AIIMS 2014 Biology Question Paper with Answer and Solution

(A) The correct answer is $A$.
During the $zygotene$ stage of prophase $I$ of meiosis,the chromosomes begin to pair up.
This process of pairing of homologous chromosomes is known as $synapsis$.
Each pair of homologous chromosomes is referred to as a $bivalent$ or a $tetrad$.

(A) Approximately $70\%$ of $CO_2$ (about $2.5 \ ml$ per $100 \ ml$ of blood) received by the blood from the tissues enters the $RBCs$,where it reacts with water to form carbonic acid $(H_2CO_3)$.
Carbonic anhydrase,an enzyme found exclusively in $RBCs$,speeds up the formation of $H_2CO_3$ and rapidly converts it back to carbon dioxide and water when the blood reaches the lungs.
Almost as rapidly as it is formed,the carbonic acid in $RBCs$ dissociates into hydrogen ions $(H^+)$ and bicarbonate ions $(HCO_3^-)$.
These bicarbonate ions are then transported in the plasma to the lungs.

(D) Statement $(i)$ is correct: As we go lower in the taxonomic hierarchy, the number of shared characteristics increases.
Statement $(ii)$ is incorrect: Order is the assemblage of families, not genera, which exhibit a few similar characters.
Statement $(iii)$ is incorrect: Cat belongs to the family $Felidae$, while dog belongs to the family $Canidae$.
Statement $(iv)$ is correct: Binomial Nomenclature was indeed introduced by Carolus Linnaeus.
Therefore, statements $(ii)$ and $(iii)$ are not correct.

(A) category is a rank or level in the hierarchical classification of organisms.
Taxon is a unit in classification which represents a group of organisms based on certain common characteristics.
While a category represents a specific rank (e.g.,Kingdom,Phylum,Class),a taxon represents the actual biological group assigned to that rank (e.g.,$Angiospermae$ is a taxon,while Class is a category).
Therefore,taxon and category are distinct concepts,and the reason correctly describes the nature of a category.

(A) The correct matches are as follows:
$1$. Phycomycetes are commonly known as Algal fungi $(A-II)$.
$2$. Ascomycetes are commonly known as Sac fungi $(B-I)$.
$3$. Basidiomycetes are commonly known as Club fungi $(C-IV)$.
$4$. Deuteromycetes are commonly known as Fungi imperfecti $(D-III)$.
Therefore, the correct combination is $A-II, B-I, C-IV, D-III$.

(B) Cockroaches belong to the class $Insecta$ and the phylum $Arthropoda$.
$Arthropoda$ is the largest phylum of $Animalia$ which includes insects.
Cockroaches are characterized by a chitinous exoskeleton,jointed appendages,and a segmented body,which are key features of the phylum $Arthropoda$.

(A) Figure $A$ shows two germinal layers: an outer ectoderm and an inner endoderm,with an undifferentiated layer called mesoglea in between. Animals with this organization are called Diploblastic (e.g.,Coelenterata).
Figure $B$ shows three germinal layers: an outer ectoderm,a middle mesoderm,and an inner endoderm. Animals with this organization are called Triploblastic (e.g.,Platyhelminthes to Chordata).

(A) Sponges are multicellular organisms that belong to the phylum $Porifera$.
They possess a unique water transport or canal system,which is a defining characteristic of this phylum.
Water enters through minute pores called $ostia$ in the body wall into a central cavity,the $spongocoel$,and goes out through the $osculum$.
This pathway of water transport is helpful in food gathering,respiratory exchange,and removal of waste.
Since the canal system is a diagnostic feature that defines the phylum $Porifera$,the Reason correctly explains the Assertion.

(B) In perigyny,the gynoecium is situated in the centre and other parts of the flower are located on the rim of the thalamus almost at the same level.
In this condition,the ovary is said to be half-inferior.
Examples of perigynous flowers include plum,rose,and peach.
Therefore,the statements describe the condition of perigyny.

(A) The root apical meristem is responsible for the growth of the root.
It is located slightly behind the tip of the root, making it subterminal.
This is because the terminal end of the root is covered by a protective structure called the root cap $(root\,cap)$.
The root cap protects the delicate meristematic tissue as the root pushes through the soil.
Therefore, the presence of the root cap at the terminal end is the reason why the apical meristem is subterminal.
Both the Assertion and the Reason are correct, and the Reason is the correct explanation of the Assertion.

