Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants

Key Concept: Structure of the Flower, Essential Organs

d) The anther typically has four microsporangia and produces pollen grains.
[Solution Description]
The androecium consists of stamens, which are the male reproductive structures of a flower. Each stamen has a filament (sterile part) and an anther (fertile part). The anther contains four microsporangia that produce pollen grains. Thus, both the presence of microsporangia and their function are critical features of the androecium.

Key Concept: Alternation of Generations

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The sporophytic phase in angiosperms is indeed diploid ($2n$) and represents the dominant phase in their life cycle, as it is the main plant body that produces flowers. This makes Assertion (A) true. The Reason (R) states that the sporophyte develops from the zygote, which is formed by the fusion of haploid male and female gametes. Since the zygote is diploid and gives rise to the sporophyte, this statement is also true. Furthermore, the Reason correctly explains why the sporophytic phase is diploid, linking it to the formation of the zygote through fertilization. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Alternation of generations, Sporophyte and Gametophyte

a) Microsporangium
[Solution Description]
The male gametophyte in angiosperms is derived from microspores, which are produced by meiosis in the microsporangium (located in the anther). The sporophytic anther ($2n$) undergoes meiosis to form haploid microspores ($n$), which later develop into the male gametophyte (pollen grain). Thus, the correct structure is the microsporangium.

Key Concept: Sporophytic & Gametophytic Phases

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The sporophytic phase in angiosperms is indeed diploid ($2n$) and produces flowers, making Assertion (A) true. Flowers contain stamens and carpels, which produce haploid microspores and megaspores, respectively, initiating the gametophytic phase. Thus, Reason (R) is also true and correctly explains Assertion (A).

Key Concept: Structure of a Typical Flower

b) Corolla
[Solution Description]
The corolla, composed of petals, is typically brightly colored and elaborate to attract pollinators like insects. This aids in the process of pollination.

Key Concept: Accessory & Essential Whorls

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The assertion states that the androecium and gynoecium are essential whorls, which is correct because they are directly involved in reproduction. The reason correctly explains why these whorls are essential, as the androecium produces male gametes (pollen) and the gynoecium contains female gametes (ovules), both necessary for sexual reproduction.

Key Concept: Hypogynous flower, Floral parts insertion

c) Brassica (mustard)
[Solution Description]
Hypogynous flowers have floral parts (sepals, petals, stamens) inserted below the ovary, resulting in a superior ovary. Examples include Brassica (mustard) and Lycopersicon (tomato). Therefore, a plant with such characteristics must be mustard or tomato.

Key Concept: Perigynous Flower Structure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Perigynous flowers have a unique floral arrangement where the thalamus forms a cup-like structure around the ovary, making the ovary semi-inferior. This is due to the insertion of floral parts (sepals, petals, stamens) on the rim of this cup-shaped thalamus, as seen in roses and strawberries. Thus, both statements are true, and the Reason correctly explains why the ovary is semi-inferior (Assertion).

Key Concept: Epigynous flowers, Inferior ovary, Superior floral parts

c) Ovary is inferior, and floral parts are superior
[Solution Description]
In epigynous flowers, the ovary is inferior because it is fused with the thalamus, and other floral parts (sepals, petals, stamens) arise above the ovary, making them superior. This is a defining feature of epigynous flowers.

Key Concept: Pollination Types

d) Geitonogamy
[Solution Description]
Geitonogamy refers to the transfer of pollen grains from the anther to the stigma of another flower on the same plant. It is functionally cross-pollination but genetically similar to autogamy since it involves the same genetic individual.

Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
A typical anther is tetrasporangiate as it has four microsporangia (two in each lobe). The assertion correctly states this fact. The reason explains that each theca (lobe) in a bilobed, dithecous anther contains two microsporangia, which justifies why the anther is tetrasporangiate. Hence, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Endothecium, Dehiscence Mechanism

b) Through contraction of thickened dead cells leading to rupture at stomium
[Solution Description]
The endothecium is a single-layered structure below the epidermis. During anther maturation, its cells develop thickenings (except at the stomium). Upon drying, these thickened dead cells contract, creating tension that ruptures the anther wall at the thin-walled stomium, facilitating pollen release.

Key Concept: Microsporogenesis and Epidermis

c) It remains as the outer protective layer
[Solution Description]
In a mature anther, the epidermis remains as the outermost layer. It does not participate directly in pollen formation but ensures structural integrity by often becoming stretched or compressed as the anther grows. It also may undergo modifications like cutinization for additional protection.

