AIIMS 2010 Biology Question Paper with Answer and Solution

(C) $Viroid$ is a small infective segment of nucleic acid,usually $RNA$,which lacks a protein coat.
$Prions$ are infectious pathogenic agents composed mainly of proteins and are devoid of nucleic acid.
$Mycoplasmas$ are the smallest known living cells and they completely lack a cell wall.
$Rickettsiae$ are bacteria that possess a cell wall.

(B) The bacterial cell wall is made of peptidoglycan (also known as murein).
The oligosaccharide backbone of peptidoglycan consists of long,linear chains of alternating $N$-acetylglucosamine $(NAG)$ and $N$-acetylmuramic acid $(NAM)$ residues.
These sugar residues are covalently linked to each other by $\beta \,(1-4)$ glycosidic linkages.
Therefore,option $B$ is the correct description.

(A) The statement 'All echinoderms are viviparous' is incorrect because animals belonging to the phylum $Echinodermata$ are oviparous,meaning they lay eggs.
Roundworms $(Aschelminthes)$ lack a circulatory system.
Bony fishes $(Osteichthyes)$ typically possess a swim bladder (air bladder) which helps in buoyancy.
Cartilaginous fishes $(Chondrichthyes)$ undergo internal fertilization.

(A) Ticks and mites belong to the class $Arachnida$ within the phylum $Arthropoda$. Other members of this class include scorpions and spiders,which are characterized by having four pairs of walking legs and lacking antennae.

(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.

(C) The $Fabaceae$ family is characterized by a monocarpellary,unilocular ovary containing one or more ovules.
Therefore,the Assertion is correct.
In $Fabaceae$,the placentation is marginal,not parietal.
Parietal placentation is characteristic of families like $Brassicaceae$.
Since the Reason states that placentation is parietal,the Reason is incorrect.
Thus,the correct option is $C$.

(A) Vessels are more efficient for water conduction compared to tracheids because they form long,continuous,tube-like structures with perforated end walls,which offer less resistance to water flow.
Tracheids are individual,elongated cells with tapered ends,whereas vessels are composed of a vertical row of cylindrical cells with dissolved end walls.
Both vessels and tracheids are dead and lignified at maturity,which provides structural support and facilitates water transport.
Since the Reason correctly describes a characteristic of vessels that contributes to their function,it is a correct explanation of the Assertion.

(B) In the Michaelis-Menten enzyme kinetics model,the reaction is represented as $E+S \underset{K_2}{\stackrel{K_1}{\rightleftharpoons}} E S \xrightarrow{K_3} E+P$
Here,$K_1$ is the rate constant for the formation of the enzyme-substrate complex,$K_2$ is the rate constant for the dissociation of the complex back into enzyme and substrate,and $K_3$ (often denoted as $k_{cat}$) is the rate constant for the formation of the product.
The Michaelis constant $K_m$ is defined as the substrate concentration at which the reaction rate is half of the maximum velocity $(V_{max})$.
Mathematically,it is expressed as $K_m = \frac{K_2 + K_3}{K_1}$.

(B) Alpha-keratin is a fibrous structural protein. It is found in high concentrations in the skin and epidermal appendages such as hair,nails,and horns in vertebrates.

(C) Starch is the reserve food material in plant cells,whereas cellulose is the most important structural component of the cell wall of plants.
Both starch and cellulose are polymers of glucose.
Starch is a branched polymer of $\alpha-D$-glucose units linked by $\alpha-1,4$-glycosidic bonds (and $\alpha-1,6$-glycosidic bonds at branching points).
Cellulose is a linear polymer of $\beta-D$-glucose units connected through $\beta-1,4$-glycosidic bonds.
Unlike starch,cellulose is insoluble in ordinary solvents and does not give any colour with iodine.

(D) Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. Non-essential amino acids are those that the body can synthesize on its own.
Glycine,serine,and tyrosine are classified as non-essential amino acids because the human body is capable of synthesizing them.
Therefore,the Assertion is incorrect because these amino acids do not need to be compulsorily included in the diet.
The Reason is a correct statement regarding the definition of essential amino acids.
Since the Assertion is incorrect and the Reason is correct,the correct option is $D$.

(C) Unsaturated fats contain one or more carbon-carbon double bonds $(C=C)$ in their fatty acid chains,which makes them more chemically reactive compared to saturated fats that contain only single bonds $(C-C)$.
Since unsaturated fats possess double bonds,they are more reactive.
The Reason statement claims that unsaturated fats have only single bonds,which is scientifically incorrect because they are defined by the presence of at least one double bond.
Therefore,the Assertion is correct,but the Reason is incorrect.

