NEET 2013 Biology Question Paper with Answer and Solution

(A) By analyzing the structure of the tetrapeptide:
$1$. The amino acid at position $a$ has a side chain $-CH_2OH$,which corresponds to Serine.
$2$. The amino acid at position $b$ has a side chain $-CH_2SH$,which corresponds to Cysteine.
$3$. The amino acid at position $c$ has a side chain $-CH_2-C_6H_5$ (phenylalanine derivative),which is an aromatic amino acid,but not Tryptophan.
$4$. The amino acid at position $d$ has a side chain $-CH_2-CH_2-CH_2-COOH$,which corresponds to Glutamic acid.
$5$. In a polypeptide chain,the $N$-terminal is on the left and the $C$-terminal is on the right. Thus,$a$ is the $N$-terminal and $d$ is the $C$-terminal.
$6$. Option $a$ is incorrect because while $d$ is Glutamic acid,it is not the only correct statement if others are wrong,but looking at the options,none of the specific claims in $a, b, c$ are fully accurate except for the identification of $d$ as Glutamic acid. However,since $d$ is indeed Glutamic acid,option $a$ is the correct choice.

(A) During the $zygotene$ stage of $Meiosis-I$,homologous chromosomes start pairing together,a process known as $synapsis$.
These paired chromosomes are referred to as homologous chromosomes.
The electron micrographs of this stage reveal that the pairing is accompanied by the formation of a complex structure known as the $synaptonemal$ $complex$.
The complex formed by a pair of synapsed homologous chromosomes is specifically called a $bivalent$ or a $tetrad$.

(C) The figure shows the telophase stage of mitotic cell division.
In this stage,the following key events occur:
- Chromosomes cluster at opposite spindle poles and their identity is lost as discrete elements.
- Nuclear envelope assembles around the chromosome clusters.
- Nucleolus,Golgi complex,and $ER$ reform.

(A) The correct answer is $A$.
During the $zygotene$ stage of prophase $I$ of meiosis,the chromosomes begin to pair up.
This process of pairing of homologous chromosomes is known as $synapsis$.
Each pair of homologous chromosomes is referred to as a $bivalent$ or a $tetrad$.

(A) During the metaphase stage of mitosis,chromosomes consisting of two sister chromatids align at the equatorial plate.
Discontinuous spindle fibres radiate from the two spindle poles and connect to the disc-shaped protein structures located on the surface of the centromere,known as kinetochores.
These fibres are referred to as chromosomal fibres or tractile fibrils.
$A$ kinetochore acts as a complex protein assembly that serves as the attachment point for spindle microtubules,facilitating the movement of chromosomes during cell division.

(B) : In metaphase,chromosomes consisting of two sister chromatids get arranged at the equator. Discontinuous fibers radiate out from two spindle poles and get connected to the disc-shaped structure at the surface of the centromere called kinetochores. These are known as chromosome fibers or tractile fibrils. $A$ kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves.

(B) The correct answer is $B$.
Facilitated transport (or facilitated diffusion) is the spontaneous movement of molecules or ions across a biological membrane through specific transmembrane integral proteins.
It is a passive process,meaning it does not require energy $(ATP)$.
Facilitated diffusion is mediated by protein channels and carrier proteins.
Most transport proteins involved in this process are highly selective and only transport specific molecules.
Since it is a passive process,molecules move down their concentration gradient,which is known as 'downhill transport'.
'Uphill transport' refers to active transport,where molecules move against their concentration gradient,requiring energy. Therefore,uphill transport is not a characteristic of facilitated transport.

(D) The correct answer is $(d)$. The enzyme nitrogenase is a $Mo-Fe$ protein that catalyzes the conversion of atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$,which is the first stable product of biological nitrogen fixation.
Nitrogen fixation is the process of converting inert atmospheric dinitrogen $(N_2)$ into usable nitrogenous compounds like ammonia,amino acids,etc.
Biological nitrogen fixation is carried out by both free-living and symbiotic microorganisms.
In leguminous plants,symbiotic nitrogen-fixing bacteria (like $Rhizobium$) reside in root nodules.
These nodules provide the necessary environment,including the enzyme nitrogenase and the oxygen-scavenging pigment leghaemoglobin,to facilitate the reduction of $N_2$ to ammonia.

(A) : Certain species of cyanobacteria $(Nostoc)$ possess some special cells called heterocysts which occur in terminal,basal,and intercalary positions.
These heterocysts are yellowish in color and their contents are homogeneous.
Heterocysts are now known as the primary sites of nitrogen fixation.
Atmospheric nitrogen is converted into ammonia by these cells in cyanobacteria.

(D) $Sulphur$ is a key structural component of the vitamin $Biotin$ (Vitamin $B_7$).
It is also present in $Thiamine$ (Vitamin $B_1$).
$Biotin$ plays a crucial role in various metabolic processes, including fatty acid synthesis and gluconeogenesis.
It is commonly found in protein-rich foods such as eggs, lettuce, and sprouts.

(D) The correct answer is $(D)$.
Denitrification is a biological process in which nitrates $(NO_3^-)$ in the soil are reduced to molecular nitrogen $(N_2)$ gas,which is then released into the atmosphere. This process is carried out by denitrifying bacteria such as $Pseudomonas$ $denitrificans$ and $Thiobacillus$ $denitrificans$.
Anaerobic ammonium oxidation (often referred to as $ANAMMOX$) is another microbial process where ammonium $(NH_4^+)$ is oxidized to dinitrogen gas $(N_2)$ under anaerobic conditions,contributing to the nitrogen cycle by returning $N_2$ to the atmosphere.

