AIPMT 2012 Biology Question Paper with Answer and Solution

(A) : The enzyme $Nitrogenase$ is found in prokaryotic nitrogen-fixing organisms. The process of biological nitrogen fixation is highly energy-intensive and requires a significant amount of $ATP$ to reduce $N_2$ to $NH_3$. This is represented by the following equation:
$N_2 + 8e^- + 8H^+ + 16ATP \xrightarrow{Nitrogenase} 2NH_3 + H_2 + 16ADP + 16P_i$

(D) $C_4$ plants are distinguished from $C_3$ plants primarily by the absence of photorespiration in the former.
Photorespiration is a light-dependent process involving the oxygenation of ribulose bisphosphate $(RuBP)$ and the release of carbon dioxide by photosynthetic organs.
In $C_3$ plants,at high temperatures and high oxygen concentrations,the enzyme $RuBP$ carboxylase acts as an oxygenase,leading to the oxidation of photosynthetic products into $CO_2$ and $H_2O$ without producing useful energy ($ATP$ or $NADPH$).
$C_4$ plants have evolved a mechanism to concentrate $CO_2$ around the enzyme,thereby suppressing photorespiration.
Peroxisomes and mitochondria are essential organelles for completing the photorespiratory pathway.

(C) The correct sequence of cell organelles involved in photorespiration is chloroplast,peroxisome,and mitochondria.
Photorespiration is a light-dependent process involving the oxygenation of ribulose bisphosphate $(RuBP)$ and the release of carbon dioxide by photosynthetic organs.
It leads to the oxidation of photosynthetic products into $CO_2$ and $H_2O$ without the production of $ATP$ or $NADPH$.
This process occurs primarily in $C_3$ plants when high temperatures and high oxygen concentrations cause the enzyme $RuBP$ carboxylase to function as $RuBP$ oxygenase.
Photorespiration is absent in $C_4$ plants due to their specialized anatomy and mechanism to concentrate $CO_2$ around the enzyme.

(A) Incorrect: Photophosphorylation and oxidative phosphorylation involve the movement of protons from the lumen/intermembrane space to the stroma/matrix,which is a downhill movement (down the electrochemical gradient) through $ATP$ synthase.
$(B)$ Incorrect: In dicot stems,the intrafascicular cambium is present,and the interfascicular cambium originates from medullary ray cells,not the pericycle. Pericycle involvement in cambium formation is specific to dicot roots.
$(C)$ Correct: Polyandrous condition refers to the presence of free stamens. Both Gloriosa and Petunia exhibit this condition.
$(D)$ Correct: Symbiotic nitrogen fixers like $Rhizobium$ and $Frankia$ can exist in a free-living state in the soil as aerobes and only fix nitrogen when they establish a symbiotic relationship.
Therefore,statements $(C)$ and $(D)$ are correct. The total number of correct statements is $2$.

(B) : Light and temperature may affect flowering in plants in various ways.
The effect of photoperiods or daily duration of light hours (and dark periods) on flowering is called photoperiodism.
For example,in short day plants,flowering occurs when day length is below the critical period,e.g.,dahlia,rice,etc.
In long day plants,flowering occurs when day length is above the critical period,e.g.,spinach,lettuce,etc.
In short-long day plants,a short photoperiod is required for floral initiation and a long photoperiod is required for blossoming,and vice-versa for long-short day plants.

(C) $ABA$ (Abscisic acid) acts as an antagonist to gibberellins. This is illustrated in the table below:

Abscisic acid	Gibberellic acid
It inhibits growth.	It promotes growth.
It promotes the dormancy of seeds,buds,and tubers.	It overcomes the natural dormancy of seeds,tubers,etc.
It inhibits the synthesis of $RNA$ and proteins.	It promotes the synthesis of $RNA$ and proteins.
Causes abscission of flowers and fruits.	Promotes development of fruits.
Promotes leaf senescence.	Prevents leaf senescence.
Promotes stomatal closure.	Promotes stomatal opening.
Prevents amylase activity.	Promotes amylase activity during seed germination.

(C) : Carrot is a biennial plant that requires a stimulus of low temperature for flowering. It remains vegetative during the warm season and bears flowers and fruits only after experiencing a cold period. It can be made to flower in one growing season by providing low-temperature treatment to young plants or seedlings,a process referred to as vernalization. Hence,vernalization stimulates flowering in carrot.

