NEET 2026 Biology Question Paper with Answer and Solution

(A) The mitochondrion is a double-membrane-bound organelle.
The outer membrane forms the continuous limiting boundary of the organelle.
The inner membrane forms a number of infoldings called cristae towards the matrix.
The inner membrane encloses the space known as the matrix, which contains enzymes for the Krebs cycle, mitochondrial $DNA$, and ribosomes.

(A) . Cristae are the infoldings of the inner mitochondrial membrane, which increase the surface area for cellular respiration. Thus, $A-II$.
$B$. Cisternae are the flattened, disc-shaped sacs that make up the Golgi apparatus. Thus, $B-IV$.
$C$. Thylakoids are the flattened, sac-like structures found within the stroma of chloroplasts, where light-dependent reactions occur. Thus, $C-I$.
$D$. Phospholipids are the primary structural components of the cell membrane (plasma membrane). Thus, $D-III$.
Therefore, the correct matching is $A-II, B-IV, C-I, D-III$.

(B) Plastids are classified based on the type of pigments they contain.
$1$. Chloroplasts contain chlorophyll and carotenoids, which are responsible for trapping light energy for photosynthesis.
$2$. Chromoplasts contain fat-soluble carotenoid pigments like carotene, xanthophylls, and others. These provide yellow, orange, or red colors to various plant parts.
$3$. Leucoplasts are colorless plastids that store nutrients. They are further classified into:
- Amyloplasts: store carbohydrates (starch).
- Elaioplasts: store oils and fats.
- Aleuroplasts: store proteins.
Therefore, the plastid that stores xanthophyll is the chromoplast.

(A) The pituitary gland is anatomically divided into two parts: the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary). Thus, statement $(a)$ is correct.
The adenohypophysis secretes several hormones, including follicle-stimulating hormone $(FSH)$, melanocyte-stimulating hormone $(MSH)$, and prolactin $(PRL)$. Thus, statement $(b)$ and $(c)$ are correct, while statement $(d)$ is incorrect because the pituitary gland does secrete prolactin.
Therefore, statements $(a)$, $(b)$, and $(c)$ are correct.

(B) In the process of photorespiration, the enzyme $RuBisCo$ acts as an oxygenase.
When $RuBP$ (a $5$-carbon compound) reacts with $O_2$, it undergoes oxygenation instead of carboxylation.
This reaction produces one molecule of $3-Phosphoglycerate$ ($3-PGA$, a $3$-carbon compound) and one molecule of $2-Phosphoglycolate$ ($2-PG$, a $2$-carbon compound).
Therefore, the product "$X$" is $2-Phosphoglycolate$.

(A) Mad cow disease, also known as Bovine Spongiform Encephalopathy $(BSE)$, is a progressive neurological disorder in cattle.
It is caused by an infectious agent known as a prion.
Prions are misfolded proteins that can induce abnormal folding of normal cellular proteins in the brain, leading to brain damage.
Unlike bacteria, viruses, or viroids, prions do not contain nucleic acids ($DNA$ or $RNA$).

(B) In the photosynthetic reaction centre $PS I$, the primary pigment molecule is a special form of $Chlorophyll \ a$.
This specific molecule has an absorption peak at $700 \ nm$, which is why the reaction centre is designated as $P700$.
$Chlorophyll \ a$ is the primary photosynthetic pigment that acts as the reaction centre in both $PS I$ and $PS II$.

(A) Frogs exhibit cutaneous respiration when they are in water. In this process, the skin acts as an aquatic respiratory organ, allowing the exchange of gases ($O_2$ and $CO_2$) directly between the blood and the surrounding water through diffusion.

(C) The human lower limb consists of several bones arranged in a specific order from the hip downwards.
$1$. The $Femur$ (thigh bone) is the longest and strongest bone in the body, connecting the hip to the knee.
$2$. The $Patella$ (kneecap) is a sesamoid bone that protects the knee joint.
$3$. The $Tibia$ (shin bone) is the larger of the two lower leg bones, extending from the knee to the ankle.
$4$. The $Tarsal$ bones are the group of seven bones located in the foot/ankle region.
Therefore, the correct anatomical sequence from proximal to distal is $Femur-Patella-Tibia-Tarsal$.

(A) Phyllotaxy is defined as the pattern of arrangement of leaves on the stem or branch. This arrangement is usually of three types: alternate, opposite, and whorled. This pattern ensures that leaves receive an adequate amount of sunlight for photosynthesis.

