Mix Examples-Sexual Reproduction in Flowering Plants Questions in English

(B) $1$. Zoospores are motile,unicellular asexual reproductive structures that possess flagella and lack a rigid cell wall.
$2$. Conidia are non-motile,unicellular asexual reproductive structures that lack flagella and possess a cell wall.
$3$. Gametes are unicellular haploid cells that may or may not possess flagella (e.g.,isogametes in Chlamydomonas are flagellated) and may or may not have a protective wall.
$4$. Comparing the table provided in the question with biological facts: Row $(b)$ (Conidia) is correctly described as unicellular,flagella absent,and wall present. Row $(c)$ (Gamete) is correctly described as unicellular,flagella can be present,and wall can be present. Row $(a)$ is incorrect because zoospores lack a cell wall.
$5$. Therefore,$(b)$ and $(c)$ are the correct descriptions.

(D) In $Mangifera$ (Angiosperms) and $Pinus$ (Gymnosperms),the male gametes are non-motile.
$1$. $Mangifera$ is an angiosperm,and in angiosperms,pollen grains carry non-motile male gametes to the ovule through a pollen tube.
$2$. $Pinus$ is a gymnosperm,and in gymnosperms,male gametes are also non-motile and are transported via pollen tubes.
$3$. In contrast,algae like $Ulothrix$,$Chara$,and $Spirogyra$ typically produce motile male gametes (antherozoids) that require water for fertilization.

(A) In an apple,the diploid chromosome number $(2n)$ is $34$.
$1$. Megasporocyte is a diploid cell $(2n)$,so it has $34$ chromosomes.
$2$. Microspore is a haploid cell $(n)$,so it has $17$ chromosomes.
$3$. Primary Endosperm Nucleus $(PEN)$ is a triploid structure $(3n)$,so it has $3 \times 17 = 51$ chromosomes.
Therefore,the correct option is $A$.

(C) In organisms with a haplontic life cycle,the main plant body is haploid $(n)$.
Since the organism is already haploid,it produces gametes through mitosis.
The fusion of gametes results in a diploid $(2n)$ zygote.
To restore the haploid state,the zygote undergoes meiosis to produce haploid spores,which then develop into the haploid organism.

(C) The life cycle of an annual plant like wheat consists of three primary phases:
$1$. Juvenile phase $(J)$: The period of growth from germination to the development of vegetative structures.
$2$. Reproductive phase $(R)$: The period where the plant produces flowers and seeds.
$3$. Senescence $(S)$: The final stage of the life cycle characterized by aging and death.
Therefore,the correct sequence is $J \rightarrow R \rightarrow S$.

(D) The zygote is the vital link that ensures the continuity of species between organisms of one generation and the next. It is a diploid $(2n)$ cell formed by the fusion of male and female gametes. Zygospore and Oospore are also diploid structures formed after fertilization in certain organisms. However,Oosphere is the female gamete (egg cell),which is haploid $(n)$. Therefore,it does not represent the link between generations in the same way as a zygote.

(D) Statement $I$ is correct: During embryogenesis,the zygote undergoes mitotic cell division to form an embryo.
Statement $II$ is incorrect: In organisms with a diplontic life cycle (like humans),the zygote undergoes mitosis to develop into a diploid individual. Meiosis occurs during gametogenesis,not in the zygote.
Statement $III$ is incorrect: The pericarp (fruit wall) develops from the ovary wall,not from the integuments of the ovule. The integuments of the ovule develop into the seed coat.
Statement $IV$ is correct: In some plants like brinjal (Solanum melongena),the calyx (sepals) remains persistent and attached to the fruit even after fertilization.
Therefore,statements $I$ and $IV$ are correct,while $II$ and $III$ are incorrect.