(A) : Indigestion is a condition in which food is not properly digested,leading to a feeling of fullness. The primary causes of indigestion include inadequate enzyme secretion,anxiety,food poisoning,overeating,and the consumption of spicy food.

(A) The correct answer is $A$.
Carboxypeptidase is a digestive enzyme synthesized in the pancreas and secreted into the small intestine.
It functions as a metalloenzyme and requires $Zn^{2+}$ (zinc) ions as a cofactor for its catalytic activity.
This enzyme plays a crucial role in protein digestion by cleaving amino acids from the carboxyl terminus of proteins and peptides.
It operates optimally in an alkaline medium and is primarily involved in the conversion of large polypeptides into smaller dipeptides and individual amino acids.

(A) The human $Caecum$ is a small blind sac which hosts some symbiotic microorganisms. These microorganisms play a role in the digestion of certain substances and the synthesis of vitamins. While the large intestine as a whole contains a vast microbiome,the $Caecum$ is specifically noted in biological texts as a site for these symbiotic organisms.

(C) The correct statement is $(c)$. In certain industries,especially those involving grinding or stone breaking,so much dust is produced that the body's defense mechanism cannot fully cope with the situation.
Long-term exposure to this dust can lead to inflammation,which causes fibrosis (proliferation of fibrous tissues),resulting in serious lung damage.
Therefore,workers in such industries are advised to wear protective masks to prevent these respiratory disorders.
Option $(a)$ is incorrect because while smoking causes bronchitis,it is not the most comprehensive statement regarding respiratory disorders in the context of occupational hazards.
Option $(b)$ is incorrect because the pneumotaxic centre reduces the duration of inspiration.
Option $(d)$ is incorrect because only about $20-25\%$ of $CO_2$ is carried by haemoglobin as carbamino-haemoglobin,while the majority is carried as bicarbonates.

(A) The correct answer is $A$. When individuals move from plains to high-altitude regions like Rohtang Pass,they initially experience altitude sickness due to low atmospheric pressure and reduced oxygen availability. However,after staying for about six months,the body undergoes physiological acclimatization. This process involves:
$1$. Increasing the production of red blood cells $(RBCs)$ to enhance oxygen-carrying capacity.
$2$. Decreasing the binding affinity of haemoglobin to $O_2$ (shifting the oxygen dissociation curve to the right),which facilitates the release of oxygen into the tissues.
$3$. Increasing the breathing rate to compensate for low oxygen levels.

(C) The correct answer is $C$. The blood group of the donor was $O$.
Individuals with blood group $O$ are considered universal donors.
This is because their red blood cells lack both $A$ and $B$ antigens on their surface.
Consequently,when $O$ type blood is transfused into a patient of any other blood group ($A, B, AB,$ or $O$),it does not trigger an immune response or cause agglutination (clumping) of the recipient's blood cells.

(C) : The $Spleen$ is a vertebrate organ located behind the stomach, primarily composed of lymphoid tissue.
Its functions include the production of lymphocytes and the destruction of foreign particles.
It acts as a reservoir for $RBCs$ and helps regulate their number in circulation.
Furthermore, it is the primary site for the breakdown of worn-out $RBCs$, which is why it is commonly referred to as the "graveyard" of $RBCs$.

(C) The correct answer is $(C)$.
During glomerular filtration in the kidneys,ultrafiltration of blood occurs,meaning almost all constituents of plasma except proteins pass into the Bowman's capsule.
Following this,nearly $99\%$ of the filtrate is reabsorbed by the renal tubules.
The Proximal Convoluted Tubule $(PCT)$ is responsible for the maximum reabsorption.
Approximately $70-80\%$ of electrolytes and water,along with nearly all essential nutrients (like glucose and amino acids),are reabsorbed in this segment of the nephron.

(C) The correct classification is based on the primary nitrogenous waste excreted by the animals:
$1$. Ammonotelic animals excrete ammonia,which is highly toxic and requires large amounts of water. Examples include aquatic amphibians.
$2$. Ureotelic animals excrete urea,which is less toxic and requires moderate water. Examples include humans and adult frogs (terrestrial stage).
$3$. Uricotelic animals excrete uric acid,which is the least toxic and requires minimal water. Examples include birds (pigeon),reptiles (lizards),and insects (cockroach).
Therefore,option $c$ correctly categorizes these animals.

