AIIMS 2017 Biology Question Paper with Answer and Solution

(B) The taxonomic classification of the potato plant (Solanum tuberosum) is as follows:
$A$. Family: Solanaceae $(V)$
$B$. Kingdom: Plantae $(IV)$
$C$. Order: Polymoniales $(II)$
$D$. Species: tuberosum $(I)$
$E$. Genus: Solanum $(III)$
Therefore, the correct matching is $A-V, B-IV, C-II, D-I, E-III$.

(A) Yeast is a unicellular fungus and does not exhibit a filamentous structure. It is a microscopic fungus consisting of a single oval cell that reproduces primarily by budding.

(C) Viruses are sub-microscopic infectious agents that replicate only inside the living cells of a host organism.
They are obligate parasites,meaning they require a host to complete their life cycle.
Because viruses are significantly smaller than bacteria,they can easily pass through bacterial-proof filters.
Therefore,the statement that viruses cannot pass through bacterial filters is incorrect.

(B) Cyanobacteria are photosynthetic autotrophs,not chemosynthetic heterotrophs. They contain chlorophyll $a$ similar to green plants and perform oxygenic photosynthesis. They are prokaryotic organisms that can be unicellular,colonial,or filamentous,and they are found in marine,freshwater,or terrestrial environments. They often form blooms in polluted water bodies.

(B) The Assertion is correct because $TMV$ (Tobacco Mosaic Virus) is indeed the causative agent of mosaic disease in tobacco plants.
The Reason is also correct because the genetic material of $TMV$ is a single-stranded $RNA$ molecule.
However,the fact that $TMV$ has $RNA$ as its genetic material does not explain why it causes mosaic disease; these are two independent biological facts about the virus. Therefore,the Reason is not the correct explanation of the Assertion.

(D) Statement $(i)$ is incorrect because in Chlorophyceae,the major pigments are chlorophyll $-a$ and $b$,not $a$ and $d$.
Statement $(ii)$ is incorrect because in Phaeophyceae,the major pigments are chlorophyll $-a, c$ and fucoxanthin,not $a$ and $b$.
Statement $(iii)$ is correct because in Rhodophyceae,the stored food is floridean starch and the major pigments are chlorophyll $-a, d$ and phycoerythrin.
Therefore,only statement $(iii)$ is correct.

(D) The correct matching of organisms with their respective excretory structures is as follows:
$A$. Cockroach: Excretes through $II$. Malpighian tubules.
$B$. Cat fish: Being a vertebrate, it excretes through $III$. Kidneys.
$C$. Earthworm: Excretes through $I$. Nephridia.
$D$. Balanoglossus: Excretes through $V$. Proboscis gland.
$E$. Flatworm: Excretes through $IV$. Flame cells.
Thus, the correct sequence is $A-II, B-III, C-I, D-V, E-IV$.

(A) The genus $Pila$ belongs to the phylum $Mollusca$.
$Molluscs$ are characterized by having a soft,unsegmented body with a distinct head,muscular foot,and visceral hump.
Therefore,the character '$(i)$ Body segmented' is incorrect for $Pila$.
While $Pila$ does possess a radula (a rasping organ in the buccal cavity),the body segmentation is not a feature of this phylum.
Thus,option $A$ is the incorrectly matched pair.

(A) The water vascular system (also known as the ambulacral system) is a unique organ system found in echinoderms that functions in locomotion,food capture,respiration,and excretion.
This system consists of a network of water-filled canals that connect to external tube feet.
The movement of echinoderms is facilitated by the hydraulic pressure of the fluid within the system and the coordinated contraction of the muscles associated with the tube feet.
Therefore,the assertion is correct,and the reason provides a correct explanation for how the ambulacral system enables locomotion.

(B) Thorns are hard,woody,and sharp-pointed structures that develop from the axillary buds of the stem. They serve as a defensive mechanism to protect plants from browsing animals. Examples include $Citrus$ and $Bougainvillea$.

(A) Leaves of dicotyledonous plants possess reticulate venation,while parallel venation is the characteristic of most monocotyledons.
In reticulate venation,the veins of the leaf form a network or a net-like arrangement.
This type of venation is commonly found in dicotyledonous plants.
In parallel venation,the veins run parallel to each other within the leaf lamina.
This type of venation is a characteristic feature of most monocotyledonous plants.

