NEET 2015 Biology Question Paper with Answer and Solution

(D) : Cohesion,adhesion,and surface tension are the forces responsible for the movement of water up the tracheary elements.
Water molecules remain attached to one another by a strong mutual force of attraction called cohesion force.
Due to the cohesion force,the water column can bear a tension or pull of up to $100 \ atm$.
Therefore,the cohesion force is also referred to as tensile strength.
Its theoretical value is about $15,000 \ atm$,but the measured value inside the tracheary elements ranges between $45 \ atm$ to $207 \ atm$.
The water column does not break its connection from the tracheary elements because of another force called adhesion force,which acts between the vessel walls and water molecules.
Additionally,surface tension accounts for high capillarity through tracheids and vessels.

(D) : In girdling or ringing experiments,a ring of bark is cut from the stem. This process removes the phloem. Nutrients accumulate above the ring,causing the bark to swell and potentially produce adventitious roots. Growth is vigorous above the ring. The tissues below the ring show a cessation of growth and begin to shrivel. The roots are starved of nutrients and die if the ring is not healed. The death of the roots eventually leads to the death of the entire plant,which demonstrates that the bark or phloem is responsible for the transport of organic solutes toward the roots.

(D) : The transpiration process pulls water upwards with the help of cohesion and adhesion properties of water molecules. According to the transpiration pull theory,due to transpiration,the water column inside the plant comes under tension. This is called 'transpiration pull'. On account of this tension,the water column is pulled up passively from below to the top of the plant (almost like a rope).
Root pressure is the pressure that forces water,absorbed from the soil,to move through the roots and up ($i.e.$,pushes it up) the stem of a plant. It may be due to both the osmosis of water from the soil into the root cells,and the active pumping of salts into xylem tissue which maintains a concentration gradient along which the water moves.

(D) The most widely accepted and recent explanation for stomatal movement is the $K^+$ ion transport theory (Potassium pump theory).
According to this theory,during the daytime,$K^+$ ions enter the guard cells from the surrounding subsidiary cells,which decreases the water potential of the guard cells.
This leads to the endosmosis of water into the guard cells,making them turgid and causing the stomata to open.
Conversely,during the night,$K^+$ ions move out of the guard cells,leading to the exosmosis of water,which makes the guard cells flaccid and causes the stomata to close.

(C) The correct answer is $C$. Oxygen is evolved during photosynthesis through the process of photolysis of water,which occurs in the membranes of grana thylakoids.
The phenomenon of breaking down water into hydrogen and oxygen in illuminated chloroplasts is called photolysis or photocatalytic splitting of water.
Light energy,an Oxygen Evolving Complex $(OEC)$,and electron carriers are required for this process. The Oxygen Evolving Complex is attached to the inner surface of the thylakoid membrane and contains four $Mn$ ions.
Light-energized changes in $Mn$ $(Mn^{2+}, Mn^{3+}, Mn^{4+})$ remove electrons from the $OH^-$ component of water,resulting in the formation of oxygen.
The liberation of $O_2$ also requires two other essential ions: $Ca^{2+}$ and $Cl^-$.
The reaction is as follows:
$4H_2O \rightleftharpoons 4H^+ + 4OH^-$
$4OH^- \xrightarrow[Mn^{2+}, Ca^{2+}, Cl^-]{\text{Oxygen evolving complex}} 2H_2O + O_2 \uparrow + 4e^-$

(C) : Leghaemoglobin is a pinkish pigment present in the root nodules of leguminous plants. It acts as an oxygen scavenger and protects the nitrogenase enzyme from oxygen poisoning,as nitrogenase is highly sensitive to molecular oxygen.

(C) The correct answer is $C$. Macroelements (macronutrients) are essential elements present in plant tissues in large amounts,typically $1-10 \text{ mg}$ per gram of dry matter.
These elements are primarily involved in the synthesis of organic molecules and the maintenance of osmotic potential.
The nine macronutrients are $C, H, O, N, P, K, S, Mg,$ and $Ca$.

(B) The light-independent reactions (also known as dark reactions or Blackman's reactions) of photosynthesis occur in the stroma or matrix of the chloroplasts.
These reactions are enzymatic processes that catalyze the assimilation of $CO_2$ into carbohydrates.

(C) : Chromatophores are the internal membrane systems of photosynthetic forms which possess photosynthetic pigments. They occur in photoautotrophic bacteria,$e.g.$,purple bacteria and green bacteria.

(A) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
In mitochondria,the $ETC$ is located in the inner mitochondrial membrane,which is folded into structures called cristae.
Therefore,cytochromes are found in the cristae of mitochondria.