(D) In the given diagram,pathway $A$ represents glycolysis,pathway $B$ represents the Krebs cycle,and pathway $C$ represents oxidative phosphorylation.
During glycolysis (pathway $A$),$ATP$ is produced as a net product (arrow $4$).
During the Krebs cycle (pathway $B$),$ATP$ (or $GTP$) is produced as a net product (arrow $8$).
During oxidative phosphorylation (pathway $C$),$ATP$ is produced as a net product (arrow $12$).
Therefore,arrows numbered $4, 8,$ and $12$ all represent the production of $ATP$.

(B) : Gibberellins are plant growth hormones that play a crucial role in seed germination. During germination,gibberellins stimulate the synthesis of hydrolytic enzymes,such as $\alpha$-amylase,in the aleurone layer of cereal seeds. These enzymes break down stored starch into simple sugars,which are then transported to the developing embryo to provide energy for growth. Thus,gibberellins are responsible for the mobilization of food reserves in germinating seeds.

(A) $NAA$ ($\alpha$-Naphthalene acetic acid) and $2, 4-D$ ($2, 4$-dichlorophenoxy acetic acid) are synthetic auxins.
Normally, auxins inhibit flowering in many plants.
However, in pineapple and litchi, the application of these synthetic auxins promotes flowering.
Therefore, they are used to induce flowering in pineapple throughout the year.

(C) The correct option is $C$.
Glycine (an amino acid) and glucose are absorbed into the blood capillaries of the small intestine via active transport,which requires energy $(ATP)$.
Fatty acids and glycerol are first incorporated into micelles,then move into intestinal cells where they are re-synthesized into chylomicrons.
Fructose is absorbed by facilitated diffusion.
$Na^+$ ions are absorbed by active transport.

(C) The correct answer is $C$. Baked potatoes consist of starch, which is a polysaccharide.
$1$. In the oral cavity, food is mixed with saliva. Saliva contains an enzyme called salivary amylase (ptyalin), which converts starch into maltose, isomaltose, and small dextrins.
$Starch \xrightarrow[\text{Salivary amylase}]{} \text{Maltose} + \text{Isomaltose} + \alpha\text{-Dextrins}$.
$2$. The pancreatic juice, which enters the small intestine, contains a starch-digesting enzyme called pancreatic amylase. This enzyme further breaks down any remaining starch into maltose, isomaltose, and $\alpha$-dextrins.
$Starch \xrightarrow[\text{Pancreatic } \alpha\text{-amylase}]{} \text{Maltose} + \text{Isomaltose} + \alpha\text{-Dextrins}$.
$3$. Finally, disaccharidases such as maltase, present in the intestinal juice (succus entericus) of the small intestine, break down disaccharides like maltose into simpler monosaccharides (glucose).

(A) The correct option is $A$.
In the given figure,$A$ represents the trachea. It is supported by incomplete cartilaginous rings which prevent its collapse during inspiration.
$B$ represents the pleural membrane,which encloses the lungs.
$C$ represents the alveoli. They are thin-walled sacs having an extensive network of capillaries for gaseous exchange.
$D$ represents the diaphragm,which is a dome-shaped muscular structure that helps in breathing.

(A) In the given figure:
$A$ represents the pulmonary vein,which brings oxygenated (pure) blood from the lungs to the left atrium.
$B$ represents the dorsal aorta,which carries oxygenated blood from the heart to various body parts.
$C$ represents the vena cava,which carries deoxygenated (impure) blood from body parts to the right auricle.
$D$ represents the pulmonary artery,which carries deoxygenated blood from the heart to the lungs.
Therefore,option $A$ correctly identifies the label $C$ and its function,noting that the $pCO_2$ in deoxygenated blood returning to the heart is approximately $45 \ mm \ Hg$.

(C) The correct answer is $(C)$.
In the given diagram,the $P$-wave represents the electrical excitation (or depolarisation) of the atria,which leads to the contraction of both the atria.
The $QRS$ complex represents the depolarisation of the ventricles,which initiates the ventricular contraction.
The contraction starts shortly after $Q$ and marks the beginning of the systole.
The $T$-wave represents the return of the ventricles from an excited to a normal state (repolarisation).
The end of the $T$-wave marks the end of systole.

(C) - Pulmonary Artery: Carries deoxygenated blood from the heart to the lungs. It is thick-walled.
$B$ - Systemic Artery: Carries oxygenated blood from the heart to different body parts. It is thick-walled and elastic. The flow of blood in it is intermittent.
$C$ - Systemic Vein: Brings deoxygenated blood from different body parts to the heart. It is thin-walled and acts as a low-resistance conduit for blood flow.
$D$ - Pulmonary Vein: Transports oxygenated blood from the lungs to the left atrium. The partial pressure of oxygen $(pO_2)$ in the pulmonary vein is approximately $95 \ mm \ Hg$.

(A) The image shows a Basophil,which is a type of granulocyte.
Basophils are the least abundant WBCs $(0.5-1.0\%)$.
They contain large,coarse granules that stain with basic dyes like methylene blue.
Their nucleus is typically lobed (often $S$-shaped or two-lobed,though sometimes appearing multi-lobed due to dense granules).
They secrete chemicals like histamine,serotonin,and heparin,which are involved in inflammatory responses.