Key Concept: Endothecium function, stomium role

c) Its thin-walled structure is mechanically weak
[Solution Description]
The stomium consists of thin-walled endothecium cells located between two microsporangia. When the anther dries, the thickened endothecium cells contract, creating tension. The stomium, being structurally weaker due to its thin walls, ruptures first under this tension, allowing pollen grains to be released. Thus, the stomium's thin-walled nature makes it the preferred site for rupture.

Key Concept: Types of Tapetum

c) Amoeboid tapetum
[Solution Description]
There are two main types of tapetum: amoeboid and secretory (glandular). In the amoeboid tapetum, the cells lose their walls, and the protoplasts fuse to form a periplasmodium, which surrounds the developing microspores. This is in contrast to the secretory tapetum, where cells remain intact and secrete substances into the locule.

Key Concept: Pollen Grain Structure

b) 2-celled stage
[Solution Description]
Pollen grains may be shed at either the 2-celled stage (tube cell + generative cell) or the 3-celled stage (tube cell + two male gametes). However, most angiosperms (>60%) shed pollen grains at the 2-celled stage.

Key Concept: Types of tetrads

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that in a tetrahedral tetrad, only three microspores are visible from one angle while the fourth lies at the back. This is correct because in a tetrahedral arrangement, the microspores are positioned at the vertices of a tetrahedron, making the fourth microspore hidden behind the other three when viewed from any angle. The reason explains the structure of tetrahedral tetrads, which correctly justifies the assertion. Hence, both the assertion and reason are true, and the reason provides the correct explanation for the assertion.

Key Concept: Exine Composition

c) Sporopollenin
[Solution Description]
The exine layer is chiefly composed of sporopollenin, which is an oxidative polymer of carotenoids and/or carotenoid esters. This substance provides resistance to physical and biological decomposition.

Key Concept: Vegetative \& Generative Cells

d) Forms the pollen tube and absorbs nutrients
[Solution Description]
The vegetative (tube) cell is responsible for forming the pollen tube and absorbing nutrients during pollen germination. It contains abundant food reserves to support this process.

Key Concept: Male gametophyte development

b) 2-celled stage
[Solution Description]
In over 60% of angiosperms, pollen grains are shed at the 2-celled stage, which consists of a vegetative (tube) cell and a generative cell.

Key Concept: Pre-pollination stage in angiosperms

b) 2-celled stage
[Solution Description]
In over 60% of angiosperms, pollen grains are shed at the **2-celled stage**, consisting of a vegetative (tube) cell and a generative cell.

Key Concept: Female Gametophyte Development

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the mature angiosperm embryo sac is 7-celled and 8-nucleate, which is correct as it consists of two synergids, one egg cell, three antipodal cells, and a central cell with two polar nuclei (totaling 7 cells and 8 nuclei). The reason explains that the functional megaspore undergoes three mitotic divisions to produce eight nuclei, which then organize into the 7-celled structure. Since the reason correctly explains why the assertion is true, both are correct and logically connected.

Key Concept: Structure of Ovule

a) Orthotropous
[Solution Description]
The orthotropous (atropous) ovule has its micropyle, chalaza, and funicle aligned in a straight line. This is seen in plants like Polygonum and Cycas.

Key Concept: Orthotropous, Anatropous, Campylotropous

b) Anatropous
[Solution Description]
The question describes an ovule where micropyle and chalaza lie in one straight line, and the funicle is parallel to this line. This description matches the anatropous ovule, as given in the syllabus. In anatropous ovules, the nucellus remains straight while the body of the ovule is inverted through 180°, bringing the micropyle close to the base of the funicle.

Key Concept: Orthotropous Ovule Structure

b) Chalaza, funicle, and micropyle
[Solution Description]
An orthotropous ovule is characterized by the micropyle, chalaza, and funicle lying in a straight line. This is the simplest type of ovule structure, as mentioned in the syllabus. Examples include Polygonum and Cycas.

Key Concept: Anatropous ovule inversion, Micropyle position

d) The micropyle is adjacent to the funicle and faces the placenta.
[Solution Description]
In an anatropous ovule, the body of the ovule inverts by 180° due to unilateral growth of the funicle. This causes the micropyle to come close to the base of the funicle. The funicle runs parallel to the micropyle and chalaza, forming a straight line. Thus, the micropyle faces the placenta and lies adjacent to the funicle post-inversion.

Key Concept: Integument Development

c) Inner integument from epidermal, outer integument from sub-epidermal layer
[Solution Description]
The inner integument arises from the epidermal layer, while the outer integument arises from the sub-epidermal layer. The growth of the outer integument is slower compared to the inner integument.