(A) : The amount of the filtrate formed by the kidneys per minute is called glomerular filtration rate $(GFR)$. $GFR$ in a healthy individual is approximately $125 \text{ ml/minute}$, $i.e.$, $180 \text{ litres}$ per day.
The kidneys have built-in mechanisms for the regulation of $GFR$. One such efficient mechanism is carried out by the juxtaglomerular apparatus $(JGA)$.
$JGA$ is a special sensitive region formed by cellular modifications in the distal convoluted tubule $(DCT)$ and the afferent arteriole at the location of their contact.
$A$ fall in $GFR$ activates the $JG$ cells to release renin, which converts angiotensinogen in the blood to angiotensin $I$ and further to angiotensin $II$. Angiotensin $II$ is a powerful vasoconstrictor that increases the glomerular blood pressure and thereby brings the $GFR$ back to normal.

(B) is the correct statement.
$1$. Osteoporosis is an age-related disorder characterized by decreased bone mass and increased chances of fractures.
$2$. Muscular dystrophy is a genetic disorder resulting in progressive degeneration of skeletal muscles.
$3$. Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction,leading to fatigue,weakening,and paralysis of skeletal muscles,caused by antibodies blocking acetylcholine receptors.
$4$. Gout is the inflammation of joints due to the accumulation of uric acid crystals,not calcium.

(C) is the correct answer.
Troponin and myosin are essential protein components of striated (skeletal) muscles.
Myosin is a thick filament protein that acts as a motor protein,while troponin is a regulatory protein complex associated with actin filaments that helps in the regulation of muscle contraction.
Option $(a)$ is incorrect because thymosin is a peptide hormone secreted by the thymus,not the thyroid.
Option $(b)$ is incorrect because prolactin is a hormone secreted by the anterior pituitary,not a digestive enzyme.
Option $(d)$ is incorrect because rhodopsin is a light-sensitive pigment found in the retina of the eye,not a hormone.

(C) The human brain is the anterior-most part of the central nervous system. It is divided into three main parts: forebrain, midbrain, and hindbrain. The hindbrain consists of three specific structures: the $pons$, the $cerebellum$, and the $medulla$ (also known as the $medulla$ $oblongata$). Therefore, the $cerebellum$ is a part of the hindbrain.

(C) The correct answer is $C$.
The vestibular apparatus is a complex structure located in the inner ear,positioned above the cochlea.
It is composed of three semicircular canals,which are responsible for detecting rotational movements of the head,and the utriculus and sacculus,which detect the orientation and position of the head relative to gravity.
While the cochlea is the primary organ for hearing,the vestibular apparatus does not contribute to the process of hearing.
However,it is essential for maintaining the body's equilibrium,balance,and posture,making it a vital component of the human ear.

(A) The correct answer is $A$.
When a person encounters a sudden threat like a snake,the body initiates a 'fight-or-flight' response.
This response is mediated by the sympathetic nervous system.
The sympathetic nervous system stimulates the adrenal medulla to secrete emergency hormones,specifically epinephrine (adrenaline) and norepinephrine (noradrenaline).
These hormones prepare the body for immediate physical action by increasing heart rate,blood pressure,and alertness.
Note that these hormones are secreted by the adrenal medulla,not the adrenal cortex.

(D) The correct answer is $D$.
Steroid hormones,such as $Cortisol$,$Testosterone$,$Estradiol$,and $Progesterone$,are lipid-soluble.
Because they are lipid-soluble,they can easily pass through the lipid bilayer of the target cell membrane.
Once inside the cell,they bind to intracellular receptors,which are often located in the nucleus.
This hormone-receptor complex then interacts with the genome to regulate gene expression or chromosome function.
In contrast,peptide hormones like $Insulin$,$Glucagon$,$Somatostatin$,and $Oxytocin$ are water-soluble and bind to membrane-bound receptors on the cell surface.