(D) : Thoracic vertebrae are $12$ in number. Joints between adjacent vertebrae are cartilaginous joints,and the opposing surfaces are connected by fibrocartilage,which allows very little movement. Osteoporosis is a disease characterized by low bone mass and loss of bone tissue that may lead to weak and fragile bones. Osteoporosis occurs when there is an imbalance between new bone formation and old bone resorption. Generalized osteoporosis is common in elderly people and in women following menopause. In osteoporosis,the osteoblastic (bone-forming) activity in the bone is usually less than normal,and consequently,the rate of bone deposition is depressed. Estrogens inhibit osteoclastic (bone-resorption) activity in the bones and therefore stimulate bone growth. After menopause,almost no estrogens are secreted by ovaries. This estrogen deficiency leads to increased osteoclastic activity in the bones,decreased bone matrix,and decreased deposition of bone calcium and phosphate. In some women,this effect results in osteoporosis.

(A) The correct answer is $A$.
Each muscle fibre contains many parallelly arranged myofibrils.
Each myofibril consists of serially arranged functional units called sarcomeres.
Each sarcomere has a central $A$-band composed of thick myosin filaments and two half $I$-bands composed of thin actin filaments on either side,marked by $Z$-lines.
In a resting state,the edges of the thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments.
The central part of the thick filament that is not overlapped by thin filaments is known as the $H$-zone.

(A) Synovial joints are characterized by the presence of a fluid-filled synovial cavity between the articulating surfaces of two bones.
This arrangement allows for considerable movement.
The joint between the atlas and axis (atlanto-axial joint) is a pivot joint,which is a specific type of synovial joint.
Therefore,option $A$ correctly identifies both the characteristic and an example.

(B) : According to the sliding-filament theory of muscle contraction,actin and myosin filaments slide past each other with the help of cross-bridges to reduce the length of the sarcomeres.
The smallest unit of muscle contraction is a sarcomere (which is delineated by $Z$-lines).
As a muscle contracts,the $Z$-lines come closer together (shortening the sarcomere),the width of the $I$-bands decreases,and the width of the $H$-zones decreases,but there is no change in the width of the $A$-band.
During relaxation,cross-bridges disappear and actin filaments slide back from $A$-bands; the width of the $I$-bands and $H$-zones increases,but there is still no change in the width of the $A$-band.

(A) : Myasthenia gravis is an autoimmune disorder in which autoantibodies bind to cholinergic receptors on muscle cells and impair the ability of the neurotransmitter acetylcholine to induce muscular contraction. This leads to fatigue,weakening,and paralysis of skeletal muscles of the mouth and throat,which may prevent normal swallowing.
$B$: Gouty arthritis is caused by the accumulation of uric acid crystals in the joints,not urea or creatine,causing inflammation.
$C$: Osteoporosis is typically caused by a deficiency of vitamin $D$,not an overdose.
$D$: Muscular dystrophy is a genetic disorder characterized by the progressive degeneration of skeletal muscles,not by rapid contractions.

(C) The correct option is $C$.
In the given figure:
$A$ is the retina,which is the innermost layer of the eyeball and contains photoreceptors,namely rods and cones,responsible for vision.
$B$ is the blind spot,the point where optic nerves leave the eye and retinal blood vessels enter it; it contains no photoreceptor cells.
$C$ is the aqueous chamber,which is the space between the cornea and the lens,filled with aqueous humor.
$D$ is the sclera,the outermost layer of the eyeball,which maintains the shape of the eyeball and protects the inner layers.

(B) The correct answer is $B$.
$K^+$ ions are the most abundant cations found in the intracellular fluid (cytoplasm) of cells.
In contrast,$Na^+$ ions are the most abundant cations found in the extracellular fluid.
This ionic gradient is maintained by the $Na^+-K^+$ pump,which is essential for maintaining the resting membrane potential of cells.

(C) Based on the provided diagram of the synapse:
$A$ points to the receptors located on the postsynaptic membrane.
$B$ points to the synaptic cleft,the space between the presynaptic and postsynaptic neurons.
$C$ points to the synaptic vesicles containing neurotransmitters.
$D$ points to the neurotransmitter molecules released into the synaptic cleft.
Comparing these with the options:
Option $A$ is incorrect because $A$ is a receptor,not a neurotransmitter.
Option $B$ is incorrect because $C$ is a synaptic vesicle,not a neurotransmitter.
Option $C$ is correct because $A$ is a receptor and $C$ represents synaptic vesicles.
Option $D$ is incorrect because $D$ represents neurotransmitters,not $K^+$ ions.

(C) Based on the provided diagram of the synapse:
$A$ represents the Receptor on the postsynaptic membrane.
$B$ represents the Synaptic cleft.
$C$ represents the Synaptic vesicles containing neurotransmitters.
$D$ represents the Neurotransmitter molecules being released.
However,evaluating the standard $NCERT$ diagram for this structure:
$A$ is the Receptor.
$B$ is the Synaptic cleft.
$C$ is the Synaptic vesicle.
$D$ is the Neurotransmitter.
Given the options provided,option $(c)$ is the most appropriate identification where $C$ is identified as a Receptor (or vesicle component) and $D$ as Synaptic vesicles,though there is a slight discrepancy in standard labeling. Based on the provided solution key,$(c)$ is the intended answer.