(A) The first formed primary xylem elements are called protoxylem and the later formed primary xylem is called metaxylem.
In stems,the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ.
This arrangement of primary xylem is known as endarch.

(D) Both sexes of the cockroach possess anal cerci,which are jointed,paired structures located on the $10^{th}$ abdominal segment.
However,the male cockroach possesses an additional pair of unjointed,needle-like structures called anal styles on the $9^{th}$ abdominal segment.
These anal styles are absent in the female cockroach,making them a key morphological feature for distinguishing between the two sexes.

(D) Frogs possess various types of sense organs to interact with their environment.
These include sensory papillae for the sense of touch,taste buds for taste,nasal epithelium for smell,eyes for vision,and the tympanum with internal ears for hearing.
Therefore,sensory papillae are specifically associated with the sense of touch.

(D) In earthworms,each segment (except the first,the last,and the clitellar segment) bears a ring of tiny,curved,chitinous structures known as setae. Setae help in locomotion and copulation.

(A) The squamous epithelium is composed of a single thin layer of flattened cells with irregular boundaries,which is a correct description of its structure. This structure is ideal for diffusion,which is why it is found in the walls of blood vessels (endothelium) and air sacs of lungs (alveoli). Since the structure (Assertion) directly facilitates the function and location (Reason),the Reason is the correct explanation of the Assertion. Therefore,both are correct and the Reason explains the Assertion.

(A) Nucleotides are the building blocks of nucleic acids.
Each nucleotide consists of three distinct components:
$1$. $A$ pentose sugar (ribose in $RNA$ or deoxyribose in $DNA$).
$2$. $A$ phosphate group.
$3$. $A$ nitrogenous base (purine or pyrimidine).
Therefore,a nucleotide is formed by the combination of a base,a sugar,and a phosphate group.

(C) $A-IV, B-III, C-II, D-I$
$1$. Metaphase $(IV)$: During metaphase, the chromosomes align at the spindle equator.
$2$. Anaphase $(III)$: During anaphase, the centromere splits, and the sister chromatids separate and move toward opposite poles.
$3$. Zygotene $(II)$: During the zygotene stage of prophase $I$, homologous chromosomes undergo pairing, a process known as synapsis.
$4$. Pachytene $(I)$: During the pachytene stage of prophase $I$, crossing over occurs between non-sister chromatids of homologous chromosomes.

(NONE OF THE OPTIONS PROVIDED ARE FULLY CORRECT BASED ON THE ANALYSIS (CORRECT SET IS $(I), (II), (III)$).) Statement $(i)$ is correct: Water,minerals,and food are moved by a mass or bulk flow system.
Statement $(ii)$ is correct: Bulk flow is achieved through positive or negative hydrostatic pressure gradients.
Statement $(iii)$ is correct: The bulk movement of substances through conducting tissues is called translocation.
Statement $(iv)$ is incorrect: Xylem mainly translocates water,mineral salts,some organic nitrogen,and hormones from roots to aerial parts.
Statement $(v)$ is incorrect: Phloem mainly translocates organic solutes (food) from leaves to other parts of the plant.
Therefore,statements $(i), (ii),$ and $(iii)$ are correct (not incorrect).

(B) The Respiratory Quotient $(RQ)$ is defined as the ratio of the volume of $CO_2$ evolved to the volume of $O_2$ consumed during respiration.
The formula is: $RQ = \frac{\text{Volume of } CO_2 \text{ evolved}}{\text{Volume of } O_2 \text{ consumed}}$.
From the given balanced chemical equation: $2(C_{51}H_{98}O_6) + 145O_2 \to 102CO_2 + 98H_2O + \text{Energy}$.
Here, the volume of $CO_2$ evolved is $102$ and the volume of $O_2$ consumed is $145$.
Therefore, $RQ = \frac{102}{145} \approx 0.703$, which is approximately $0.7$.
This value is characteristic of fatty substances (like tripalmitin).

(A) Alcoholic fermentation is an anaerobic process where glucose is converted into ethanol and carbon dioxide.
In the final step of this pathway,acetaldehyde is reduced to ethanol by the enzyme alcohol dehydrogenase.
During this specific reduction reaction,$NADH + H^+$ is oxidized back to $NAD^+$.
This regeneration of $NAD^+$ is crucial for the continuation of glycolysis.