(A) Meiosis $II$ is known as equational or homotypic division because it resembles mitosis.
In this process,the sister chromatids separate,and the number of chromosomes in the resulting daughter cells remains the same as that in the parent cell that entered meiosis $II$.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why it is called an equational division.

(A) The $Na^+ - K^+$ pump is an active transport mechanism that maintains the electrochemical gradient across the cell membrane.
During one cycle of this pump,$3Na^+$ ions are transported out of the cell,and $2K^+$ ions are transported into the cell.
This process requires energy in the form of $ATP$ to move these ions against their respective concentration gradients.

(A) $Amaranthus$ $sp.$ and sugarcane are $C_4$ plants,which are also known as Hatch and Slack plants because they follow the Hatch-Slack pathway (or $C_4$ cycle).
In the $C_4$ cycle,the fixation of $CO_2$ occurs twice. To produce one molecule of glucose $(C_6H_{12}O_6)$,$6$ molecules of $CO_2$ must be fixed through the Calvin cycle,which is integrated with the $C_4$ pathway. Thus,the statement that one glucose is formed by the fixation of $6 \,CO_2$ is correct.

(A) $D.C.M.U.$ (Dichlorophenyl dimethyl urea) is a potent herbicide that acts as a photosynthetic inhibitor.
It specifically blocks the electron flow from Photosystem $II$ $(PSII)$ to plastoquinone by binding to the $Q_B$ binding site.
Because the electron transport chain is blocked,the photolysis of water (which requires a continuous supply of electrons to the oxidized $P_{680}$ reaction center) is also inhibited.
Therefore,both the Assertion and the Reason are correct,and the Reason provides a correct explanation for the Assertion.

(C) The enzyme $Pyruvate \ kinase$ catalyzes the third and final irreversible step of glycolysis.
In this reaction,$Phosphoenolpyruvate$ $(PEP)$ is converted into $Pyruvic \ acid$ with the production of $ATP$.
The reaction is as follows:
$Phosphoenolpyruvate + ADP \xrightarrow{Pyruvate \ kinase, Mg^{2+}, K^+} Pyruvic \ acid + ATP$

(C) Xerophthalmia is a condition caused by a severe deficiency of Vitamin $A$.
In India,Vitamin $A$ deficiency is a major public health concern,particularly among children in lower socioeconomic groups who lack access to a balanced diet rich in fruits and vegetables.
It is considered a top priority for remedial action because it can lead to permanent blindness if left untreated.

(D) The normal human body temperature is $37\,^{\circ}C$.
To convert temperature from Celsius to Kelvin,we use the formula: $T(K) = T(^{\circ}C) + 273.15$.
Using the standard approximation of $273$,the calculation is: $37 + 273 = 310\,K$.
Therefore,the normal body temperature on the Kelvin scale is $310\,K$.

(C) Pancreatic amylase is a carbohydrate-digesting enzyme (amylolytic enzyme) that hydrolyzes starch and glycogen into maltose,isomaltose,and limit dextrins.
Proteins are digested by proteolytic enzymes such as trypsin,chymotrypsin,and carboxypeptidase,not by amylase.
Therefore,the Assertion is correct,but the Reason is incorrect.

(C) Oxyhaemoglobin is the form of haemoglobin that has bound to oxygen.
During the transport of carbon dioxide,haemoglobin also plays a role by binding to $CO_2$ to form carbaminohaemoglobin.
Under normal physiological conditions,every $100\, ml$ of oxygenated blood can deliver about $5\, ml$ of $O_2$ to the tissues,while every $100\, ml$ of deoxygenated blood delivers approximately $4\, ml$ of $CO_2$ to the alveoli.
Specifically,oxyhaemoglobin facilitates the transport of approximately $3\, ml$ of $CO_2$ per $100\, ml$ of blood.

(A) The Bohr effect describes how an increase in $CO_2$ concentration and a decrease in $pH$ (increase in $H^+$ ions) shift the oxygen-haemoglobin dissociation curve to the right,thereby reducing the affinity of haemoglobin for oxygen.
Near the organ tissues,the partial pressure of $CO_2$ is high and the partial pressure of $O_2$ is low. This environment promotes the dissociation of oxyhaemoglobin,allowing oxygen to be released into the tissues.
Since the Reason directly explains the mechanism (reduced affinity due to high $CO_2$) that causes the phenomenon described in the Assertion,the Reason is the correct explanation of the Assertion.