(C) : Auxin bioassay is a quantitative test as it measures the concentration of auxin required to produce a specific effect and the magnitude of that effect. The $Avena$ Curvature test is based on the experiments of Went $(1928)$. $A$ $10^{\circ}$ curvature is produced by an auxin concentration of $150 \ mg/L$ at $25^{\circ}C$ and $90\%$ relative humidity. This test can measure auxin concentrations up to $300 \ mg/L$. Auxin from a shoot tip or any other plant organ is allowed to diffuse into a standard-sized agar block (generally $2 \times 2 \times 1 \ mm$). Alternatively,auxin can be dissolved directly into the agar. $A$ $15-30 \ mm$ long oat coleoptile grown in the dark is held vertically over water. $A$ $1 \ mm$ tip of the coleoptile is removed without injuring the primary leaf. After $3$ hours,a second decapitation is performed at a distance of $4 \ mm$. The primary leaf is then pulled loose,and the agar block is placed against the tip of the decapitated coleoptile. After $90-110$ minutes,the coleoptile is observed to have bent. The curvature is then measured,or it can be photographed and determined via a shadow graph.

(B) : Auxins induce cell elongation. In a differentially illuminated plant,they accumulate in the shaded part,causing elongation of the cells in the shaded part. This unequal elongation on two sides causes the plant to curve or bend towards the light source,$i.e.$,phototropic curvature.

(C) The correct answer is $C$.
Geometric growth cannot be sustained for long in natural conditions due to limited nutrient availability,which eventually slows down the growth rate.
This leads to a stationary phase or even a decline in growth.
When plotting the growth against time,it results in a typical $S$-shaped or sigmoid curve.
$A$ sigmoid growth curve is characteristic of most organisms in their natural environment,including plants.

(D) : Succus entericus or intestinal juice $(pH = 7.8)$ refers to the secretions of the glands of the small intestine.
It contains many enzymes such as maltase,isomaltase,lipase,lactase,$\alpha$-dextrinase,enterokinase,aminopeptidase,nucleotidase,and nucleosidase for the digestion of carbohydrates,proteins,fats,and nucleic acids.
Nuclease is not a digestive enzyme found in intestinal juice; it is primarily associated with pancreatic secretions or intracellular processes.

(D) The correct answer is $D$.
In humans,the primary dentition (milk teeth) consists of $20$ teeth in total,which include $8$ incisors,$4$ canines,and $8$ molars.
Premolars are completely absent in the primary dentition.
In contrast,the permanent dentition consists of $32$ teeth,which include $8$ incisors,$4$ canines,$8$ premolars,and $12$ molars.
Therefore,premolars are the type of teeth that are not present in the primary dentition.

(A) The secretion of the cells of the gastric glands forms gastric juice with a $pH$ of $2$ to $3.7$.
It contains two proenzymes,pepsinogen and prorennin (rennin),along with gastric lipase,mucus,and hydrochloric acid.
Rennin (chymosin) is responsible for clotting milk by acting on the soluble milk protein caseinogen and converting it into insoluble calcium paracaseinate (curd).
This ensures that milk remains in the stomach long enough to be acted upon by protein-digesting enzymes.
The concentration of rennin is highest in young mammals (as their primary diet is milk),which reduces gradually with age.

(C) is the incorrect statement.
Brunner's glands are located in the submucosa of the duodenum,not the stomach.
These glands secrete an alkaline,watery fluid containing mucus and some enzymes,which helps neutralize the acidic chyme entering from the stomach.
Pepsinogen is secreted by the chief cells (or peptic cells) located in the gastric glands of the stomach mucosa,not by Brunner's glands.

(D) : Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. Cigarette smoking is a major cause of this disease. In this condition,the septa between the alveoli are destroyed,reducing the surface area available for gas exchange. The lungs lose their elasticity,and the alveolar sacs remain filled with air even after expiration,making exhalation difficult.

(D) The correct answer is $(d)$.
When you hold your breath,the concentration of $CO_2$ in the blood increases because it is not being exhaled.
This rise in $CO_2$ concentration (hypercapnia) is the primary stimulus that acts on the central chemoreceptors in the medulla oblongata of the brain.
These receptors detect the increase in $H^+$ ions resulting from the reaction of $CO_2$ with water,which triggers the respiratory centre to increase the rate and depth of breathing.
While a decrease in $O_2$ (hypoxia) can also stimulate breathing via peripheral chemoreceptors,the rise in $CO_2$ is the most sensitive and immediate trigger for the urge to breathe under normal physiological conditions.

(A) Whale is a mammal,and in mammals,two separate circulatory pathways are found: systemic circulation and pulmonary circulation.
Oxygenated and deoxygenated blood received by the left and right atria respectively pass on to the left and right ventricles.
Thus,oxygenated and deoxygenated bloods are not mixed.
This is referred to as double circulation,which is a characteristic feature of mammals,birds,and crocodiles.