(B) Auxins,such as $IAA$ (Indole$-3-$acetic acid),play a dual role in the process of abscission.
In the early stages of development,auxins prevent the formation of the abscission layer,thereby preventing the premature drop of young leaves and fruits.
Conversely,in older or mature leaves and fruits,auxins promote the process of abscission.
Since the Assertion describes the inhibitory role in early stages and the Reason describes the promoting role in mature stages,both statements are correct,but the Reason does not explain why auxins prevent drop in early stages. Thus,the Reason is not the correct explanation of the Assertion.

(D) Milk protein (casein) can be digested by both pepsin and chymotrypsin. Pepsin is a proteolytic enzyme found in the stomach that acts on proteins,including casein. Chymotrypsin is a pancreatic enzyme that also breaks down proteins,including casein. Therefore,the statement that chymotrypsin can digest casein is correct.

(D) The Assertion is incorrect because the primary site for the absorption of water and electrolytes is the small intestine,not the large intestine. While the large intestine does absorb some water and electrolytes,it is not the site where they are 'almost fully' absorbed.
The Reason is also incorrect because,although haustral contractions do occur in the large intestine to mix and move contents,the primary function of the large intestine is the absorption of water,some minerals,and certain vitamins produced by symbiotic bacteria,not the primary absorption of electrolytes as implied.
Therefore,both the Assertion and the Reason are incorrect.

(B) Step $A$: Attachment of myosin head to actin forming a cross-bridge.
Step $B$: Release of phosphate. Myosin changes shape to pull actin.
Step $C$: Attachment of new $ATP$ to myosin head. The cross-bridge detaches.
Step $D$: Splitting of $ATP$ into $ADP$ and $Pi$. Myosin cocks into its high-energy conformation.

(A) The assertion is correct because inflammation of joints (arthritis) leads to stiffness and reduced mobility.
The reason is also correct as it describes specific causes of joint disorders: accumulation of uric acid crystals causes gout,and ossification of articular cartilage (ankylosis) leads to the fusion and immobilization of joints.
Therefore,the reason correctly explains why inflammation and associated pathological changes lead to the immobilization of joints.

(B) The cerebellum is a part of the hindbrain,located dorsally to the medulla oblongata and the pons.
It plays a crucial role in maintaining posture,equilibrium,and muscle tone.
While the cerebellum coordinates voluntary movements (making them smooth and precise),it does not initiate them; rather,it refines them.
Since the cerebellum is indeed a part of the hindbrain and is located behind the pons,the reason correctly explains the anatomical position,though the assertion focuses on its functional role. Both statements are scientifically accurate.

(C) $ADH$ (also known as vasopressin) is secreted by the posterior pituitary gland.
It acts on the renal tubules (specifically the distal convoluted tubules and collecting ducts) and blood capillaries.
It promotes the reabsorption of water and electrolytes,thereby reducing the loss of water through urine (diuresis) and concentrating the urine.

(C) The Assertion is correct because it defines the biological species concept,which states that species are groups of interbreeding natural populations that are reproductively isolated from other such groups.
The Reason is incorrect because distinctive morphological characters are not primarily displayed due to reproductive isolation; rather,they are the result of genetic divergence,natural selection,and adaptation to specific environments. Reproductive isolation is a mechanism that maintains species boundaries,not the cause of morphological variation.

(C) The Assertion is correct because $A-T$ base pairs are held together by two hydrogen bonds,while $G-C$ base pairs are held together by three hydrogen bonds.
Because $G-C$ pairs have more hydrogen bonds,they are more stable and require more energy to break (melt) compared to $A-T$ pairs.
The Reason provided is incorrect because it states the number of hydrogen bonds in reverse: $A$ and $T$ have two hydrogen bonds,while $G$ and $C$ have three hydrogen bonds.

(D) Parthenogenesis is a form of asexual reproduction in which an unfertilized egg develops into a new individual.
In organisms like rotifers, honeybees, and some lizards and birds (like turkeys), the female gamete undergoes development to form new organisms without fertilization.
This process is known as Parthenogenesis.
Therefore, the correct pair is Honeybee and Parthenogenesis.