(B) The correct matches are as follows:
$1$. $A$. Starch: It is a polysaccharide that serves as the primary energy storage molecule in plants. Thus, $A-II$.
$2$. $B$. Antibody: These are proteins produced by the immune system to fight infections. Thus, $B-I$.
$3$. $C$. Concanavalin $A$: It is a well-known lectin, which is a protein that binds to specific carbohydrates. Thus, $C-IV$.
$4$. $D$. Glut-$4$: This is a protein responsible for the transport of glucose into cells. Thus, $D-III$.
Therefore, the correct sequence is $A-II, B-I, C-IV, D-III$.

(C) Statement $I$ is correct: Radial symmetry is defined as the condition where any plane passing through the central axis of the body divides the organism into two identical halves.
Statement $II$ is incorrect: In phylum Echinodermata, the adults exhibit radial symmetry (specifically pentamerous radial symmetry), but the larvae are bilaterally symmetrical.
Therefore, Statement $I$ is correct and Statement $II$ is incorrect.

(A) The endomembrane system is a group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.
It consists of the endoplasmic reticulum $(ER)$, Golgi complex, lysosomes, and vacuoles.
These organelles are considered part of the endomembrane system because their functions are coordinated.
Organelles like mitochondria and chloroplasts are not part of the endomembrane system because their functions are not coordinated with the components of this system.

(D) Glycolysis is the process in which one molecule of glucose $(C_6H_{12}O_6)$ is broken down into two molecules of pyruvic acid $(CH_3COCOOH)$.
Given that $1$ molecule of glucose produces $2$ molecules of pyruvic acid.
Therefore, $206$ molecules of glucose will produce $206 \times 2 = 412$ molecules of pyruvic acid.
Thus, the correct option is $D$.

(A) $2,4-D$ ($2,4$-dichlorophenoxyacetic acid) is a synthetic auxin. It is widely used as a herbicide to kill broad-leaved weeds. It does not affect mature monocotyledonous plants, which makes it useful for protecting cereal crops from weeds.

(A) Statement $I$ is correct: In gymnosperms, the male and female gametophytes do not have an independent free-living existence. They remain within the sporangia that are retained on the sporophytes.
Statement $II$ is correct: The term gymnosperm is derived from the Greek words 'gymnos' meaning naked and 'sperma' meaning seed. Thus, gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. Consequently, the seeds that develop post-fertilization are not covered.
Therefore, both statements are correct.

(D) The shapes of bacteria are classified as follows:
$1$. Spherical bacteria are called $Cocci$ $(A-II)$.
$2$. Rod-shaped bacteria are called $Bacilli$ $(B-IV)$.
$3$. Comma-shaped bacteria are called $Vibrio$ $(C-I)$.
$4$. Spiral-shaped bacteria are called $Spirilla$ $(D-III)$.
Therefore, the correct matching is $A-II, B-IV, C-I, D-III$.

(A) The $Solanaceae$ family, also known as the potato family, exhibits the following characteristics:
$1$. Flowers are bisexual and actinomorphic (radial symmetry).
$2$. Calyx consists of $5$ sepals, which are gamosepalous (united).
$3$. Corolla consists of $5$ petals, which are gamopetalous.
$4$. Androecium consists of $5$ stamens, which are epipetalous (attached to the petals).
$5$. Gynoecium is bicarpellary, syncarpous, and the ovary is superior (not inferior).
Therefore, statements $(a)$, $(b)$, and $(c)$ are correct, while statement $(d)$ is incorrect because the ovary is superior in $Solanaceae$.

(B) The historical development of our understanding of photosynthesis followed this sequence:
$1$. Role of air: Joseph Priestley $(1770)$ demonstrated that plants restore air that has been breathed by animals or burned by candles.
$2$. Release of oxygen: Jan Ingenhousz $(1779)$ showed that sunlight is essential to the plant process that purifies air, specifically releasing oxygen.
$3$. Production of glucose: Julius von Sachs $(1854)$ provided evidence for the production of glucose when plants grow, which is stored as starch.
$4$. Absorption spectra of chlorophyll a and b: $T$.$W$. Engelmann $(1882)$ described the first action spectrum of photosynthesis, which corresponds to the absorption spectra of chlorophyll $a$ and $b$.

(B) The sino-atrial node $(SAN)$ is known as the natural pacemaker of the heart.
It has the ability to generate action potentials without any external stimuli, a property known as autorhythmicity.
In a healthy human adult, the $SAN$ generates action potentials at a rate of approximately $70-75$ times per minute, which corresponds to the normal resting heart rate.

(B) In the Calvin cycle, $6$ turns are required to produce $1$ molecule of glucose $(C_6H_{12}O_6)$.
Since $1$ molecule of glucose requires $6$ turns, $3$ molecules of glucose will require $3 \times 6 = 18$ turns.
Therefore, the correct answer is $18$.

