AIPMT 1988 Biology Question Paper with Answer and Solution

(C) The natural system of classification for flowering plants was proposed by George Bentham and Joseph Dalton Hooker.
This system is based on morphological characters and is widely used in many herbaria throughout the world.

(D) The term 'New systematics' (also known as biosystematics) was introduced by Sir Julian Huxley in $1940$.
This approach emphasizes the study of species based on their evolutionary relationships,genetics,and population dynamics rather than just morphological characteristics.

(B) The static concept of species,which suggests that species are fixed and do not change over time,was proposed by Carolus Linnaeus. He famously stated that species are immutable and were created in their present form. This concept is documented in his seminal work,$Systema$ $Naturae$.

(B) The size of the given organisms is as follows:
$1$. $E. coli$ (a bacterium) is approximately $1-2 \mu m$ in length.
$2$. $Neurospora$ (a fungus) is a multicellular organism,much larger than bacteria and viruses.
$3$. $Bacteriophage$ (a virus) typically ranges from $20-200 \ nm$.
$4$. $TMV$ (Tobacco Mosaic Virus) is a rod-shaped virus with a size of approximately $300 \ nm \times 18 \ nm$.
Among these,$TMV$ and $Bacteriophage$ are viruses,but $TMV$ is generally considered smaller in terms of overall volume and complexity compared to many complex bacteriophages. However,in standard biological comparisons,$TMV$ is often cited as one of the smallest infectious agents listed here.

(B) The moss capsule is the sporophytic structure responsible for spore production.
It consists of parts like the $operculum$,$peristome$ teeth,$annulus$,and $theca$.
$Protonema$ is the filamentous,haploid gametophytic stage that develops after the germination of spores released from the capsule.
Therefore,$Protonema$ is not a part of the capsule itself.

(B) $Tubipora$ is commonly known as the organ pipe coral. It belongs to the phylum $Cnidaria$ (or $Coelenterata$). The name is derived from the arrangement of its calcareous tubes,which resemble the pipes of a musical organ.

(B) $Teredo$ is commonly known as the 'shipworm'.
It is a highly specialized marine bivalve mollusc that is very destructive to wood submerged in seawater.
The body is long and slender with a small anterior shell.
The shell is used for burrowing into the wood of ships,piers,or wharves.

(B) The correct answer is $B$.
$A$ Frog,$C$ Salamander,and $D$ Toad are all members of the class $Amphibia$.
$B$ Tortoise is a reptile belonging to the order $Chelonia$ (or $Testudines$). Reptiles are characterized by dry,cornified skin and epidermal scales,which distinguishes them from amphibians.

(D) $Necturus$ is commonly known as the Mud puppy. It is an aquatic salamander belonging to the family $Proteidae$, characterized by the retention of external gills throughout its adult life (neoteny). It is primarily found in North America.

(D) $Bombinator$ is a small-sized amphibian found in Europe.
It is commonly known as the Fire-bellied toad.

(A) $Typhlopidae$ includes burrowing snakes that possess a vestigial pelvic girdle and reduced eyes covered by scales.
These organisms are commonly known as blind snakes or worm snakes.
They are classified as true snakes because they belong to the order $Squamata$ and suborder $Serpentes$.
They are found in almost all parts of the world except $New$ $Zealand$.

(D) $Typhlops$ is a genus of non-venomous snakes commonly known as blind snakes.
These snakes are adapted for a burrowing lifestyle, which has led to the reduction of their eyes, making them appear blind.
They belong to the family $Typhlopidae$ and are found in various tropical and subtropical regions worldwide.

(D) The feet of a Kingfisher are adapted for its specific lifestyle and habitat.
Kingfishers are generally associated with water bodies where they hunt for fish.
Their feet are classified as $Syndactyl$ type,which is a variation of the $Anisodactyl$ arrangement where the third and fourth toes are fused for a portion of their length.
However,among the given options,they are most functionally categorized as $Wading$ type feet,as they are adapted for perching on branches near water and occasionally wading in shallow water to hunt.