(D) Sclerenchyma consists of long,narrow cells with thick and lignified cell walls having a few or numerous pits.
They are usually dead and without protoplasts.

(B) The provided figure shows Adipose tissue,which is a type of loose connective tissue located mainly beneath the skin.
The cells of this tissue,called adipocytes,are specialised to store fats.
Excess nutrients that are not used immediately are converted into fats and stored in this tissue.
Additionally,it acts as a heat insulator for the body.

(C) Mitochondria and chloroplasts are considered semi-autonomous organelles because they contain their own $DNA$ and ribosomes,which allow them to synthesize some of their own proteins.
They are formed by the division of preexisting organelles.
However,the statement that they 'lack protein-synthesizing machinery' is incorrect because they possess $70S$ ribosomes,which are essential for protein synthesis.
Therefore,the Assertion is correct,but the Reason is incorrect.

(B) carbohydrate is considered non-reducing if it lacks a free aldehyde or ketone group capable of acting as a reducing agent.
In $Sucrose$,the glycosidic linkage is formed between the $C1$ of glucose and the $C2$ of fructose.
Since both the anomeric carbons are involved in the glycosidic bond,there is no free aldehyde or keto group available.
Therefore,$Sucrose$ is a non-reducing sugar,whereas $Maltose$,$Lactose$,and $Ribose$ $5$-phosphate contain free anomeric carbons and are reducing sugars.

(C) The $Km$ value,also known as the Michaelis constant,is defined as the substrate concentration at which the reaction velocity is exactly half of the maximum velocity $(V_{max})$.
This constant is a measure of the affinity of an enzyme for its substrate.

(B) Activation energy is the minimum amount of energy required for a chemical reaction to proceed. Living systems cannot provide high levels of activation energy for most biochemical reactions.
Enzymes function as biological catalysts that lower the activation energy barrier,allowing reactions to occur at physiological temperatures.
Substrate specificity is a fundamental property of enzymes,meaning a particular enzyme acts only on a specific substrate.
While both statements are scientifically correct,the fact that an enzyme is specific to a substrate does not explain *how* or *why* it lowers the activation energy. Therefore,the Reason is not the correct explanation for the Assertion.

(C) Simple diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration without the expenditure of energy.
This process does not require any membrane proteins or carrier molecules to facilitate the movement of substances across the plasma membrane.
In contrast,active transport,facilitated diffusion,and the $Na^+ -K^+$ pump all require specific membrane proteins or carrier molecules to transport substances across the membrane.

(C) Imbibition is a special type of diffusion where water is absorbed by solids—colloids—causing them to enormously increase in volume.
This process involves the adsorption of water by hydrophilic surfaces of a substance without forming a solution.
The solid particles that adsorb water are called Imbibants,and the liquid absorbed is called the Imbibate.
Common examples include the swelling of seeds and dry wood when placed in water.

(A) Magnesium $(Mg^{2+})$ is the central structural component of the chlorophyll molecule's porphyrin ring.
Manganese $(Mn^{2+})$ is involved in the photolysis of water during photosynthesis and acts as an enzyme activator,but it is not a structural component of chlorophyll.
Calcium $(Ca^{2+})$ is required for the formation of calcium pectate in the middle lamella of cell walls.
Zinc $(Zn^{2+})$ acts as an activator for various enzymes,such as alcohol dehydrogenase and carbonic anhydrase.
Iron $(Fe)$ is a vital component of ferredoxin and cytochromes,which are involved in electron transport.
Therefore,the match in option $A$ is incorrect.

(C) The Assertion is correct because sulphur deficiency leads to chlorosis (yellowing of leaves) in plants,particularly in younger leaves.
However,the Reason is incorrect because sulphur is not a constituent of chlorophyll. The central atom of the chlorophyll molecule is magnesium $(Mg^{2+})$.
Sulphur is a component of certain amino acids (like cysteine and methionine),vitamins (like biotin and thiamine),and coenzymes,but it is not part of the chlorophyll structure.

(C) In the Calvin cycle,the fixation and reduction of one molecule of $CO_2$ involves three distinct phases: carboxylation,reduction,and regeneration.
During the reduction phase,$2$ molecules of $ATP$ and $2$ molecules of $NADPH$ are used for the reduction of $1,3$-bisphosphoglycerate to glyceraldehyde-$3$-phosphate.
Additionally,$1$ molecule of $ATP$ is required during the regeneration phase to convert ribulose-$5$-phosphate back into ribulose-$1,5$-bisphosphate.
Therefore,the total requirement for fixing one molecule of $CO_2$ is $3$ molecules of $ATP$ and $2$ molecules of $NADPH$.

