AIPMT 2005 Biology Question Paper with Answer and Solution

(B) is the correct answer because gene flow is a fundamental characteristic of a species.
Gene flow refers to the transfer of genetic material from one population to another through the movement of individuals or their gametes/propagules (e.g.,spores,seeds).
This process ensures that all populations of a given species share a common gene pool,which helps maintain genetic homogeneity and reduces differences between populations.
Therefore,the statement that gene flow does not occur between populations of a species is false.
In contrast,reproductive isolation (Option $C$) is a key criterion for defining a species,and interbreeding (Option $A$) and variations (Option $D$) are standard biological characteristics of species members.

(A) The cranial nerves are classified based on their function as sensory,motor,or mixed.
$I$ (Olfactory),$II$ (Optic),and $VIII$ (Vestibulocochlear) are purely sensory nerves.
$III$ (Oculomotor),$IV$ (Trochlear),$VI$ (Abducens),$XI$ (Accessory),and $XII$ (Hypoglossal) are motor nerves.
$V$ (Trigeminal),$VII$ (Facial),$IX$ (Glossopharyngeal),and $X$ (Vagus) are mixed nerves.
Since $II$ (Optic nerve) is a sensory nerve,it is not a motor nerve.

(C) Barophilic prokaryotes,also known as piezophiles,are organisms that thrive at high atmospheric pressures.
These organisms are typically found in deep-sea environments,such as deep-sea sediments or hydrothermal vents,where the pressure is significantly higher than at the surface.
They have evolved specialized cellular structures and metabolic pathways to function optimally under these extreme pressure conditions.
Therefore,the correct description is that they grow and multiply in deep sea sediments.

(A) The presence of two types of nuclei,a large macronucleus and a small micronucleus,is a characteristic feature of the phylum $Ciliophora$ (ciliates).
$Paramecium$,$Vorticella$,$Nyctotherus$,and $Balantidium$ are all examples of ciliates.
However,among the given options,$Paramecium$ and $Vorticella$ are the most classic examples of organisms exhibiting nuclear dimorphism (macronucleus and micronucleus).
Therefore,the correct option is $A$.

(C) Auxospores are specialized cells produced by certain diatoms to restore their normal size after repeated asexual divisions lead to a reduction in cell size.
Hormocysts are thick-walled, resting structures produced by many cyanobacteria (such as $Westiellopsis$ and $Hapalosiphon$) under unfavorable conditions to survive and propagate.
Therefore, auxospores are produced by certain diatoms and hormocysts are produced by many cyanobacteria.

(A) The correct matching is as follows:
$(a)$ Peritrichous flagellation: Found in bacteria like $Escherichia \ coli$ ($E$. coli),where flagella are distributed over the entire surface of the cell. Thus,$(a-3)$.
$(b)$ Living fossil: $Ginkgo \ biloba$ is a classic example of a living fossil among gymnosperms. Thus,$(b-1)$.
$(c)$ Rhizophore: $A$ specialized structure found in the pteridophyte $Selaginella$ that produces roots. Thus,$(c-4)$.
$(d)$ Smallest flowering plant: $Wolffia$ is known as the smallest angiosperm. Thus,$(d-5)$.
$(e)$ Largest perennial alga: $Macrocystis$ (a brown alga or kelp) can grow to massive sizes. Thus,$(e-2)$.
Therefore,the correct sequence is $a-3, b-1, c-4, d-5, e-2$.

(D) The correct answer is $D$.
Most animals of the phylum $Porifera$ are marine,but some species like $Spongilla$ are found in freshwater.
Therefore,the statement that 'animals of the phylum $Porifera$ are exclusively marine' is incorrect.
The other statements are correct:
$A$: Prawns belong to the phylum $Arthropoda$ and possess two pairs of antennae.
$B$: $Cnidoblasts$ (or $cnidocytes$) are a characteristic feature of the phylum $Cnidaria$.
$C$: In millipedes,each body segment bears two pairs of appendages.

(C) The organism $Paramecium$ exhibits nuclear dimorphism,meaning it possesses two types of nuclei:
$1$. $A$ large $macronucleus$ (vegetative nucleus) which controls metabolic and nutritional activities.
$2$. $A$ small $micronucleus$ (generative nucleus) which is involved in reproduction and genetic exchange during conjugation.
Therefore,the correct option is $C$.