Key Concept: Amphitropous ovule characteristics, Comparison with other ovule types

b) The embryo sac bends into a horse-shoe shape only in amphitropous ovules.
[Solution Description]
The amphitropous ovule is characterized by a pronounced curvature and a horse-shoe shaped embryo sac, while the anatropous ovule is inverted through $180^\circ$ but lacks this specific bending of the embryo sac. The correct answer must highlight the unique horse-shoe shape of the embryo sac in amphitropous ovules.

Key Concept: Megasporogenesis

c) Haploid
[Solution Description]
The megaspore mother cell (MMC) undergoes meiosis to form four haploid megaspores, out of which only one remains functional. Thus, the functional megaspore is haploid.

Key Concept: Polygonum type embryo sac

b) Diploid (2n)
[Solution Description]
The two polar nuclei in the central cell of the embryo sac fuse to form a secondary nucleus. Since both nuclei are haploid, their fusion results in a diploid ($2n$) secondary nucleus.

Key Concept: Egg Apparatus Components

c) 3 cells
[Solution Description]
The egg apparatus is composed of 1 egg cell and 2 synergid cells, totaling 3 cells.

Key Concept: Double fertilization product

b) Primary endosperm nucleus ($3n$)
[Solution Description]
During double fertilization, one male gamete ($n$) fuses with the secondary nucleus ($2n$), which is formed by the fusion of two polar nuclei. The ploidy of the resulting structure is $n + 2n = 3n$, known as the primary endosperm nucleus.

Key Concept: Connective Structure

b) To provide structural support to the anther lobes
[Solution Description]
The connective provides structural support to the anther lobes and contains vascular tissues that supply nutrients and water to the developing anther, as mentioned in the syllabus.

Key Concept: Structure of Ovule

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion (A) states that the ovule in Polygonum is orthotropous. According to the syllabus, Polygonum has an orthotropous ovule, which means the assertion is true. The reason (R) explains that in orthotropous ovules, the micropyle, chalaza, and funicle lie in a straight line, which is also correct as per the syllabus. Moreover, the reason correctly explains why the assertion is true since the alignment of these structures defines the orthotropous condition.

Key Concept: Anatropous ovule, Megasporogenesis

c) Assertion is true, but Reason is false.
[Solution Description]
The Assertion is true because, in an anatropous ovule, unilateral growth of the funicle causes the ovule to invert 180°, bringing the micropyle near the funicle base. However, the Reason is false because the inner integument arises from the epidermal layer while the outer integument originates from the sub-epidermal layer, and their growth rates differ (outer grows slower than inner). Hence, Assertion is true, but Reason is false.

Key Concept: Campylotropous Ovule Characteristics

d) Its curvature is less than that of an anatropous ovule.
[Solution Description]
A campylotropous ovule has a curved body, but its curvature is less than that of an anatropous ovule. The nucellus and integuments are present, with the micropyle formed by the inner and outer integuments. The correct answer is option d).

Key Concept: Amphitropous ovule, Female gametophyte development

c) Assertion is true, but Reason is false.
[Solution Description]
Assertion (A) is true because, as mentioned in the syllabus, the amphitropous ovule has a pronounced curved body like that of an anatropous ovule, and the embryo sac bends to become horse-shoe shaped (e.g., Alisma).
Reason (R) is false because the bending of the embryo sac in amphitropous ovules is not caused by differential growth rates of integuments. Instead, it is due to the curvature of the nucellus itself, as specified in the syllabus. The integuments primarily contribute to the formation of the micropyle and do not directly cause the embryo sac's horse-shoe shape.
Therefore, the correct answer is (C): Assertion is true, but Reason is false.

Key Concept: Hydrophily

b) Epi-hydrophily
[Solution Description]
Hydrophily is of two types: hypo-hydrophily (underwater pollination) and epi-hydrophily (surface-level pollination). Epi-hydrophily occurs when pollination takes place at the water's surface, as seen in Vallisneria spiralis, where male flowers float and contact female flowers on the surface.

Key Concept: Autogamy

c) Transfer of pollen grains from the anther to the stigma of the same flower
[Solution Description]
Autogamy refers to the transfer of pollen grains from the anther to the stigma of the same flower. It is a type of self-pollination and occurs only in bisexual flowers where both male and female reproductive parts mature simultaneously. Examples include plants like Viola and Oxalis.

Key Concept: Autogamy and Cleistogamous Flowers

b) They remain closed and ensure self-pollination.
[Solution Description]
Cleistogamous flowers are a type of flower that do not open at all. The anthers dehisce inside the bud, ensuring that the pollen grains come in contact with the stigma of the same flower, leading to autogamy. This eliminates the possibility of cross-pollination.