(C) Coronary arteries are the specialized vessels that supply oxygenated blood to the heart muscle (myocardium) itself.
Carotid arteries are responsible for supplying blood to the head and neck region.
Hepatic arteries supply oxygenated blood to the liver.
Pulmonary arteries carry deoxygenated blood from the heart to the lungs for oxygenation.

(B) Individuals with blood group $O, Rh^-$ are known as universal donors.
This is because their red blood cells lack both $A$ and $B$ antigens,and they also lack the $Rh$ antigen.
Consequently,their blood does not trigger an immune response (agglutination) when transfused into recipients of any other blood group.
Therefore,in emergency situations where the patient's blood group is unknown,$O, Rh^-$ blood is the safest choice for transfusion.
Thus,option $B$ is correct.

(D) In human blood,the count of blood platelets is approximately $1.5$ to $3.5$ lakhs per cubic mm,whereas the count of $WBCs$ is approximately $6000$ to $8000$ per cubic mm. Therefore,the blood has significantly more platelets than $WBCs$.
Veins and arteries are both types of blood vessels. Arteries carry blood away from the heart,while veins return blood to the heart. At any given time,the volume of blood in the venous system is generally higher than in the arterial system.
Blood consists of two main parts: Plasma,which constitutes about $55-60\%$ of the total blood volume,and the formed elements (cells),which constitute about $40-45\%$ of the total blood volume.
$WBCs$ are primarily produced in the red bone marrow,though some types are also produced in lymph nodes,the spleen,and the thymus.

(A) $Prothrombinase$ is a complex enzyme formed during the blood clotting process that converts $prothrombin$ into $thrombin$.
It functions as an antiheparin because it neutralizes the anticoagulant effect of $heparin$.
$Heparin$ is a naturally occurring anticoagulant produced by the liver and mast cells that prevents the clotting of blood within the intact blood vessels.
Since the $Prothrombinase$ enzyme neutralizes $heparin$ to allow the clotting cascade to proceed,the Reason correctly explains why the enzyme acts as an antiheparin.

(A) Veins are known as capacitance vessels because they contain a large volume of blood (about $60-70\%$ of the total blood volume) at any given time.
When blood pressure drops due to a decrease in blood volume (e.g.,hemorrhage),the sympathetic nervous system triggers vasoconstriction of the veins.
This constriction reduces the capacity of the venous system,forcing the stored blood to move toward the heart and into the arterial system.
This mechanism helps to maintain venous return and blood pressure,making the Reason a correct explanation for the Assertion.

(C) Ultrafiltration occurs in the renal corpuscle of the nephron. It is driven by the effective filtration pressure $(EFP)$.
During this process,blood is filtered through the glomerular capillary wall,the basement membrane,and the podocytes of Bowman's capsule.
The resulting glomerular filtrate is essentially protein-free and lacks blood corpuscles.
Therefore,the statement that the filtered fluid contains proteins and blood corpuscles is incorrect.
Thus,the Assertion is correct,but the Reason is incorrect.

(D) During prolonged strenuous physical work,the demand for $ATP$ in muscle cells increases significantly. When the oxygen supply is insufficient to meet this demand through aerobic respiration,muscle cells switch to anaerobic respiration. In this process,glucose is broken down into lactic acid. The accumulation of lactic acid in the muscle tissue leads to a decrease in $pH$ and interferes with muscle contraction,resulting in the sensation of fatigue.

(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.

(B) The blood glucose level in the human body is clinically measured and commonly expressed in units of $mg/dL$ (milligram per decilitre). This unit represents the concentration of glucose present in a specific volume of blood plasma.

(A) The thyroid gland secretes a hormone known as thyroxine $(T_4)$.
Thyroxine is an iodinated derivative of the amino acid tyrosine,meaning it contains iodine atoms in its structure.
Iodine is essential for the synthesis of thyroid hormones.
$A$ deficiency of iodine in the diet leads to a decrease in the production of thyroxine,which can cause the thyroid gland to enlarge,a condition known as goitre.

(D) The pituitary gland acts as the master gland,regulating most other endocrine glands through its tropic hormones.
However,the parathyroid gland functions independently of the pituitary gland.
It secretes parathormone $(PTH)$,which regulates the levels of $Ca^{2+}$ and $PO_4^{3-}$ ions in the blood based on the body's calcium requirements,rather than being controlled by pituitary secretions.