(A) The process of double fertilization involves the fusion of one male gamete $(n)$ with the secondary nucleus $(2n)$ to form the primary endosperm nucleus $(3n)$.
This process is known as triple fusion.
The primary endosperm nucleus develops into the endosperm,which is a triploid $(3n)$ nutritive tissue.
The endosperm provides essential nutrients to the developing embryo.

(C) Oogonia are referred to as gamete mother cells.
$A$ represents a primary follicle.
$B$ represents a tertiary follicle.
$C$ represents a Graafian follicle,which is a mature follicle that ruptures to release the secondary oocyte during ovulation.
$D$ represents the corpus luteum,which is formed from the remains of the Graafian follicle after ovulation.
$A$ large number of primary follicles degenerate during the phase from birth to puberty,a process known as follicular atresia.
Therefore,option $C$ is the correct identification and description.

(D) $ICSI$ (Intracytoplasmic sperm injection) - Formation of embryo by directly injecting sperm into the ovum $(III)$.
$IUI$ (Intrauterine insemination) - Artificial introduction of semen into the vagina or uterus $(I)$.
$IUT$ (Intrauterine transfer) - Transfer of embryo with more than $8$ blastomeres into the uterus $(V)$.
$GIFT$ (Gamete intrafallopian transfer) - Transfer of ovum collected from a donor into the fallopian tube where fertilization occurs $(II)$.
$ZIFT$ (Zygote intrafallopian transfer) - Transfer of the zygote or early embryo (with up to $8$ blastomeres) into a fallopian tube $(IV)$.
Therefore, the correct match is $A-III, B-I, C-V, D-II, E-IV$.

(C) In humans,sex determination is based on the $XY$ type. Males produce two types of gametes: $50\%$ carrying the $X$ chromosome and $50\%$ carrying the $Y$ chromosome. Females produce only one type of gamete,all carrying the $X$ chromosome. Therefore,the sex of the child is determined by the sperm (male gamete) that fertilizes the egg. Thus,the Assertion is correct.
Sex in humans is not a polygenic trait; it is determined by the presence or absence of the $Y$ chromosome,specifically the $SRY$ gene located on it. The Reason statement is scientifically incorrect because sex determination in humans is primarily a monogenic trait controlled by the $Y$ chromosome,not a polygenic trait.

(A) nucleosome is the basic structural unit of eukaryotic chromatin,which consists of a segment of $DNA$ wrapped around a core of histone proteins.
In the provided figure:
$A$ represents the $DNA$ molecule that wraps around the histone core.
$B$ represents the $H_1$ histone protein,which binds to the $DNA$ where it enters and leaves the nucleosome.
$C$ represents the histone octamer,which is the core complex consisting of two molecules each of four histone proteins ($H2A, H2B, H3,$ and $H4$).
Therefore,the correct identification is $A - DNA, B - H_1$ histone,and $C -$ Histone octamer.

$(A)$ The genetic code specifies the relationship between codons and amino acids:
$1$. $UUU$ codes for Phenylalanine $(A-III)$.
$2$. $GGG$ codes for Glycine $(B-IV)$.
$3$. $UCU$ codes for Serine $(C-I)$.
$4$. $CCC$ codes for Proline $(D-V)$.
$5$. $AUG$ codes for Methionine $(E-II)$.
Thus, the correct matching is $A-III, B-IV, C-I, D-V, E-II$.

(A) The Hardy-Weinberg principle states that allele frequencies in a population remain constant in the absence of evolutionary forces.
The assumptions for Hardy-Weinberg equilibrium include:
$1.$ Large population size.
$2.$ Random mating.
$3.$ No mutation.
$4.$ No gene flow (migration).
$5.$ No natural selection.
Comparing these with the given list:
- $iv.$ Occurrence of natural selection: This violates the principle because natural selection causes changes in allele frequencies.
- $v.$ Small size of population: This violates the principle because small populations are subject to genetic drift,which changes allele frequencies.
Therefore,$iv$ and $v$ are the conditions that do not meet the criteria for Hardy-Weinberg equilibrium.