Key Concept: Geitonogamy, Advantages and Disadvantages of Self-pollination

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion states that geitonogamy leads to genetic variation in the offspring. However, geitonogamy involves pollen transfer between different flowers of the same plant, which means the genetic material comes from the same parent plant. Thus, it does not introduce new genetic variation. Therefore, the assertion is false.
The reason states that geitonogamy is genetically equivalent to autogamy because the pollen grains come from the same plant. This statement is true, as per the syllabus definition, since both processes involve pollen from the same plant, leading to genetically similar outcomes despite the functional differences in pollination mechanisms.

Key Concept: Cleistogamy Characteristics

a) Cleistogamous flowers open fully during pollination.
[Solution Description]
Cleistogamous flowers ensure self-pollination in closed buds, preventing cross-pollination. They do not open at all, unlike chasmogamous flowers. The anthers dehisce inside the bud, allowing pollen grains to directly reach the stigma. However, they are not dependent on pollinators, which supports seed production even in unfavorable conditions.

Key Concept: Anemophily, Adaptations

d) Sticky pollen
[Solution Description]
Anemophilous (wind-pollinated) plants have specific adaptations to facilitate pollen transfer via wind. These adaptations include:
1. Light, smooth, and dry pollen grains for easy dispersal by wind.
2. Versatile anthers that swing freely in the wind.
3. Inconspicuous flowers (lack of bright colors, scent, or nectar) since they do not rely on pollinators.
4. Large and feathery stigmas to catch airborne pollen.
The adaptation not associated with anemophily is sticky pollen, as this is characteristic of insect-pollinated (entomophilous) plants. Sticky pollen would hinder wind dispersal.
Thus, the correct answer is sticky pollen.

Key Concept: Self-incompatibility

c) A condition where pollen does not grow on the stigma of the same flower
[Solution Description]
Self-incompatibility is a condition where the pollen of a flower fails to germinate or grows very slowly on the stigma of the same flower, preventing self-fertilization. This mechanism ensures cross-pollination by recognizing and rejecting incompatible pollen.

Key Concept: Dichogamy

c) Helianthus
[Solution Description]
Protandry refers to the condition where anthers release pollen before the stigma of the same flower becomes receptive. Examples include Salvia, Gossypium, and Helianthus. Among the given options, only Helianthus represents protandry.

Key Concept: Herkogamy Definition

b) A condition preventing autogamy due to spatial separation of reproductive parts
[Solution Description]
Herkogamy is a condition in some bisexual flowers where the structure of anthers and styles prevents autogamy (self-pollination). In plants like Caryophyllaceae, the style is longer than the stamens, making it mechanically impossible for pollen to reach the stigma. Similarly, in Gloriosa, anthers dehisce away from the stigma. This promotes cross-pollination.

Key Concept: Unisexuality Types

b) Maize
[Solution Description]
Monoecious plants have both male and female flowers on the same plant, such as castor and maize. Among the given options, maize is an example of a monoecious plant.

Key Concept: Anemophily

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Anemophilous (wind-pollinated) plants produce an enormous quantity of pollen grains because most pollen is wasted during wind dispersal and does not reach the stigma. The reason correctly explains why these plants produce a large number of pollen grains, as it compensates for the inefficiency of wind as a pollination agent.

Key Concept: Anemophily

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Anemophilous plants rely on wind for pollination, which is an inefficient process as most pollen grains do not land on the stigma. To compensate, these plants produce a large quantity of pollen grains. The assertion is true because wind-pollinated flowers indeed produce abundant pollen. The reason is also true because it correctly explains why they produce large quantities—most pollen grains are lost during transit. Furthermore, the reason directly justifies the assertion, making it the correct explanation.

Key Concept: Hypo-hydrophily and Epi-hydrophily

c) Vallisneria spiralis
[Solution Description]
The question describes epi-hydrophily, where pollination occurs at the water surface. In Vallisneria spiralis, male flowers detach and float on the water surface, while female flowers are raised to the surface by a long spiral stalk for pollination.

Key Concept: Entomophily

c) Dull-colored petals
[Solution Description]
Flowers adapted for insect pollination (entomophily) have bright colors, fragrance, sticky pollen, and nectar. The characteristic not associated with entomophily is dull-colored petals, which are more common in malacophily or abiotic pollination.

Key Concept: Mechanism of Pollen Transfer

c) Versatile anthers
[Solution Description]
$Salvia$ has versatile anthers and other balancing features that facilitate the dusting of insects with pollen when they visit the flower. This ensures effective pollen transfer when the same insect visits another flower.