(C) The correct statement is $(c)$.
Hormone action involves their reception by target cells.
Specific proteins called hormone receptors,which are located in target tissues,bind with these hormones.
$FSH$ (Follicle Stimulating Hormone) is a peptide hormone that cannot pass through the cell membrane.
Therefore,it binds to specific membrane-bound receptors located on the surface of ovarian cells to initiate its action.
Glucagon is secreted by $\alpha$-cells,not $\beta$-cells.
Thymosin secretion decreases with aging.
$FSH$ primarily stimulates follicular development and estrogen secretion,but progesterone is mainly stimulated by $LH$.

(B) : The nucleolus is the primary site for the synthesis of ribosomal $RNA$ $(rRNA)$,which is essential for the formation of ribosomal subunits.
Ribosomal proteins are synthesized in the cytoplasm and then migrate into the nucleolus.
Inside the nucleolus,these proteins are assembled with $rRNA$ to form ribonucleoprotein complexes.
These complexes are then transported back to the cytoplasm,where they mature into functional ribosome particles.

(A) Archaebacteria are unique organisms that can survive in some of the most extreme environmental conditions on Earth.
These conditions include high salinity (halophiles),extreme temperatures (thermophiles),and highly acidic environments.
Deep-sea hydrothermal vents are characterized by extremely high temperatures and high pressure,which are conditions where only $Archaebacteria$ (specifically thermoacidophiles) can thrive.
Therefore,the correct option is $A$.

(D) In some prokaryotes like cyanobacteria,there are other membranous extensions into the cytoplasm called chromatophores which contain pigments.
These structures are responsible for photosynthesis in these organisms.
Heterocysts are specialized cells for nitrogen fixation,basal bodies are associated with flagella,and pneumatophores are respiratory roots in plants.

(B) In humans,mature red blood cells $(RBCs)$ are enucleated (lack a nucleus) to provide more space for hemoglobin. In contrast,the red blood cells of a frog are nucleated (possess a nucleus) and contain hemoglobin,which is the respiratory pigment responsible for oxygen transport.

(C) The human ear consists of three parts: the outer ear,middle ear,and inner ear.
The inner ear contains the cochlea and the vestibular apparatus.
The cochlea is primarily responsible for hearing.
The vestibular apparatus,which consists of the semicircular canals and the otolith organ (saccule and utricle),is responsible for maintaining the balance of the body and posture.
Therefore,the vestibular apparatus does not play a direct role in hearing but is essential for equilibrium.

(A) When a person encounters a sudden threat (like a snake),the body initiates the '$fight-or-flight$' response.
This response is mediated by the sympathetic nervous system.
The sympathetic nerves stimulate the adrenal medulla to secrete catecholamines,specifically epinephrine (adrenaline) and norepinephrine (noradrenaline).
These hormones prepare the body for immediate action by increasing heart rate,blood pressure,and alertness.
Therefore,option $A$ is correct because the adrenal medulla is the site of secretion for these hormones,not the adrenal cortex.

(D) $1$. Cigarette smoking is a major cause of emphysema and chronic bronchitis,which involves inflammation of the bronchi. Thus,statement $(A)$ is correct.
$2$. The pneumotaxic center present in the pons region of the brain primarily acts as a 'switch off' point for inspiration. It reduces the duration of inspiration,thereby altering the respiratory rate. Thus,statement $(B)$ is incorrect.
$3$. In certain industries,especially those involving grinding or stone-breaking,so much dust is produced that the defense mechanism of the body cannot fully cope with the situation. Long-term exposure can give rise to inflammation leading to fibrosis (proliferation of fibrous tissues) and thus cause serious lung damage. Thus,statement $(C)$ is correct.
$4$. Since both $(A)$ and $(C)$ are correct,the correct option is $(D)$.

(D) Heterotrophic bacteria are the most abundant bacteria in nature.
Many of these are important to human beings in making curd from milk (e.g.,$Lactobacillus$),production of antibiotics (e.g.,$Streptomyces$),fixing nitrogen in legume roots,etc.
They act as decomposers and play a vital role in nutrient cycling.

(C) The kingdom $Monera$ (which includes bacteria) exhibits the most extensive nutritional diversity among all biological groups.
Bacteria can be autotrophic (photoautotrophic or chemoautotrophic) or heterotrophic (saprophytic,parasitic,or symbiotic).
This metabolic versatility allows them to survive in diverse and extreme environments,unlike other kingdoms which have more restricted modes of nutrition.

