NEET Sexual Reproduction in Flowering Plants Previous Year Questions with Solutions

A typical angiosperm anther is a bilobed structure with each lobe having two theca (chambers), making it dithecous. Often a longitudinal groove runs lengthwise separating the two theca.

• • Bilobed structure with a total of 4 microsporangia located at the corners (tetrasporangiate).

The question specifically asks: "How many theca are present in each lobe?". In each lobe, there are 2 theca. Across both lobes combined, the whole anther contains 4 theca / 4 microsporangia.

• • Watch out for the whole-anther trap (4 theca) versus per-lobe count (2 theca).

Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus, in turn, consists of two synergids and one egg cell.

• • Located at the micropylar pole of the 7-celled, 8-nucleate female gametophyte.

The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.

• • One synergid degenerates as the pollen tube enters and discharges its two male gametes.

Non-albuminous seeds have no residual endosperm as it is completely consumed during embryo development (e.g., pea, groundnut, beans). Food reserves are stored in swollen, fleshy cotyledons.

• • Cotyledons store nutrients for the future germinating seedling.

Albuminous seeds retain a part of endosperm as it is not completely used up during embryo development (e.g., wheat, maize, barley, castor, sunflower).

• • Castor is a dicot but albuminous; maize and wheat are monocots and albuminous.

Given that the diploid number of chromosomes (2n) of the angiospermic plant is 36, the haploid number (n) present in gametes is half of this value.

• • Haploid number n = 18 applies to male gametes, egg cell, synergids, and antipodals.

In angiosperms, double fertilization involves triple fusion where one haploid male gamete (n) fuses with two haploid polar nuclei (or one secondary diploid nucleus 2n) to produce the triploid primary endosperm nucleus (PEN).

• • In gymnosperms, endosperm is haploid (n = 18); in angiosperms, it is triploid (3n = 54).

Analyze evolutionary energy allocation in anemophilous and hydrophilous angiosperms:

• • NCERT states verbatim: "Both wind and water pollinated flowers are not very colourful and do not produce nectar."
• • Assertion (A) is completely TRUE.

Analyze the reproductive efficiency of wind and water transport:

• • NCERT states verbatim: "To compensate for this uncertainties and associated loss of pollen grains, the flowers produce enormous amount of pollen when compared to the number of ovules available for pollination."
• • Reason (R) is completely TRUE.

Determine if R explains A:

• • The true cause of absent color/nectar is the lack of a need to attract biotic pollinators.
• • The true purpose of high pollen output is to overcome statistical wastage in abiotic currents.
• • While both statements are independently true facts, Reason R does not provide the causal mechanism for Assertion A.
• • Matches Option (2).

Development of the female gametophyte (embryo sac) in typical angiosperms (Polygonum type):

• • A single functional megaspore undergoes three successive free nuclear mitotic divisions to produce an 8-nucleate stage.
• • Cytokinesis subsequently partitions 6 of the nuclei into separate cells, while 2 nuclei remain in the central compartment.
• • The mature embryo sac comprises 7 cells: 3 antipodal cells at chalazal end, 1 three-celled egg apparatus at micropylar end, and 1 large central cell containing 2 polar nuclei.
• • Hence, Assertion (A) is completely TRUE.

Composition of the Egg Apparatus vs Central Cell:

• • The egg apparatus is located strictly at the micropylar end and consists of THREE cells: two synergids (with filiform apparatus) and one egg cell (female gamete).
• • The 2 polar nuclei are located in the large central cell, situated below the egg apparatus.
• • Therefore, asserting that "The egg apparatus has 2 polar nuclei" is anatomically and biologically FALSE.

Assertion (A) is true, but Reason (R) is false. This leads directly to Option (3).

Analyzing each specialized botanical structure:

• • A. Scutellum: In monocot embryos (especially the grass family / Poaceae), the single shield-shaped cotyledon situated towards one side of the embryonal axis is called the scutellum. Hence, A matches II.
• • B. Non-albuminous seed: Non-albuminous (exalbuminous) seeds retain no residual endosperm because it is entirely consumed during embryo development. Classic examples include groundnut, pea, and bean. Hence, B matches III.
• • C. Epiblast: In grass embryos, a small flap-like rudimentary outgrowth situated opposite the scutellum represents the reduced remnant of the second cotyledon, termed the epiblast. Hence, C matches IV.
• • D. Perisperm: In most seeds, the nucellus is completely consumed during embryo sac enlargement and endosperm development. However, in certain seeds such as black pepper (*Piper nigrum*) and beet (*Beta vulgaris*), remnants of persistent nucellus are retained, known as perisperm. Hence, D matches I.