(D) The cardiac cycle produces two main sounds,often described as 'lub' and 'dup'.
$1$. The first heart sound,'lub',is associated with the closure of the atrioventricular $(AV)$ valves.
$2$. The second heart sound,'dup',is associated with the closure of the semilunar valves.
$3$. This closure occurs at the end of ventricular systole,preventing the backflow of blood from the pulmonary artery and aorta into the ventricles.
Therefore,the correct option is $(d)$.

(B) $Erythropoiesis$ is the process of formation of red blood cells $(erythrocytes)$ which occurs in the red bone marrow in adults.
$Proerythroblast$ is the earliest precursor cell which gives rise successively to the early $erythroblast$,intermediate $erythroblast$,and late $erythroblast$.
Then,the nucleus is extruded and a biconcave,enucleated cell called $reticulocyte$ is formed,which is released into the blood.
In the blood,it matures into functional $erythrocytes$.

(B) The correct option is $B$.
$1$. Blood is a connective tissue consisting of a fluid matrix,plasma,and formed elements ($RBCs$,$WBCs$,and platelets).
$2$. Lymph is a fluid that lacks $RBCs$ and platelets; it is essentially plasma with $WBCs$ (lymphocytes).
$3$. Plasma is the straw-colored fluid matrix of blood,obtained after removing all cellular components ($RBCs$,$WBCs$,and platelets).
$4$. Serum is the fluid remaining after blood has clotted,which means it is plasma minus the clotting factors (like fibrinogen).

(A) : The temporary rise in blood pressure during the contraction of the heart is called systolic pressure,and the temporary fall in blood pressure during the relaxation of the heart is called diastolic pressure.
Blood pressure is expressed as the ratio of the systolic pressure over the diastolic pressure.
For a healthy resting adult person,the average systolic/diastolic pressures are $120/80 \ mmHg$.
The aorta is directly supplied by the left ventricle; thus,the blood pressure in the aorta is highest during the systole of the left ventricle.
During this phase,the left ventricle contracts and pushes blood into the aorta.

(B) The human urine is usually acidic because the renal tubules,specifically the proximal convoluted tubule $(PCT)$ and the distal convoluted tubule $(DCT)$,actively secrete hydrogen ions $(H^+)$ into the filtrate.
This process helps in maintaining the acid-base balance of the body fluids.
Additionally,the reabsorption of bicarbonate ions $(HCO_3^-)$ from the filtrate back into the blood further contributes to the acidic nature of the urine.

(A) The correct answer is $A$.
$Renin$ is a key component of the $Renin-Angiotensin-Aldosterone$ System $(RAAS)$.
When blood pressure or blood volume decreases,$Renin$ is released,which leads to the production of $Angiotensin-II$.
$Angiotensin-II$ stimulates the adrenal cortex to release aldosterone.
Aldosterone increases the reabsorption of $Na^+$ and water from the distal convoluted tubule and collecting duct,thereby reducing urine volume and making it more concentrated.
In contrast,$Atrial$ $natriuretic$ $factor$ $(ANF)$ is a vasodilator that inhibits $Renin$ secretion and promotes $Na^+$ excretion,leading to increased urine volume.
$Alcohol$ and $Caffeine$ are known to inhibit the release of $Antidiuretic$ $Hormone$ $(ADH)$,which leads to the production of large quantities of dilute urine.

(D) The correct answer is $D$.
Approximately $65\%$ of the glomerular filtrate is normally reabsorbed in the proximal convoluted tubule $(PCT)$ before reaching the loop of Henle.
The $PCT$ is responsible for the reabsorption of essential nutrients such as glucose,amino acids,vitamins,hormones,$Na^+$,$K^+$,$Cl^-$,phosphates,bicarbonates,water,and urea.
If the $PCT$ is removed,the reabsorption of these solutes and water is significantly impaired.
Consequently,a larger volume of fluid reaches the distal parts of the nephron,but because the primary reabsorptive site for water and solutes is absent,the final urine produced will be more concentrated due to the inability to regulate the osmotic balance effectively.

(A) The skeletal system performs several vital functions,including providing structural support,protecting internal organs,facilitating movement (locomotion) through its attachment to muscles,storing minerals like $Ca^{2+}$ and $PO_4^{3-}$,and producing blood cells (hematopoiesis) in the red bone marrow.
Production of body heat is primarily a function of the muscular system through metabolic processes and muscle contraction,not the skeletal system.
Therefore,the correct option is $A$.

(C) : Fibrous or immovable joints are the joints in which no movement occurs between the bones concerned. White fibrous tissue is present between the ends of the bones. Fibrous joints occur between the bones of the skull,known as sutures,and the joints between the teeth and the maxilla or mandible.