(D) The correct answer is $(d)$.
Gene therapy is a collection of methods that allows the correction of a gene defect that has been diagnosed in a child or embryo.
In this process,functional genes are inserted into a person's cells and tissues to treat a disease.
Correction of a genetic defect involves the delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene.
The first clinical gene therapy was given in $1990$ to a $4$-year-old girl suffering from adenosine deaminase $(ADA)$ deficiency.
This enzyme is crucial for the proper functioning of the immune system.
$SCID$ (Severe Combined Immunodeficiency) is caused due to a defect in the gene responsible for the enzyme adenosine deaminase.
In some children,$ADA$ deficiency can be cured by bone marrow transplantation or by introducing the functional gene into cells at early embryonic stages,which can provide a permanent cure.

(A) $Cuscuta$ is a total stem parasite which is a classic example of ectoparasitism.
It is commonly found growing on hedge plants.
During the course of evolution,it has lost its chlorophyll and leaves.
It attaches and wraps itself around the stem of the host plant and produces haustoria that are inserted into the vascular system of the host.
The parasitic plant absorbs all the nutrients from the host plant with the help of these haustoria.
$Cuscuta$ is also known to derive the flower-inducing hormone,florigen,from the host.

(B) : Biogeochemical cycles are of two types: gaseous and sedimentary.
In gaseous nutrient cycles,the materials involved in circulation between biotic and abiotic components of the biosphere are gases or vapours,and the reservoir pool is the atmosphere or hydrosphere,$e.g.$,carbon,hydrogen,oxygen,nitrogen,and water.
In sedimentary nutrient cycles,materials involved in circulation between biotic and abiotic components of the biosphere are non-gaseous,and the reservoir pool is the lithosphere,$e.g.$,phosphorus,calcium,and magnesium.
Sulphur has both sedimentary and gaseous nutrient cycles.

(C) In a food chain,energy flows from producers to consumers.
Plant (Producer) $\rightarrow$ Insect (Primary Consumer) $\rightarrow$ Frog (Secondary Consumer) $\rightarrow$ $A$ (Tertiary Consumer) $\rightarrow$ Eagle (Quaternary/Apex Consumer).
In this sequence,the organism $A$ must be a predator that feeds on frogs and is preyed upon by eagles. $A$ cobra (snake) is a common predator of frogs and is often preyed upon by eagles in such ecosystems. Therefore,$A$ is a cobra.

(A) The given pyramid of numbers shows a single producer $(PP = 1)$ supporting a large number of primary consumers $(PC = 500)$, which in turn support secondary consumers $(SC = 50)$ and tertiary consumers $(TC = 10)$.
This is a spindle-shaped or inverted-type pyramid, which is characteristic of a tree ecosystem where a single large tree $(PP)$ supports many insects $(PC)$, which are then eaten by a smaller number of birds $(SC)$, and finally by a few top predators $(TC)$.
Option $(A)$ correctly identifies this relationship: $PP$ (tree) $\rightarrow$ $PC$ (insects) $\rightarrow$ $SC$ (insectivorous birds) $\rightarrow$ $TC$ (top predators).

(D) The four important functional aspects of an ecosystem are:
$1$. Productivity
$2$. Decomposition
$3$. Energy flow
$4$. Nutrient cycling
Stratification refers to the vertical distribution of different species occupying different levels in an ecosystem,which is a structural feature rather than a functional one. Therefore,$D$ is the correct answer.

(B) In a forest ecosystem,the pyramid of number is inverted or spindle-shaped rather than upright. This is because a single large tree (producer) can support a large number of herbivorous birds or insects (primary consumers),which in turn support a smaller number of predatory birds (secondary consumers). Since the base representing the producers is narrower than the level representing the primary consumers,the pyramid is not upright.

(B) : The rate of resynthesis of organic matter by consumers or the rate at which food energy is assimilated at the trophic level of consumers is called secondary productivity.
In a grassland ecosystem,the rabbit acts as a primary consumer (herbivore).
Therefore,the rate of formation of new organic matter by the rabbit is referred to as secondary productivity.