Key Concept: Characteristics of Ornithophilous Flowers

d) Brightly colored and sturdy flowers with copious nectar
[Solution Description]
Ornithophilous flowers have specific adaptations to attract and utilize birds for pollination, such as being brightly colored and producing copious nectar. This is directly mentioned in the syllabus under "Characteristics of Ornithophilous Flowers."

Key Concept: Cheiropteriphily, Nocturnal Pollination

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that cheiropteriphilous flowers emit a strong musty odor to attract bats due to bats' reliance on olfactory cues. This is true as bats are known to be attracted to such odors, especially in low-light conditions where visual cues are less effective.
The reason states that bats have poorly developed vision and depend on smell and echolocation. While it is true that bats rely on echolocation and olfaction more than vision, they do not have "poorly developed" vision; rather, their vision is adapted to low-light conditions. Thus, the reason incorrectly generalizes bat vision as poor.
Therefore, Assertion is true, but Reason is false.

Key Concept: Malacophily, Pollination agents

d) Reduced mobility of snails limits pollen dispersal, affecting genetic diversity.
[Solution Description]
Malacophily is less efficient than entomophily because snails and slugs move slower, cover smaller distances, and visit fewer flowers per unit time. This reduces pollen transfer rates, limiting genetic diversity. Additionally, malacophilous plants often have restricted habitats, unlike insect-pollinated plants that benefit from wider pollinator ranges.

Key Concept: Malacophily Definition

c) Pollination by snails and slugs
[Solution Description]
Malacophily is a type of pollination where snails and slugs act as pollinators, transferring pollen grains from one flower to another. It occurs in both terrestrial and aquatic plants. The key examples include Chrysanthemum leucanthemum land plant and Lemna (aquatic plant). Thus, the correct option should specify pollination by snails and slugs.

Key Concept: Examples of Malacophily

c) Chrysanthemum leucanthemum
[Solution Description]
Examples of plants that show malacophily include terrestrial plants like $Chrysanthemum$ $leucanthemum$ and aquatic plants like $Lemna$.

Key Concept: Self-pollination, Genetic Variation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Self-pollination results in homozygosity as the same parental genes are repeatedly passed on, which preserves parental characters. However, this also means no new genetic combinations arise, leading to reduced genetic variability. The assertion correctly states that self-pollination maintains purity of the species (preserves parental characters) and does not introduce variation. The reason correctly explains why this happens—because homozygosity prevents new trait introduction. Thus, both statements are true, and the reason justifies the assertion.

Key Concept: Self-pollination

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Cleistogamous flowers are those that do not open at all, and pollination occurs within the closed flower bud. The pollen grains from the anthers directly fall onto the stigma of the same flower, leading to autogamy. Therefore, both Assertion and Reason are true, and the Reason correctly explains why cleistogamous flowers always undergo autogamy.

Key Concept: Agents of Pollination

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion states that wind-pollinated flowers are bright and scented, which is false. Wind-pollinated flowers are typically small, dull-colored, and lack scent or nectar since they do not need to attract biotic pollinators. The reason claims that bright colors and scents attract wind, which is also false because wind is an abiotic agent and does not respond to visual or olfactory cues.

Key Concept: Pollen-Pistil Interaction

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that the pistil recognizes compatible pollen and promotes fertilization, which aligns with the syllabus description of pollen-pistil interaction. The Reason explains that pollination alone does not ensure fertilization because the pistil selectively accepts or rejects pollen based on compatibility. The Reason correctly explains the Assertion because it highlights the filtering mechanism described in the syllabus.

Key Concept: Porogamy, Entry of Pollen Tube

c) Synergids guide the pollen tube's entry by positioning themselves near the micropylar end.
[Solution Description]
Synergids play a crucial role in guiding the entry of the pollen tube into the embryo sac. The pollen tube may enter: (i) between the egg cell and one of the synergids, (ii) between the wall of the embryo sac and one or both synergids, (iii) between the two synergids, or (iv) directly penetrating one of the synergids. Thus, synergids influence not only the entry point but also the dissemination of male gametes.

Key Concept: Double Fertilization

c) Triploid ($3n$)
[Solution Description]
During double fertilization, one male gamete ($n$) fuses with two polar nuclei ($n$ each) to form the primary endosperm nucleus (PEN). Therefore, its ploidy is $3n$ (triploid).

Key Concept: Mesogamy, Pollen Tube Entry

c) Cucurbita
[Solution Description]
Mesogamy is observed in certain plants where the pollen tube enters the ovule through the integument. According to the syllabus, Cucurbita and Populus are examples of mesogamy. Thus, among the options provided, the correct answer should be one of these two plants.
First, we identify the known examples of mesogamy from the syllabus: Cucurbita and Populus. We then match these with the given options to select the correct choice.