(B) Based on the provided sagittal section of the human brain:
$A$ represents the Cerebral hemisphere (part of the forebrain).
$B$ represents the Thalamus (part of the forebrain).
$C$ represents the Pons varolii (part of the hindbrain).
$D$ represents the Cerebellum (part of the hindbrain).
Therefore,option $B$ correctly identifies $A$ as the Cerebrum (Cerebral hemisphere) and $C$ as the Pons.

(C) : In the given figure, $A$ is the adrenal gland which secretes two catecholamines; adrenaline (epinephrine) and noradrenaline (norepinephrine). Adrenaline increases the conversion of glycogen to glucose, providing quick energy for the "fight or flight" response. $B$ is the renal pelvis, which is a sac-like cavity of the kidney leading to the ureters; it is not directly connected to the loop of Henle. $C$ is the medulla, the inner region of the kidney containing the loop of Henle, collecting ducts, and ducts of Bellini. $D$ is the cortex, which has proximal and distal convoluted tubules and contains Malpighian corpuscles.

(C) The correct answer is $C$. Iodine is essential for the synthesis of thyroid hormones $T_3$ and $T_4$.
Iodine binds to tyrosine residues in thyroglobulin,which is then processed to form triiodothyronine $(T_3)$ and thyroxine $(T_4)$.
If a pregnant female has a deficiency of iodine in her diet,it leads to improper synthesis of thyroid hormones in the developing fetus.
The deficiency of thyroid hormones in infants results in a condition known as 'cretinism'.
The symptoms of cretinism include stunted growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.

(A) : Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
$B$: Releasing and inhibitory hormones are produced by the hypothalamus,not the pituitary gland.
$C$: The adenohypophysis is under the control of hypothalamic hormones via the hypophyseal portal system,whereas the neurohypophysis is under direct neural regulation.
$D$: Several organs like the gastrointestinal tract,heart,kidney,and liver produce hormones (e.g.,$ANF$ from the heart,erythropoietin from the kidney).

(A) : Iodine is essential for the synthesis of thyroxine. $A$ deficiency of iodine in the diet leads to low production of thyroxine (hypothyroidism) and enlargement of the thyroid gland,a condition known as goitre.
$B$: Corpus luteum secretes progesterone,not testosterone. Progesterone is essential for maintaining the endometrium.
$C$: Oxytocin is synthesized by the hypothalamus and stored/released by the posterior pituitary,not the anterior pituitary.
$D$: Growth hormone $(GH)$ is secreted by the anterior pituitary,not the posterior pituitary.

(C) : Interstitial cells (or Leydig's cells) are the cells located between the seminiferous tubules of the testis.
They secrete androgens,primarily testosterone,in response to stimulation by Luteinizing Hormone $(LH)$ from the anterior pituitary gland.
Androgens are responsible for the development and maintenance of male secondary sexual characteristics and stimulate the germinal epithelium to undergo spermatogenesis (production of sperms).

(A) Norepinephrine is a neurotransmitter released by the postganglionic fibers of the sympathetic nervous system.
It is also secreted by the adrenal medulla along with epinephrine.
It acts to increase the heart rate and force of contraction.
It generally causes vasoconstriction,which leads to an increase in blood pressure,not a decrease.
Therefore,statements $(i)$ and $(iii)$ are correct.

(B) : Insulin is a peptide hormone,secreted by the $\beta$-cells of the islets of Langerhans in the pancreas. It promotes the uptake of glucose by body cells,particularly in the liver (hepatocytes) and muscles (adipocytes). By facilitating the conversion of glucose into glycogen (glycogenesis) in the liver and muscles,it effectively lowers the blood glucose concentration.

(D) In most seeds,the seed coat is thin and membranous. However,in coconut,the seed coat is not thin and membranous; instead,it is thick and fibrous. The coconut fruit is a drupe,and the fibrous part is the mesocarp,while the seed coat is part of the hard endocarp and the seed itself.

(D) : Plant viruses often contain parasites of their own,referred to as satellites.
Satellite $RNAs$ are highly dependent on their helper virus for both replication and encapsidation.
Their size varies from $194$ to $1500$ nucleotides (approx.).
The larger satellites contain open reading frames and express proteins,whereas smaller satellites do not produce functional proteins.

(C) $Ascaris$ infection is acquired by humans through the direct ingestion of $Ascaris$ eggs,which contain the infective second-stage larva,via contaminated food or water.
$Ascaris$ has a monogenetic life cycle.
There is no vector or intermediate host involved in its transmission.

(D) The correct answer is $D$.
In $Cycas$,specialized roots known as coralloid roots are formed.
These roots show a symbiotic association with nitrogen-fixing cyanobacteria,such as $Nostoc$ and $Anabaena$.
Coralloid roots are irregular,negatively geotropic,and dichotomously branched,resembling coral structures.
They lack root hairs and root caps,and the cyanobacteria reside in the cortical region of these roots to provide fixed nitrogen to the plant.

(D) : Denitrification is a biological process in which nitrates $(NO_3^-)$ in the soil are reduced to molecular nitrogen $(N_2)$ gas, which is then released into the atmosphere. This process is carried out by denitrifying bacteria such as $Pseudomonas \text{ } denitrificans$ and $Thiobacillus \text{ } denitrificans$. Additionally, the anaerobic oxidation of ammonium $(NH_4^+)$, also known as the $Anammox$ process, involves the conversion of ammonium and nitrite directly into dinitrogen gas $(N_2)$ under anaerobic conditions.