(D) The series of biotic communities that develop one after the other in a newly formed pond or lake is called hydrosere.
It starts as soon as the muddy water becomes clear.
The pioneer stage of hydrosere is the phytoplankton stage.
Death and decomposition of phytoplankton in the first seral stage produce organic matter,which mixes with clay and silt at the bottom to form soft mud.
This soft mud is favourable for the growth of submerged hydrophytes in the next seral stage.
Therefore,the second stage of hydrosere is occupied by submerged hydrophytes like $Vallisneria$.

(A) In a typical terrestrial food web,organisms are categorized based on their trophic levels. Primary consumers (herbivores) feed directly on producers (plants).
$(1)$ and $(2)$ represent primary consumers such as Deer and Rabbit,which are strictly herbivorous.
$(3)$ and $(4)$ represent secondary or tertiary consumers such as Frog and Rat,which occupy higher trophic levels by feeding on insects or primary consumers.
Therefore,option $(A)$ provides the most ecologically accurate classification for these positions in a standard food web.

(A) The correct answer is $A$.
According to global biodiversity estimates,$Fungi$ represent the largest group of species among the options provided.
$Fungi$ are achlorophyllous,heterotrophic,spore-forming,non-vascular,eukaryotic organisms that possess chitin in their cell walls and store food as glycogen.
They act as major decomposers in various ecosystems and play a crucial role in nutrient cycling.

(D) : Biodiversity hotspots are regions characterized by high levels of species richness and a significant degree of endemism,while also facing severe threats to their habitats due to degradation and fragmentation.
India hosts three recognized biodiversity hotspots: the Himalayas,the Indo-Burma region,and the Western Ghats-Sri Lanka region.
The Western Ghats are globally recognized for their high degree of endemism,particularly in flowering plants,amphibians,reptiles,and various mammals.
Therefore,among the given options,the Western Ghats is the correct biodiversity hotspot.

(C) : Hotspots are areas with high density of biodiversity or megadiversity which are also the most threatened ones.
Ecologically,hotspots are determined by four factors: number of species/species diversity,degree of endemism,degree of threat to habitat due to its degradation and fragmentation,and degree of exploitation.
India has three hotspots: Indo-Burma,Himalayas,and Western Ghats-Sri Lanka.
India is a country of megadiversity with $2.4\%$ of the global land area and having $8.1\%$ of global biodiversity.
Major centers of biodiversity include Agasthyamalai hills,Silent Valley,and Anamalai reserve.
There is a high degree of endemism as well as richness of species of flowering plants,amphibians,reptiles,some mammals,and butterflies in the Western Ghats.

(D) : Sacred groves are an example of $in-situ$ conservation of forests and wildlife,especially rare and threatened species.
These forest patches are found around places of worship and are held in high esteem by tribal communities.
They are the most undisturbed forest patches,often surrounded by highly degraded landscapes.
Not a single branch is allowed to be cut from these forests.
As a result,many endemic species which are rare or have become extinct elsewhere can be seen to flourish here.
Such sacred groves are found in the Khasi and Jaintia hills of Meghalaya,Aravalli hills of Rajasthan,Western Ghat regions of Karnataka and Maharashtra,and the Sarguja,Chanda,and Bastar areas of Madhya Pradesh.

(D) $DDT$ undergoes biomagnification in the food chain. In birds,high concentrations of $DDT$ interfere with calcium metabolism. This leads to the thinning of eggshells. Consequently,these thin-shelled eggs break prematurely during incubation,preventing the embryos from developing fully and hatching. Thus,the population of birds declines significantly.

(B) is the incorrect statement. Ozone present in the upper atmosphere (stratosphere) forms a protective layer known as the ozone layer. This layer is essential for the survival of life on Earth because it absorbs harmful $UV$ radiation from the Sun,preventing it from reaching the Earth's surface. In contrast,ozone at the ground level (troposphere) is considered a pollutant and is harmful to animals and plants.

(A) : Biochemical oxygen demand $(BOD)$ is the amount of dissolved oxygen required by aerobic microorganisms to break down the organic matter present in a given volume of water sample.
It serves as a direct indicator of the level of organic pollution in water bodies.
Higher $(BOD)$ values indicate higher levels of organic pollution,making it a standard method for estimating the amount of organic matter in sewage water.

(A) According to the global biodiversity estimates,among the groups listed,$Fungi$ represent a very high number of species. In the context of biological classification and biodiversity,$Fungi$ have a greater number of described species compared to $Algae$,$Bacteria$,or $Lichens$.