(A) In most higher organisms,the male and female gametes are produced in different individuals (dioecious).
Since the gametes are formed in separate bodies,they cannot meet by chance or simple diffusion.
Therefore,these organisms must evolve a special mechanism for the transfer of male gametes to the female gametes to facilitate fertilization.
Thus,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(D) The $Pollen$ $\text{grain}$ is the male reproductive unit of an angiospermic plant.
In contrast, the $Micropyle$, $Embryo$ $\text{sac}$, and $Nucellus$ are all components of the ovule, which is the female reproductive part of the plant.
Therefore, the $Pollen$ $\text{grain}$ is the odd one out.

(B) The root cells of a flowering plant are diploid $(2n = 24)$.
Gametes are haploid cells produced through meiosis,which reduces the chromosome number by half.
Therefore,the number of chromosomes in the gamete is $n = 24 / 2 = 12$.

$A$ represents Chasmogamous flowers, which are open flowers with exposed anthers and stigma, allowing for cross-pollination or self-pollination.
$B$ represents Cleistogamous flowers, which are closed flowers that do not open at all. In such flowers, the anthers and stigma lie close to each other. When anthers dehisce in the closed flower, pollen grains come in contact with the stigma to effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollination landing on the stigma.

(C) $1$. Endosperm Genotype: Endosperm is formed by the fusion of one male gamete $(A)$ and two polar nuclei $(BB)$. Therefore, the genotype of the endosperm is $ABB$.
$2$. Embryo Genotype: The embryo is formed by the fusion of one male gamete $(A)$ and one female gamete $(B)$. Therefore, the genotype of the embryo is $AB$.

(D) Autogamy (self-pollination) involves the transfer of pollen grains from the anther to the stigma of the same flower.
Devices that promote self-pollination include:
$1$. Bisexuality: Presence of both male and female reproductive organs in the same flower.
$2$. Homogamy: Maturation of anthers and stigma at the same time.
$3$. Cleistogamy: Flowers remain closed,ensuring self-pollination.
Dicliny (unisexuality),dichogamy,and heterostyly are devices that promote cross-pollination (allogamy) by preventing self-pollination.
Therefore,none of the given options are devices for self-pollination.

(B) In angiosperms,the $Megaspore$ $Mother$ $Cell$ $(MMC)$ is diploid $(2n)$.
It undergoes meiosis to produce four megaspores,which are haploid $(n)$.
Therefore,the statement '$Megaspore$ - $Diploid$' is incorrect because megaspores are haploid.
Pollen grains are haploid $(n)$,synergids are haploid $(n)$,and the endosperm formed after double fertilization is triploid $(3n)$.

(C) The statement in option $C$ is incorrect because the functional megaspore undergoes three successive mitotic divisions to form an eight-nucleate embryo sac,not two.
$1$. Pollen grains are typically released at the $2$-celled stage in most angiosperms.
$2$. In many species,a sporogenous cell directly functions as the megaspore mother cell $(MMC)$.
$3$. The functional megaspore undergoes three rounds of free nuclear mitosis to produce $8$ nuclei,which then organize into the embryo sac.
$4$. The egg apparatus,consisting of the egg cell and two synergids,is always located at the micropylar end.

(D) In maize,the cob represents the female inflorescence.
The long,silky,thread-like structures that protrude from the cob are the elongated styles and stigmas.
These structures are adapted to catch wind-borne pollen grains,which is essential for fertilization in wind-pollinated plants like maize.

(C) The modes of entry of the pollen tube into the ovule are as follows:
$(i)$ Porogamy: The entry of the pollen tube takes place through the micropyle,e.g.,Lily.
$(ii)$ Chalazogamy: The entry of the pollen tube takes place through the chalazal end,e.g.,Casuarina,Juglans.
$(iii)$ Mesogamy: The entry of the pollen tube takes place through the integuments,e.g.,Cucurbita,Populus.
Based on the provided diagrams:
- Diagram $A$ shows the pollen tube entering through the micropyle,which is Porogamy.
- Diagram $B$ shows the pollen tube entering through the chalaza,which is Chalazogamy.
- Diagram $C$ shows the pollen tube entering through the integuments,which is Mesogamy.
Therefore,the correct sequence is $A-Porogamy, B-Chalazogamy, C-Mesogamy$.