(B) The wishbone,also known as the $furcula$ or $merrythought$ bone,is a $V$-shaped bone found in birds. It is formed by the fusion of the two clavicles and the interclavicle. This structure is a part of the pectoral girdle and provides structural support during flight.

(C) Mammals are characterized by the presence of hair on their skin. However,in the order $Cetacea$ (which includes whales,dolphins,and porpoises),hair is either completely absent or restricted to a few sensory bristles around the mouth in adults. This is an adaptation to their fully aquatic lifestyle,where hair would increase drag and interfere with swimming efficiency.

(A) In onion $(Allium \text{ } cepa)$, the fleshy leaves are modified to store food. The primary form of stored carbohydrate in these leaves is sugar (specifically glucose and sucrose), rather than starch, which is the common storage form in many other plants.

(D) The Tunica-Corpus theory was proposed by Schmidt in $1924$.
This theory explains the organization of the shoot apical meristem in angiosperms.
According to this theory,the shoot apex consists of two distinct zones:
$(1)$ Tunica: The peripheral layer$(s)$ of cells that divide anticlinally to increase the surface area.
$(2)$ Corpus: The central mass of cells that divide in various planes to increase the volume of the shoot apex.
Therefore,it is related to the shoot apex.

(A) Cork,also known as phellem,is produced by the activity of the cork cambium,which is technically called the phellogen.
The phellogen is a secondary meristem that develops in the cortex region of the stem during secondary growth.
It cuts off cells on both sides: the cells cut off towards the outside differentiate into cork (phellem),while the cells cut off towards the inside differentiate into secondary cortex (phelloderm).
Together,phellogen,phellem,and phelloderm are collectively known as periderm.

(B) The fat stored below the skin is known as subcutaneous fat. This fat is stored within specialized connective tissue cells called adipocytes. These cells aggregate to form adipose tissue,which acts as an energy reserve and provides insulation to the body.

(D) The correct answer is $(d)$.
Pleuropneumonia-like organisms $(PPLO)$,also known as Mycoplasma,are the smallest known living cells.
Specifically,Mycoplasma gallisepticum has an average size of approximately $0.1$ to $0.3$ $\mu m$.

(C) The fluid mosaic model,proposed by $Singer$ and $Nicolson$ in $1972$,describes the plasma membrane as a fluid structure.
It consists of a phospholipid bilayer in which various proteins are embedded.
These proteins are classified as extrinsic (peripheral) proteins,which are located on the surface,and intrinsic (integral) proteins,which are partially or fully embedded within the lipid bilayer.
Therefore,the plasma membrane is composed of phospholipids,extrinsic proteins,and intrinsic proteins.

(C) The water potential $(\psi_w)$ of a cell is determined by the sum of the pressure potential $(\psi_p)$ and the solute potential $(\psi_s)$.
Mathematically,it is expressed as $\psi_w = \psi_p + \psi_s$.
Here,$P$ represents the pressure potential (often denoted as $\psi_p$) and $\psi_s$ represents the solute potential (also known as osmotic potential,$\pi$ or $\psi_s$).
Therefore,option $C$ is the correct representation.

(A) Transpiration is the process of water loss from plants in the form of water vapor. The rate of transpiration is inversely proportional to the relative humidity of the atmosphere.
$(a)$ When the atmosphere is highly humid,the water potential gradient between the leaf interior and the outside air is reduced,which significantly slows down the rate of transpiration.
$(b)$ High wind velocity generally increases the rate of transpiration by removing the humid air layer around the leaf.
$(c)$ Excess water in the cell typically promotes higher transpiration rates.
$(d)$ Dry environmental conditions increase the water potential gradient,leading to higher transpiration rates.
Therefore,transpiration is lowest when humidity is high.