(C) Acetyl $CoA$ is the common metabolite in the respiratory breakdown of fats,carbohydrates,and proteins.
Fats are broken down into fatty acids and glycerol; fatty acids are then degraded into Acetyl $CoA$.
Proteins are first degraded by proteases into individual amino acids,which are deaminated to form pyruvic acid or other intermediates,and eventually converted into Acetyl $CoA$ to enter the Krebs cycle.

(A) Glycolysis occurs in the cytoplasm because all the necessary enzymes for this metabolic pathway are present there.
This process is common to both aerobic and anaerobic respiration.
In this process,one molecule of glucose is partially oxidized to form $2$ molecules of pyruvic acid.

(A) The physiological calorific value of carbohydrates is $4.0 \, kcal/g$,proteins is $4.0 \, kcal/g$,and fats is $9.0 \, kcal/g$. Lignin is a dietary fiber that cannot be digested by humans,so it provides $0 \, kcal$.
$1$. Raw sugar (carbohydrate): $5 \, g \times 4.0 \, kcal/g = 20.0 \, kcal$.
$2$. Albumin (protein): $4 \, g \times 4.0 \, kcal/g = 16.0 \, kcal$.
$3$. Total fat (pure ghee + vegetable ghee): $10 \, g + 2 \, g = 12 \, g$. Energy from fat: $12 \, g \times 9.0 \, kcal/g = 108.0 \, kcal$.
$4$. Lignin: $5 \, g \times 0 \, kcal/g = 0 \, kcal$.
Total energy = $20.0 + 16.0 + 108.0 + 0 = 144 \, kcal$.

(D) The $P-$ wave represents the electrical excitation (or depolarisation) of the atria,which leads to the contraction of both the atria.
The $QRS$ complex represents the depolarisation of the ventricles,which initiates the ventricular contraction.
The contraction of the ventricles starts shortly after $Q$ and marks the beginning of the ventricular systole.

(A) In patients suffering from renal failure,the blood urea level rises abnormally,a condition known as uremia.
In uremic patients,an artificial kidney (hemodialyzer) is used to remove accumulated nitrogenous waste products like urea from the blood through the process of hemodialysis.
Since hemodialysis effectively clears the toxic urea that the damaged kidneys cannot filter,it serves as a life-saving procedure that prolongs the life of these patients.
Therefore,the Reason correctly explains why hemodialysis is beneficial for uremic patients.

(D) gliding joint is a type of synovial joint formed between bones that have flat or nearly flat articular surfaces.
These joints allow bones to glide past one another in any direction along the plane of the joint.
In the human body,gliding joints are found between the carpal bones of the wrist,between the tarsal bones of the ankle,and between the zygapophyses of the adjacent vertebrae.
Therefore,the matching of a gliding joint with the carpals is correct.
Cartilaginous joints are found between adjacent vertebrae,not between frontal and parietal bones (which are fibrous joints).
Pivot joints allow rotational movement (e.g.,between atlas and axis),not between the third and fourth cervical vertebrae.
Hinge joints allow movement in one plane (e.g.,elbow joint),whereas the joint between the humerus and pectoral girdle is a ball and socket joint.

(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.

(B) The root cells of a wheat plant are diploid $(2n)$ in nature.
Given that the number of chromosomes in root cells is $2n = 42$.
Therefore,the haploid number $(n)$ is calculated as $n = \frac{42}{2} = 21$.
Pollen grains are male gametophytes and are haploid $(n)$ in nature.
Thus,the number of chromosomes in a pollen grain cell is $21$.

(A) The correct match is $A$ (Onion - Bulb).
$B$ (Ginger) reproduces via Rhizome,not Sucker.
$C$ (Chlamydomonas) reproduces via Zoospores,not Conidia.
$D$ (Yeast) reproduces via Budding,not Zoospores.

(C) During pregnancy,the placenta produces human chorionic gonadotropin $(hCG)$.
This hormone acts similarly to $LH$ and maintains the corpus luteum in the ovary.
The corpus luteum then continues to secrete estrogen and progesterone,which are essential for maintaining the pregnancy.
Therefore,a high level of $hCG$ stimulates the synthesis of estrogen and progesterone.