(A) $1$. Onion $(Allium \text{ } cepa)$ reproduces vegetatively through a specialized underground stem structure known as a $Bulb$.
$2$. Ginger reproduces through $Rhizomes$, not suckers.
$3$. $Chlamydomonas$ reproduces through $Zoospores$, not conidia.
$4$. $Yeast$ reproduces through $Budding$, not zoospores.
Therefore, the correct match is Onion - Bulb.

(A) The menstrual cycle is regulated by hormones. During the luteal phase,the corpus luteum secretes large amounts of progesterone,which is essential for maintaining the endometrium. If fertilization does not occur,the corpus luteum degenerates,leading to a sharp decrease in the levels of progesterone. This withdrawal of progesterone causes the breakdown of the endometrial lining and its blood vessels,which results in menstruation.

(A) The correct answer is $A$.
$1$. In the treatment of viper snake bites,'passive immunity' is utilized,where preformed antibodies (antivenom) are injected directly into the patient's body.
$2$. $T$-lymphocytes do not produce antibodies themselves; instead,they assist $B$-lymphocytes in the immune response.
$3$. An antibody molecule consists of two light chains and two heavy chains,not four light chains.
$4$. The rejection of a transplanted organ (graft rejection) is primarily mediated by cell-mediated immunity,which is governed by $T$-lymphocytes,not $B$-lymphocytes.

(A) The human body has innate immunity consisting of four types of barriers:
$1$. Physical barriers: Skin and mucus coating of the respiratory,gastrointestinal,and urogenital tracts.
$2$. Physiological barriers: Acid in the stomach,saliva in the mouth,and tears from eyes.
$3$. Cellular barriers: Polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells.
Option $A$ is correct because $PMNL$ and monocytes are examples of cellular barriers.
Option $B$ is incorrect because these are examples of passive immunity (pre-formed antibodies).
Option $C$ is incorrect because saliva and tears are physiological barriers,not physical.
Option $D$ is incorrect because mucus coating is a physical barrier,while $HCl$ is a physiological barrier.

(D) $I.$ $Spirulina$ is a unicellular cyanobacterium that is a rich source of protein,minerals,and vitamins. This statement is correct.
$II.$ $Methylophilus$ $methylotrophus$ has a high rate of biomass production and protein synthesis due to its high rate of biomass doubling. It can produce $25$ tonnes of protein from $250$ grams of microorganisms in a day,which is significantly higher than a cow. This statement is correct.
$III.$ Mushrooms are generally rich in proteins and fibers,not Vitamin-$C$. This statement is incorrect.
$IV.$ Biofortified rice varieties are typically rich in iron or Vitamin-$A$,not calcium. This statement is incorrect.
Therefore,only statements $I$ and $II$ are correct.

(C) Yeast, specifically $Saccharomyces \text{ } cerevisiae$ (also known as Brewer's yeast), is widely used in the food and beverage industry.
It is used in the production of bread by fermenting sugars in the dough, which releases $CO_2$ and causes the dough to rise.
It is also used in the production of alcoholic beverages like beer and wine through the process of fermentation.

(C) Many members of the genus $Glomus$ form symbiotic associations with plants,which are known as mycorrhiza. In this association,the fungal symbiont absorbs phosphorus from the soil and passes it to the plant. Plants having such associations show other benefits like resistance to root-borne pathogens,tolerance to salinity and drought,and an overall increase in plant growth and development. Therefore,$Glomus$ acts as a biofertilizer.

(D) The gene gun method,also known as biolistics or microprojectile bombardment,is a technique used to introduce foreign $DNA$ into host cells. In this process,microparticles of heavy metals are coated with the target $DNA$. These particles are then accelerated at high velocity to penetrate the cell wall and membrane. The microparticles used for this purpose are typically made of $Gold$ or $Tungsten$ because they are inert,dense,and non-toxic to the cells.

(D) The $DNA$ polymerase used in $PCR$ is known as $Taq$ polymerase.
It is isolated from a thermophilic bacterium called $Thermus$ $aquaticus$.
Because $PCR$ involves repeated cycles of heating (denaturation) to separate $DNA$ strands,the enzyme must be thermostable.
Therefore,$Taq$ polymerase remains active even at high temperatures,allowing the amplification process to continue without needing to add fresh enzyme in every cycle.