(A) Phenyl mercuric acetate $(PMA)$ is a well-known antitranspirant.
It works by inducing the partial closure of stomata in plants.
By reducing the aperture of the stomata,it significantly lowers the rate of transpiration without severely affecting other physiological processes like photosynthesis or respiration.
Therefore,the correct option is $A$.

(C) The opening and closing of stomata in angiosperms are primarily regulated by changes in the turgor pressure of the guard cells.
When the guard cells become turgid due to the influx of water,the stomatal aperture opens.
Conversely,when the guard cells lose water and become flaccid,the stomatal aperture closes.

(B) The opening of stomata is primarily driven by the increase in the turgor pressure of the guard cells. When water enters the guard cells through the process of $Endosmosis$,they become turgid. Due to the presence of thick inner walls and thin outer walls,the turgid guard cells bulge outwards,causing the stomatal pore to open.

(B) The correct answer is $B$.
In non-cyclic photophosphorylation,both $PS-I$ and $PS-II$ work in series.
The flow of electrons is unidirectional,starting from water and ending at $NADP^+$.
During this process,the electrons released from the electron transport chain are used to reduce $NADP^+$ to $NADPH_2$ (or $NADPH + H^+$),which is essential for the biosynthetic phase of photosynthesis.

(B) The photosynthetic pathway is divided into two main phases: the light-dependent reaction and the light-independent reaction,commonly known as the dark reaction or the Calvin cycle.
During the light reaction,solar energy is captured to produce $ATP$ and $NADPH$.
In the dark reaction,these products ($ATP$ and $NADPH$) are utilized to fix atmospheric $CO_2$ into carbohydrates.
Therefore,$CO_2$ fixation occurs specifically during the dark reaction phase of photosynthesis.

(D) $C_4$ plants are adapted to high temperatures and high light intensities.
Maize ($Zea$ $mays$) is a classic example of a $C_4$ plant.
In $C_4$ plants,the initial $CO_2$ fixation occurs in mesophyll cells to form a $4$-carbon compound called oxaloacetate,which is why they are called $C_4$ plants.
Papaya,Pea,and Potato are examples of $C_3$ plants.

(B) $R.Q.$ stands for Respiratory Quotient.
It is defined as the ratio of the volume of $CO_2$ evolved to the volume of $O_2$ consumed during respiration.
The formula is: $R.Q. = \frac{\text{Volume of } CO_2 \text{ evolved}}{\text{Volume of } O_2 \text{ consumed}}$.
Therefore,the correct representation is $\frac{CO_2}{O_2}$.

(B) The correct answer is $B$. Kinin (a type of cytokinin) is a plant hormone that promotes cell division (cytokinesis) in plants. In the presence of kinin,the rate of mitotic cell division increases significantly,which is essential for plant growth and development.

(B) The phenomenon where cytokinins delay the senescence (aging) of leaves is known as the $Richmond-Lang$ effect. When an excised leaf is induced to form roots,the roots synthesize cytokinins. These cytokinins are transported to the leaf,where they prevent the breakdown of chlorophyll and delay the yellowing process (senescence). Therefore,cytokinins are responsible for retarding leaf aging.

(C) Phytochrome is a light-sensitive pigment found in plants that acts as a photoreceptor. It plays a crucial role in photoperiodism,which is the physiological response of plants to the relative lengths of light and dark periods. The stimulus of light is perceived by the phytochrome present in the leaves,which then triggers flowering and other developmental processes.

(B) The movement of leaves in the sensitive plant, $Mimosa \text{ } pudica$ (touch-me-not, family $Mimosaceae$), is known as seismonasty.
Seismonasty is a type of nastic movement in plants that occurs in response to mechanical stimuli such as touch, vibration, or shock.
When the leaves are touched, the turgor pressure in the pulvinus (the swollen base of the leaf) decreases, causing the leaves to fold inward.

(D) When red blood cells are destroyed in the spleen,liver,and bone marrow,haemoglobin is broken down into its components.
Haemoglobin consists of a protein part (globin) and a prosthetic group (haem).
The haem group is further broken down into iron $(Fe^{2+})$ and a pigment called biliverdin.
Biliverdin is subsequently converted into bilirubin.
Therefore,iron,biliverdin,and bilirubin are all products of the breakdown of haemoglobin.