(C) In $Cycas$,the pollen grain undergoes two equational divisions to produce male gametes. The first division produces a prothallial cell and an antheridial cell,and the second division of the antheridial cell produces the tube cell and the generative cell,which eventually forms two male gametes. Thus,$2$ divisions are involved.
In angiosperms,the microspore (pollen grain) undergoes one mitotic (equational) division to form a vegetative cell and a generative cell. The generative cell then undergoes one more mitotic division to form two male gametes. However,the question specifically asks for the divisions leading to the formation of male gametes from the pollen grain. In angiosperms,the generative cell divides once to form two male gametes,totaling $1$ division from the generative stage.
Therefore,the ratio of equational divisions in $Cycas$ to angiosperms is $2: 1$.

(A) Based on the provided diagram of the embryo sac during fertilization:
$A$ represents the male gametes released from the pollen tube.
$B$ represents the antipodal cells located at the chalazal end.
$C$ represents the egg cell.
$D$ represents the pollen tube entering through the micropyle.
Therefore, the correct identification is $A - \text{Male gametes}, B - \text{Antipodals}, C - \text{Egg cell}, D - \text{Pollen tube}$.

(C) Given,the diploid number of chromosomes in the stem is $2n = 10$. Therefore,the haploid number $(n)$ is $10 / 2 = 5$.
$A$ - Endosperm is triploid $(3n)$. Thus,$3 \times 5 = 15$ chromosomes.
$B$ - The egg cell is haploid $(n)$. Thus,$1 \times 5 = 5$ chromosomes.
$C$ - Each polar nucleus is haploid $(n)$. Thus,$1 \times 5 = 5$ chromosomes. However,in the central cell,there are two polar nuclei,making the total $2n = 10$ chromosomes.
Therefore,the sequence is $15, 5, 10$.

(B) Statement $I$ is correct: The tapetum is the innermost layer of the microsporangium wall that provides nourishment to the developing pollen grains.
Statement $II$ is correct: The hilum is the point of attachment where the body of the ovule fuses with the funicle.
Statement $III$ is incorrect: In many aquatic plants like water hyacinth and water lily,the flowers emerge above the water level and are pollinated by insects or wind,not by water.
Statement $IV$ is correct: The primary endosperm nucleus $(PEN)$ is formed by the fusion of two polar nuclei and one male gamete,making it triploid $(3n)$.

(C) Pollen allergy,also known as hay fever,is a common allergic reaction to pollen grains released by various plants.
Among the given options,$Parthenium$ (also known as carrot grass) is a well-known invasive weed that was introduced into India as a contaminant with imported wheat.
It is notorious for causing severe pollen allergy and respiratory issues in humans.
While other plants like roses and sunflowers produce pollen,they are typically insect-pollinated (entomophilous) and produce larger,stickier pollen grains that are less likely to become airborne compared to the wind-pollinated (anemophilous) pollen of $Parthenium$.

(A) Pollen viability is the period during which pollen grains remain capable of germinating and fertilizing the ovule.
In some cereals like rice ($Oryza$ $sativa$) and wheat,pollen grains lose viability within $30$ minutes of their release.
In contrast,in members of some families like $Leguminosae$ (e.g.,pea),$Solanaceae$,and $Rosaceae$,the pollen grains maintain viability for several months.
Therefore,the correct sequence for rice and pea is $30$ minutes and several months,respectively.

(A) Cryopreservation is a technique used to preserve biological materials such as pollen grains,seeds,or tissues by keeping them at extremely low temperatures.
This process involves storing the materials in liquid nitrogen at a temperature of $-196^{\circ} C$.

(C) The correct answer is $C$. In papaya,the number of ovules is many,whereas in mango,the number of ovule is one. Therefore,the statement that the number of ovules in papaya and mango is one is incorrect.