(D) Blood coagulation is a process involving a cascade of enzymatic reactions.
When an injury occurs, the enzyme thrombin converts inactive fibrinogen (a plasma protein) into active fibrin threads.
These fibrin threads form a meshwork that traps blood cells to form a clot.
Therefore, fibrinogen is produced in the liver and circulates in the blood, while fibrin is the product formed during coagulation.
Thus, the statement that 'Fibrinogen is produced from fibrin' is incorrect.

(D) To match the taxonomic categories with their respective examples for the mango plant $(Mangifera \text{ } indica)$:
$1$. Family: The family of mango is Anacardiaceae $(A-III)$.
$2$. Genus: The genus of mango is Mangifera $(B-V)$.
$3$. Class: Mango belongs to the class Dicotyledonae $(C-II)$.
$4$. Phylum (Division): Mango belongs to the division Angiospermae $(D-IV)$.
$5$. Order: The order of mango is Sapindales $(E-I)$.
Therefore, the correct matching is $A-III, B-V, C-II, D-IV, E-I$.

(A) The taxonomic hierarchy in ascending order (from smallest to largest) is as follows:
$1$. Species $(g)$
$2$. Genus $(a)$
$3$. Family $(e)$
$4$. Order $(c)$
$5$. Class $(b)$
$6$. Phylum $(d)$
$7$. Kingdom $(f)$
Therefore, the correct sequence is $(g), (a), (e), (c), (b), (d), (f)$.

(D) The correct matches for placentation types are as follows:
$1$. Marginal placentation: The placenta forms a ridge along the ventral suture of the ovary, as seen in $Pea$ $(IV)$.
$2$. Axile placentation: The placenta is axial and ovules are attached to it in a multilocular ovary, as seen in $Tomato$ $(II)$.
$3$. Parietal placentation: The ovules develop on the inner wall of the ovary or on peripheral part, as seen in $Argemone$ $(I)$.
$4$. Free central placentation: The ovules are borne on the central axis and septa are absent, as seen in $Primrose$ $(III)$.
Therefore, the correct matching is $A-IV, B-II, C-I, D-III$.

(D) The plant kingdom is classified into various groups. Pteridophytes are further classified into four main classes: $Psilopsida$, $Lycopsida$, $Sphenopsida$, and $Pteropsida$. $Sphenopsida$ includes plants like $Equisetum$ (horsetails). Therefore, the $Sphenopsida$ class belongs to the $Pteridophytes$ group.

(D) Photorespiration is a wasteful process that occurs in $C3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
Statement $(a)$ is incorrect because photorespiration occurs specifically in $C3$ plants.
Statement $(b)$ is incorrect because $O_2$ is consumed and $CO_2$ is released during photorespiration.
Statement $(c)$ is correct because the oxygenation of $RuBP$ results in the formation of one molecule of $3-phosphoglycerate$ and one molecule of $2-phosphoglycolate$.
Statement $(d)$ is correct because photorespiration does not produce $ATP$ or $NADPH$; instead, it consumes energy.
Therefore, statements $(c)$ and $(d)$ are correct.

(B) The endoplasmic reticulum is divided into two types: Rough Endoplasmic Reticulum $(RER)$ and Smooth Endoplasmic Reticulum $(SER)$.
$RER$ has ribosomes attached to its surface, which are responsible for protein synthesis.
$SER$ lacks ribosomes on its surface and is primarily involved in the synthesis of lipids, such as steroids and phospholipids.
Therefore, the correct statement is that the smooth endoplasmic reticulum is the major site for the synthesis of lipids.

(B) The pancreas contains endocrine cells known as the Islets of Langerhans.
These islets consist of different types of cells, primarily $\alpha$-cells and $\beta$-cells.
$\alpha$-cells are responsible for the secretion of the hormone glucagon, which increases blood glucose levels.
$\beta$-cells are responsible for the secretion of the hormone insulin, which decreases blood glucose levels.
Glucagon stimulates glycogenolysis, which is the breakdown of glycogen into glucose in the liver.
Therefore, the statement that $\alpha$-cells secrete insulin is incorrect, as insulin is secreted by $\beta$-cells.

(C) In biological classification, the taxonomic hierarchy follows the order: Kingdom, Phylum, Class, Order, Family, Genus, and Species.
$A$ $Genus$ is a taxonomic category that comprises a group of closely related species that share a common evolutionary ancestor and exhibit many similar characteristics.
For example, in the genus $Panthera$, species like $Panthera leo$ (lion) and $Panthera tigris$ (tiger) are grouped together due to their close evolutionary relationship.
Therefore, the correct option is $C$.