(A) The epithelial cells of the $PCT$ (Proximal Convoluted Tubule) possess a brush border.
This brush border is formed by the presence of numerous microvilli on the apical surface of the cells.
The primary function of these microvilli is to increase the surface area for the reabsorption of water,electrolytes,and nutrients from the filtrate.

(C) The presence of red blood cells $(RBCs)$ in the urine is medically termed as $Hematuria$.
$Proteinuria$ refers to the presence of excess proteins in the urine.
$Alkaptonuria$ is a rare genetic disorder where the body cannot process the amino acids phenylalanine and tyrosine,leading to the accumulation of homogentisic acid.
$Urolithiasis$ refers to the formation of stones in the urinary tract.

(B) . Intercostal muscles are located between the ribs in the thoracic cavity.
They play a crucial role in the process of respiration.
These muscles move the sternum and ribs inwards and outwards,which changes the volume and pressure within the thoracic cavity,facilitating the movement of air into and out of the lungs.

(B) statolith is a specialized structure found in many invertebrates and some plants. In animals,it is a dense particle (often calcium carbonate) located within a statocyst. As the organism moves,the statolith shifts due to gravity,stimulating sensory hairs that provide information about the organism's orientation and balance. Therefore,it is primarily involved in maintaining equilibrium.

(A) Vultures are birds of prey known for their exceptionally sharp and acute vision,which allows them to spot carcasses from great heights while soaring. This high visual acuity is due to a high density of photoreceptor cells in their retina,specifically in the fovea,which provides them with superior resolution compared to other animals listed.

(C) The intermediate lobe of the pituitary gland,also known as the pars intermedia,secretes Melanocyte Stimulating Hormone $(MSH)$.
$MSH$ acts on melanocytes (melanin-containing cells) and regulates skin pigmentation.
In many fishes,amphibians,and reptiles,$MSH$ stimulates the dispersion of melanin granules within melanocytes,which results in the darkening of the skin.

(B) The correct answer is $B$.
Insulin is a hypoglycemic hormone that decreases blood glucose levels by facilitating the uptake of glucose into cells.
In contrast,cortisol is a glucocorticoid hormone that acts as an anti-insulin agent.
It increases blood glucose levels through the process of gluconeogenesis,which involves the synthesis of glucose from non-carbohydrate sources like amino acids and lipids.

(B) The vermiform appendix is a small, pouch-like structure attached to the large intestine.
Inflammation of this organ is medically termed as $Appendicitis$.
$Amoebic \text{ dysentery}$ is an infection of the intestines caused by the parasite $Entamoeba \text{ histolytica}$.
$Intestinal \text{ cancer}$ refers to the growth of malignant cells in the digestive tract.
$Appendectomy$ is the surgical procedure to remove the appendix, not the name of the disease itself.

(A) The disease caused by the deficiency of plasma thromboplastin component $(PTC)$,also known as Factor $IX$,is called Christmas disease or Haemophilia $B$.
This condition leads to a prolonged blood clotting time because $PTC$ is essential for the formation of the thromboplastin complex in the intrinsic pathway of the coagulation cascade.
While Haemophilia $A$ is caused by a deficiency of Factor $VIII$,Christmas disease is specifically associated with the lack of $PTC$ (Factor $IX$).

(B) The development of a sporophyte directly from a gametophyte without the fusion of gametes (fertilization) is called $Apogamy$.
In ferns,the prothallus (gametophyte) normally produces gametes that fuse to form a zygote,which then develops into a sporophyte.
However,in $Apogamy$,the sporophyte arises vegetatively from the cells of the prothallus.
$Apospory$ is the opposite process,where a gametophyte develops from a sporophyte without meiosis.
$Parthenocarpy$ refers to the development of fruit without fertilization.
$Parthenogenesis$ is the development of an embryo from an unfertilized egg.