(D) The $Cro-Magnon$ man is considered the most similar to modern humans ($Homo$ $sapiens$).
Their skeletal structure,cranial capacity,and physical features were almost identical to those of modern humans.
They lived approximately $10,000$ to $40,000$ years ago and are known for their advanced tool-making and artistic capabilities.

(B) The human immunodeficiency virus $(HIV)$ is a retrovirus that belongs to the genus Lentivirus.
It consists of a protein coat (capsid) that encloses its genetic material.
The genetic material of $HIV$ is single-stranded $RNA$ $(ssRNA)$.
Upon entering the host cell,the viral $RNA$ is reverse-transcribed into $DNA$ by the enzyme reverse transcriptase,which then integrates into the host genome.

(D) Yellow fever is a viral disease caused by the yellow fever virus and is transmitted by the $Aedes$ $aegypti$ mosquito.
Dengue is also a viral disease caused by the dengue virus and is primarily transmitted by the $Aedes$ $aegypti$ mosquito.
Elephantiasis is caused by a filarial worm (parasite),sleeping sickness is caused by a protozoan $(Trypanosoma)$,and encephalitis can be caused by various agents including viruses,but the specific pair that is both viral and mosquito-borne is yellow fever and dengue.

(A) Artificially acquired passive immunity is a type of immunity where pre-formed antibodies or sensitized lymphocytes are introduced into the host's body.
This provides immediate protection but is short-lived because the host's immune system does not produce these antibodies itself.
Bone marrow transplantation involves the transfer of stem cells that can differentiate into immune cells,which is a form of adoptive immunotherapy.
Since the introduced cells (lymphocytes/stem cells) are produced outside the host and provide immunity,it is classified as artificially acquired passive immunity.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains the Assertion.

(D) Biodiversity loss is primarily driven by human activities that negatively impact ecosystems. The four major causes,often referred to as the 'Evil Quartet',are:
$1$. Habitat loss and fragmentation: This is the most significant cause,where natural habitats are destroyed or broken into smaller pieces.
$2$. Over-exploitation: Humans over-harvest species for food,medicine,or trade,leading to population decline.
$3$. Alien species invasion: The introduction of non-native species can outcompete or prey upon native species,causing their extinction.
$4$. Co-extinction: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct.
Since all four factors listed $(i, ii, iii, iv)$ are recognized as primary causes of biodiversity loss,the correct option is $(D)$.

(C) Before transferring the explant onto the culture medium,it must be disinfected through surface sterilization. This process typically involves the use of chemical agents such as clorax water,sodium hypochlorite,calcium hypochlorite,or methiolate. Extreme care is required during this procedure to ensure that the explant cells remain viable and do not die due to the chemical treatment.

(B) Ranikhet disease, also known as Newcastle disease, is a highly contagious viral disease affecting poultry birds.
Anthrax is a bacterial disease caused by $Bacillus \text{ } anthracis$.
Coccidiosis is a protozoan disease caused by $Eimeria$ species.

(A) The concept of $Totipotency$ states that any living plant cell has the genetic potential to differentiate and develop into a whole plant or somatic embryo under appropriate culture conditions. Somatic embryos are non-zygotic embryo-like structures that can be induced from various types of plant tissues in vitro. Since the ability to form somatic embryos is a direct consequence of the $Totipotency$ of plant cells,the Reason correctly explains the Assertion.

(A) Somatic hybridization is a significant technique in plant tissue culture that involves the fusion of protoplasts from two different plant varieties.
Protoplasts are plant cells whose cell walls have been enzymatically removed,leaving them 'naked'.
When these naked protoplasts from two different plants are fused,they form a somatic hybrid.
This process allows for the combination of desirable traits from two different species or varieties that might not be crossable through traditional sexual reproduction.
Therefore,protoplast fusion is indeed a major advantage and application of tissue culture technology,and the reason provided correctly explains the process of forming such a hybrid.

(A) $BOD$ (Biochemical Oxygen Demand) refers to the amount of dissolved oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
Greater $BOD$ indicates a higher concentration of organic pollutants in the water,which requires more oxygen for decomposition.
Therefore,a higher $BOD$ value directly correlates to a higher polluting potential of the waste water.
Thus,the correct statement is that the greater the $BOD$ of waste water,the more is its polluting potential.