(A) : During muscle contraction,the laterally projecting heads (cross bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them.
This pulls the thin myofilaments toward the middle of the sarcomere,past the thick myofilaments.
The $Z$ lines come closer together and the sarcomere becomes shorter.
Length of the $A$ band remains constant.
Myofilaments (both actin and myosin) stay the same length.
Free ends of actin myofilaments move closer to the centre of the sarcomere,bringing $Z$ lines closer together.
$I$ bands shorten and $H$ zone narrows.
$A$ similar action in all the sarcomeres results in shortening of the entire myofibril and thereby of the whole fibre and the whole muscle.

(B) The correct answer is $B$. The glenoid cavity is a shallow,pyriform articular surface located on the lateral angle of the scapula. It articulates with the head of the humerus to form the shoulder joint (glenohumeral joint). This ball-and-socket joint allows for a wide range of movement in the upper limb.

(D) The anterior horns of the spinal cord contain the cell bodies of lower motor neurons.
These neurons send their axons through the anterior (ventral) roots to innervate skeletal muscles.
These cells are essential for both voluntary movements and reflex activities of the muscles they supply.
If the anterior horn motor cells are destroyed,the motor signals cannot reach the muscles,leading to a loss of voluntary motor control and muscle paralysis.

(C) : $A$ small oval, yellowish area of the retina lying exactly opposite the center of the cornea is named the $macula \, lutea$ or yellow spot, which has at its middle a shallow depression, the $fovea \, centralis$. The $fovea \, centralis$ has cone cells only. It is devoid of rods and blood vessels. The $fovea \, centralis$ is the place of most distinct vision.

(D) : The vestibular apparatus is a part of the inner ear located above the cochlea.
It consists of three semicircular canals,which detect head movements,and the utriculus and sacculus,which detect the position of the head.
It does not play any role in hearing but is responsible for maintaining the balance of the body and posture.

(D) : Language comprehension is a function of the cerebrum.
Cerebellum coordinates and controls rapid muscular activities such as running,typing,etc.
Although it does not initiate such voluntary movements,it is an important center for coordinating movements and for controlling posture and balance.
Cerebellum's function is almost exclusively motor; however,it is also implicated in some forms of learning.

(D) $Insulin$,$Glucagon$,and $Cortisone$ play significant roles in the regulation of blood sugar levels (glucose metabolism).
$Insulin$ lowers blood glucose,while $Glucagon$ and $Cortisone$ (a glucocorticoid) increase blood glucose levels.
$Aldosterone$ is a mineralocorticoid secreted by the adrenal cortex that primarily regulates the balance of sodium and potassium ions in the body,as well as water retention.
Therefore,$Aldosterone$ is not involved in sugar metabolism.

(C) The correct answer is $(C)$.
Two hormones,namely oxytocin $(OT)$ and antidiuretic hormone $(ADH)$ (also known as vasopressin),are synthesised in the hypothalamus.
These hormones are transported axonally to the posterior pituitary (neurohypophysis).
The posterior pituitary gland stores and releases these hormones into the blood circulation upon stimulation.

(A) The correct answer is $A$.
Epinephrine and norepinephrine are hormones secreted by the adrenal medulla.
These are known as emergency hormones or hormones of fight or flight,as they are released during stress or emergency conditions.
Additionally,epinephrine and norepinephrine are released by the adrenergic nerve fibers of the sympathetic nervous system,where they function as neurotransmitters,thus serving both endocrine and neural roles.

(C) : The rhizome is a thickened,underground,dorsiventral stem that grows horizontally at a particular depth within the soil.
It is brown in colour and shows cymose branching.
It can be distinguished from the modified root by the presence of nodes,internodes,terminal buds,axillary buds,and scale leaves.
The rhizomes are perennial and propagate vegetatively.
They store food materials and appear tuberous.
$E.g.$,$Zingiber$ $officinale$ (ginger),$Curcuma$ $longa$ (turmeric),$Canna$ $indica$.

(D) The correct answer is $(d)$. In cucumber,flowers are unisexual,meaning individual flowers are either male (staminate) or female (pistillate). Both types of flowers are present on the same plant,making it a monoecious plant. In contrast,China rose,onion,and pea possess bisexual (hermaphrodite) flowers.

(B) : In certain developmental stages,polytene chromosomes exhibit conspicuous swellings known as chromosome puffs. The larger swellings are referred to as Balbiani rings.
In the region of a puff or Balbiani ring,the $DNA$ strands uncoil,become transcriptionally active,and produce numerous copies of $mRNA$.
The $mRNA$ molecules may be temporarily stored in the puff,where they undergo translation to synthesize proteins.
Thus,Balbiani rings are the primary sites of $RNA$ and protein synthesis.

