AIIMS 2011 Biology Question Paper with Answer and Solution

(A) The coralloid roots of $Cycas$ contain a specialized region known as the algal zone.
This zone is inhabited by symbiotic blue-green algae (cyanobacteria),such as $Anabaena$ and $Nostoc$.
This is a mutualistic relationship where the algae receive shelter and nutrients from the $Cycas$ plant,while the $Cycas$ plant benefits from the nitrogen-fixing capabilities of the algae.

(C) Nymphaea,Sagittaria,Ceratophyllum,and Vallisneria are hydrophytes that grow in water.
Nymphaea,Sagittaria,and Vallisneria are rooted hydrophytes,meaning they are anchored in the mud.
Ceratophyllum is a submerged,free-floating hydrophyte.
It remains completely underwater but is not rooted in the mud.
Ceratophyllum lacks roots even during its embryonic stage.

(A) Red algae,specifically members of the order $Corallinales$,are known as coralline algae.
These algae secrete and deposit calcium carbonate $(CaCO_3)$ in their cell walls,which makes them hard and stony.
These calcareous deposits contribute significantly to the formation of coral reefs and limestone deposits in marine environments.
Therefore,the Reason correctly explains why red algae contribute to the production of coral reefs.

(B) The peristome is a specialized structure consisting of a fringe of teeth-like projections located at the mouth of the capsule in mosses.
These teeth help in the gradual dispersal of spores.
Peristome teeth are classified into two main types based on their structure:
$1$. Nematodontous: These are solid structures composed of bundles of dead cells. Examples include $Polytrichum$,$Pogonatum$,and $Tetraphis$.
$2$. Orthodontous: These are composed of thin,membranous,transversely barred teeth,formed by the thickened portions of the cell walls of adjacent cells.
Since both the definition of the peristome and its classification are correct,the Assertion and Reason are both true,but the Reason does not explain why the peristome is a fringe of teeth-like projections.

(A) In isobilateral leaves,the upper epidermis contains specialized cells known as bulliform or motor cells.
These cells are large,empty,and colorless,and they are capable of storing water.
When the plant has sufficient water,these cells become turgid,which helps in the unrolling of the leaf.
Conversely,during water stress,these cells lose water and become flaccid,causing the leaf to roll inward to minimize water loss.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why bulliform cells are involved in the movement of the leaf.

(C) Non-essential amino acids are those amino acids that do not need to be supplied in the diet because they can be synthesized by the human body,typically from carbohydrate metabolites.
Glycine is a non-essential amino acid because the body can synthesize it.
Essential amino acids are those that cannot be synthesized by the body and must be obtained through the diet.
Since the Assertion states that glycine is non-essential,it is correct.
However,the Reason states that it cannot be synthesized in the body,which is the definition of an essential amino acid,making the Reason incorrect.
Therefore,the Assertion is correct but the Reason is incorrect.

(D) Many cells,such as animal cells,function properly and undergo mitotic division even in the absence of plastids. Plastids are organelles found primarily in plant cells and algae,responsible for photosynthesis and storage,but they are not essential for the basic cellular processes of metabolism or mitosis in all cell types.

(B) Essential elements are classified into macronutrients and micronutrients based on the quantity required by plants.
Micronutrients (trace elements) are required in very small amounts (less than $10 \text{ mmol kg}^{-1}$ of dry matter).
The micronutrients include Iron $(Fe)$, Manganese $(Mn)$, Copper $(Cu)$, Molybdenum $(Mo)$, Zinc $(Zn)$, Boron $(B)$, Chlorine $(Cl)$, and Nickel $(Ni)$.
Macronutrients are required in larger amounts and include Carbon $(C)$, Hydrogen $(H)$, Oxygen $(O)$, Nitrogen $(N)$, Phosphorus $(P)$, Sulfur $(S)$, Potassium $(K)$, Calcium $(Ca)$, and Magnesium $(Mg)$.
Option $B$ contains $Cu, Fe, Zn, B, Mn$, all of which are micronutrients.

(D) Glycolysis is the process of the breakdown of glucose to pyruvic acid.
In this process,one molecule of glucose $(C_6H_{12}O_6)$ undergoes partial oxidation through a series of ten enzyme-catalyzed reactions to form $2$ molecules of pyruvic acid $(CH_3COCOOH)$.

(C) Option $C$ is the incorrect statement. The addition of sodium bicarbonate $(NaHCO_3)$ to water provides a source of $CO_2$,which actually enhances the rate of photosynthesis in aquatic plants like $Vallisneria$,rather than retarding it.
$A$ is correct: The $C_4$ pathway was indeed discovered by Hatch and Slack.
$B$ is correct: $CO_2$ is a fundamental substrate required for the Calvin cycle in photosynthesis.
$D$ is correct: Phloem tissue is responsible for the translocation of organic solutes (sugars) from source to sink.