(D) In Pteridophytes,the gametophyte (prothallus) is small but multicellular,free-living,and mostly photosynthetic. Some Pteridophytes like Selaginella exhibit heterospory,which is considered a precursor to the seed habit. Option $A$ is incorrect because the prothallus is the gametophyte itself,not a stage within it. Option $B$ is incorrect because the female gametophyte in Gymnosperms is retained within the megasporangium and is not free-living. Option $C$ is incorrect as these structures are typically associated with Bryophytes (like Marchantia). Therefore,option $D$ is the correct statement.

(B) Cycas is a gymnosperm,and Adiantum is a pteridophyte (fern).
Both Cycas and Adiantum possess motile male gametes (antherozoids) that require water or a fluid medium to reach the female gamete for fertilization.
While both have vascular tissues,the presence of motile male gametes is a specific shared characteristic often highlighted in evolutionary biology comparisons between these groups.
Seeds are present in Cycas but absent in Adiantum.
Cambium is present in Cycas but absent in Adiantum.

(C) Statement $(1)$ is correct: In bryophytes (liverworts and mosses) and pteridophytes (ferns),the gametophyte phase is free-living.
Statement $(2)$ is correct: Gymnosperms are heterosporous,and some pteridophytes like Selaginella and Salvinia are also heterosporous.
Statement $(3)$ is correct: In Fucus (algae),Volvox (algae),and Albugo (fungi),sexual reproduction is of the oogamous type.
Statement $(4)$ is incorrect: The sporophyte in mosses is more elaborate than in liverworts.
Therefore,there are $3$ correct statements.

(B) Cyanobacteria,specifically $Anabaena$ and $Nostoc$,form a symbiotic association with the coralloid roots of $Cycas$.
These cyanobacteria fix atmospheric nitrogen,which is beneficial for the plant.
Therefore,in paddy fields or other environments,cyanobacteria are commonly found associated with the coralloid roots of $Cycas$.

(D) In most monocots like maize $(Zea \, mays)$, the seed coat is membranous and generally fused with the fruit wall. In dicots like gram $(Cicer \, arietinum)$, groundnut $(Arachis \, hypogaea)$, and coconut $(Cocos \, nucifera)$, the seed coat is distinct, thick, and not membranous. However, specifically in the context of $NCERT$ biology, the seed coat of maize is described as membranous and fused with the fruit wall. Among the given options, the seed coat of maize is thin and membranous, whereas in gram, groundnut, and coconut, it is not thin and membranous. Given the standard textbook phrasing, the question asks for the exception where the seed coat is not thin and membranous. Since maize is the classic example of a membranous seed coat, the other options (gram, groundnut, coconut) fit the criteria of having a non-membranous seed coat. However, in many competitive exams, 'Maize' is the correct answer for having a thin, membranous seed coat. If the question asks where it is $NOT$ thin and membranous, any of the others would technically be correct. Based on standard curriculum, 'Maize' is the intended answer for having a membranous seed coat.

(A) In $China$ $rose$ ($Hibiscus$ $rosa-sinensis$):
$1$. The flowers are $Actinomorphic$ (radial symmetry),which means they can be divided into two equal radial halves in any radial plane passing through the center.
$2$. The flowers are $Hypogynous$,meaning the ovary is superior and other floral parts (sepals,petals,stamens) are situated below the ovary.
$3$. The aestivation is $Twisted$,where one margin of the sepal or petal overlaps that of the next one and so on.

(D) Hypogynous flowers are those in which the gynoecium occupies the highest position while the other parts are situated below it. This is characteristic of superior ovaries.
$1$. Bitter gourd: Epigynous
$2$. Mustard: Hypogynous
$3$. Brinjal: Hypogynous
$4$. Pumpkin: Epigynous
$5$. China rose: Hypogynous
$6$. Lupin: Hypogynous
$7$. Cucumber: Epigynous
$8$. Sunn hemp: Hypogynous
$9$. Gram: Hypogynous
$10$. Guava: Epigynous
$11$. Bean: Hypogynous
$12$. Chilli: Hypogynous
$13$. Plum: Perigynous
$14$. Petunia: Hypogynous
$15$. Tomato: Hypogynous
$16$. Rose: Perigynous
$17$. Withania: Hypogynous
$18$. Potato: Hypogynous
$19$. Onion: Hypogynous
$20$. Aloe: Hypogynous
$21$. Tulip: Hypogynous
Counting the hypogynous ones: Mustard,Brinjal,China rose,Lupin,Sunn hemp,Gram,Bean,Chilli,Petunia,Tomato,Withania,Potato,Onion,Aloe,and Tulip. Total = $15$.

(B) is the correct answer. Somatic embryos develop from somatic cells,not from microspores. Their development is comparable to that of a zygotic embryo. They are similar to a normal embryo except that their development is induced from a diploid somatic cell. Somatic embryo culture is typically induced by a high concentration of an auxin,such as $2, 4-D$. Microspores are haploid cells that give rise to pollen grains,not somatic embryos.

(C) good producer of citric acid is $Aspergillus$ $niger$.
$Clostridium$ $butylicum$ is used for the production of butyric acid.
$Saccharomyces$ $cerevisiae$ is used for the commercial production of ethanol.
$Pseudomonas$ is known for producing alkaline proteases.