(B) In all angiosperms (flowering plants),the male gametes are non-motile and are morphologically dissimilar to the female gamete (oogamy).
$A$ is incorrect because some plants have polysiphonous pollen tubes.
$C$ is incorrect because pollinia are specific to families like Orchidaceae and Asclepiadaceae.
$D$ is incorrect because in many plants,the generative cell divides into two male gametes before pollination (two-celled stage).

(A) The statement in option $A$ is incorrect because the $Exine$ (outer wall),not the $Intine$ (inner wall),exhibits a fascinating array of patterns and designs.
$Intine$ is a thin,continuous layer made of cellulose and pectin.
$Exine$ is made of sporopollenin and is responsible for the patterns.
Options $B$,$C$,and $D$ are scientifically correct statements regarding pollen grain structure,allergy,and viability respectively.

(C) The leaf cells are diploid $(2n)$. Given $2n = 24$,therefore the haploid number $(n)$ is $12$.
$1$. Synergid cells are haploid $(n)$,so they contain $12$ chromosomes.
$2$. Pollen grains are haploid $(n)$,so they contain $12$ chromosomes.
$3$. Nucellus cells are diploid $(2n)$,so they contain $24$ chromosomes.
$4$. Endosperm in angiosperms is triploid $(3n)$,so it contains $3 \times 12 = 36$ chromosomes.
Thus,the sequence is $12, 12, 24, 36$.

(D) The statement $A$ is incorrect because a restitutional nucleus is typically observed in the tapetum cells,not the endothecium cells. During the development of the microsporangium,tapetal cells often undergo endomitosis or nuclear fusion,leading to polyploidy and the formation of a restitutional nucleus.
The statement $R$ is also incorrect because endothecium cells are diploid $(2n)$ in nature,derived from the primary parietal layer of the microsporangium. They are not triploid $(3n)$.
Therefore,both Assertion and Reason are incorrect.

(D) In $60\%$ of angiosperms,pollen grains are shed at the two-celled stage. The formation of a mature male gametophyte involves one meiotic division (to form microspores) and two mitotic divisions (one to form vegetative and generative cells,and another to divide the generative cell into two male gametes). Therefore,the Assertion is incorrect because it mentions only one mitotic division. The Reason is also incorrect because,in the majority of angiosperms,pollination occurs at the two-celled stage,not the three-celled stage. Thus,both statements are incorrect.

(C) The phenomenon where more than one pollen tube enters the embryo sac is known as polysiphony. While usually only one pollen tube enters,in some species,multiple tubes can reach the embryo sac,although only one participates in fertilization. Thus,the Assertion is correct.
Double fertilization is a unique process in angiosperms involving the fusion of one male gamete with the egg cell (syngamy) and the other with the two polar nuclei (triple fusion). This process requires two male gametes from the same pollen tube. Double fertilization cannot occur by the contribution of gametes from different pollen tubes. Therefore,the Reason is incorrect.

(A) In angiosperms,the pollen grain represents the partially developed male gametophyte.
It is typically released from the anther at the $2$-celled stage (vegetative cell and generative cell) in about $60\%$ of angiosperms.
Since the development is only partial at the time of release,the remaining growth of the male gametophyte (including the formation of the pollen tube and the division of the generative cell into two male gametes) occurs on the stigma of the female reproductive organ.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why the growth must be completed on the female reproductive organ.

(D) Assertion $(A)$ is incorrect because continued self-pollination leads to inbreeding depression,not checks it. Inbreeding depression is the reduction in fitness and vigor due to the accumulation of harmful recessive alleles in a population.
Reason $(R)$ is correct because in many self-pollinating plants,pollen release and stigma receptivity are synchronized to ensure successful self-pollination.
Therefore,the correct option is $D$.

(A) Sexual reproduction involves the process of meiosis,which is essential for the formation of gametes.
During the prophase-$I$ stage of meiosis,specifically in the pachytene sub-stage,crossing over occurs between non-sister chromatids of homologous chromosomes.
This process of crossing over results in the exchange of genetic material,leading to genetic recombination.
Therefore,sexual reproduction is a significant source of genetic variation in a population.