(B) In Gymnosperms like $Pinus$ and $Cycas$,the endosperm is formed before fertilization from the female gametophyte tissue.
Since the female gametophyte is derived from a haploid megaspore,the endosperm in Gymnosperms is haploid $(n)$.
In contrast,the endosperm in Angiosperms is formed after fertilization (double fertilization) and is triploid $(3n)$.

(B) The vertebrae of birds are $Heterocoelous$.
In $Heterocoelous$ vertebrae,the centrum is saddle-shaped at both ends,which allows for significant flexibility and movement of the neck,enabling birds to turn their heads in various directions.

(D) Mammals are characterized by the presence of hair on their skin. However,in the order $Cetacea$ (which includes whales,dolphins,and porpoises),hair is either completely absent or reduced to a few sensory bristles around the mouth in adults. This is an adaptation to their fully aquatic lifestyle.

(B) Kingfishers are birds that typically hunt fish by diving into water. Their feet are adapted for perching on branches or other structures while waiting for prey. Unlike wading birds (which have long legs for walking in shallow water) or running birds (which have strong legs for terrestrial locomotion),the kingfisher's feet are small and syndactyl,specifically suited for gripping branches.

(D) The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosa.
It is found in various organs,including the respiratory tract,the urinary tract,and the gastrointestinal tract.
In the context of the digestive system,the lamina propria is a component of the mucosa of the intestine,providing structural support and housing blood vessels and immune cells.
Therefore,it is most directly associated with the wall of the intestine.

(B) The relationship between a suckerfish $(Remora)$ and a shark is an example of commensalism.
In this interaction,the suckerfish attaches itself to the shark using its dorsal fin modified into a sucker.
The suckerfish benefits by gaining transportation and feeding on the leftover scraps of the shark's prey,while the shark is neither harmed nor benefited by the presence of the suckerfish.
Therefore,this is a type of commensalism,specifically ectocommensalism.

(B) Pigeons are noted for their unique ability to produce 'pigeon milk' using their crop glands.
This substance is formed by the degeneration of the epithelial cells lining the crop.
This milk is produced by both male and female pigeons to feed their young ones.

(A) The process of formation of fruits without fertilization is known as parthenocarpy.
In this process,the ovary develops into a fruit without undergoing the fertilization process.
This is commonly used to produce seedless fruits,such as bananas and grapes.

(B) The correct answer is $B$.
Periblastula,also known as a superficial blastula,is formed by superficial meroblastic cleavage.
This type of cleavage occurs in centrolecithal eggs,which are characteristic of insects.
In this process,the blastoderm forms a single layer of epithelial cells surrounding the centrally located yolk mass.
Unlike other types of blastulae,a periblastula lacks a central cavity or blastocoel.

(D) Let the colour-blind man be $X^cY$ and the daughter of a colour-blind person be $X^cX$ (carrier).
When they marry,the cross is $X^cY \times X^cX$.
The possible genotypes of the offspring are $X^cX^c$ (colour-blind daughter),$X^cX$ (carrier daughter),$X^cY$ (colour-blind son),and $XY$ (normal son).
Thus,half of their sons will be colour-blind.

(D) The correct answer is $D$. $A$ single amino acid is specified by a sequence of three nucleotides in $mRNA$,which is called a codon. Due to this triplet nature,the genetic code consists of $64$ possible codons $(4^3 = 64)$.

(C) Thalidomide is a drug that was used as a sedative for pregnant women.
It was found to be a potent teratogen,causing severe birth defects known as phocomelia.
Phocomelia is a condition characterized by the congenital absence or shortening of the proximal portion of the limbs,where the hands or feet are attached directly to the trunk by a small,irregularly shaped bone.
Therefore,this condition illustrates the malformation of the foetus due to the teratogenic effects of the drug.