(D) Prokaryotes are organisms whose cells lack a membrane-bound nucleus and other membrane-bound organelles.
Bacteria, Blue-green algae (Cyanobacteria), and Mycoplasma are all examples of prokaryotic organisms.
Fungi, on the other hand, are eukaryotic organisms. Their cells contain a well-defined nucleus enclosed within a nuclear membrane and possess membrane-bound organelles such as mitochondria and endoplasmic reticulum.
Therefore, the correct answer is $D$ (Fungi).

(B) The phenomenon of internode elongation just prior to flowering is known as bolting. In plants like cabbage (rosette habit) and beet, bolting is induced by the application of $Gibberellins$ $(GA)$. $Gibberellins$ are plant hormones that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, and leaf and fruit senescence.

(C) The eukaryotic cell cycle consists of four distinct phases: $G1$ phase, $S$ phase, $G2$ phase, and $M$ phase.
$1$. $G1$ phase (Gap $1$): The cell grows and prepares for $DNA$ replication.
$2$. $S$ phase (Synthesis): $DNA$ replication occurs.
$3$. $G2$ phase (Gap $2$): The cell continues to grow and prepares for mitosis.
$4$. $M$ phase (Mitosis): The cell undergoes division.
Therefore, the correct sequence is $G1 \rightarrow S \rightarrow G2 \rightarrow M$.

(A) The process of sexual reproduction in fungi involves three distinct steps:
$1$. Plasmogamy: This is the fusion of protoplasms between two motile or non-motile gametes.
$2$. Karyogamy: This is the fusion of two nuclei.
$3$. Meiosis: This is the process that occurs in the zygote resulting in the generation of haploid spores.
Therefore, the correct matching is:
$A$ (Fusion of protoplasms) $\rightarrow II$ (Plasmogamy)
$B$ (Fusion of two nuclei) $\rightarrow III$ (Karyogamy)
$C$ (Generation of haploid spores) $\rightarrow I$ (Meiosis)
Thus, the correct sequence is $A-II, B-III, C-I$.

(C) Statement $I$ is correct: The term 'Reptilia' is derived from the Latin word 'repere' or 'reptum',which means 'to creep' or 'to crawl'. This refers to their mode of locomotion.
Statement $II$ is incorrect: While most reptiles have a three-chambered heart (two atria and one partially divided ventricle), crocodiles, alligators, and gharials (members of the order Crocodilia) possess a four-chambered heart. Therefore, the statement that 'all' organisms in Reptilia have a three-chambered heart is false.
Conclusion: Statement $I$ is correct, but Statement $II$ is incorrect.

(C) Statement $I$ is correct: During prophase $I$ of meiosis, chromosomes undergo condensation. By the end of diakinesis (the final stage of prophase $I$), the chromosomes are fully condensed and the nucleolus disappears.
Statement $II$ is incorrect: Meiosis $I$ is a reductional division where homologous chromosomes separate, whereas mitosis is an equational division where sister chromatids separate. Meiosis $II$ is the phase that more closely resembles mitosis.

(C) The fundamental characteristics of chordates include the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits at some stage of their life cycle. Additionally, they possess a post-anal tail. Therefore, the 'Absence of gills' is not a characteristic of chordates, as they possess pharyngeal gill slits at some stage of development.

(C) In arithmetic growth, the growth rate is constant over time.
The formula for arithmetic growth is given by: $L_t = L_0 + (r \times t)$
Where:
$L_t$ is the length at time $t$,
$L_0$ is the initial length at time $0$,
$r$ is the growth rate per unit time,
$t$ is the time elapsed.
Given:
$L_0 = 20 \ cm$,
$r = 30 \ cm/day$,
$t = 7 \ days$.
Substituting the values into the formula:
$L_7 = 20 + (30 \times 7)$
$L_7 = 20 + 210$
$L_7 = 230 \ cm$.
Therefore, the length of the stem at the end of the $7^{th}$ day is $230 \ cm$.

(B) The percentage weight of elements in the human body is approximately as follows:
$(a)$ Oxygen: $65.0\%$
$(b)$ Carbon: $18.5\%$
$(c)$ Hydrogen: $9.5\%$
$(d)$ Nitrogen: $3.3\%$
Arranging these in descending order gives: Oxygen > Carbon > Hydrogen > Nitrogen.
Therefore, the correct sequence is $(a), (b), (c), (d)$.

(C) In frogs $(Rana \text{ } tigrina)$, there are $10$ pairs of cranial nerves that arise from the brain.
These nerves are responsible for sensory and motor functions in the head and neck region.
Therefore, the correct answer is $10$ pairs.