(C) The correct matching is as follows:
$A$. Gonads secrete sex hormones like Progesterone $(II)$.
$B$. Pituitary gland secretes Growth hormone $(III)$.
$C$. Pancreas secretes Insulin $(I)$.
$D$. Adrenal gland secretes Cortisone $(IV)$.
Therefore, the correct sequence is $A-II, B-III, C-I, D-IV$.

(C) Vasopressin,also known as Antidiuretic Hormone $(ADH)$,is secreted by the posterior pituitary gland.
Diabetes insipidus is a disorder caused by the deficiency (hyposecretion) of vasopressin,not its excess.
Due to the lack of $ADH$,the kidneys are unable to reabsorb water effectively,leading to the excretion of large volumes of dilute urine (polyuria).
This excessive loss of water leads to dehydration,which causes the person to feel extremely thirsty (polydipsia).
Therefore,the Assertion is correct,but the Reason is incorrect.

(C) $Phytotron$ is a specialized growth chamber or facility designed to allow researchers to grow plants under strictly controlled environmental conditions,such as temperature,humidity,light intensity,and photoperiod. This allows for the study of plant responses to specific environmental factors.

(A) In a bisexual flower,if the androecium (male reproductive part) and gynoecium (female reproductive part) mature at different times,this condition is known as dichogamy. This mechanism prevents self-pollination and promotes cross-pollination. Dichogamy can be further classified into protandry (anthers mature first) and protogyny (stigma matures first).

(A) The fat present below the skin surface is known as subcutaneous fat.
It acts as an insulator for the body,which helps in preventing the loss of heat from the body to the external environment,thereby maintaining body temperature.

(A) The average fat content in buffalo milk is approximately $7.2\%$.
This value is significantly higher than the fat content found in human milk or cow milk.
In contrast,human milk contains a higher concentration of lactose compared to both cow and buffalo milk.

(A) Fish is considered a healthy food source because it is rich in polyunsaturated fatty acids (PUFAs),specifically Omega-$3$ fatty acids. These fatty acids are beneficial for cardiovascular health as they help in reducing cholesterol levels and act as natural antioxidants,unlike the saturated fats commonly found in the flesh of many land animals.

(A) Endoscopy is a medical procedure that uses an instrument called an endoscope to examine the interior of a hollow organ or body cavity.
An endoscope consists of a bundle of optical fibers.
These optical fibers work on the principle of total internal reflection of light.
When light enters the fiber at an appropriate angle,it undergoes multiple total internal reflections,allowing the light to travel through the fiber without significant loss of intensity,even if the fiber is bent.
Therefore,the correct phenomenon is total internal reflection.

(A) Lathyrism is a neurological disease characterized by paralysis of the lower limbs.
It is caused by the excessive consumption of khesari dal $(Lathyrus \text{ } sativus)$,which contains a toxic amino acid known as $\beta$-$ODAP$ ($\beta$-$N$-oxalylamino-$L$-alanine).

(B) Corpus luteum is a yellow-coloured mass of cells found in the ovary.
It is formed from the ruptured follicle after ovulation.
Corpus luteum secretes the hormone progesterone, which is essential for maintaining pregnancy; therefore, it is also known as the "pregnancy hormone."

(B) Pleiotropy is the genetic phenomenon in which a single gene influences two or more seemingly unrelated phenotypic traits.
Apomixis is a form of asexual reproduction in plants that mimics sexual reproduction but occurs without fertilization.
Polyploidy refers to a condition where an organism possesses more than two complete sets of chromosomes.
Polyteny refers to the condition of having giant chromosomes,known as polytene chromosomes,formed by repeated $DNA$ replication without cell division.

(A) In incomplete linkage,genes located on the same chromosome do not always stay together during inheritance.
Crossing over occurs between non-sister chromatids of homologous chromosomes during meiosis,which leads to the exchange of genetic material.
This process separates the linked genes,resulting in the formation of new gene combinations (recombinants) in addition to the parental combinations.
Therefore,the Reason correctly explains why incomplete linkage results in new combinations.

(A) The $TATA$ box,also known as the $Goldberg-Hogness$ box,is a $DNA$ sequence found in the promoter region of genes in eukaryotes and archaea.
It is typically located approximately $25$ base pairs $(bp)$ upstream of the transcription start site.
This sequence serves as the binding site for transcription factors and $RNA$ polymerase $II$,playing a crucial role in the initiation of transcription.