(D) The common bread wheat ($Triticum$ $aestivum$ $=$ $T.$ $vulgare$) is an allohexaploid.
It contains three distinct genomes ($A$,$B$,and $D$),each present in two copies,resulting in a total of $6n$ chromosomes.
Its somatic chromosome complement is represented as $AA\, BB\, DD$.

(C) In a cross-breeding experiment,the gametes from each parent combine to form the zygote.
For plant $A$ $(2n = 12)$,the gamete $(n)$ will have $n = 6$ chromosomes.
For plant $B$ $(2n = 16)$,the gamete $(n)$ will have $n = 8$ chromosomes.
The hybrid plant (zygote) formed by the fusion of these gametes will have a chromosome number equal to the sum of the haploid sets: $6 + 8 = 14$.
Therefore,the chromosome number of the hybrid plant is $14$.

(C) monoecious plant is one that bears both male and female reproductive structures on the same individual plant.
In the given options:
$1$. $Carica$ $papaya$ (Papaya) is dioecious,meaning male and female flowers are on separate plants.
$2$. $Marchantia$ $polymorpha$ is dioecious,as the male and female thalli are separate.
$3$. $Chara$ is a monoecious alga,where both the male sex organ (antheridium) and the female sex organ (oogonium) are present on the same plant body.
$4$. $Cycas$ $circinalis$ is dioecious,with male and female cones on separate plants.
Therefore,$Chara$ is the correct answer.

(D) The period for which pollen grains remain viable is highly variable and depends on the prevailing temperature and humidity.
In some cereals such as rice and wheat,pollen grains lose viability within $30$ minutes of their release.
In contrast,in some members of the families $Solanaceae$,$Rosaceae$,and $Leguminosae$,pollen grains maintain their viability for several months.
Therefore,among the given options,the pair $Rosaceae$ and $Leguminosae$ correctly represents families where pollen grains can remain viable for months.

(C) - Some bamboo species flower only once in their lifetime,generally after $50$-$100$ years,produce a large number of fruits,and then die.
- $Strobilanthes$ $kunthiana$ (Neelakuranji) flowers once in $12$ years. Its mass flowering transforms large tracts of hilly areas in Kerala,Karnataka,and Tamil Nadu into blue stretches and attracts a large number of tourists.

(N/A) Post-fertilization events are the events in sexual reproduction that occur after the formation of the zygote.
$1$. Zygote formation: In organisms like fungi and algae,the zygote develops a thick wall that is resistant to damage and desiccation,allowing it to undergo a period of rest before germination.
The further development of the zygote depends on the life cycle of the organism and the environment in which it survives.
In all sexually reproducing organisms,a diploid zygote is formed as a result of fertilization,which eventually develops into a new organism.
$2$. Embryogenesis: The process of development of an embryo from the zygote is called embryogenesis. This process involves cell division (mitosis) and cell differentiation.
Cell division increases the number of cells,while cell differentiation helps these cells undergo modifications to form specialized tissues and organs,leading to a fully developed organism.
Depending on whether the zygote develops inside or outside the body of the female parent,animals are classified as oviparous or viviparous.
Oviparous animals (e.g.,amphibians,fishes,birds,reptiles) lay eggs that develop into new organisms. In many oviparous animals like birds and reptiles,the fertilized eggs are covered by a hard calcareous shell (cleidoic eggs).
Viviparous animals (e.g.,mammals) give birth to their young ones.
$3$. Post-fertilization changes in flowering plants: The zygote is formed inside the ovule. After fertilization,the sepals,petals,and stamens of the flower usually wither and fall off.
The zygote develops into the embryo,the ovules develop into seeds,and the ovary develops into the fruit.
The ovary wall develops into a protective layer called the pericarp.

(N/A) Sexual reproduction involves the formation of gametes in the gonads,meiosis,and the fusion of gametes.
These processes produce variations due to new combinations of genes resulting from crossing over,the random segregation of chromosomes,and the random fusion of gametes.
Consequently,daughter offspring are genetically different from their parents.
Thus,sexual reproduction serves as a primary source of variation within a population.