(B) The correct matches are as follows:
$A$. Excess growth hormone leads to $III$. Acromegaly, a condition characterized by abnormal growth of bones and tissues.
$B$. Luteinizing hormone $(LH)$ is responsible for $IV$. Ovulation in females.
$C$. Vasopressin (also known as Antidiuretic Hormone or $ADH$) is responsible for $I$. Reabsorption of water and electrolytes in the kidney.
$D$. Oxytocin is responsible for $II$. Contraction of the uterus during childbirth.
Therefore, the correct matching is $A-III, B-IV, C-I, D-II$.

(B) The human heart has four chambers: two atria and two ventricles.
The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, which is known as the $tricuspid \text{ valve}$.
This valve prevents the backflow of blood from the right ventricle into the right atrium during ventricular contraction.
The bicuspid valve (mitral valve) is located between the left atrium and the left ventricle.

(A) Sponges belong to the phylum Porifera. They lack specialized respiratory organs. The exchange of gases ($O_2$ and $CO_2$) in sponges occurs through the process of simple diffusion across their entire body surface, which is in direct contact with the surrounding water.

(A) Muscle contraction is initiated by a signal sent by the central nervous system $(CNS)$ via a motor neuron.
When the action potential reaches the axon terminal of the motor neuron, it triggers the release of a neurotransmitter called acetylcholine into the synaptic cleft.
This acetylcholine binds to the receptors on the sarcolemma of the muscle fiber, generating an action potential that leads to muscle contraction.

(D) Statement $(a)$ is correct: The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes.
Statement $(b)$ is correct: As water is reabsorbed in the descending limb, the filtrate becomes concentrated.
Statement $(c)$ is incorrect: Reabsorption of water does not take place in the ascending limb of Henle's loop as it is impermeable to water.
Statement $(d)$ is correct: The ascending limb is impermeable to water but allows for the transport of electrolytes (actively or passively).
Therefore, statements $(a)$, $(b)$, and $(d)$ are correct.

(D) The human vertebral column is arranged in a specific sequence from the skull (head) downwards to the pelvis (toe/base).
$1$. The $Cervical$ vertebrae are located in the neck region ($7$ vertebrae).
$2$. The $Thoracic$ vertebrae are located in the chest region ($12$ vertebrae).
$3$. The $Lumbar$ vertebrae are located in the lower back region ($5$ vertebrae).
$4$. The $Sacrum$ is located below the lumbar region ($1$ fused bone).
$5$. The $Coccyx$ is at the very end ($1$ fused bone).
Therefore, the correct order from head to toe is $Cervical \rightarrow Thoracic \rightarrow Lumbar \rightarrow Sacrum$.

(B) Natural selection acts on populations in three primary ways regarding the distribution of phenotypic traits:
$1$. Stabilising selection: Favours intermediate phenotypes and eliminates extreme variants.
$2$. Directional selection: Favours one extreme phenotype over the other, causing a shift in the population's mean trait value.
$3$. Disruptive selection: Favours both extreme phenotypes at the expense of intermediate variants.
Genetic drift, however, is a random process caused by chance events in small populations, not a direct outcome of natural selection.
Therefore, natural selection leads to stabilisation, directional change, and disruption. The correct options are $(a)$, $(c)$, and $(d)$.

(C) Intra cytoplasmic sperm injection $(ICSI)$ is a specialized procedure in assisted reproductive technology where a single sperm is directly injected into the cytoplasm of an ovum. This technique is used to treat male infertility cases where sperm count or motility is low.

(D) The male reproductive system includes the testes, rete testis, vasa efferentia, epididymis, vas deferens, and accessory glands.
$Infundibulum$ is a funnel-shaped structure that forms the proximal part of the fallopian tube in the female reproductive system.
Therefore, $Infundibulum$ is not a part of the male reproductive system.

(A) According to the data provided in the $NCERT$ textbook for the Amazonian rain forest, the number of species is as follows:
$(d)$ Invertebrates: $1,25,000$
$(a)$ Plants: $40,000$
$(c)$ Fishes: $3,000$
$(b)$ Birds: $1,300$
$(e)$ Mammals: $427$
Therefore, the descending order is $(d) > (a) > (c) > (b) > (e)$.

(C) Statement $I$ is correct. The $LH$ surge (a rapid increase in Luteinizing Hormone) triggers the rupture of the mature Graafian follicle, releasing the secondary oocyte, a process known as ovulation.
Statement $II$ is incorrect. After ovulation, the ruptured Graafian follicle transforms into the corpus luteum. The corpus luteum primarily secretes large amounts of progesterone, which is essential for maintaining the endometrium, rather than large amounts of estrogen.