(C) 'Enterobiasis' is an infection caused by the pinworm, $Enterobius \text{ } vermicularis$.
It is commonly known as pinworm infection or seatworm infection.
The parasite lives in the human intestine and lays eggs around the anus, causing itching.

(B) Silk is produced by the larva of the silkworm. The larva secretes a proteinaceous fluid from its salivary glands,which hardens upon contact with air to form the silk thread used to construct the cocoon.

(A) $Sporeine$ is the first commercial bioinsecticide developed in $Germany$ using the bacterium $Bacillus$ $thuringiensis$ $(Bt)$.
It contains the spores and crystalline toxins of the bacterium,which are effective against specific insect pests.

(A) In a typical terrestrial ecosystem,the pyramid of numbers is upright.
This means that the number of primary producers (plants) is significantly higher than the number of primary consumers (herbivores) that feed on them.
As we move up the trophic levels,the number of individuals generally decreases because energy is lost at each transfer,making it impossible to support a larger population of higher-level consumers.
Therefore,the population of primary producers is greater than that of primary consumers.

(B) The correct answer is $B$.
$CO_2$ is a naturally occurring gas in the atmosphere and is essential for the process of photosynthesis in plants.
It is not considered a pollutant in normal concentrations as it is non-toxic to humans and animals.
In contrast,$CO$,$SO_2$,and hydrocarbons are harmful substances that degrade air quality and are classified as atmospheric pollutants.

(B) . Acid rain is primarily caused by the emission of sulphur dioxide $(SO_2)$ and nitrogen oxides ($NO_x$,including $NO_2$) into the atmosphere.
These gases are released in large quantities due to the burning of fossil fuels in industries and vehicles.
When these gases react with water vapor in the atmosphere,they form sulphuric acid $(H_2SO_4)$ and nitric acid $(HNO_3)$.
These acids then fall to the earth along with rain,resulting in acid rain,which is harmful to aquatic life,soil,and buildings.

(C) The correct answer is $C$. In India,wheat is one of the most important food crops and covers a significant portion of the total cultivated land,approximately $29$ million hectares (often cited as $29$ million acres in older texts). Among the given options,wheat occupies the largest area under cultivation.

(B) The correct answer is $B$.
Rice is the principal cereal crop in India.
Approximately $50\%$ of the total area under cultivation of cereal crops in India is dedicated to rice.
It serves as the main staple food for a vast majority of the Indian population.

(B) $Cocos$ $nucifera$ (Coconut) belongs to the family $Arecaceae$ (formerly $Palmae$).
It is a monocotyledonous plant,and its coir fibres are obtained from the mesocarp of the fruit.

(D) Commercial fibres,such as jute,flax,and hemp,are derived from the sclerenchyma tissue.
Specifically,these are sclerenchymatous fibres found in the phloem or pericycle of plants.
Sclerenchyma cells are dead at maturity and possess thick,lignified secondary cell walls,which provide mechanical strength and durability,making them suitable for industrial use.

(A) $Parthenium \ argentatum$ (Guayule) is a plant primarily known as a source of natural rubber,not furniture wood. Therefore,this pair is incorrectly matched.
$Leucaena \ leucocephala$ is a leguminous plant that fixes atmospheric nitrogen.
$Simmondsia \ chinensis$ (Jojoba) is well-known for producing liquid wax from its seeds.
$Psophocarpus \ tetragonolobus$ (Winged bean) is a highly nutritious plant where seeds are consumed for their protein content.

(D) In $Chlamydomonas$,sexual reproduction can occur through the fusion of two vegetative cells that act as gametes. When the entire organism functions as a gamete and fuses with another,the process is called $Hologamy$. $Isogamy$ refers to the fusion of morphologically similar gametes,while $Somatogamy$ involves the fusion of somatic cells in fungi. Therefore,the correct term for the fusion of two cells in $Chlamydomonas$ is $Hologamy$.