(B) : $A$ protoplast is a plant,bacterial,or fungal cell that has had its cell wall completely removed by mechanical or enzymatic means,leaving only the plasma membrane and its contents.

(C) : Lichens are highly sensitive to $SO_2$ pollution. They are unable to survive in areas with high concentrations of sulfur dioxide in the atmosphere. Because of this sensitivity,they serve as excellent biological indicators for monitoring $SO_2$ pollution levels in the environment.

(A) Chromatophores are specialized membranous extensions into the cytoplasm in some prokaryotes,such as cyanobacteria. These structures contain pigments that are essential for the process of photosynthesis. Therefore,they are involved in photosynthesis.

(A) The fungi belonging to the class $Deuteromycetes$ are commonly known as 'imperfect fungi' because only their asexual or vegetative phases are known.
Many members of this group are saprophytes or parasites,while a large number of them are decomposers of litter and help in mineral cycling.
Therefore,the correct option is $A$.

(B) Statement $B$ is incorrect because $Mucor$ (a member of Zygomycetes) produces non-motile spores called aplanospores,not flagellated zoospores.
Archegonia are indeed present in bryophytes,pteridophytes,and gymnosperms.
Haploid endosperm is a unique characteristic of gymnosperms,formed before fertilization.
Brown algae (Phaeophyceae) contain chlorophyll $a$,$c$,and the pigment fucoxanthin,which gives them their characteristic brown color.

(B) Metagenesis is a phenomenon observed in certain members of the phylum $Cnidaria$ (e.g.,$Obelia$).
It refers to the alternation of generation between the asexual polyp form and the sexual medusa form.
In this process,polyps produce medusae asexually,and medusae produce polyps sexually.
Therefore,it represents the alternation of generation between asexual and sexual phases.

(C) To determine the number of plants with a superior ovary,we classify each plant based on its floral symmetry and ovary position:
$1$. $Hibiscus$ (China rose): Superior ovary (Hypogynous).
$2$. $Mustard$: Superior ovary (Hypogynous).
$3$. $Brinjal$: Superior ovary (Hypogynous).
$4$. $Potato$: Superior ovary (Hypogynous).
$5$. $Guava$: Inferior ovary (Epigynous).
$6$. $Cucumber$: Inferior ovary (Epigynous).
$7$. $Onion$: Superior ovary (Hypogynous).
$8$. $Tulip$: Superior ovary (Hypogynous).
Counting the plants with a superior ovary: $Hibiscus$,$Mustard$,$Brinjal$,$Potato$,$Onion$,and $Tulip$.
Total count = $6$.
Therefore,the correct option is $C$.

(C) In axile placentation,the placenta is axial and the ovules are attached to it in a multilocular ovary.
Examples of plants with axile placentation include China rose,tomato,and lemon.
- $Argemone$ (poppy) shows parietal placentation.
- $Dianthus$ shows free central placentation.
- $Pea$ shows marginal placentation.
Therefore,the correct option is $C$ (Lemon).

(B) In aquatic plants like $Pistia$,the roots are often reduced or poorly developed because the plant can absorb water and nutrients directly through its surface from the surrounding aquatic environment. In contrast,terrestrial plants like $Sunflower$,$Pea$,and $Wheat$ rely heavily on their root systems for water and mineral absorption from the soil.

(A) $AIDS$ (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus $(HIV)$.
$HIV$ is a retrovirus that specifically targets and destroys $CD4^+$ $T$-helper lymphocytes.
These cells are crucial for the immune system as they coordinate the immune response by activating $B$-lymphocytes to produce antibodies and stimulating cytotoxic $T$-cells.
By infecting and destroying $T$-helper cells,$HIV$ severely compromises the body's immune system,making the individual susceptible to opportunistic infections.

(A) $Outbreeding$ is the breeding of unrelated animals, which may be between individuals of the same breed (but having no common ancestors), or between different breeds (cross-breeding) or different species (interspecific hybridization).
$Outbreeding$ is an important strategy of animal husbandry as it helps to overcome inbreeding depression, which occurs due to continuous inbreeding.

(D) $Micropropagation$ is a modern technique used to obtain a large number of plantlets through plant tissue culture.
It is termed $micropropagation$ due to the very small size of the propagules used.
This process involves the repeated subculturing of an explant by modifying the culture medium to induce the formation of numerous plantlets from a single explant.
$Somatic$ $embryogenesis$,which refers to the development of embryos from somatic cells,is a key technique utilized within $micropropagation$.

(D) The correct answer is $D$.
Somatic hybridization is a technique used to produce somatic hybrids by fusing protoplasts from two different plant varieties or species.
To achieve this,the cell walls of the plant cells are first removed using enzymes.
The resulting protoplasts are then brought into contact and induced to fuse using specific agents known as fusogens.
Commonly used chemical fusogens include Polyethylene glycol $(PEG)$ and sodium nitrate $(NaNO_3)$.
Electrofusion is another physical method used for this purpose.
Once fused,the protoplasts regenerate their cell walls and develop into somatic hybrid cells.