Compiling the verified associations:

• • A -> II (Cotyledon of Monocot seed)
• • B -> III (Groundnut)
• • C -> IV (Rudimentary cotyledon)
• • D -> I (Persistent nucellus)

The unambiguous combination is A-II, B-III, C-IV, D-I, which is Option (1).

A typical microsporangium is bounded by four distinct concentric wall layers: epidermis, endothecium, middle layers, and tapetum:

• • The tapetum is the innermost nutritive somatic layer in direct contact with the sporogenous tissue.
• • Tapetal cells are physiologically active, possessing dense cytoplasm and abundant organelles (mitochondria, ribosomes, endoplasmic reticulum).
• • During early development, tapetal nuclei undergo endomitosis (karyokinesis without cytokinesis) or polyteny, resulting in cells that generally have more than one nucleus (binucleate or multinucleate).
• • Therefore, Assertion (A) is completely TRUE.

Connecting nuclear multiplicity to functional efficiency:

• • The primary physiological role of the tapetum is to provide continuous nutrition to developing microspore mother cells (MMCs) and maturing pollen grains.
• • The presence of multiple nuclei (or polyploidy) increases gene dosage and elevates transcription rates for critical enzymes (such as callase, which dissolves callose walls of microspore tetrads) and precursors of sporopollenin (pro-Ubisch bodies).
• • This amplifies the metabolic capacity and nutritive throughput of the tapetum.
• • Therefore, Reason (R) is scientifically and biologically TRUE.

Reason (R) provides the definitive functional adaptation explaining why tapetal cells undergo endomitosis to become multinucleate. Hence, Reason (R) is the correct explanation of Assertion (A).

The process of formation of megaspores from the megaspore mother cell is called megasporogenesis:

• • A single diploid megaspore mother cell (MMC) differentiates in the micropylar region of the nucellus.
• • The MMC undergoes a single meiotic division (1 Meiosis) to produce a linear tetrad of four haploid megaspores.
• • In a majority of angiosperms (monosporic development), three megaspores at the micropylar end degenerate, and only one functional megaspore (chalazal) develops into the female gametophyte.

Development of the female gametophyte from the functional megaspore:

• • Mitosis 1: The nucleus of the functional megaspore divides mitotically to form two nuclei, which move to the opposite poles, forming the 2-nucleate embryo sac.
• • Mitosis 2: Another mitotic division results in the formation of the 4-nucleate embryo sac.
• • Mitosis 3: A third mitotic division leads to the formation of the 8-nucleate stage of the embryo sac.
• • Total mitotic divisions = 3 Mitosis (free nuclear).

The complete development of a mature female gametophyte from an MMC requires precisely 1 Meiotic division followed by 3 Mitotic divisions.

NCERT states: "Pollination by water is quite rare in flowering plants and is limited to about 30 genera, mostly monocotyledons." Therefore, Statement A is incorrect.

In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and are pollinated by insects or wind as in most of the land plants. Statement B is true.

In seagrasses such as Zostera, female flowers remain submerged and pollen grains are long, ribbon-like and carried passively inside the water. In most water-pollinated species, pollen grains are protected from wetting by a mucilaginous covering. Statements C, D, and E are all true.

The correct set of statements is B, C, D and E only, matching Option (2).

In the monocotyledonous embryo of the grass family (maize/wheat), the embryo consists of one large, shield-shaped cotyledon known as scutellum situated towards one side of the embryonal axis.

At the upper end, the embryonal axis has the shoot apex and a few leaf primordia enclosed in a hollow foliar structure called coleoptile. At its lower end, the embryonal axis has the radical and root cap enclosed in an undifferentiated sheath called coleorhiza.

The radicle (labeled C) is the embryonic root that gives rise to the primary root system upon germination.

The figure displays a spike-like compact inflorescence where numerous flowers are closely aggregated. Long filaments project out from the axis, exposing stamens to the surrounding air currents.

Wind pollination requires that pollen grains are light and non-sticky so that they can be transported in wind currents. They often possess well-exposed stamens so that the pollens are easily dispersed into wind currents, and large feathery stigmas to easily trap airborne pollen grains.

Option (3) provides the exact descriptive caption from NCERT Biology.

Flowers have evolved specific morphological and physiological suites of traits (pollination syndromes) to attract target biotic vectors:

NCERT explicitly states: "Majority of insect-pollinated flowers are large, colourful, fragrant and rich in nectar. When the flowers are small, a number of flowers are clustered into an inflorescence to make them conspicuous."

Nectar and pollen grains constitute the canonical floral rewards provided to insect visitors for facilitating pollen transfer.