(D) In woody dicot plants,secondary growth occurs in the stems and roots,leading to the formation of secondary tissues. However,the apical meristems,which are responsible for primary growth,are located at the shoot tips and root tips. These regions continuously produce primary tissues throughout the life of the plant. Therefore,the shoot tips and root tips are the parts that contain primary tissues.

(A) The resolution $(d)$ of a light microscope is determined by the formula $d = 0.61 \lambda / NA$,where $\lambda$ is the wavelength of light used and $NA$ is the numerical aperture of the objective lens.
To obtain the best resolution,the value of $d$ must be as small as possible.
Since $d$ is directly proportional to the wavelength $(\lambda)$,using light with the shortest wavelength will result in the smallest $d$,thereby providing the highest resolution.
Among the given options,blue light has the shortest wavelength (approximately $450-495 \ nm$) compared to green,yellow,and red light.
Therefore,blue light provides the best resolution.

(A) Chlorophyll is the primary photosynthetic pigment found in chloroplasts.
In higher plants,chloroplasts contain a system of thylakoids,which are flattened sac-like structures.
These thylakoids are stacked like coins to form structures called grana.
Chlorophyll molecules are embedded within the thylakoid membranes of the grana,where they capture light energy for the light-dependent reactions of photosynthesis.
Therefore,the correct location for chlorophyll is the grana.

(D) During prolonged fasting,the body exhausts its glycogen stores and begins to break down stored adipose tissue (fats) for energy.
This process leads to the production of fatty acids,which are metabolized in the liver into ketone bodies (such as acetoacetate,beta-hydroxybutyrate,and acetone).
As the concentration of these ketone bodies increases in the blood (ketosis),they are excreted through the urine,a condition known as ketonuria.
Therefore,the presence of abnormal amounts of ketones in the urine is a characteristic sign of prolonged fasting or starvation.

(A) The net filtration pressure $(NFP)$ is calculated by subtracting the opposing pressures from the glomerular hydrostatic pressure.
Glomerular hydrostatic pressure $(GHP)$ = $60 \, mm \, Hg$.
Blood colloidal osmotic pressure $(BCOP)$ = $30 \, mm \, Hg$.
Capsular hydrostatic pressure $(CHP)$ = $20 \, mm \, Hg$.
$NFP = GHP - (BCOP + CHP) = 60 - (30 + 20) = 60 - 50 = 10 \, mm \, Hg$.

(B) The $acromion$ process is a bony projection on the scapula (shoulder blade).
It articulates with the clavicle (collarbone) to form the acromioclavicular joint.
The scapula is a key component of the pectoral girdle (shoulder girdle) in mammals.
Therefore,the correct option is $B$.

(C) The autonomic nervous system $(ANS)$ controls involuntary visceral functions of the body.
$A$. Swallowing is a somatic reflex involving skeletal muscles.
$B$. Pupillary reflex is a cranial reflex.
$C$. Peristalsis is the involuntary contraction and relaxation of the muscles of the intestine,which is regulated by the autonomic nervous system.
$D$. Knee-jerk reflex is a spinal somatic reflex.

(B) In eukaryotic cells,$DNA$ replication occurs during the $S$ phase (Synthesis phase) of the cell cycle.
Since histone proteins are essential for packaging the newly synthesized $DNA$ into chromatin,their synthesis is tightly coupled with $DNA$ replication.
Therefore,the synthesis of histone proteins occurs primarily during the $S$ phase of the cell cycle.

(D) $C_4$ plants are highly efficient in photosynthesis because they possess a specialized mechanism to concentrate $CO_2$ around the enzyme Rubisco.
In $C_4$ plants,the primary fixation of $CO_2$ occurs in the mesophyll cells,where $PEP$ carboxylase $(PEPCase)$ acts as the primary carboxylating enzyme.
$PEPCase$ has a very high affinity for $CO_2$ and,unlike Rubisco,it does not show oxygenase activity.
This enzyme fixes $CO_2$ into a four-carbon compound (oxaloacetate),which is then transported to the bundle sheath cells.
In the bundle sheath cells,this compound is decarboxylated to release a high concentration of $CO_2$,which is then utilized by Rubisco for the Calvin cycle.
This mechanism minimizes photorespiration and ensures efficient carbon fixation even at low $CO_2$ concentrations.