(D) The thylakoid membranes are differentiated into two regions: grana lamellae and stroma lamellae.
The grana lamellae (or grana stacks) are rich in $PS\, II$ and $LHC$ (Light Harvesting Complex),but they contain very little $ATP$ synthetase.
In contrast,the stroma lamellae (stromal thylakoids) are rich in $PS\, I$ and $ATP$ synthetase,but they are poor in $PS\, II$ and $LHC$.
Since the Assertion states that stromal thylakoids are rich in both $PS\, I$ and $PS\, II$,the Assertion is incorrect because they are poor in $PS\, II$.
The Reason states that stroma membranes are rich in $ATP$ synthetase,which is correct.
Therefore,the Assertion is incorrect,but the Reason is correct.

(A) Cytokinins promote cell division and inhibit the degradative processes in detached leaves,thereby delaying senescence in intact leaves. The phenomenon of cytokinin-induced retardation of aging is known as the $Richmond-Lang$ Effect.

(A) Trypsin is a protein-digesting enzyme present in the intestine of animals.
In predator animals that consume the blood of their prey,trypsin hydrolyzes the $fibrinogen$ present in the blood into $fibrin$.
This process leads to blood coagulation,which facilitates the digestion of blood proteins.
Therefore,both the Assertion and the Reason are correct,and the Reason is the correct explanation of the Assertion.

(D) The Assertion is incorrect because bile does not contain lipases; it contains bile salts which are responsible for the emulsification of fats.
Bile salts are steroids secreted by the liver into the bile. In the intestinal lumen,they reduce the surface tension of fat droplets,causing their breakdown into many smaller ones,thereby forming a stable fine emulsion.
The Reason is also incorrect because lipases are enzymes that hydrolyze fats and oils into fatty acids and glycerol,not agents that perform physical emulsification. Lipases can only digest fat efficiently after bile salts have broken large fat droplets into tiny droplets (emulsification). Thus,both the Assertion and the Reason are incorrect.

(A) Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. Cigarette smoking is a major cause of this. In this disease,many alveoli coalesce together to form large chambers due to the destruction of their walls. This reduces the surface area available for gas exchange. Therefore,option $A$ is correct. Pneumonia is an infection of the lungs,not an occupational disease. Silicosis is an occupational respiratory disorder caused by the inhalation of silica dust. Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.

(A) Mammalian skin is thick and keratinized,making it impermeable to gases,which helps in preventing water loss.
Because mammals have high metabolic rates,they require a significantly higher amount of oxygen compared to lower animals.
Since cutaneous respiration (skin breathing) is insufficient to meet these high oxygen demands,mammals have evolved a complex respiratory system consisting of the nasal cavity,nasopharynx,larynx,trachea,bronchi,bronchioles,and lungs to provide a large surface area for gas exchange.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why a complex respiratory system is necessary in mammals.

(C) The $Spleen$ is referred to as the blood bank of the body because it stores red blood cells and platelets.
It acts as a reservoir for blood and releases these cells into the bloodstream when the body requires them, such as during conditions of hemorrhage, shock, or intense physical activity.

(B) The normal fasting blood glucose level in a healthy adult is approximately $70-110\, mg/100\, ml$ (or $mg/dl$).
Option $B$ provides the range $70-100\, mg/100\, ml$, which is clinically accepted as the normal fasting blood sugar range.
Total blood volume in a normal adult human is typically $5-6\, litres$.
Blood is a fluid connective tissue consisting of formed elements (corpuscles) suspended in plasma.
It is mesodermal in origin and slightly alkaline with a $pH$ of $7.3-7.4$.

(D) Vasopressin,also known as anti-diuretic hormone $(ADH)$,reduces the volume of urine by increasing the reabsorption of water from the distal convoluted tubules,collecting tubules,and collecting ducts in the kidney.
Failure of $ADH$ secretion leads to diabetes insipidus,which is characterized by the production of large amounts of dilute urine,not diabetes mellitus.
Diabetes mellitus is caused by the deficiency or failure of insulin hormone secretion from the pancreatic islets,leading to high blood glucose levels and the presence of glucose in the urine.
Therefore,the Assertion is incorrect because the condition caused by $ADH$ deficiency is diabetes insipidus,not diabetes mellitus.
The Reason is also incorrect because $ADH$ decreases the volume of urine by increasing water reabsorption,rather than increasing the volume of urine.

(D) Coconut water is a rich source of cytokinin.
Cytokinins are plant hormones that promote cell division (cytokinesis) and are typically found in areas of rapid growth and dividing tissues.
Because of this property,coconut water is widely used as a supplement in plant tissue culture media to stimulate cell division and growth.
Coconut water is essentially the liquid endosperm of the coconut seed.

(B) Tectonics is the study of the structure and evolution of the earth's crust. It is based on the theory that the earth's lithosphere is divided into several large and small tectonic plates that move over the underlying mantle.

(C) Sweet clover,when spoilt,contains a compound called dicumarol.
Dicumarol acts as an anticoagulant by inhibiting the synthesis of vitamin $K$-dependent clotting factors in the liver.
As a result,cattle consuming this hay may experience a functional deficiency of vitamin $K$,leading to an inability of the blood to clot properly,which causes prolonged and potentially fatal bleeding.