(B) $Trichoderma$ is a free-living saprophytic fungus that commonly lives on dead organic matter in the soil and rhizosphere (root ecosystem).
It acts as an effective biocontrol agent by inhibiting soil-borne plant pathogens.
It produces secondary metabolites like gliotoxin,viridin,gliovirin,and trichodermin,which suppress the growth of harmful fungi and bacteria,thereby protecting plants from diseases.

(B) selectable marker is a gene that facilitates the selection of transformants (cells that have taken up the recombinant vector) by eliminating non-transformants. Option $B$ is incorrect because a selectable marker permits the growth of transformants,not non-transformants.

(A) Alternative selectable markers have been developed to differentiate recombinants from non-recombinants based on their ability to produce color in the presence of a chromogenic substrate.
When a recombinant $DNA$ is inserted into the coding sequence of the enzyme $\beta -$ galactosidase,the gene becomes non-functional.
This process is known as insertional inactivation.
Consequently,the bacteria containing the recombinant plasmid cannot produce the functional $\beta -$ galactosidase enzyme.
As a result,they fail to produce color in the presence of a chromogenic substrate,leading to the formation of colorless colonies.
Non-recombinant bacteria,which do not have the insert,produce functional $\beta -$ galactosidase and form blue-colored colonies.

(C) Basmati rice was patented by a $U.S.$ company in $1997$ through the $U.S.$ Patent and Trademark Office. This was controversial because India has been cultivating diverse varieties of Basmati rice for centuries,and it is a traditional crop of the Indian subcontinent.

(C) In an $Urn$-shaped age pyramid,the number of individuals in the pre-reproductive age group is significantly lower than those in the reproductive age group.
This indicates a shrinking population base,which leads to a negative growth rate.
Therefore,the population trend is considered declining.

(D) Net primary productivity $(NPP)$ is the amount of biomass or energy stored by producers per unit area per unit time,after accounting for respiratory losses.
In general,productivity is highest in tropical regions due to abundant sunlight,high temperature,and sufficient rainfall,and lowest in polar or temperate regions.
The approximate mean $NPP$ values are:
$1.$ Temperate coniferous forest: $\approx 8 \text{ Tonnes/ha/year}$
$2.$ Temperate deciduous forest: $\approx 12 \text{ Tonnes/ha/year}$
$3.$ Tropical deciduous forest: $\approx 15 \text{ Tonnes/ha/year}$
$4.$ Tropical rain forest: $\approx 22 \text{ Tonnes/ha/year}$
Therefore,the increasing order is $B < D < A < C$.

(A) In a food chain, energy is transferred from one trophic level to the next. According to the $10\%$ law of energy transfer, only about $10\%$ of the energy available at one trophic level is transferred to the next higher level.
Due to this significant loss of energy, the amount of biomass and the number of organisms that can be supported decreases as we move to higher trophic levels.
Therefore, the Assertion is correct because higher trophic levels have fewer organisms.
The Reason is also correct because the population size at any trophic level is limited by the energy and food supply provided by the lower trophic level.
Since the limitation of food/energy at lower levels directly causes the reduction in the number of individuals at higher levels, the Reason is the correct explanation of the Assertion.

(C) Communities with a higher number of species are more stable as they can resist occasional disturbances.
According to David Tilman's long-term ecosystem experiments,plots with more species showed less year-to-year variation in total biomass.
Therefore,the Assertion is correct,but the Reason provided is scientifically inaccurate because higher species diversity leads to less variation in total biomass,not just 'animal' variation.

(A) The Government of India,through a new auto fuel policy,has laid out a roadmap to cut down vehicular pollution in Indian cities.
According to the Euro $II$ norms,sulphur content must be controlled at $350\, ppm$ in diesel and $150\, ppm$ in petrol to reduce harmful emissions.

(C) Eutrophication is a natural process that literally means 'well-nourished' or 'enriched'.
It is a natural state in many lakes and ponds that have a rich supply of nutrients.
Eutrophication becomes excessive when abnormally high amounts of nutrients from sewage,fertilizers,animal waste,and detergents enter streams and lakes,causing excessive growth or blooms of microorganisms.
With increasing eutrophication,the diversity of the phytoplankton community of a lake decreases,not increases,because the lake eventually becomes dominated by a few species of blue-green algae,leading to a loss of overall biodiversity.