(B) In $C_3$ plants,the synthesis of one molecule of glucose $(C_6H_{12}O_6)$ requires $18$ $ATP$ and $12$ $NADPH$.
In $C_4$ plants,an additional $ATP$ is required per $CO_2$ molecule fixed to regenerate phosphoenolpyruvate $(PEP)$ from pyruvate.
Since $6$ molecules of $CO_2$ are required to synthesize one molecule of hexose sugar,$6$ additional $ATP$ molecules are consumed in $C_4$ plants compared to $C_3$ plants.
Therefore,the total $ATP$ required for $C_4$ plants is $18 + 6 = 24$ $ATP$.

(D) The chemiosmotic hypothesis,proposed by Peter Mitchell,explains how $ATP$ is synthesized in mitochondria and chloroplasts.
It states that the energy for $ATP$ synthesis is derived from a proton gradient ($H^+$ gradient) across the inner mitochondrial membrane or the thylakoid membrane.
As protons move down their electrochemical gradient through the $ATP$ synthase enzyme,the energy released is used to phosphorylate $ADP$ to $ATP$.
Therefore,the establishment and maintenance of a proton gradient are essential for this process.

(D) The complete oxidation of glucose involves several stages: Glycolysis,the Link reaction,the Krebs cycle,and the Electron Transport Chain $(ETC)$.
$1$. Glycolysis produces a net gain of $2 \ ATP$ molecules.
$2$. The Krebs cycle produces $2 \ GTP$ (which is equivalent to $2 \ ATP$) per glucose molecule.
$3$. The Electron Transport Chain $(ETC)$ is the final stage where the majority of $ATP$ is synthesized via oxidative phosphorylation.
$4$. During $ETC$,the oxidation of $NADH$ and $FADH_2$ provides the energy to pump protons,creating a gradient that drives $ATP$ synthase to produce approximately $28$ to $30 \ ATP$ molecules per glucose molecule.
Therefore,the maximum number of $ATP$ molecules is produced during the $ETC$.

(B) Secretin and cholecystokinin $(CCK)$ are gastrointestinal hormones.
These hormones are secreted by the endocrine cells present in the mucosa of the duodenum.
Secretin stimulates the exocrine pancreas to secrete bicarbonate ions,while $CCK$ stimulates the gallbladder to release bile and the pancreas to secrete digestive enzymes.
Therefore,the correct site of secretion is the duodenum.

(B) Kwashiorkor is a form of protein-energy malnutrition characterized by a severe deficiency of dietary protein.
Since meat,lentils,milk,and eggs are rich sources of high-quality proteins,they are recommended to patients suffering from Kwashiorkor to restore protein levels in the body.
Scurvy is caused by Vitamin $C$ deficiency.
Rickets is caused by Vitamin $D$ deficiency.
Anemia is typically associated with iron deficiency.

(B) The epithelial cells of the intestinal mucosa,specifically the enterocytes,are responsible for the absorption of nutrients.
To increase the surface area for efficient absorption,these cells possess numerous microscopic projections on their apical surface known as $Microvilli$.
These $Microvilli$ form a brush border,which significantly enhances the absorptive capacity of the small intestine.

(D) Blood clotting (coagulation) is a complex process involving a cascade of clotting factors.
$Thromboplastin$ is a lipoprotein released by injured tissues or platelets that initiates the extrinsic pathway of blood coagulation.
When $Thromboplastin$ is introduced into the bloodstream,it acts as a catalyst for the conversion of prothrombin to thrombin,which subsequently converts fibrinogen into fibrin,leading to the formation of a blood clot at the site of introduction.
$Fibrinogen$ and $Prothrombin$ are inactive precursors already present in the blood,while $Heparin$ is an anticoagulant that prevents clotting.

(D) species is defined as a group of organisms that can interbreed to produce fertile offspring.
$1$. Members of a species share a common gene pool,which means gene flow occurs between populations of the same species.
$2$. Variations naturally arise among members of a species due to mutations and recombination.
$3$. Reproductive isolation is a key characteristic that separates one species from another.
$4$. Therefore,the statement that 'there is no gene flow between populations of a species' is incorrect,as gene flow is a fundamental process that maintains the genetic integrity of a species.

(C) Botanical gardens serve as centers for $ex-situ$ conservation. The most significant role they play is the preservation of plant species,particularly rare and endangered ones,by maintaining their germplasm in a controlled environment outside their natural habitat. This ensures the genetic diversity of plants is protected for future research and restoration efforts.