(B) Leydig cells,also known as interstitial cells,are located in the interstitial spaces between the seminiferous tubules of the testes in mammals.
These cells are responsible for the synthesis and secretion of testicular hormones called androgens,primarily testosterone.
Testosterone plays a crucial role in the development of secondary sexual characteristics in males and the regulation of spermatogenesis.
Since the rabbit is a mammal,Leydig cells are present in its testes.

(C) Meroblastic cleavage is a type of cleavage where the division of the egg is incomplete or partial. This occurs in eggs with a large amount of yolk,such as those of birds and reptiles,where the cleavage furrow does not penetrate the entire egg cytoplasm.

(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.

(C) Aneuploidy is the gain or loss of one or more chromosomes. It is classified as hypoploidy (loss of chromosomes) or hyperploidy (gain of chromosomes).
Monosomy is represented as $(2n - 1)$,which means the loss of a single chromosome,not a pair of chromosomes.
Therefore,the Assertion is correct,but the Reason is incorrect.

(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) Wings of pigeons (birds),mosquitoes (insects),and bats (mammals) are analogous organs,meaning they perform the same function (flight) but have different anatomical structures and embryonic origins.
This similarity in function,which has developed in distantly related groups,is an adaptation to the same environmental pressure (the need for flight).
Therefore,this phenomenon is known as analogy or convergent evolution.

(D) Opium is a narcotic substance obtained from the dried latex of the immature seed pods of the opium poppy plant,$Papaver \text{ } somniferum$.
It contains various alkaloids,with morphine being the most abundant,accounting for approximately $10\%-16\%$ of the total alkaloid content.
Opium and its derivatives are known for their potent analgesic properties but carry significant risks of addiction and harmful side effects,including respiratory depression,lung edema,coma,and potential cardiac or respiratory failure.

(A) Oncoviruses are cancer-causing viruses that can be either $DNA$ or $RNA$ viruses.
Examples include the Epstein-Barr virus,Hepatitis $B$ virus,and Human Papillomavirus.
These viruses contain oncogenes or stimulate the host cell's genes to promote uncontrolled cell division,leading to the development of cancerous tumors.
Therefore,the Epstein-Barr virus is classified as an oncovirus because it promotes the growth of cancer.

(A) Usually,a person shows symptoms of $HIV$ infection within $2$ to $6$ weeks of exposure to the virus.
But in some persons,the virus may remain silent for long periods (up to $10$ years) before symptoms of full-blown $AIDS$ are observable.
The symptoms of $HIV$ infection include fever,lethargy,pharyngitis,nausea,headache,rashes,etc.
Persons suffering from $AIDS$ have a weakened immune system due to the depletion of $T$-helper cells.
Such persons show opportunistic infections,i.e.,infections by those fungi,bacteria,and viruses to which a person with a normal immune system is expected to be resistant.
Therefore,persons prone to opportunistic infections may be suspected to be infected by $HIV$,particularly if the count of $T$-helper cells is $200/\,ml$ or lower.
Since the depletion of $T$-helper cells directly leads to a weakened immune system,which in turn makes the body susceptible to opportunistic infections,the Reason correctly explains the Assertion.

(C) Essential oils are volatile,concentrated plant extracts that contain the characteristic aromatic compounds of the plant. They are primarily used in the production of perfumes,fragrances,and aromatherapy due to their strong,pleasant,and distinct aromatic properties.

(C) The Assertion is correct because $Saccharomyces \text{ } cerevisiae$ (brewer's yeast) is widely used in the baking industry to ferment sugars in the dough.
The Reason is incorrect because the rising of the bread dough is caused by the entrapment of $CO_2$ gas bubbles produced during fermentation, not by thermal expansion. Thermal expansion would only occur during the actual baking process in the oven, whereas the 'rising' of the dough occurs primarily due to the accumulation of gas.

(C) food web is a complex network of interconnected food chains within an ecosystem,representing the various pathways through which energy and nutrients flow.
In a food web,organisms occupy different trophic levels,such as producers,primary consumers,secondary consumers,and tertiary consumers.
Since a kite is a bird of prey (a secondary or tertiary consumer),it feeds on various organisms like small mammals,reptiles,or insects,making it an integral part of multiple food chains within a food web.
Therefore,the Assertion is correct,but the Reason is incorrect.

(D) The pyramid of energy is always upright because energy flow in an ecosystem is unidirectional and follows the $10\%$ law.
According to the $10\%$ law proposed by Lindemann,only $10\%$ of the energy available at one trophic level is transferred to the next trophic level.
Since energy is lost as heat at each step,it is impossible for the pyramid of energy to be inverted.
Therefore,both the Assertion (which claims it can be inverted) and the Reason (which claims $20\%$ transfer) are incorrect.

(A) Option $A$ is correct because $DDT$ (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant that is non-biodegradable and accumulates in the food chain.
Excess fluoride in drinking water causes fluorosis, which leads to the hardening of bones and stiffness of joints, not osteoporosis.
Black foot disease is caused by chronic exposure to arsenic in drinking water.
"Itai-Itai" disease is caused by cadmium poisoning, not methylmercury.