Key Concept: Syngamy, Triple fusion

c) The seed aborts due to lack of triploid endosperm for nourishment.
[Solution Description] The primary endosperm nucleus (PEN) forms via triple fusion ($\text{male gamete} + \text{polar nuclei} \rightarrow \text{PEN (3n)}$). Without this fusion, endosperm development would halt, starving the embryo of nutrients and causing seed abortion. The zygote may still form but cannot mature without endosperm support.

Key Concept: Discharge of male gametes from pollen tube

b) It disorganizes
[Solution Description]
The tube nucleus disorganizes before the bursting of the pollen tube. This is a key step in the process of fertilization where the tube nucleus breaks down to release the male gametes.

Key Concept: Double fertilization

c) Double fertilization
[Solution Description]
Double fertilization is a unique phenomenon in angiosperms where one male gamete fertilizes the egg (forming a zygote) and the second male gamete fuses with the two polar nuclei (forming the triploid primary endosperm nucleus). This process does not occur in gymnosperms or other plant groups.

Key Concept: Double fertilization, Endosperm types

d) Nuclear endosperm
[Solution Description]
The three types of endosperm are nuclear, cellular, and helobial.
Step 1: Nuclear endosperm is characterized by free nuclear divisions without immediate cell wall formation.
Step 2: In cellular endosperm, the first division is followed by the formation of cell walls.
Step 3: Helobial endosperm is an intermediate type, where the first division is followed by partial wall formation.
Step 4: Coconut (*Cocos nucifera*) exhibits nuclear endosperm development, where multiple free nuclei are formed initially before cellularization occurs later.

Key Concept: Pollen-Pistil Interaction

a) Porogamy
[Solution Description]
The pollen tube can enter the ovule through three routes: porogamy, chalazogamy, and mesogamy. Porogamy, where the pollen tube enters through the micropyle, is the most common mode of entry in angiosperms.

Key Concept: Recognition \& Compatibility, Artificial Hybridization

d) Rebagging was skipped after pollination
[Solution Description]
Artificial hybridization involves:
Step 1: Emasculation (removal of stamens from the female parent).
Step 2: Bagging (covering the emasculated flower to prevent contamination).
Step 3: Pollination (dusting mature pollen grains from the male parent onto the stigma).
Step 4: Rebagging (to protect the pollinated flower).
If undesired hybrid seeds are produced, the most likely missed step is rebagging after pollination, which allows unwanted pollen to contaminate the flower.

Key Concept: Pollen Germination & Tube Growth

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The Assertion is true because, as per the syllabus, regardless of the entry route into the ovule (porogamy, chalazogamy, or mesogamy), the pollen tube always enters the embryo sac from the micropylar end. The Reason is also true because synergids play a crucial role in guiding the pollen tube toward the egg cell by releasing chemotropic signals. However, the Reason does not explain why the pollen tube enters only through the micropylar end; it merely states the function of synergids during fertilization. Therefore, both are true, but Reason is not the correct explanation of Assertion.

Key Concept: Pollen Tube Entry Routes

c) Porogamy
[Solution Description]
The pollen tube can enter the ovule through three routes: porogamy (through the micropyle), chalazogamy (through the chalazal end), and mesogamy (through the integument). Porogamy is the most common mode of entry, where the pollen tube enters through the micropyle.

Key Concept: Embryo Development

b) Zygote → Globular stage → Heart stage → Mature embryo
[Solution Description]
Embryogenesis involves the zygote undergoing divisions to form the proembryo, globular stage, heart-shaped stage (due to cotyledon formation), and finally the mature embryo. In dicots, two cotyledons are attached laterally to the embryonal axis.

Key Concept: Endosperm Development

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the endosperm in coconut is an example of nuclear endosperm. This is correct because coconut (Cocos nucifera) is a classical example of nuclear endosperm, where the primary endosperm nucleus undergoes free nuclear divisions initially without cell wall formation. The reason explains that nuclear endosperm involves free nuclear divisions without cell wall formation at the beginning, which is accurate and correctly explains why coconut endosperm is categorized as nuclear. Thus, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Nuclear, Cellular, and Helobial Endosperm