(A) Organisms that float passively on the surface of water are called $Planktons$.
$Pelagic$ organisms inhabit the open water column.
$Benthos$ are organisms that live on the bottom of a water body.
$Neritic$ refers to the relatively shallow part of the ocean above the drop-off of the continental shelf.

(B) The interaction between a sucker fish $(Remora)$ and a shark is an example of $Commensalism$.
In this relationship,the $Remora$ fish attaches itself to the shark to obtain food scraps and transportation without harming or benefiting the shark.
$Commensalism$ is a type of population interaction where one species benefits while the other remains unaffected ($+/0$ interaction).

(C) Pigeons produce a substance known as 'crop milk' to feed their young ones. This substance is produced by the sloughing off of fluid-filled cells from the lining of the crop. Both male and female pigeons possess this specialized structure called the crop,which is an expansion of the esophagus used for food storage and the production of crop milk.

(A) The life cycle of a silkworm ($Bombyx$ $mori$) consists of four stages: egg,larva (caterpillar),pupa (cocoon),and adult (moth).
Silk is produced by the silkworm during its larval stage to form a protective covering called a cocoon.
In the commercial production of silk (sericulture),the cocoons are harvested during the pupal stage before the adult moth emerges,as the emergence of the moth would break the continuous silk fiber.

(B) In angiosperms,the pollen grain represents the male gametophyte.
In about $60\%$ of angiosperms,pollen grains are shed at the $2$-celled stage (a vegetative cell and a generative cell).
In the remaining species,the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed,resulting in a $3$-celled stage.
Therefore,the male gametophyte is shed at either the $2$-celled or $3$-celled stage. Among the given options,the $3$-celled stage is the correct developmental stage for shedding.

(C) In angiosperms,the formation of a seed involves the fusion of a male gamete with an egg cell to form a zygote (which develops into an embryo) and the fusion of a male gamete with two polar nuclei to form the primary endosperm nucleus (which develops into endosperm).
For the production of $1$ seed,$1$ meiotic division is required for the formation of the female gametophyte (megasporogenesis) and $1/4$ meiotic division is required for the formation of male gametophytes (microsporogenesis).
Total meiotic divisions for $1$ seed = $1 + 1/4 = 5/4 = 1.25$.
For $100$ seeds,the total number of meiotic divisions required = $100 \times 1.25 = 125$.

(A) The formation of a gametophyte directly from a sporophyte without undergoing meiosis is known as $Apospory$. In this process,the diploid cells of the sporophyte develop into a gametophyte without the reduction division. Conversely,$Apogamy$ is the development of a sporophyte directly from a gametophyte without fertilization. $Apomixis$ is a general term for asexual reproduction that mimics sexual reproduction,and $Amphimixis$ refers to normal sexual reproduction involving the fusion of gametes.

(B) Double fertilization and triple fusion were discovered by $S.G. \text{Nawaschin}$ and $L. \text{Guignard}$ in $1898$ in the plants $Lilium$ and $Fritillaria$.
Double fertilization involves the fusion of one male gamete with the egg cell to form a diploid zygote,and the fusion of the second male gamete with two polar nuclei to form the primary endosperm nucleus (triple fusion).

(C) In a haploid organism,the genome consists of only one set of chromosomes $(n)$.
Since there is only one copy of each gene present in the cell,there is no second allele to mask the expression of a recessive allele.
Therefore,any allele present,whether dominant or recessive,will be expressed phenotypically.
This is why haploid organisms are ideal for genetic studies involving mutations,as even recessive mutations are immediately expressed.

(D) Gregor Mendel's success in his experiments on pea plants was primarily due to his systematic approach.
$1$. He maintained accurate records of all observations and performed a statistical/quantitative analysis of the data.
$2$. He focused on one or a few traits at a time,which simplified the analysis of inheritance patterns.
$3$. He chose true-breeding pea plant varieties.
Therefore,the most significant methodological reason among the options provided is that he considered one trait at a time (or a limited number of traits) to avoid complexity.