(C) The correct matches are as follows:
$1$. $(A)$ Saccharomyces cerevisiae is used for the commercial production of ethanol $(iii)$.
$2$. $(B)$ Monascus purpureus produces statins, which are blood-cholesterol lowering agents $(iv)$.
$3$. $(C)$ Trichoderma polysporum is the source of cyclosporin $A$, an immuno-suppressive agent $(i)$.
$4$. $(D)$ Propionibacterium shermanii is responsible for the ripening of Swiss cheese $(ii)$.
Therefore, the correct sequence is $A-(iii), B-(iv), C-(i), D-(ii)$.

(A) : Methanogens like $Methanobacterium$ are found in the rumen (a part of the stomach) of cattle.
$A$ lot of cellulosic material is also available in the rumen.
In the rumen,these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.

(B) : Golden rice is a transgenic variety of rice ($Oryza$ $sativa$) which contains significant quantities of $\beta$-carotene,which is a provitamin $A$ (an inactive state of vitamin $A$).
$\beta$-carotene serves as a primary precursor for the synthesis of vitamin $A$ in the human body.
The grains of this rice appear yellow due to the presence of $\beta$-carotene,which is why it is commonly referred to as golden rice.

(C) : $Ti$ plasmid (tumor-inducing) from the soil bacterium $Agrobacterium \text{ } tumefaciens$ is effectively used as a vector for gene transfer to plant cells.
The part of the $Ti$ plasmid transferred into the plant cell $DNA$ is called the $T-DNA$.
This $T-DNA$, with the desired $DNA$ spliced into it, is inserted into the chromosomes of the host plant.
It integrates into the host genome, allowing the foreign gene to be expressed throughout the new plant.
Such transformed plant cells are then cultured and induced to differentiate to form plantlets, which grow into mature transgenic plants.

(C) The correct answer is $C$.
Soil bacterium $Bacillus$ $thuringiensis$ produces proteins that kill certain insects like lepidopterans (tobacco budworm,armyworm),coleopterans (beetles),and dipterans (flies,mosquitoes).
$B. thuringiensis$ forms protein crystals containing a toxic insecticidal protein.
This toxin does not kill the bacterium because it exists as an inactive protoxin.
Once an insect ingests the plant tissue,the protoxin is converted into an active form of toxin due to the alkaline $pH$ of the insect's alimentary canal.
The activated toxin binds to the surface of midgut epithelial cells and creates pores,which cause swelling and lysis,eventually leading to the death of the insect.

(A) The correct answer is $A$.
Genetic modification of organisms can have unpredictable results when such organisms are introduced into the ecosystem.
Therefore,the Government of India has set up organizations such as $GEAC$ (Genetic Engineering Approval Committee).
This committee makes decisions regarding the validity of $GM$ research and the safety of introducing $GM$ organisms for public services.

(B) : Glyphosate is a broad-spectrum herbicide that specifically kills broad-leaved weeds. Since crop plants can also be affected by this herbicide,they are genetically engineered to be resistant to glyphosate. Consequently,when glyphosate is applied to the field,only the weeds are eliminated,while the crop plants remain unharmed.

(C) : Competition is the rivalry between two or more organisms for obtaining the same resources such as food,light,water,space,shelter,mate,etc. In this interaction,both species involved are adversely affected as they compete for limited resources.

(D) The correct answer is $D$.
Biological or biotic community is an assemblage of populations of different species of plants,animals,bacteria,and fungi which live in a particular area and interact with one another through competition,predation,mutualism,etc.
Each biotic community has a specific composition and structure,$e.g.$,a pond community.

(D) The correct answer is $(d)$.
Both populations are herbivorous,thus they do not consume each other.
If the food sources for these populations $A$ and $B$ had decreased,both populations would have declined.
If population $A$ had produced more offspring,the graph for population $A$ would have shown an increase.
Based on the graph,population $B$ is more successful in competing for limited resources than population $A$. This interspecific competition leads to an increase in the number of organisms in population $B$ while the number of organisms in population $A$ decreases.

(B) : Benthos is the community of organisms that live on,in,or near the sea bed,also known as the benthic zone.
Since no light is available in this zone of the sea,the energy source for deep benthic ecosystems is often organic matter from higher up in the water column which drifts down to the depths.
This dead and decaying matter sustains the benthic organisms.
Therefore,most organisms in the benthic zone,$i.e.$,in deep oceanic waters,are scavengers or detritivores.