(C) In a food chain, organisms are classified based on their trophic levels.
$1$. Producers (autotrophs) form the first trophic level.
$2$. Primary consumers are organisms that feed directly on producers. Since producers are plants or algae, primary consumers are always herbivores.
$3$. Secondary consumers feed on primary consumers, and tertiary consumers feed on secondary consumers.
Therefore, herbivores are the primary consumers.

(A) According to the Hardy-Weinberg principle, for a gene with two alleles $A$ and $a$, let the frequency of allele $A$ be $p$ and the frequency of allele $a$ be $q$.
Given that the frequency of allele $A$ $(p)$ is $0.1$.
The frequency of the homozygous dominant genotype $AA$ is given by $p^2$.
Therefore, the frequency of $AA = (0.1)^2 = 0.01$.
Thus, the correct option is $A$.

(A) typical angiosperm anther is bilobed, meaning it consists of two lobes.
Each lobe of the anther contains two theca (singular: theca), making it dithecous.
Therefore, each lobe contains $2$ theca.
Since there are two lobes, the entire anther contains $4$ theca in total (tetrasporangiate).

(A) $1$. The $lac$ operon consists of a regulatory gene $(i)$, a promoter $(p)$, an operator $(o)$, and three structural genes $(z, y, a)$.
$2$. The gene $i$ codes for the repressor protein of the $lac$ operon. It is constitutively expressed, meaning it is always transcribed at a constant rate regardless of the presence or absence of lactose.
$3$. Lactose acts as an inducer. It binds to the repressor protein, preventing it from binding to the operator, which allows transcription to proceed.
$4$. Genes $z, y,$ and $a$ are transcribed together as a single polycistronic mRNA under the control of a single promoter, but gene $i$ has its own separate promoter.
$5$. Therefore, the statement that gene $i$ is constitutively expressed is correct.

(B) In the female gametophyte (embryo sac) of an angiosperm, the $Synergids$ are specialized cells located at the micropylar end.
These cells contain a special cellular thickening at the micropylar tip called the $filiform$ $apparatus$.
The primary function of the $filiform$ $apparatus$ is to secrete chemical substances that attract and guide the pollen tube towards the egg cell for fertilization.

(D) Non-albuminous seeds (also known as exalbuminous seeds) are those in which the endosperm is completely consumed by the developing embryo during seed maturation.
Examples of plants that produce non-albuminous seeds include pea, groundnut, and beans.
In contrast, wheat, maize, and barley are monocots that produce albuminous (endospermic) seeds, where the endosperm persists in the mature seed to provide nourishment during germination.
Therefore, the correct option is $D$ (Pea).

(C) In angiosperms, the diploid chromosome number $(2n)$ is given as $36$.
Therefore, the haploid chromosome number $(n)$ is $36 / 2 = 18$.
The endosperm in angiosperms is formed by the fusion of one male gamete $(n)$ with two polar nuclei $(n + n)$, resulting in a triploid $(3n)$ structure.
Thus, the chromosome number in the endosperm is $3n = 3 \times 18 = 54$.

(C) The embryological support for evolution, as proposed by Ernst Haeckel (the biogenetic law or 'ontogeny recapitulates phylogeny'), was later disproved. Haeckel's theory suggested that embryos of higher vertebrates pass through stages resembling the adult forms of their ancestors, which was found to be scientifically inaccurate and is not considered valid evidence for evolution in modern biology. Other options like fossil records, divergent evolution (homologous organs), and convergent evolution (analogous organs) are widely accepted pieces of evidence for the process of evolution.

(B) Statement $I$ is incorrect because modern $Homo$ $sapiens$ arose in Africa, not Australia.
Statement $II$ is incorrect because $Homo$ $sapiens$ evolved much earlier, approximately $300,000$ years ago, not $75,000$ to $10,000$ years ago.
Therefore, both statements are incorrect.

(C) The rate of change of population size $(N)$ is given by the formula: $\frac{dN}{dt} = (b - d)N$, where $b$ is the per-capita birth rate and $d$ is the per-capita death rate.
Given: $b = 0.002$ and $d = 0.002$.
Therefore, the intrinsic rate of increase $(r)$ is $r = b - d = 0.002 - 0.002 = 0$.
Since the intrinsic rate of increase is $0$, the population size remains constant over time.
Thus, after $10$ generations, the population size will remain $10$ million.

(C) The $PCR$ ($Polymerase$ $Chain$ $Reaction$) process consists of three main steps:
$1$. $Denaturation$: The double-stranded $DNA$ is heated to separate it into two single strands.
$2$. $Annealing$: The temperature is lowered, allowing the primers to bind (anneal) to their complementary sequences on the single-stranded $DNA$ templates.
$3$. $Extension$: The $DNA$ polymerase enzyme synthesizes a new $DNA$ strand by adding nucleotides to the primers.
Therefore, the step where primers bind to the $DNA$ strands is known as $Annealing$.