In maize ($\textit{Zea mays}$), the ear (cob) is a female inflorescence (spadix). The silks or tassels emerging from the husk leaves represent extremely elongated styles and feathery stigmas attached to each ovule:

Wind pollination requires large, exposed, feathery stigmas to maximize the probability of intercepting non-motile, lightweight pollen carried by air currents:

NCERT states verbatim: "The tassels you see are nothing but the stigma and style which wave in the wind to trap pollen grains."

Analyzing the ploidy of cells present in a fertilized angiosperm embryo sac following double fertilization:

The question specifically requires the sequence: haploid ($n$), diploid ($2n$), and triploid ($3n$):

Option (1) lists synergids ($n$), antipodals ($n$), polar nuclei ($n+n$). Option (2) lists synergids ($n$), PEN ($3n$), zygote ($2n$)—violating sequential order. Option (3) lists antipodals ($n$), synergids ($n$), PEN ($3n$). Only Option (4) strictly adheres to the requested $n \to 2n \to 3n$ sequence.

The single functional megaspore undergoes three consecutive mitotic nuclear divisions without immediate cytokinesis:

Cytokinesis and cell wall deposition partition the eight nuclei into specific cellular domains: - Micropylar End (Egg Apparatus): 3 cells total — 1 female gamete (egg cell) and 2 synergids with filiform apparatus. - Chalazal End (Antipodal Cells): 3 distinct uninucleate antipodal cells. - Central Region (Central Cell): 1 very large central cell retaining the 2 remaining polar nuclei.

Summing up the cellular and nuclear inventory at complete maturity:

Angiosperm pollination is categorized into three types depending on the genetic relatedness of the pollen donor and recipient:

Because pollen originates from a genetically distinct donor sporophyte, xenogamy introduces novel allele combinations and promotes outcrossing vigor, providing the ultimate raw material for adaptive evolutionary variation.

The period for which pollen grains remain viable is highly variable and depends on ambient temperature and relative humidity:

Because Poaceae exhibits short-lived viability (30 minutes), any option featuring Poaceae is automatically disqualified: - Option (1): Poaceae ; Rosaceae $\to$ Disqualified due to Poaceae. - Option (2): Poaceae ; Leguminosae $\to$ Disqualified due to Poaceae. - Option (3): Poaceae ; Solanaceae $\to$ Disqualified due to Poaceae. - Option (4): Rosaceae ; Leguminosae $\to$ Both families retain viability for months!

In angiosperms, the dominant conspicuous plant body is the diploid sporophyte ($2n$). The haploid gametophyte ($n$) is extremely reduced, non-photosynthetic, and parasitic, developing entirely within sporophytic parental tissues: - (a) Pollen grains inside the anther: The stamen and anther walls (epidermis, endothecium, middle layers, tapetum) are parental sporophytic tissues ($2n$). The pollen grain represents the immature male gametophyte ($n$) developing within the microsporangium. This represents generation $n$ nested directly inside generation $2n$. - (d) Embryo sac inside the ovule: The ovule (megasporangium with funicle, integuments, and nucellus) is parental sporophytic tissue ($2n$). Within the nucellus sits the 7-celled, 8-nucleate female gametophyte / embryo sac ($n$). This is another classic example of generation $n$ nested directly inside generation $2n$.

- (b) Germinated pollen grain with two male gametes: Both the pollen tube/vegetative cell ($n$) and the generative-derived sperm cells ($n$) belong to the exact same haploid gametophytic generation ($n$). - (c) Seed inside the fruit: The seed represents the next sporophytic generation ($2n$ embryo) along with endosperm ($3n$) inside the maternal ovary fruit wall ($2n$).

Pollination by water (hydrophily) is quite rare in flowering plants (limited to about 30 genera, mostly monocotyledons), exemplified by Vallisneria, Hydrilla (freshwater), and Zostera (marine seagrass).

In a majority of aquatic plants such as water hyacinth (Eichhornia) and water lily (Nymphaea), the flowers emerge above the level of water and are pollinated by insects or wind, just as in most land plants.

Water lily and water hyacinth possess conspicuous, colorful, fragrant petals designed to attract insect pollinators (entomophily) or produce wind-borne pollen (anemophily), rendering water currents completely uninvolved in their pollination.

Therefore, pollination takes place by insects or wind (Option 1).

An ovule is a small structure attached to the placenta by means of a stalk called funicle.

NCERT states verbatim: "The body of the ovule fuses with funicle in the region called hilum. Thus, hilum represents the junction between ovule and funicle."

- Micropyle: Small pore at the tip of the integuments where integuments do not encircle the nucellus. - Chalaza: Represents the basal part of the ovule opposite the micropylar end. - Nucellus: The central mass of parenchymatous nutritive cells enclosed within the integuments.

The point of attachment and fusion between the ovule body and funicle is unequivocally the Hilum.