(C) In a $DNA$ molecule,the nitrogenous bases are held together by hydrogen bonds.
$A$ (Adenine) pairs with $T$ (Thymine) via two hydrogen bonds,while $G$ (Guanine) pairs with $C$ (Cytosine) via three hydrogen bonds.
Because $G-C$ pairs have three hydrogen bonds,they are more stable and require more energy to break compared to $A-T$ pairs,which have only two hydrogen bonds.
Therefore,$A-T$ rich regions melt at lower temperatures than $G-C$ rich regions.
The Assertion is correct,but the Reason is incorrect because it states the number of hydrogen bonds in reverse.

(D) Tuberculosis is caused by $Mycobacterium$ $tuberculosis$, and leprosy is caused by $Mycobacterium$ $leprae$. Both are bacterial infections. Rifampicin is a broad-spectrum antibiotic that is highly effective against both $Mycobacterium$ $tuberculosis$ and $Mycobacterium$ $leprae$, making it a standard drug used in the multi-drug therapy for both diseases.

(C) An antigen is a foreign substance that enters the body and triggers the immune system to produce specific antibodies.
These antibodies then neutralize the antigen through an antigen-antibody reaction,which is a fundamental mechanism of the body's adaptive immunity.

(B) $IgM$ is a pentameric immunoglobulin,meaning it consists of five monomeric units joined together by a $J$-chain.
It is the largest antibody and is the first immunoglobulin to be produced during the primary immune response to an antigen.
$IgG$ is a monomer,$IgA$ is typically a dimer in secretions,and $IgE$ and $IgD$ are monomers.

(A) $DNA$ fingerprinting is a highly sensitive technique that relies on the analysis of repetitive sequences in the genome known as Variable Number Tandem Repeats $(VNTRs)$.
Because these sequences are unique to every individual,they serve as a molecular signature.
Trace biological evidences such as hair follicles,saliva,and dried semen contain sufficient nucleated cells to extract $DNA$ for analysis.
Therefore,the ability to identify individuals from minute biological samples makes $DNA$ fingerprinting a powerful tool for forensic investigations,including paternity testing and criminal identification.
Both the Assertion and the Reason are correct,and the Reason provides the scientific basis for why $DNA$ fingerprinting is effective.

(A) $Bt-$ cotton is a transgenic crop. Transgenic plants are those plants which have a foreign gene incorporated into their $DNA$. This insect-resistant gene is derived from a bacterium, $Bacillus$ $thuringiensis$. The insertion of this specific gene allows the cotton plant to produce an insecticidal protein, making it resistant to pests. Therefore, the Reason correctly explains why the $Bt$ gene is used to produce insect-resistant cotton.

(A) Within biological communities,some species are crucial in determining the ability of a large number of other species to persist in the community. These species are known as $keystone$ species.
$Allopatric$ species are those that occupy mutually exclusive geographic areas.
$Sympatric$ species are those that inhabit the same or overlapping geographic areas.
$Threatened$ species are those likely to become endangered in the near future.

(D) In desert conditions,most of the activity of plants and animals occurs during the night due to the extremely high temperatures during the day.
As a result,desert insects are active and pollinate flowers at night.
To attract these nocturnal pollinators,most desert plants bloom during the night.

(B) The tree species in question is the Calvaria major (tambalacoque) tree.
It was found that the tree species failed to reproduce because of the extinction of the Dodo bird,which was native to Mauritius.
The Dodo bird played a crucial role in the germination of the seeds of this tree by passing them through its digestive tract,which helped in breaking the hard seed coat.
Following the extinction of the Dodo in the $17^{th}$ century due to over-exploitation by humans,the tree species also faced the threat of extinction.

(C) Biomagnification is the phenomenon of increasing concentration of a non-biodegradable compound in the tissues of organisms at successive trophic levels in a food chain,usually as a result of food intake.
In this process,the concentration of the pollutant increases as we move up the trophic levels.
The sequence of energy flow is: Producers $\to$ Primary consumers $\to$ Secondary consumers $\to$ Tertiary consumers $\to$ Top carnivores.
In the given options,the grasshopper is a primary consumer,the toad is a secondary consumer,the cattle is a primary consumer,and the snake acts as a tertiary consumer.
Since the snake occupies the highest trophic level among the given organisms,it will accumulate the highest concentration of $DDT$ due to biomagnification.