(A) The exponential growth model assumes that resources are unlimited, which allows a population to grow at its maximum biotic potential. However, in nature, resources such as food and space are finite, leading to competition and environmental resistance.
The logistic growth model accounts for these finite resources by incorporating the carrying capacity $(K)$ of the environment. As the population size approaches $K$, the growth rate slows down, making it a more realistic model for natural populations.
Since the limitation of resources is the fundamental reason why the logistic model is more realistic than the exponential model, $R$ is the correct explanation of $A$.

(B) Adaptive radiation refers to the evolution of different species from a common ancestor in a given geographical area starting from a point and radiating to other areas of geography.
When more than one adaptive radiation appears to have occurred in an isolated geographical area (representing different habitats), one can call this convergent evolution.
Placental mammals in Australia and Australian marsupials exhibit similar traits (e.g.,placental wolf and Tasmanian wolf) despite being distantly related, which is a classic example of convergent evolution.

(A) Lymphoid organs are classified into two types: primary and secondary lymphoid organs.
$(1)$ Primary lymphoid organs: These are the sites where lymphocytes originate and/or mature and become antigen-sensitive. Examples include the bone marrow and the thymus.
$(2)$ Secondary lymphoid organs: These are the sites where lymphocytes interact with the antigen and then proliferate to become effector cells. Examples include the spleen, lymph nodes, tonsils, Peyer's patches of the small intestine, and the appendix.
Therefore, among the given options, $(b)$ Tonsils and $(c)$ Spleen are secondary lymphoid organs.

(D) The human placenta acts as an endocrine tissue and produces several hormones essential for pregnancy. These include Human Chorionic Gonadotropin $(hCG)$, Human Placental Lactogen $(hPL)$, estrogens, and progestogens. $LH$ (Luteinizing Hormone) is secreted by the anterior pituitary gland, not the placenta.

(B) In eukaryotic cells, there are three main types of $RNA$ polymerases responsible for transcription:
$1$. $RNA$ polymerase $I$ transcribes $rRNA$ ($28S, 18S,$ and $5.8S$).
$2$. $RNA$ polymerase $II$ transcribes the precursor of $mRNA$, which is known as heterogeneous nuclear $RNA$ $(hnRNA)$.
$3$. $RNA$ polymerase $III$ transcribes $tRNA$, $5S$ $rRNA$, and $snRNA$.
Therefore, $RNA$ polymerase $II$ is responsible for synthesizing precursor $mRNA$.

(A) Plasmids are small, circular, double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
Statement $I$ is correct because plasmids possess an origin of replication $(ori)$, which allows them to replicate independently of the chromosomal $DNA$.
Statement $II$ is correct because plasmids exist outside the main chromosomal $DNA$ in the cytoplasm of bacteria and some eukaryotes.
Therefore, both statements are correct.

(D) person with blood group '$O$' has the genotype '$ii$'. This means the person must inherit one '$i$' allele from the father and one '$i$' allele from the mother.
$(A)$ Father: $I^Ai$, Mother: $I^Bi$: Possible offspring genotypes include $I^AI^B, I^Ai, I^Bi, ii$. Thus, blood group '$O$' $(ii)$ is possible.
$(B)$ Father: $I^Ai$, Mother: $I^Ai$: Possible offspring genotypes include $I^AI^A, I^Ai, ii$. Thus, blood group '$O$' $(ii)$ is possible.
$(C)$ Father: $I^Bi$, Mother: $I^Bi$: Possible offspring genotypes include $I^BI^B, I^Bi, ii$. Thus, blood group '$O$' $(ii)$ is possible.
$(D)$ Father: $I^AI^B$, Mother: $I^Ai$: Possible offspring genotypes include $I^AI^A, I^AI^i, I^AI^B, I^Bi$. The possible blood groups are $A$ and $AB$. Blood group '$O$' $(ii)$ is not possible because the father does not carry the '$i$' allele.

(A) Homologous organs are those that have the same basic structural plan and embryonic origin, even if they perform different functions.
Forelimbs of humans and bats share a similar anatomical structure (humerus, radius, ulna, carpals, metacarpals, and phalanges), which indicates a common ancestry.
Therefore, the forelimbs of humans and bats are considered homologous organs because of this shared anatomical structure.
Thus, both Assertion $A$ and Reason $R$ are correct, and $R$ is the correct explanation of $A$.