(B) : Biopesticides are biological agents used for the control of weeds, insects, and pathogens. The microorganisms used as biopesticides include viruses, bacteria, protozoa, fungi, and mites. Some of these are used on a commercial scale. The most important example is the soil bacterium, $Bacillus \text{ } thuringiensis$ $(Bt)$. Spores of this bacterium produce an insecticidal $Cry$ protein. When ingested by butterfly caterpillars, these spores release the toxin, which kills the larvae.

(D) $Bt$ toxin genes were isolated from $Bacillus$ $thuringiensis$ and incorporated into several crop plants,such as cotton.
The choice of genes depends upon the crop and the targeted pest,as most $Bt$ toxins are insect-group specific.
The toxin is coded by a gene named $cry$. There are numerous such genes.
Two $cry$ genes,$cryIAc$ and $cryIIAb$,have been incorporated into cotton.
The genetically modified crop is called $Bt$ cotton as it contains $Bt$ toxin genes that provide resistance against cotton bollworms.

(B) $RNA$ interference $(RNAi)$ is a biological process in which $RNA$ molecules inhibit gene expression or translation,by neutralizing targeted $mRNA$ molecules.
This method involves the silencing of a specific $mRNA$ due to a complementary $dsRNA$ molecule.
The complementary $dsRNA$ binds to the target $mRNA$,preventing its translation and thereby causing its silencing.
This mechanism serves as a method of cellular defense in all eukaryotic organisms.

(A) : Gene therapy is a corrective therapy used to treat diseases caused by genetic defects.
In this process,functional genes are inserted into a patient's cells or tissues to replace or compensate for the defective gene.
Viral vectors,such as $Adenovirus$ or $Retrovirus$,are commonly used to deliver the normal,functional gene into the target cells because of their high efficiency in infecting human cells.

(D) The correct answer is $D$.
Sea anemone attaches itself to the shell of a hermit crab.
This association is a classic example of mutualism,which is a type of symbiosis.
The sea anemone provides camouflage and protection to the hermit crab using its stinging cells (nematocysts).
In return,the hermit crab provides mobility to the sea anemone,allowing it to reach new food sources.
Since both organisms derive benefit from this interaction,it is classified as symbiosis (mutualism).

(B) The population growth is determined by the formula: $\text{Net Increase} = (\text{Natality} + \text{Immigration}) - (\text{Mortality} + \text{Emigration})$.
Natality and immigration are factors that increase the population size.
Mortality and emigration are factors that decrease the population size.
Given values:
$\text{Natality} = 250$
$\text{Immigration} = 20$
$\text{Mortality} = 240$
$\text{Emigration} = 30$
$\text{Net Increase} = (250 + 20) - (240 + 30) = 270 - 270 = 0$.
Therefore, the net increase in the population is zero.

(D) The correct answer is $D$.
An age pyramid is a graphical representation of the abundance of individuals in different age groups,with pre-reproductive individuals at the base,reproductive individuals in the middle,and post-reproductive individuals at the top.
$A$ triangular age pyramid (broad base) indicates a high proportion of pre-reproductive individuals,a moderate number of reproductive individuals,and fewer post-reproductive individuals.
This structure represents a young or rapidly growing population.
In contrast,a bell-shaped pyramid represents a stable population,and an urn-shaped pyramid represents a declining population.

(C) : Parasitism is a relationship between two living organisms of different species in which one organism,called the parasite,obtains its food directly from another living organism,called the host. The parasite spends a part or whole of its life either on or inside the body of the host.
The general parasitic adaptations are $(i)$ anaerobic respiration in internal parasites,$(ii)$ loss of certain unnecessary organs,$(iii)$ presence of adhesive organs,$(iv)$ excessive multiplication,$(v)$ resistant cysts and eggs for safe transfer of their progeny to new hosts,and $(vi)$ well-developed and complicated reproductive organs.
Therefore,the loss of reproductive capacity is not a parasitic adaptation; in fact,parasites typically exhibit a high reproductive capacity to ensure the survival of their species.

(C) : Benthic organisms are bottom-dwelling forms found crawling on or attached to the substrate at the bottom of aquatic ecosystems. The physical and chemical characteristics of the sediment,such as particle size,organic content,and oxygen availability,directly determine the type of benthic organisms that can thrive in that specific environment.

(A) : The reservoir pool of phosphorus is found in phosphate rocks,while the cycling pool consists of soil and water for terrestrial and aquatic ecosystems,respectively.
Small amounts of phosphate are continuously added to the cycling pool through the weathering of rocks.
Phosphate is generally found in the soil in combination with calcium,iron,and aluminium.
Unlike carbon or nitrogen,an atmospheric or gaseous cycle is absent for phosphorus.
Phosphate circulates in the abiotic environment within both the lithosphere and the hydrosphere.

(A) Secondary productivity is defined as the rate of formation of new organic matter by consumers.
It represents the amount of energy stored as biomass by heterotrophs (consumers) after accounting for the energy lost through respiration and other metabolic processes.
Primary productivity is associated with producers (plants),whereas secondary productivity is associated with consumers that feed on these producers or other consumers.

(C) : Decomposition is the process in which decomposers break down complex organic matter into inorganic substances like carbon dioxide,water,and nutrients.
The important steps in the process of decomposition are fragmentation,leaching,catabolism,humification,and mineralisation.
Detritivores (e.g.,earthworm) break down detritus into smaller particles. This process is called fragmentation.
By the process of leaching,water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called catabolism.
Humification leads to the accumulation of a dark-coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
The humus is further degraded by some microbes and the release of inorganic nutrients occurs by the process known as mineralisation.