(A) Vegetative propagation is a type of asexual reproduction where new plants are formed from vegetative parts of the parent plant.
In plants like $Bryophyllum$ and $Begonia$,the leaves are specialized to perform vegetative propagation.
These leaves possess adventitious buds (also known as foliar buds) in the notches of their margins.
When these leaves fall on moist soil,the adventitious buds develop into new plantlets.
Therefore,both the Assertion and the Reason are correct,and the Reason is the correct explanation of the Assertion.

(A) Geitonogamy is a type of pollination where pollen grains are transferred from the anther of one flower to the stigma of another flower on the same plant. Although it is functionally cross-pollination involving a pollinating agent,genetically it is similar to self-pollination because the pollen grains come from the same plant.

(C) The head of a sperm consists of an acrosome and a nucleus,not mitochondria.
The spiral row of mitochondria is present in the middle piece of the sperm,which provides energy for motility.
Therefore,both the Assertion and the Reason are incorrect.

(C) Males generally have a greater stature than females after puberty due to the action of the male sex hormone,testosterone,which is secreted by the testes.
Testosterone secretion begins at puberty under the influence of Luteinizing Hormone $(LH)$ from the anterior pituitary gland.
Testosterone promotes secondary sexual characteristics in males,including bone growth,calcium retention,and the closure of epiphyseal cartilage,which contributes to increased height and bone density.
$hCG$ (Human Chorionic Gonadotropin) is a hormone secreted by the placenta during pregnancy,not a hormone responsible for stature.
Therefore,the Assertion is correct,but the Reason is incorrect.

(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.

(C) The Assertion is correct because condoms act as a physical barrier that prevents the exchange of body fluids,thereby reducing the risk of $HIV$ transmission.
The Reason is incorrect because condoms are made of latex or polyurethane and do not secrete any biological substances like anti-viral interferons. They function solely as a mechanical barrier.

(C) Copper $-T$ is an Intra-Uterine Device $(IUD)$ that is highly effective in preventing pregnancy.
It works by releasing copper ions $(Cu^{2+})$ which suppress sperm motility and the fertilizing capacity of sperms.
It does not prevent the passage of sperms from the vagina to the fallopian tubes; rather,it acts within the uterus to prevent fertilization and implantation.
Therefore,the Assertion is correct,but the Reason is incorrect.

(B) Thalassemia is an autosomal recessive disorder. Let '$A$' represent the dominant normal allele and '$a$' represent the recessive mutant allele.
Carrier parents have the genotype '$Aa$'.
When two carrier parents $(Aa \times Aa)$ reproduce,the possible genotypes of the offspring are determined by a Punnett square:
- $AA$ (Normal child): $25\%$
- $Aa$ (Carrier child): $50\%$
- $aa$ (Affected child): $25\%$
Therefore,the probability of having an affected child $(aa)$ is $25\%$.

(A) In $Mirabilis$ $jalapa$ (four o'clock plant),flower colour exhibits incomplete dominance.
When $F_1$ pink flowered plants $(Rr)$ are selfed,the $F_2$ generation results in a phenotypic and genotypic ratio of $1:2:1$.
The ratio is as follows:
$1$ $RR$ (Red) : $2$ $Rr$ (Pink) : $1$ $rr$ (White).
Since both the phenotypic ratio ($1$ Red : $2$ Pink : $1$ White) and the genotypic ratio ($1$ $RR$ : $2$ $Rr$ : $1$ $rr$) are identical $(1:2:1)$,the Assertion is correct.
This occurs specifically because the gene for flower colour shows incomplete dominance,making the Reason the correct explanation for the Assertion.

(A) During the process of transcription,$RNA$ polymerase catalyzes the synthesis of $RNA$ in the $5'-3'$ direction.
This means that the new $RNA$ strand is synthesized by adding nucleotides to the $3'$ end.
To achieve this,the $RNA$ polymerase enzyme moves along the template $DNA$ strand in the $3'-5'$ direction.
Therefore,the direction of $RNA$ synthesis is $5'-3'$ and the direction of reading the template $DNA$ strand is $3'-5'$.