(C) In humans,sex determination is based on the $XY$ chromosome system.
During fertilization,the male gamete (sperm) can carry either an $X$ or a $Y$ chromosome,while the female gamete (ovum) always carries an $X$ chromosome.
When an $X$-bearing sperm fertilizes an egg,the zygote becomes $XX$ (female).
When a $Y$-bearing sperm fertilizes an egg,the zygote becomes $XY$ (male).
Since the probability of a sperm carrying an $X$ or a $Y$ chromosome is equal ($50\%$ each),the probability of having a boy or a girl for any pregnancy is always $50\%$,regardless of the gender of previous children.
Therefore,the probability of the sixth child being a boy is $50\%$.

(D) The genetic code is based on the sequence of nitrogenous bases in $mRNA$.
These bases are Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Uracil $(U)$.
$A$ codon consists of a triplet of these bases.
Since all four nitrogenous bases $(A, G, C, U)$ are involved in forming the genetic code,the correct answer is 'All of the above'.

(A) The $DNA$ double helix model,proposed by $Watson$ and $Crick$,describes the structure of $DNA$ as two polynucleotide chains that are coiled around a common axis in a right-handed fashion. The strands are antiparallel and held together by hydrogen bonds between complementary nitrogenous bases. Therefore,the two strands are coiled around a common axis.

(B) $RNA$ (Ribonucleic Acid) is a nucleic acid composed of nucleotides containing a ribose sugar,a phosphate group,and one of four nitrogenous bases: Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Uracil $(U)$.
Thymine $(T)$ is a nitrogenous base found in $DNA$ but is replaced by Uracil in $RNA$.
Therefore,$RNA$ does not contain Thymine.

(D) Hummingbirds and hawks are both birds that have evolved wings for flight, which is a common function. However, they belong to different evolutionary lineages. The development of similar functional structures (wings) in unrelated organisms to adapt to a similar environment (aerial mode of life) is known as $Convergent evolution$. This process results in analogous organs, not homologous ones.

(A) The phenomenon where an organism evolves to resemble another organism (often a dangerous or unpalatable species) to avoid predation is known as $Mimicry$. This is a survival strategy used by many insects and animals to deceive their predators.

(B) Competition occurs when organisms share the same limited resources.
According to Gause's Competitive Exclusion Principle,two species competing for the same limiting resources cannot coexist at constant population values.
Competition is most severe between closely related species because they have similar requirements for food,light,nutrients,and space.
When these organisms occupy the same area or niche,the struggle for survival becomes intense,leading to competitive exclusion or character displacement.

(A) Mutualism is a type of population interaction in which both interacting species benefit from each other. In many cases,this relationship is obligate,meaning the organisms are essential for each other's survival (e.g.,lichens,mycorrhizae). Commensalism is an interaction where one species benefits and the other is neither harmed nor benefited. Therefore,the correct term for a mutually beneficial interaction essential for survival is Mutualism.

(A) Acid rain is primarily caused by the emission of sulfur dioxide $(SO_2)$ and nitrogen oxides ($NO_x$,specifically $NO_2$) into the atmosphere.
These gases are released in large quantities during the combustion of fossil fuels (like coal and petroleum) in power plants,vehicles,and industries.
When these gases react with water vapor,oxygen,and other chemicals in the atmosphere,they form sulfuric acid $(H_2SO_4)$ and nitric acid $(HNO_3)$,which then fall to the ground as acid rain.

(B) pollutant is defined as a substance or energy introduced into the environment that has undesired effects,or adversely affects the usefulness of a resource.
$CO$ (Carbon monoxide),hydrocarbons,and $SO_2$ (Sulfur dioxide) are primary air pollutants that cause significant harm to human health and the environment.
$CO_2$ (Carbon dioxide) is a natural component of the atmosphere and is essential for photosynthesis in plants. While it is a greenhouse gas contributing to global warming at high concentrations,it is not classified as a pollutant in the same sense as toxic gases like $CO$ or $SO_2$ in standard biological and environmental contexts.