(A) The correct answer is $A$.
Primary consumers are herbivorous organisms that feed directly on producers (plants).
In a maize field ecosystem,maize plants act as producers.
Grasshoppers are herbivores that feed on these maize plants,making them primary consumers.
Wolf and lion are carnivores,which act as secondary or tertiary consumers.
Phytoplanktons are producers found in aquatic ecosystems,not in a maize field.

(A) : The transfer of food energy from producers to consumers through a series of organisms with repeated eating and being eaten is known as a food chain.
Green plants are always the first link of a food chain because they alone are capable of synthesizing organic food by using light energy through photosynthesis.
In the given chain: Small plants (Producers) $\rightarrow$ Zooplanktons (Primary Consumers) $\rightarrow$ Fish (Secondary Consumers) $\rightarrow$ Man (Tertiary Consumer).
Therefore,the producer in this chain is small plants.

(A) : Ex situ conservation is the conservation of selected rare plants or animals in places outside their natural habitats. It includes botanical gardens, zoological parks, seed banks, cryopreservation, field gene banks, and tissue culture.
Shifting cultivation is an agricultural practice where land is cleared and cultivated for a short period, which often leads to deforestation and loss of biodiversity, rather than its conservation.
Botanical gardens, field gene banks, and seed banks are all established methods used for the ex situ conservation of plant species.

(A) The correct answer is $A$.
According to global biodiversity estimates,$Fungi$ represent the largest group of species among the options provided.
$Fungi$ are achlorophyllous,heterotrophic,spore-forming,non-vascular,eukaryotic organisms that possess chitin in their cell walls and store food as glycogen.
They act as major decomposers in various ecosystems and play a crucial role in nutrient cycling.

(D) The correct answer is $D$.
Genetic diversity refers to the variation in the number and types of genes, as well as chromosomes, present in different species and the variations in genes and their alleles within the same species.
In India, $Oryza \text{ } sativa$ (rice) exhibits the highest genetic diversity.
There are more than $50,000$ genetically different strains of rice in India alone, which is a prime example of high genetic diversity within a single species.

(A) $(A) : IUCN$ stands for International Union for Conservation of Nature and Natural Resources,which is now known as the World Conservation Union $(WCU)$.
Its headquarters are located in Gland,Switzerland.
It maintains the 'Red Data Book' or 'Red List',which is a catalogue of taxa (species) facing the risk of extinction.
The 'Red Data Book' or 'Red List' was initiated in $1963$.
The $2000$ Red List provided an assessment of $18,000$ species.

(C) The Kyoto Protocol is an international treaty aimed at reducing the emission of greenhouse gases.
It was adopted at the third session of the Conference of Parties $(CoP-3)$ to the $UNFCCC$ (United Nations Framework Convention on Climate Change) in $1997$,held in Kyoto,Japan.

(C) Global warming is primarily caused by the increase in greenhouse gases like $CO_2$ in the atmosphere.
$1$. Reducing deforestation helps in maintaining forest cover,which acts as a carbon sink by absorbing $CO_2$ through photosynthesis.
$2$. Cutting down the use of fossil fuels (like coal,oil,and natural gas) reduces the emission of $CO_2$ and other greenhouse gases,thereby mitigating the greenhouse effect.
Therefore,option $C$ is the correct method to control global warming.

(D) The Air (Prevention and Control of Pollution) Act was enacted in $1981$ to provide for the prevention,control,and abatement of air pollution in India. It was later amended in $1987$ to include noise as an air pollutant.

(C) The correct answer is $C$.
International conferences held in Kyoto, Japan, established commitments from various countries to reduce overall greenhouse gas emissions to a level $5\%$ below that of $1990$ for the period $2008-2012$.
In Doha, Qatar, on $8^{th}$ December $2012$, the "Doha Amendment to the Kyoto Protocol" was adopted.
The second commitment period spans from $1^{st}$ January $2013$ to $31^{st}$ December $2020$.

(B) : Carbon dioxide is a greenhouse gas with a warming effect of $60\%$. Greenhouse gases are essential for keeping the Earth warm and hospitable. They prevent a substantial part of long-wave radiations emitted by the Earth from escaping into space and radiate a part of this energy back to the Earth. This phenomenon is called the greenhouse effect. Because of the greenhouse effect,the mean annual temperature of the Earth is $15^{\circ}C$. Recently,the concentration of greenhouse gases has started rising,which is resulting in an increase in the mean global temperature. This is called global warming. Deforestation has reduced carbon dioxide assimilation,causing excess $CO_2$ to remain in the air. Excessive use of fossil fuels is adding more $CO_2$ to the atmosphere,which intensifies the greenhouse effect.

(B) $PM\ 2.5$ refers to particulate matter with a diameter of $2.5 \ \mu m$ or less. These particles are considered the most harmful to human health according to the Central Pollution Control Board $(CPCB)$.
They are small enough to be inhaled deep into the lungs,where they cause respiratory problems,irritation,inflammation,and damage to lung tissues,potentially leading to premature death.
While they significantly impact the respiratory system,they do not directly enter the circulatory system; their effects on the circulatory system are indirect,occurring through the respiratory pathway.
Therefore,the statement that they can directly enter the circulatory system is incorrect.