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that in helobial endosperm development, the first division of the primary endosperm nucleus results in two unequal chambers with immediate wall formation. This is true because helobial endosperm begins with a transverse wall forming after the first division, creating a small chalazal chamber and a large micropylar chamber.
The Reason explains that the micropylar chamber undergoes free nuclear divisions followed by cellularization, while the chalazal chamber often degenerates. This is also correct and directly explains why the Assertion is true. The initial wall formation divides the embryo sac into two chambers, and subsequent events (free nuclear divisions in the micropylar chamber and degeneration of the chalazal chamber) are consequences of this division.
Therefore, both Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Dicot vs Monocot Embryo Development, Suspensor Function

c) Radicle and root cap
[Solution Description]
The basal cell (cb) undergoes transverse division to form cells cm and ci, which contribute to the suspensor. The suspensor is crucial for nutrient transport and forms the hypophysis (which later develops into the radicle). If cb does not divide, the suspensor will not form, leading to the absence of the radicle and root cap.
Step-by-step reasoning:
1. The basal cell (cb) divides to form cm and ci.
2. These cells further divide to form the suspensor.
3. The distal end of the suspensor (hypophysis) gives rise to the radicle and root cap.
4. Without division of cb, these structures will not form.

Key Concept: Heart-Shaped Stage, Cotyledon Development

d) Plumule
[Solution Description]
At the heart-shaped stage, the two cotyledons become prominent, and the groove between them contains a group of cells that differentiate into the plumule (future shoot apex). The plumule is the precursor to the stem and leaves.

Key Concept: Monocot embryo development, differentiation of scutellum and embryonal axis

d) The plumule and upper cotyledon, as they originate from region $1'$.
[Solution Description]
The quadrant in the monocot embryo differentiates into two regions, $1$ and $1'$. Region $1$ forms the basal part of the cotyledon (scutellum), while region $1'$ gives rise to the upper part of the cotyledon, hypocotyl, and plumule. If $1'$ is missing due to a mutation, the structures derived from it (upper cotyledon, hypocotyl, and plumule) would be absent or malformed. The plumule is enclosed within the coleoptile, so its absence would directly affect the shoot system.

Key Concept: Seed classification

c) Monocotyledonous seed
[Solution Description]
Monocotyledonous seeds have only one cotyledon, as seen in plants like rice and maize.

Key Concept: Albuminous vs. Exalbuminous Seeds

c) Cotyledons
[Solution Description]
Exalbuminous seeds do not retain endosperm at maturity; instead, food is stored in the cotyledons. The cotyledons become thick and fleshy to provide nourishment to the developing embryo during germination.

Key Concept: Embryo Structure

d) Plumule
[Solution Description]
The embryonal axis consists of radicle, hypocotyl, and plumule. The plumule is the part between the cotyledons that grows into the shoot system (stem and leaves) during germination.

Key Concept: Monocot Seed Structure

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion (A) states that the maize grain is a one-seeded fruit called caryopsis where the pericarp is fused with the seed coat. This is true as per the syllabus, which describes the maize grain as a caryopsis with the pericarp inseparably fused with the seed coat. The reason (R) states that the grains are attached to the cob by their pointed end. While this is also true, it does not explain why the maize grain is a caryopsis or the fusion of the pericarp with the seed coat. Therefore, both statements are true, but the reason is not the correct explanation of the assertion.

Key Concept: Types of Seeds: Dicotyledonous vs. Monocotyledonous

c) Maize
[Solution Description]
Monocotyledonous seeds have only one cotyledon. Examples include maize, rice, and wheat. Among the given options, maize is a monocotyledonous seed, while gram, pea, and castor are dicotyledonous seeds.

Key Concept: Albuminous Seeds

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that castor seeds are albuminous because they retain endosperm at maturity, which is true as per the syllabus. However, the reason claims that the endosperm is utilized by the developing embryo, which is false because in albuminous seeds like castor, the endosperm persists and nourishes the seedling during its early development. Thus, Assertion is true, but Reason is false.

Key Concept: Non-albuminous seeds

c) Their endosperm is fully utilized during development
[Solution Description]
Non-albuminous (exalbuminous) seeds do not retain endosperm at maturity as it is consumed by the developing embryo. In such seeds, food is stored in cotyledons, which become thick and fleshy. Examples include gram, pea, and mustard.

Key Concept: Perisperm Definition

c) Assertion is true, but Reason is false.
[Solution Description]
The Assertion (A) is true because the perisperm is indeed the residual, persistent nucellus found in seeds like black pepper and beet, as mentioned in the syllabus. However, the Reason (R) is false because the perisperm does not provide nourishment to the developing embryo; this role is primarily played by the endosperm in albuminous seeds or cotyledons in exalbuminous seeds. Therefore, Assertion is true, but Reason is false.

