\text{Ascorbic acid}$.
Vitamin $A$ is $\text{Retinol}$.
$\text{Riboflavin}$ is Vitamin $B_2$ and $\text{Thiamine}$ is Vitamin $B_1$.

(A) In the $ABO$ blood grouping system,blood group '$O$' is characterized by the absence of both '$A$' and '$B$' antigens on the surface of red blood cells $(RBCs)$.
However,the plasma of individuals with blood group '$O$' contains both anti-$A$ (antibody '$a$') and anti-$B$ (antibody '$b$') antibodies.
Therefore,the correct statement is that there is an absence of antigens but a presence of '$a$' and '$b$' antibodies.

(A) Lung cancer in coal miners is primarily caused by the inhalation of coal dust over long periods. This condition is often associated with occupational hazards like pneumoconiosis,where the accumulation of coal particles in the lungs leads to chronic inflammation and tissue damage,eventually increasing the risk of developing lung cancer. Among the given options,coal mines are the direct source of the particulate matter responsible for this respiratory pathology.

(B) Most plants grow best in soil that is slightly acidic to neutral.
The optimal $pH$ range for the growth of most plants is generally considered to be between $6.5$ and $7.5$.
This range allows for the best availability of essential nutrients in the soil for plant uptake.

(C) The concept of the '$RNA$ World' was proposed because $RNA$ is capable of both storing genetic information and acting as a catalyst. In the $1980s$,it was discovered that certain $RNA$ molecules,known as ribozymes,possess enzymatic activity (e.g.,self-splicing introns and ribosomal $RNA$ acting as a peptidyl transferase). This dual functionality suggests that $RNA$ could have been the first self-replicating molecule in the early stages of evolution.

(B) $DNA$ replication is semi-conservative in nature.
When $E. coli$ cells are grown in a medium containing radioactive thymidine,the newly synthesized $DNA$ strands incorporate the radioactive label.
After $5$ minutes,the $DNA$ molecules will have one radioactive strand (template) and one newly synthesized radioactive strand (if replication occurred) or just the labeled template.
When these cells are transferred to a normal medium,the new strands synthesized will use non-radioactive nucleotides.
Since the original $DNA$ molecule had one radioactive strand and one non-radioactive strand (or both radioactive depending on the duration),the resulting daughter $DNA$ molecules will retain the radioactive strand as a template.
Specifically,in this experiment,one strand of the $DNA$ duplex will remain radioactive because it serves as the template for the new,non-radioactive strand.
Therefore,one strand of the $DNA$ will be radioactive.

(C) In molecular biology,a $Gene$ is defined as the functional unit of inheritance.
According to the $One$ $Gene-One$ $Enzyme$ hypothesis (later modified to $One$ $Gene-One$ $Polypeptide$ hypothesis),a single $Gene$ codes for a single polypeptide chain.
$A$ $Cistron$ is defined as a segment of $DNA$ coding for a polypeptide.
Therefore,in eukaryotes,since a $Gene$ typically codes for one polypeptide,it is functionally equivalent to one $Cistron$ (monocistronic). Thus,the terms are often used synonymously.

(A) During the process of transcription,the enzyme $RNA$ polymerase synthesizes $m-RNA$ by reading the $DNA$ template strand in the $3' \to 5'$ direction.
As a result,the newly synthesized $m-RNA$ strand is always formed in the $5' \to 3'$ direction due to the antiparallel nature of the nucleic acid strands.

(A) In a negative operon system,the regulator gene produces a repressor protein that binds to the operator to prevent transcription. In a repressible negative operon,the repressor is initially inactive. $A$ co-repressor molecule binds to the inactive repressor,activating it so that it can bind to the operator and block transcription. Therefore,the correct statement is that a co-repressor binds to the repressor.

(B) The half-life of a radioactive isotope is the time required for half of the radioactive atoms in a sample to decay.
Carbon-$14$ $(C^{14})$ is a radioactive isotope of carbon used in radiocarbon dating to determine the age of organic materials.
The accepted scientific value for the half-life of $C^{14}$ is approximately $5730$ years.
Therefore,option $B$ is the correct answer.

(D) Darwin proposed the theory of Pangenesis to explain how traits are passed from parents to offspring. According to this theory,every part of the body produces minute particles called 'gemmules' or 'pangenes' that migrate to the reproductive cells. This implies that changes occurring in the body parts during an individual's life could be transmitted to the next generation,which is similar to the concept of the inheritance of acquired characters proposed by Lamarck. Both theories suggest that there must be some physical basis or material particles responsible for the inheritance of traits.

(C) Diversity among living organisms is primarily the result of long-term evolutionary changes.
Evolution is a process that occurs over millions of years,leading to the accumulation of genetic variations through mechanisms like mutation,natural selection,and genetic drift.
These accumulated changes over vast geological time scales result in the speciation and the immense biological diversity observed today.