(D) Multicellular fungi,filamentous algae,and the protonema of mosses all share the characteristic of reproducing through fragmentation. In this process,the body of the organism breaks into distinct pieces or fragments,and each fragment grows into a new individual. This is a common method of vegetative propagation or asexual reproduction in these groups.

(C) Perisperm is the persistent nucellus in a seed,which is diploid $(2n)$ in nature because it is derived from the maternal sporophytic tissue. In contrast,the endosperm is a triploid $(3n)$ tissue formed by the fusion of one male gamete with the secondary nucleus (double fertilization). Therefore,the key difference is that perisperm is a diploid tissue,whereas endosperm is a triploid tissue.

(C) Sexual reproduction involves the fusion of male and female gametes,which are formed through meiosis.
This process involves independent assortment and crossing over,which leads to the creation of new genetic combinations in the offspring.
These genetic variations are crucial for evolution and adaptation to changing environments.
Therefore,the primary outcome of sexual reproduction is the generation of new genetic combinations that lead to variation.

(C) The incorrect statement is $C$. In $Oomycetes$ (a group of water molds),the sexual reproduction is oogamous. In oogamy,the female gamete is typically large and non-motile (egg/ovum),while the male gamete is small and motile (antherozoid/sperm). The statement provided in option $C$ incorrectly reverses these characteristics. Options $A$,$B$,and $D$ are biologically correct descriptions of gametic types and reproductive strategies in algae and fungi.

(D) Amniocentesis is a prenatal diagnostic technique used to determine chromosomal abnormalities and fetal sex by analyzing the amniotic fluid surrounding the fetus.
$1$. Klinefelter syndrome is a chromosomal disorder $(47, XXY)$ which can be detected by karyotyping cells from the amniotic fluid.
$2$. The sex of the fetus can be determined by identifying the presence of Barr bodies or by chromosomal analysis.
$3$. Down syndrome is a chromosomal disorder (Trisomy $21$) which is detectable via amniocentesis.
$4$. Jaundice is a physiological condition related to liver function and bilirubin levels,which cannot be diagnosed through the chromosomal analysis of amniotic fluid.
Therefore,the correct option is $D$.

(B) Recombination frequency of $50\%$ indicates that the genes are either located on different chromosomes or are so far apart on the same chromosome that they assort independently.
$1$. If genes are on different chromosomes,they show independent assortment.
$2$. If genes are on the same chromosome but very far apart,multiple crossovers occur,resulting in $50\%$ recombination.
$3$. Tightly linked genes show very low recombination frequency (much less than $50\%$).
Therefore,the statement that genes are tightly linked is incorrect.

(B) Cell-mediated immunity $(CMI)$ is an immune response that does not involve antibodies.
Instead,it involves the activation of phagocytes,antigen-specific cytotoxic $T$-lymphocytes,and the release of various cytokines in response to an antigen.
$T$-lymphocytes are responsible for $CMI$,whereas $B$-lymphocytes are responsible for humoral immunity (antibody-mediated immunity).
Therefore,the correct option is $B$.

(B) During the process of sewage treatment,specifically in the anaerobic sludge digesters,anaerobic bacteria (methanogens) act on the organic matter present in the sludge.
These bacteria produce a mixture of gases,which is known as biogas.
The primary components of this biogas are $CH_4$ (Methane),$H_2S$ (Hydrogen sulfide),and $CO_2$ (Carbon dioxide).
Therefore,the correct combination is Methane,Hydrogen sulfide,and Carbon dioxide.

(B) The blue-white screening method is based on the insertional inactivation of the $lacZ$ gene.
$1$. The $lacZ$ gene encodes the enzyme $\beta$-galactosidase.
$2$. In non-recombinant bacteria,the $lacZ$ gene is intact and functional,so the bacteria produce $\beta$-galactosidase. This enzyme reacts with the chromogenic substrate $X-gal$ to produce a blue color.
$3$. In recombinant bacteria,the foreign $DNA$ is inserted into the $lacZ$ gene,causing insertional inactivation. Consequently,no functional $\beta$-galactosidase is produced,and the colonies remain white.

(D) Restriction endonucleases cut $DNA$ at specific recognition sequences,resulting in fragments of varying lengths.
These $DNA$ fragments are negatively charged due to the phosphate backbone.
Gel electrophoresis is the technique used to separate these $DNA$ fragments based on their size (molecular weight).
Under an electric field,the fragments move through a matrix (usually agarose gel) towards the anode (positive electrode).
Smaller fragments move faster and travel further through the gel pores compared to larger fragments,allowing for their separation.

(D) Pollen grains are generally spherical and possess a prominent two-layered wall.
The hard outer layer,called the exine,is made up of sporopollenin,which is one of the most resistant organic materials known.
It can withstand high temperatures,strong acids,and strong alkalis,and no enzyme is known that degrades sporopollenin.

(C) hybridization probe is a fragment of $DNA$ of variable length which is used in $DNA$ samples to detect the presence of nucleotide sequences (the $DNA$ target) that are complementary to the sequence in the probe.
The probe hybridizes to single-stranded $DNA$ whose base sequence allows probe-target base-pairing due to complementarity between the probe and the target.
Therefore,$DNA$ probes are specifically used to identify and select genes of interest from a genomic library.

(C) Nagarjunsagar-Srisailam Tiger Reserve is the largest Tiger reserve in India.
It is located in the state of Andhra Pradesh and Telangana.
It covers a vast area,making it the largest protected area for tigers in the country.