(A) The enzyme $Reverse \text{ } transcriptase$ is an $RNA$-dependent $DNA$ polymerase.
It catalyzes the synthesis of $DNA$ using an $RNA$ molecule as a template.
This process is known as $Reverse \text{ } transcription$ and is commonly observed in retroviruses like $HIV$.

(C) Darwin's theory of natural selection states that individuals with favorable variations are better adapted to their environment and have a higher chance of survival and reproduction.
In the case of pesticide-resistant insects,the application of pesticides acts as a selective pressure.
Insects that possess a random mutation conferring resistance to the pesticide survive,while others die.
These resistant insects then reproduce and pass the resistance gene to their offspring.
Over generations,the population of resistant insects increases,which is a classic example of natural selection in action.

(A) The experiment used to prove that antibiotic-resistant bacterial mutants are pre-existing and not induced by the environment is the $Replica \ plating$ technique.
This experiment was performed by $Joshua \ Lederberg$ and $Esther \ Lederberg$.
In this process,a master plate containing bacterial colonies is pressed onto a velvet-covered block and then transferred to a new plate containing an antibiotic (like streptomycin).
The colonies that grow on the antibiotic plate correspond exactly to the positions of the colonies on the master plate,proving that the resistance was already present in the population before exposure to the antibiotic.

(C) Hugo de Vries, a Dutch botanist, proposed the mutation theory of evolution in $1901$. He conducted his experiments on the evening primrose, scientifically known as $Oenothera$ $lamarckiana$. He observed sudden, heritable changes in the phenotype of these plants, which he termed as 'mutations'. Unlike Darwin's theory, which emphasized small, continuous variations, de Vries proposed that evolution is a saltatory process caused by large, discontinuous variations (mutations).

(B) The study of mitochondrial $DNA$ $(mtDNA)$ variation has provided significant evidence regarding human evolution. Because $mtDNA$ is inherited maternally and accumulates mutations at a relatively steady rate,it acts as a molecular clock. Research shows that human populations in Africa exhibit higher levels of genetic diversity compared to populations in other parts of the world. This higher genetic diversity in African populations suggests that they have existed for a longer period,supporting the 'Out of Africa' theory,which posits that modern humans ($Homo$ $sapiens$) originated in Africa before migrating to other continents.

(D) The experiment described in option $D$ is based on the work of $Francesco$ $Redi$ and later $Louis$ $Pasteur$.
By boiling meat broth or meat in a sealed container,the heat kills any pre-existing microorganisms,and the seal prevents new ones from entering.
Since no life appeared in the sealed,boiled container,it provided strong evidence against the theory of 'Spontaneous Generation' (Abiogenesis),which claimed that life could arise from non-living matter.

(B) The $Radio-carbon$ dating method is primarily used for relatively recent organic materials (up to $50,000$ years).
However,for determining the age of ancient fossils and geological strata,the $Potassium-Argon$ $(K-Ar)$ dating method is considered highly accurate and reliable.
It measures the decay of radioactive $Potassium-40$ into $Argon-40$ within volcanic rocks associated with the fossils,allowing scientists to date samples that are millions of years old.

(A) Valium (a type of benzodiazepine) acts as a central nervous system depressant. It enhances the effect of the neurotransmitter $GABA$ in the brain,which leads to a calming effect,relaxation,and drowsiness. Morphine is an opioid analgesic,Hashish is a cannabinoid (hallucinogen),and Amphetamines are stimulants.

(B) Pashmina wool is obtained from the $Capra \text{ } hircus$ species, commonly known as the Pashmina goat. These goats are found in the high-altitude regions of the Himalayas, particularly in Ladakh and Kashmir. The fine undercoat of these goats is harvested to produce the world-renowned, highly valuable Pashmina wool.

(C) Mutation breeding is a technique used in plant breeding to create genetic variation.
Gamma rays,which are ionizing radiations emitted from radioactive isotopes like Cobalt-$60$,are the most commonly used physical mutagens to induce mutations in crop plants,including cereals.
These radiations penetrate deep into the plant tissues and cause changes in the $DNA$ sequence,which can lead to desirable traits such as disease resistance or higher yield.

(B) Vivipary is a phenomenon where seeds germinate while still attached to the parent plant. In annual crop plants,this is highly undesirable because if seeds germinate on the mother plant,they cannot be harvested,dried,or stored for the next planting season. This makes the storage of seeds for agricultural purposes impossible,leading to a loss of the crop yield and the inability to preserve seeds for future use.