(D) $Probe$ is a single-stranded $DNA$ or $RNA$ molecule that is tagged with a radioactive isotope or a fluorescent molecule.
It is used to detect the presence of complementary sequences in a sample of $DNA$ or $RNA$ by the process of hybridization.
Since it is labeled,it allows for the identification of specific gene sequences in techniques like Southern blotting or colony hybridization.

(D) $PCR$ (Polymerase Chain Reaction) and $RFLP$ (Restriction Fragment Length Polymorphism) are fundamental techniques employed in $DNA$ fingerprinting.
$DNA$ fingerprinting involves identifying differences in specific regions of $DNA$ sequences.
$PCR$ is used to amplify small amounts of $DNA$ samples,while $RFLP$ is used to analyze the variations in the length of $DNA$ fragments produced by restriction enzymes.
These techniques together allow for the identification of individuals based on their unique genetic makeup.

(D) The plasmid $pBR322$ is a widely used cloning vector in $E. coli$.
$1$. $ori$ stands for the origin of replication,which is the sequence where replication starts.
$2$. $rop$ codes for the proteins involved in the replication of the plasmid.
$3$. $Hind III$ and $Eco RI$ are restriction sites (recognition sites) for specific restriction enzymes,not selectable markers.
$4$. $amp^R$ (ampicillin resistance) and $tet^R$ (tetracycline resistance) are the selectable markers that help in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.

(D) Based on the provided food web diagram:
$1$. Organism $I$ consumes plants/seeds and is eaten by the tiger. In this context, it represents a herbivore like a squirrel.
$2$. Organism $II$ consumes plants/seeds and is eaten by the fox. It represents a herbivore like a cat (or similar small mammal).
$3$. Organism $III$ is eaten by the snake and consumes grasshoppers. It represents a predator like a mouse.
$4$. Organism $IV$ consumes plants/seeds and is eaten by the hawk. It represents a bird like a pigeon.
Therefore, the correct sequence is $I = \text{Squirrel}, II = \text{Cat}, III = \text{Mouse}, IV = \text{Pigeon}$.

(A) Domestic sewage in large cities is characterized by high organic content.
$1$. $BOD$ (Biochemical Oxygen Demand) is a measure of the organic matter present in water.
$2$. Domestic sewage contains a large amount of biodegradable organic matter,which serves as food for microorganisms like aerobic and anaerobic bacteria.
$3$. As these microorganisms decompose the organic matter,they consume dissolved oxygen,leading to a high $BOD$ value.
$4$. Therefore,domestic sewage is characterized by high $BOD$ due to the presence of high organic load and associated microbial activity.

(B) The correct answer is $B$.
$1$. The ozone found in the stratosphere (upper atmosphere) is known as 'good' ozone because it absorbs harmful ultraviolet $(UV)$ radiation from the sun,protecting living organisms.
$2$. The ozone found in the troposphere (lower atmosphere) is considered 'bad' or harmful to animals and plants.
$3$. Therefore,the statement that ozone in the upper atmosphere is harmful is incorrect.
$4$. Tropical forests are indeed being lost at a rapid rate.
$5$. The greenhouse effect is a naturally occurring phenomenon that is responsible for heating the Earth's surface and atmosphere.
$6$. Eutrophication is the natural aging of a lake by nutrient enrichment of its water.

(D) $DDT$ (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant that undergoes biomagnification in the food chain.
In birds,high concentrations of $DDT$ interfere with calcium metabolism.
This interference leads to the thinning of eggshells.
Consequently,the eggshells break prematurely during incubation,preventing the eggs from hatching and leading to a significant decline in the bird population.

(C) The figure shows a tubectomy. This is a surgical method of contraception used in females. In this procedure,a small part of the fallopian tube is removed or tied through a small incision in the abdomen or through the vagina. It is a highly effective method of birth control,but its reversibility is very poor.

(B) Streptokinase is a clot-buster enzyme produced by the bacterium Streptococcus and modified by genetic engineering. It is administered to patients who have suffered from myocardial infarction (heart attack) to dissolve blood clots (thrombi) in the blood vessels,thereby restoring blood flow to the heart muscle.