(C) : Ecological succession is the gradual and predictable change in the species composition of a given area.
It is a natural process where a series of biotic communities develop at the same site,one after another,until a climax community is established.
The climax community is in near equilibrium with the environment and does not change further.
During succession,the number and types of animals and plants increase over time.
The establishment of a new biotic community is very slow in its primary phase because it starts on a bare area,whereas it is faster in the secondary phase.

(C) The correct answer is $C$.
Biogeochemical cycles are classified into two types: gaseous and sedimentary.
In gaseous nutrient cycles,the materials involved in circulation between the biotic and abiotic components of the biosphere are gases or vapours,and the reservoir pool is the atmosphere or hydrosphere. Examples include carbon,nitrogen,oxygen,and water.
In sedimentary nutrient cycles,the materials involved in circulation are non-gaseous,and the reservoir pool is the lithosphere (Earth's crust). Examples include phosphorus,calcium,and magnesium.
Sulphur is unique as it exhibits both sedimentary and gaseous nutrient cycles,but in standard classifications,it is often grouped with sedimentary cycles due to its primary reservoir in the lithosphere.

(B) The correct answer is $B$.
Standing crop is defined as the total mass of living material (biomass) present at a specific trophic level in an ecosystem at a particular time.
It is usually measured as the biomass per unit area or its equivalent in terms of energy.
Standing crop varies seasonally; for example,the biomass of deciduous trees changes significantly between summer and winter.

(D) The vertical distribution of different species occupying different levels in a biotic community is called $stratification$.
In a forest ecosystem,for example,trees occupy the top vertical strata,followed by shrubs,and then herbs and grasses at the bottom. This arrangement allows different species to utilize resources like sunlight and space efficiently.

(D) : Secondary succession (subsere) is the biotic succession that occurs in an area which has become secondarily bare due to the destruction of the community previously present there.
Secondary succession starts from previously built-up substrata with already existing living matter or soil.
The action of any external force,such as a sudden change in climatic factors,biotic intervention,fire,or deforestation,results in the destruction of the previous community.
Thus,the area becomes devoid of living matter,but its substratum remains intact.
It contains organic matter,making it biologically fertile,and thus,the successions are comparatively more rapid than primary succession.

(B) : Tropical rainforests have a very dense plant cover. They also experience a large amount of precipitation,thus the forest floor is always damp. These conditions have led animals to adapt to arboreal (tree-dwelling) habitats. Most animals found there are tree dwellers because almost every space on the forest floor is occupied by dense vegetation.

(D) The rate of production of organic matter during photosynthesis is known as $Gross \ Primary \ Productivity$ $(GPP)$.
$GPP$ represents the total amount of energy or biomass produced by producers (green plants) through the process of photosynthesis per unit area over a specific time period.
$Net \ Primary \ Productivity$ $(NPP)$ is the amount of biomass remaining after accounting for the energy used by plants for respiration $(R)$,expressed as $NPP = GPP - R$.

(A) Species that are restricted to a specific geographical area and are not naturally found anywhere else in the world are known as $endemic$ species.
For example,many species found in the Western Ghats or on islands are endemic to those regions.

(C) $In \text{ situ}$ (on-site) conservation involves the protection and conservation of the entire ecosystem and its biodiversity at all levels to protect threatened species. Examples include national parks, wildlife sanctuaries, biosphere reserves, and sacred groves.
$Ex \text{ situ}$ (off-site) conservation involves the conservation of selected rare plants or animals outside their natural habitats. Examples include botanical gardens, zoological parks, seed banks, gene banks, tissue culture, and cryopreservation.
Option $C$ correctly identifies $In \text{ situ}$ conservation with a National Park and $Ex \text{ situ}$ conservation with a Botanical Garden.

(D) : Cryopreservation is an advanced method of $ex$ $situ$ conservation.
It involves preservation at $-196^{\circ}C$ in liquid nitrogen.
It can maintain tissue culture, embryos, animal cells/tissues, and spermatozoa indefinitely.
The cryopreserved material is revived through a special technique when required.

(C) The correct answer is $C$. Acid rain refers to rainfall or other forms of precipitation that have a $pH$ of less than $5.6$.
It is primarily caused by the large-scale emission of acidic gases into the atmosphere from thermal power plants,industries,and automobiles.
The most significant contributors are sulphur dioxide $(SO_2)$ and nitrogen oxides ($NO_x$,such as $NO_2$).
In the atmosphere,these gases react with oxygen and water vapor to form sulphuric acid $(H_2SO_4)$ and nitric acid $(HNO_3)$.
These acids then fall to the Earth's surface in the form of acid rain,which can cause significant damage to ecosystems,buildings,and soil health.