(A) palindromic sequence is a nucleic acid sequence ($DNA$ or $RNA$) that is the same when read $5'$ to $3'$ on one strand and $5'$ to $3'$ on the complementary strand.
In the option $A$:
$5' - GAATTC - 3'$
$3' - CTTAAG - 5'$
Reading the top strand from $5'$ to $3'$ gives $GAATTC$. Reading the bottom strand from $5'$ to $3'$ (which is right to left in the representation) also gives $GAATTC$.
This is a classic palindromic sequence recognized by the restriction enzyme $EcoRI$.

(A) Transformation is a process where a bacterium takes up naked $DNA$ from its environment. This process is not a passive diffusion of $DNA$ molecules through the cell wall and membrane.
It is an active,energy-requiring process that occurs only in specific bacteria that possess the necessary enzymatic machinery for active uptake and subsequent recombination of the $DNA$ into the host genome.
Even within a population of such bacteria,only 'competent' cells,which express specific competence factors,are capable of performing this uptake.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for why the process is active.

(A) The synthesis of a polypeptide chain terminates when a stop codon (nonsense codon) of $mRNA$ reaches the $A-$site of the ribosome.
There are three stop codons: $UAA, UAG$,and $UGA$.
These codons do not code for any amino acid and are not recognized by any $tRNA$ molecule.
Because no $tRNA$ can bind to these codons,no further aminoacyl-$tRNA$ reaches the $A-$site.
Consequently,the polypeptide chain is released from the $P-$site $tRNA$ in the presence of release factors,terminating the translation process.

(C) Organs that share a common fundamental anatomical structure and similar embryonic origin,despite performing different functions,are known as homologous organs.
In the case of the forelimbs of a cat,lizard,whale,and bat,they all possess the same basic skeletal arrangement (humerus,radius,ulna,carpals,metacarpals,and phalanges).
Although these limbs are adapted for different functions like walking,swimming,or flying,their underlying structural similarity indicates a common evolutionary ancestry.
Therefore,they are classic examples of homologous organs.

(B) For a gene with two alleles,$A$ and $a$,if the frequency of $A$ is $p$ and the frequency of $a$ is $q$,then the frequencies of the three possible genotypes ($AA, Aa,$ and $aa$) are expressed by the Hardy-Weinberg equation: $p^2 + 2pq + q^2 = 1$.
Here,$p$ is the frequency of allele $A$ and $q$ is the frequency of allele $a$.
Given that $p = 0.7$,we know that $p + q = 1$,so $q = 1 - 0.7 = 0.3$.
The frequency of the heterozygous genotype $Aa$ is represented by $2pq$.
Substituting the values: $2pq = 2 \times 0.7 \times 0.3 = 0.42$.

(B) $ELISA$ (Enzyme-Linked Immunosorbent Assay) is a fundamental tool of clinical immunology.
It is based on the principle of antigen-antibody interaction,where specific antibodies or antigens are used to detect the presence of the target molecule.
This test is widely used as an initial screen for $HIV$ detection and allows for easy visualization of results through enzymatic color changes.

(A) Molecule $(A)$ is the chemical structure of Cocaine,which is obtained from the plant Erythroxylum coca. It interferes with the transport of the neurotransmitter dopamine.
Molecule $(B)$ is the chemical structure of a Cannabinoid,which is obtained from the inflorescences of the plant Cannabis sativa. Cannabinoids are known for their effects on the cardiovascular system and can produce hallucinations.
Option $(A)$ is incorrect because while the source is correct,the structure shown is Cocaine,not Morphine.
Option $(D)$ is incorrect because the structure shown in $(A)$ is Cocaine,not Morphine.
Therefore,the correct identification and association based on the provided structures is that $(A)$ is Cocaine and $(B)$ is a Cannabinoid. However,looking at the options provided,option $(A)$ correctly identifies the source and action of Cocaine,which matches the structure $(A)$.

(C) Interferons are antiviral proteins produced by virus-infected cells. They protect non-infected cells from further viral infection by inhibiting viral protein synthesis.
While interferons can now be produced using genetic engineering,they are naturally synthesized by the body's cells in response to viral infections. Therefore,the claim that they can be synthesized 'only' by genetic engineering is false.
Thus,the Assertion is correct,but the Reason is incorrect.

(A) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$Azolla$ is a water fern that has a symbiotic relationship with the cyanobacterium $Anabaena azollae$,which fixes atmospheric nitrogen.
$BGA$ (Blue-Green Algae),such as $Nostoc$ and $Anabaena$,are also well-known biofertilizers that fix nitrogen and increase soil fertility.
Therefore,$Azolla$ and $BGA$ represent a correct pair of biofertilizers.