(C) Convergent evolution occurs when organisms that are not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.
Even if the genotypes are different,the phenotypic similarity arises due to similar selective pressures in the environment.
This process leads to the development of analogous structures.

(B) The chronological order of human evolution is as follows:
$1$. Peking man ($Homo$ $erectus$ $pekinensis$): Lived approximately $750,000$ to $200,000$ years ago.
$2$. Neanderthal ($Homo$ $neanderthalensis$): Lived approximately $400,000$ to $40,000$ years ago.
$3$. Homo sapiens (Modern humans): Appeared around $300,000$ years ago.
$4$. Cro-Magnon: Early modern humans in Europe,appearing around $40,000$ to $10,000$ years ago.
Therefore,the correct sequence is Peking man $\rightarrow$ Neanderthal $\rightarrow$ Homo sapiens $\rightarrow$ Cro-Magnon.

(B) The principle stated in the question is known as the $Gause's$ Competitive Exclusion Principle.
According to this principle, two species competing for the same limiting resources cannot coexist indefinitely.
The species that is more efficient at utilizing the resources will eventually eliminate the other species from that niche.
Therefore, the correct option is $B$.

(C) The common cold is a highly infectious disease caused by rhinoviruses. It infects the nose and respiratory passage but not the lungs. It spreads easily through droplets resulting from coughs or sneezes of an infected person,or through contaminated objects like pens,books,cups,doorknobs,etc. Hepatitis-$B$,$AIDS$,and malaria are not transmitted through such casual contact.

(A) $Salmonella \text{ } typhi$ is a pathogenic bacterium that causes typhoid fever in human beings.
It is transmitted through the ingestion of contaminated food and water.
Symptoms include high fever, weakness, stomach pain, constipation, headache, and loss of appetite.

(A) $LSD$ stands for Lysergic Acid Diethylamide. It is a well-known psychoactive drug that belongs to the class of hallucinogens. Hallucinogens are substances that alter a person's thoughts, feelings, and awareness of their surroundings, often causing them to see or hear things that are not actually there.

(A) Reserpine is a drug derived from the plant $Rauwolfia$ $\text{serpentina}$, which acts as a tranquilizer to reduce blood pressure and treat mental disorders.
Cocaine is a stimulant obtained from $Erythroxylum$ $\text{coca}$, not an opiate.
Morphine is an analgesic (painkiller) obtained from the latex of the poppy plant, not a hallucinogen.
Bhang is a preparation from the leaves of $Cannabis$ $\text{sativa}$ and acts as a hallucinogen, not an analgesic.
Therefore, the correct pair is $A$.

(C) Interferons $(IFNs)$ are a group of signaling proteins made and released by host cells in response to the presence of several pathogens,such as viruses,bacteria,parasites,or tumor cells.
However,they are most characteristically known for being produced by virus-infected cells to protect non-infected neighboring cells from further viral infection.
Therefore,among the given options,the synthesis of interferons is primarily associated with the response to viral infections.

(A) The center of origin of a plant species is the geographical area where that species first evolved and developed its distinctive characteristics.
According to $N.I. Vavilov$,these centers are characterized by a high degree of genetic diversity and variability within the species.
This diversity exists because the plants have been evolving in that specific environment for a long period,allowing for the accumulation of various alleles and traits.
Therefore,the correct statement is that there is greater diversity in varieties at the center of origin.

(A) Many vegetables and crops that are now common in India were introduced by Europeans (specifically the Portuguese). Potatoes,tomatoes,and green chillies were not native to India and were brought by the Europeans during their colonial presence.

(A) $Azolla$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This association allows $Azolla$ to fix atmospheric nitrogen,making it an excellent biofertilizer for rice paddies.
It is widely used in agriculture to increase soil fertility naturally.

(A) plasmid is an extrachromosomal,circular,double-stranded $DNA$ molecule found in bacteria.
It is capable of autonomous replication within the host cell.
In biotechnology,plasmids are extensively used as vectors to carry foreign $DNA$ fragments into host cells for cloning or expression.

(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'.

(B) The intensity of sound is measured in decibels $(dB)$.
$A$ normal conversation typically occurs at a sound level ranging between $30$ and $60\,dB$.
- $0-20\,dB$ represents very faint sounds like whispering or rustling leaves.
- $70-90\,dB$ represents loud sounds like heavy traffic or a lawnmower.
- $120-150\,dB$ represents extremely loud,painful sounds like a jet engine or a rock concert.
Therefore,the correct range for a normal conversation is $30-60\,dB$.

(B) $BOD$ stands for Biochemical Oxygen Demand.
It is defined as the amount of dissolved oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
Therefore,it represents the amount of $O_2$ required by aerobic microorganisms to decompose the organic matter present in a water sample.
Thus,option $B$ is the correct answer.