Key Concept: Parthenocarpy

b) Banana
[Solution Description]
Parthenocarpic fruits develop without fertilization. Examples include banana, citrus, grapes, pineapple, and some varieties of apples and pears.

Key Concept: True and False Fruits, Parthenocarpy

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the edible part of an apple is derived from the thalamus, making it a false fruit. This is true because in apples, the fleshy part we eat develops from the thalamus, while the ovary forms the core. The reason explains that the thalamus becomes fleshy and forms the major portion, which is also correct. Moreover, the reason correctly justifies why the assertion is true as it explains the involvement of the thalamus in forming the edible part, confirming its classification as a false fruit.

Key Concept: Significance of Parthenocarpy

c) They have a higher proportion of edible parts compared to normal fruits
[Solution Description]
Parthenocarpic fruits hold great importance in horticulture because they are seedless and have a higher proportion of edible parts than normal fruits. This makes them more desirable for consumption and commercial purposes.

Key Concept: Apomixis

c) Recurrent apomixis
[Solution Description]
Recurrent apomixis involves the formation of a diploid embryo sac directly from a diploid cell of the archesporium (generative apospory) or nucellus (somatic apospory). The diploid egg develops into an embryo without fertilization, ensuring genetic uniformity.

Key Concept: Recurrent apomixis, Non-recurrent apomixis

c) Recurrent apomixis
[Solution Description]
In recurrent apomixis, the embryo sac nuclei are diploid, and the embryo sac can arise either from a cell of the archesporium (generative apospory) or from some other cell of the nucellus (somatic apospory). Since the question mentions that the embryo sac originates from a nucellar cell and the nuclei are diploid, this clearly indicates recurrent apomixis. Non-recurrent apomixis involves haploid embryo sacs formed via meiosis, which contradicts the given scenario.

Key Concept: Polyembryony, Cleavage polyembryony, Adventive embryos

c) Assertion is true, but Reason is false.
[Solution Description]
The Assertion (A) is true because cleavage polyembryony indeed involves the splitting of the zygote or proembryo, leading to multiple embryos in a seed. However, the Reason (R) is incorrect because cleavage polyembryony does not involve the secretion of growth-stimulating substances by nucellus cells; rather, it is due to the splitting of the zygote or proembryo itself. The formation of adventive embryos from nucellus cells is associated with other types of polyembryony, not cleavage polyembryony.

Key Concept: Fruit Classification

c) Mango
[Solution Description]
A true fruit develops exclusively from the ovary. Mango, guava, and grapes are examples of true fruits because they form solely from the ovary and do not involve other floral parts in fruit formation.

Key Concept: Formation of Fruit

d) Ovary
[Solution Description]
After fertilization, the ovary of the flower undergoes changes and develops into the fruit. The fruit protects the seeds and aids in their dispersal. Other floral parts may contribute to false fruits, but true fruits develop only from the ovary.

Key Concept: Fruit Formation

a) Ovary wall
[Solution Description]
The ovary wall matures into the wall of the fruit, known as the pericarp. It differentiates into outer epicarp, middle mesocarp, and inner endocarp.

Key Concept: Seed Formation and Fruit Development

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that parthenocarpic fruits develop without fertilization, which is true. This is because parthenocarpy is the process where fruits are formed without fertilization. The reason given is that banana is an example of such a fruit, which is also correct as bananas are indeed parthenocarpic fruits. Moreover, the reason correctly explains why the assertion is true.

Key Concept: Parthenocarpy

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that banana is a parthenocarpic fruit, which is correct as per the syllabus. The Reason explains that parthenocarpic fruits develop without fertilization, which is also true and directly explains why banana is a parthenocarpic fruit. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Seed Dormancy and Viability

d) Low metabolic activity and protective seed coats
[Solution Description]
Seed longevity is influenced by factors such as low metabolic activity, dehydration, and protective seed coats. In species like Lupinus articus and Phoenix dactylifera, these adaptations allow seeds to remain viable for thousands of years under favorable conditions.

Key Concept: Seed Structure, Apomixis

c) Apomixis allows plants to produce seeds without fertilization, preserving specific genetic traits.
[Solution Description]
Apomixis is the asexual reproduction process that bypasses meiosis and fertilization, leading to seed formation without genetic recombination. This mechanism helps preserve desirable traits in plants indefinitely, as it avoids segregation and recombination of chromosomes. It is particularly useful in agriculture for maintaining hybrid vigor.

Key Concept: Seed coat structure in bean seed

c) It allows water absorption during germination.
[Solution Description]
The micropyle is a minute pore present at one end of the raphe in a bean seed. When soaked, water and air bubbles ooze out through this pore, indicating its role in water absorption during germination.