(B) : Eutrophication is the excessive growth of algae,plants,and animals in water bodies due to nutrient enrichment,particularly with nitrogen and phosphate. Nutrients present in sewage,agricultural wastes,and fertilizers cause dense growth of plants and planktonic algae. The excessive growth of planktonic algae that causes coloration of water is called algal bloom,which is toxic to animals and humans. Eutrophic water bodies also support excessive growth of floating plants. Algal blooms and floating plants cut off light from submerged plants,resulting in their death. There is a drastic decrease in oxygen replenishment inside the water. Non-availability of oxygen results in the death of aquatic animals such as fish,which further adds to the organic loading of water. Decomposition is replaced by putrefaction,which is anaerobic,leading to the absence of oxygen in water and the death of aquatic animals.

(D) The $UN$ Climate Change Conference in $2012$ was the $18$th session of the Conference of the Parties ($COP$ $18$) to the $UN$ Framework Convention on Climate Change $(UNFCCC)$.
It was held in Doha,Qatar,from November $26$ to December $8$,$2012$.
Therefore,the correct option is $D$.

(C) The increase in the concentration of toxic substances at successive trophic levels is known as biomagnification.
This occurs because a toxic substance accumulated by an organism cannot be metabolized or excreted,and thus is passed on to the next higher trophic level.
For example,$DDT$ is a persistent pesticide that accumulates in the fatty tissues of organisms.
As it moves up the food chain,its concentration increases significantly per unit weight of the organism.
For instance,the concentration of $DDT$ in water is $0.003 \ ppb$,which increases to $0.003 \ ppm$ in phytoplankton,$0.04 \ ppm$ in zooplankton,$0.5 \ ppm$ in small fish,$2.0 \ ppm$ in large fish,and reaches $25 \ ppm$ in fish-eating birds.

(D) The $UN$ Conference of Parties $(COP17)$ on climate change in the year $2011$ was held in Durban,South Africa. This conference is officially known as the $17$th session of the Conference of the Parties $(COP17)$ to the $UN$ Framework Convention on Climate Change $(UNFCCC)$.

(B) $UV$ radiations are of three types: $UV-C$ $(100-280 \ nm)$,$UV-B$ $(280-320 \ nm)$,and $UV-A$ $(320-390 \ nm)$.
Shorter $UV$ radiations $(UV-C)$ are absorbed by the atmosphere.
The longer ones $(UV-A)$ are not very harmful.
The intermediate $UV-B$ radiations are harmful and capable of deep penetration.
Thinning of the ozone layer increases the amount of $UV-B$ radiations reaching the Earth.
$UV-B$ radiations damage skin cells,cause skin ageing,skin cancer,and eye damage (such as snow blindness or cataracts),and can also suppress the immune system.
Liver cancer is not directly associated with $UV$ radiation exposure.

(D) $BOD$ (Biochemical Oxygen Demand) refers to the amount of dissolved oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
Greater $BOD$ indicates that there is a higher concentration of organic matter in the water,which requires more oxygen for microbial decomposition.
Therefore,a high $BOD$ value signifies that the water is highly polluted due to the presence of significant organic waste.

(C) Rachel Carson's book "Silent Spring", published in $1962$, is a landmark work in the environmental movement.
It documented the detrimental environmental effects caused by the indiscriminate use of pesticides, particularly $DDT$.
This book played a crucial role in raising public awareness about the hazards of chemical pesticides to wildlife and human health, eventually leading to changes in pesticide regulations.

(D) The filiform apparatus consists of finger-like projections of the cell wall that extend into the cytoplasm of the synergids.
These structures are located at the micropylar end of the synergids.
Their primary function is to guide the entry of the pollen tube into the synergids during the process of fertilization.
Therefore,the filiform apparatus is a characteristic feature of the synergids.

(C) In recombinant $DNA$ technology,a $Vector$ is a $DNA$ molecule used as a vehicle to artificially carry foreign genetic material into another cell,where it can be replicated and/or expressed. Common examples of vectors include plasmids and bacteriophages.

(B) Restriction enzymes,also known as 'molecular scissors',are enzymes that cut $DNA$ molecules at specific nucleotide sequences called recognition sites. This discovery was a fundamental breakthrough in recombinant $DNA$ technology,allowing scientists to isolate specific genes and insert them into vectors.

(D) Parturition is induced by a complex neuroendocrine mechanism.
$1$. The signals for parturition originate from the fully developed fetus and the placenta,which induce mild uterine contractions called the Fetal Ejection Reflex.
$2$. This triggers the release of Oxytocin from the maternal pituitary,which acts on the uterine muscle and causes stronger uterine contractions.
$3$. The ratio of estrogen to progesterone increases,which enhances the sensitivity of the uterus to oxytocin.
$4$. Prostaglandins are also synthesized,which help in further stimulating uterine contractions.
$5$. Prolactin is primarily responsible for milk production (lactogenesis) after childbirth and is not involved in the initiation of parturition.