(D) Statement $I$ is correct: Cleistogamous flowers do not open at all. Therefore,the anthers and stigma lie close to each other,and when anthers dehisce in the flower buds,pollen grains come in contact with the stigma to effect pollination. Thus,they are invariably autogamous.
Statement $II$ is correct: Cleistogamy ensures seed set even in the absence of pollinators. However,it is considered disadvantageous because it prevents cross-pollination,which limits genetic variation and the potential for evolutionary adaptation.

(B) The correct matching is as follows:
$P$. Pistil (or Megasporophyll in gymnosperms) corresponds to $I$. Megasporophyll.
$Q$. Ovule corresponds to $II$. Megasporangium.
$R$. Embryo sac corresponds to $III$. Female gametophyte.
Therefore, the correct sequence is $(P-I), (Q-II), (R-III)$.

(A) To determine the ploidy of the given structures:
$1$. Haploid $(n)$ structures:
- Egg cell $(III)$
- Male gamete $(IV)$
- Synergid $(V)$
- Antipodal cell $(VII)$
- Megaspore $(IX)$
- Microspore $(X)$
$2$. Diploid $(2n)$ structures:
- Megaspore mother cell $(I)$
- Microspore mother cell $(II)$
- Embryo $(VI)$
- Zygote $(VIII)$
Therefore,the haploid structures are $(III, IV, V, VII, IX, X)$ and the diploid structures are $(I, II, VI, VIII)$.

(A) In flowering plants, after the process of double fertilization, the floral parts undergo significant changes:
$1$. The $P$. Ovule develops into the $II$. Seed.
$2$. The $Q$. Ovary matures into the $I$. Fruit.
$3$. The $R$. Integument (covering of the ovule) hardens to form the $III$. Seed coat.
$4$. The $S$. Ovary wall transforms into the $IV$. Pericarp (fruit wall).
Therefore, the correct matching is $(P-II), (Q-I), (R-III), (S-IV)$.

(B) In the life cycle of an angiosperm:
$1$. $P$ represents Microspores, which are produced after meiosis in the anther.
$2$. $Q$ represents Gametes (male gametes), which are involved in fertilization.
$3$. $R$ represents the Sporophyte (the mature flowering plant), which is the dominant phase in the life cycle of angiosperms.
Therefore, the correct sequence is $P = \text{Microspores}, Q = \text{Gametes}, R = \text{Sporophyte}$.

(C) In flowering plants,after fertilization,the ovule matures into a seed and the ovary matures into a fruit. The ovule is attached to the placenta within the ovary. However,the number of ovules in an ovary varies significantly among different plant species. While some ovaries contain only one ovule (e.g.,wheat,paddy,mango),many others contain multiple ovules (e.g.,papaya,watermelon,orchids). Therefore,the statement that the ovary always contains only one ovule is incorrect.

(A) In the plant kingdom,some species exhibit unusual flowering patterns:
$1$. Bamboo species flower only once in their lifetime,generally after $50-100$ years,producing a large number of fruits and then dying.
$2$. Strobilanthes kunthiana (Neelakuranji) flowers once every $12$ years.
Therefore,option $A$ correctly describes these biological phenomena.

(D) $Strobilanthus$ $kunthiana$ (Neelakurinji) is a plant that flowers once in $12$ years.
It is native to the shola forests in the Western Ghats of India,specifically in the hilly regions of Kerala,Tamil Nadu,and Karnataka.
The flowers are distinctively blue in color.
It was observed to flower en masse during September-October $2006$.
Therefore,all the given statements are correct.

(D) Gametes are specialized reproductive cells.
$1$. In organisms with a haploid plant body,gametes are produced by mitosis,whereas in diploid organisms,they are produced by meiosis.
$2$. Gametes are always haploid $(n)$ regardless of the ploidy of the parent organism.
$3$. The fusion of male and female gametes results in the formation of a diploid zygote $(2n)$.
Therefore,all the given statements are correct.