(A) Antibiotics are chemical substances produced by some microbes and can kill or retard the growth of other disease-causing microbes.
Chloramphenicol and erythromycin are well-known broad-spectrum antibiotics.
These antibiotics are primarily produced by bacteria belonging to the genus $Streptomyces$.
$Streptomyces$ species are filamentous bacteria known for their ability to produce a wide variety of secondary metabolites,including many clinically important antibiotics.

(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.

(B) Vitamin $B_2$ (Riboflavin) is naturally found in cereals,green vegetables,brewer's yeast,egg white,milk,and liver. This makes the Assertion correct.
Vitamin $B_2$ is also produced commercially using microorganisms,specifically certain yeasts and fungi like $Ashbya$ $gossypii$. This makes the Reason correct.
However,the commercial production of vitamin $B_2$ by yeasts is a separate industrial fact and does not explain why it is found in the specific food sources mentioned in the Assertion. Therefore,the Reason is not the correct explanation for the Assertion.

(C) hybridization probe is a fragment of $DNA$ of variable length which is used in $DNA$ samples to detect the presence of nucleotide sequences (the $DNA$ target) that are complementary to the sequence in the probe.
The probe hybridizes to single-stranded $DNA$ whose base sequence allows probe-target base-pairing due to complementarity between the probe and the target.
Therefore,$DNA$ probes are specifically used to identify and select genes of interest from a genomic library.

(C) The variety $Pusa$ $Swarnim$ (also known as $Karan$ $rai$) is a disease-resistant variety of $Brassica$ (mustard).
It was developed through conventional plant breeding techniques to provide resistance against the white rust disease caused by the fungus $Albugo$ $candida$.
$Himgiri$ is a variety of wheat resistant to leaf and stripe rust.
$Pusa$ $Kamal$ is a variety of wheat.
$Pusa$ $Sadabahar$ is a variety of chilli resistant to chilli mosaic virus and leaf curl.

(A) Gene therapy is an experimental technique that uses genes to treat or prevent disease.
The first clinical gene therapy was performed in $1990$ to treat adenosine deaminase deficiency.
$A$ four-year-old girl became the first patient to receive gene therapy on September $14, 1990$,at the $NIH$ Clinical Center.
Adenosine deaminase deficiency,also known as $ADA$ deficiency or $ADA-SCID$,is an autosomal recessive metabolic disorder that leads to severe combined immunodeficiency.
This condition is caused by the lack of the enzyme adenosine deaminase,which is essential for the proper functioning of the immune system.

(B) Mortality or death rate refers to the number of deaths in a population per unit time.
The formula for calculating the death rate is:
$\text{Death rate} = \frac{\text{Number of deaths}}{\text{Total population}}$
Given:
Number of deaths = $4$
Total population = $40$
$\text{Death rate} = \frac{4}{40} = 0.1$ individuals per fruitfly per week.

(C) Nagarjunsagar-Srisailam Tiger Reserve is the largest Tiger reserve in India.
It is located in the state of Andhra Pradesh and Telangana.
It covers a vast area,making it the largest protected area for tigers in the country.

(C) The Assertion is correct. Gamma diversity refers to the total species diversity in a landscape or a large geographical area,which includes the diversity of different habitats within that region.
The Reason is incorrect. Biodiversity generally increases from high altitude to low altitude (or from poles to the equator) because lower altitudes (or tropical regions) provide more stable,favorable,and resource-rich environments for a wider variety of species.
Therefore,the Assertion is correct but the Reason is incorrect.

(B) The Assertion is correct because a wildlife sanctuary is a protected area specifically designated for the conservation of wild animals.
The Reason is also correct because,unlike national parks,sanctuaries allow certain human activities such as the harvesting of timber,collection of minor forest products,and private ownership rights,provided these activities do not adversely affect the wildlife.
However,the Reason does not explain why a sanctuary is formed for animals only; it merely describes the management policy of the sanctuary. Therefore,the Reason is not the correct explanation of the Assertion.

(A) Greenhouse gases contribute to global warming by trapping heat in the atmosphere.
According to the relative contribution to the greenhouse effect,carbon dioxide $(CO_2)$ accounts for approximately $60\%$ of the total greenhouse effect,while methane $(CH_4)$ accounts for approximately $20\%$.
Therefore,these two gases are the primary contributors to the greenhouse effect.