(A) Norman Borlaug is widely known as the 'Father of the Green Revolution' globally. He developed high-yielding varieties of wheat,which significantly increased food production in countries like Mexico and India,thereby preventing famine and ensuring food security. Therefore,his name is associated with the Green Revolution.

(A) The three major crops that contribute most to global food grain production are wheat ($Triticum$ $aestivum$),rice ($Oryza$ $sativa$),and maize ($Zea$ $mays$).
These crops are the primary sources of calories and nutrition for a large portion of the global human population.
Therefore,the correct option is $A$.

(D) The introduction of genetically engineered $(GE)$ crops raises several ethical and safety concerns. One of the primary concerns is the potential for horizontal gene transfer,which could lead to the development of new viral strains or the accidental introduction of allergens and toxic substances into the food chain. Additionally,there are concerns regarding the long-term impact on biodiversity and the potential for creating 'superweeds' through gene flow. Therefore,option $D$ is the most scientifically significant reason among the choices provided.

(D) The genetic code is universal,meaning that the same codons specify the same amino acids in almost all living organisms,from bacteria to humans. Because of this universality,when a human gene is inserted into a bacterial plasmid and introduced into a bacterial cell,the bacterial machinery can successfully transcribe and translate the human gene into the corresponding human protein.

(C) The correct answer is $C$.
$A$. Tundra is characterized by $Permafrost$,which is a layer of soil that remains frozen throughout the year. This is a correct match.
$B$. Savanna biomes are dominated by grasses and scattered trees,with $Acacia$ being a characteristic tree genus. This is a correct match.
$C$. Prairie is a temperate grassland biome. $Epiphytes$ (plants that grow on other plants) are characteristic of tropical rainforests,not temperate grasslands. Therefore,this pair is mismatched.
$D$. Coniferous forests (taiga) are dominated by gymnosperms like pines and spruces,which are $Evergreen$ trees. This is a correct match.

(B) Predator avoidance mechanisms are adaptations that help organisms survive.
$1$. Puffer fish inflate their bodies to appear larger and harder to swallow.
$2$. Chameleons change color to camouflage with their surroundings.
$3$. Venomous fangs in snakes are primarily used for hunting prey or defense against predators.
$4$. Color change in moths is not a standard mechanism for predator avoidance; while some moths use mimicry or cryptic coloration,the ability to actively change color like a chameleon is not a characteristic trait of moths. Therefore,option $B$ is the incorrect example.

(A) The total freshwater on Earth is distributed in various forms. Approximately $70\%$ of the world's total freshwater is trapped in the form of polar ice and glaciers. This water is not readily available for human consumption as it is frozen in the ice caps of Antarctica,Greenland,and mountain glaciers.

(C) When irrigation is practiced for a long period without proper drainage,the water evaporates,leaving behind salts in the soil. This process leads to the accumulation of salts in the top layer of the soil,a condition known as soil salinity. This is a significant environmental issue in agricultural practices.

(D) The Biological Diversity Act in India was enacted by the Parliament in the year $2002$.
This act was established to provide for the conservation of biological diversity,sustainable use of its components,and fair and equitable sharing of the benefits arising out of the use of biological resources,knowledge,and for matters connected therewith or incidental thereto.

(D) The Red Panda $(Ailurus fulgens)$ is classified as $Endangered$ by the $IUCN$ Red List of Threatened Species.
This classification is due to a significant decline in their population caused by habitat loss,fragmentation,and poaching.

(D) Chlorine,Ozone,and Chloramine are commonly used as disinfectants for the purification of drinking water to kill pathogens and ensure safety. Phenyl is a disinfectant used primarily for cleaning floors and surfaces,but it is toxic and not suitable for the purification of drinking water.

(C) The correct answer is $C$.
Solar energy is a clean and renewable source of energy that does not contribute to the greenhouse effect.
In contrast,the combustion of fossil fuels and biomass releases $CO_2$,which is a greenhouse gas.
Nuclear energy is associated with the production of hazardous radioactive waste.
Therefore,the pairing of solar energy with the greenhouse effect is incorrect.

(C) Solar energy reaching the Earth is not responsible for the greenhouse effect.
It is the increase in greenhouse gases in the atmosphere,such as $CO_2$,which is released by the complete combustion of fossil fuels or biomass in industries or transportation vehicles,that prevents the reradiation of infrared radiation from the Earth and results in an increase in the Earth's temperature.