(C) Colostrum is the yellowish fluid secreted by the mother during the initial days of lactation.
It is rich in antibodies, specifically $IgA$, which provide essential passive immunity to the newborn infant.
$IgA$ is crucial for protecting the infant's gastrointestinal tract from pathogens during the early stages of life.

(A) The Abingdon tortoise in the Galapagos Islands became extinct within a decade after goats were introduced on the island.
This occurred because goats are more efficient browsers (they eat vegetation more quickly and effectively) than the tortoises.
As a result, the food resources for the tortoises were depleted, leading to their extinction.
Therefore, both Assertion $A$ and Reason $R$ are correct, and $R$ is the correct explanation of $A$.

(C) At the time of ovulation, the secondary oocyte is released from the Graafian follicle.
This released ovum is surrounded by a non-cellular layer called the $zona \ pellucida$, which is secreted by the oocyte itself.
Additionally, it is surrounded by layers of follicular cells known as the $corona \ radiata$.
Among the given options, $zona \ pellucida$ is the primary protective covering associated with the ovum structure at the time of ovulation.

(D) The interactions between species are classified based on the effect on each species:
$1$. Competition $(A)$: Both species are harmed ($-/-$ interaction).
$2$. Predation $(B)$: One species is harmed and the other is benefited ($+/-$ interaction).
$3$. Mutualism $(C)$: Both species are benefited ($+/+$ interaction).
$4$. Commensalism $(D)$: One is benefited while the other has no effect ($+/0$ interaction).
Therefore, the correct matching is $A-III, B-I, C-II, D-IV$.

(A) Assertion $A$ is correct because in Mendel's monohybrid cross between a pure tall plant $(TT)$ and a pure dwarf plant $(tt)$, all $F1$ progeny are heterozygous tall $(Tt)$.
Reason $R$ is also correct because stem height is indeed a contrasting trait where the tall allele $(T)$ is dominant over the dwarf allele $(t)$.
Since the $F1$ generation expresses only the dominant trait (tallness), the reason $R$ correctly explains why all $F1$ plants are tall and none are dwarf.
Therefore, both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.

(A) $1$. Assertion $A$ states that lysozyme is used to break down bacterial cell walls and cellulase is used for plant cell walls. This is scientifically accurate because bacterial cell walls are made of peptidoglycan (degraded by lysozyme) and plant cell walls are made of cellulose (degraded by cellulase).
$2$. Reason $R$ states that isolation of genetic material requires the disruption of cells. This is also correct because the $DNA$ is enclosed within the cell membrane and cell wall, which must be broken to release the genetic material.
$3$. Since the specific enzymes mentioned in $A$ are the standard tools used to achieve the cell disruption mentioned in $R$, $R$ is the correct explanation of $A$.

(C) $Morphine$ is a potent opioid analgesic derived from the opium poppy plant. It is widely used in clinical settings as an effective sedative and painkiller, particularly for patients recovering from major surgeries, as it acts on the central nervous system to reduce the perception of pain.

(B) Statement $(a)$ is correct: Energy flow in an ecosystem is always unidirectional, moving from producers to consumers and then to decomposers.
Statement $(b)$ is correct: An energy pyramid represents the amount of energy at each trophic level and is always upright because energy is lost as heat at each transfer, making it impossible to be inverted.
Statement $(c)$ is incorrect: The transfer of energy follows the $10\%$ law (Lindeman's Law), which states that only about $10\%$ of the energy available at one trophic level is transferred to the next, not the $1\%$ law.
Therefore, statements $(a)$ and $(b)$ are correct.

(D) The life cycle of $Plasmodium$ involves two hosts: humans and female $Anopheles$ mosquitoes.
$1$. In humans, $Plasmodium$ undergoes asexual reproduction (schizogony) in liver cells and $RBCs$.
$2$. Gametocytes (male and female gametes) are formed in human $RBCs$ but do not undergo fertilization there.
$3$. When a female $Anopheles$ mosquito bites an infected human, it ingests these gametocytes.
$4$. Fertilization and sexual reproduction occur in the gut of the mosquito, leading to the formation of a zygote, which then develops into an ookinete and eventually sporozoites.

(A) The correct matching is as follows:
$A$. Transformation: It is the process of transferring $DNA$ into host bacteria $(A-II)$.
$B$. Cloning site: These are specific recognition sequences for restriction enzymes $(B-I)$.
$C$. Selection: Antibiotic resistance genes are used as selectable markers to identify transformants $(C-IV)$.
$D$. Ori: The origin of replication is the sequence where replication starts $(D-III)$.
Therefore, the correct sequence is $A-II, B-I, C-IV, D-III$.