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Chapter 1 · Sexual Reproduction in Flowering 15 Plants

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#1 SUB 2M

Question

How are flowers important for human beings? Describe in brief.

Answer

Human beings have had an intimate relationship with flowers since time immemorial.
Flowers are the objects of aesthetic, ornamental, social, religious and cultural value.
They have always been used as symbols for conveying important human feelings such as love, affection, happiness, grief, mourning, etc.
Flowers with ornamental value are commonly cultivated at homes and in garden.
In addition to that, the myriads of flowers that we enjoy gazing at, the scents and the perfumes that we swoon over, the rich colours that attract us, are all there as an aid to sexual reproduction.
To a biologist, flowers are morphological and embryological marvels and the site of sexual reproduction.
#2 SUB 🖼 2

Question

Draw a schematic diagram of L.S. of a typical flower.

Answer

#3 SUB 2M

Question

Describe accessory organs of a typical flower.

Answer

The accessory organs of a typical flower are calyx and corolla.
(1) Calyx
The calyx is the outermost whorl of the flower and the members are called sepals.
Generally, sepals are green, leaf like and protect the flower in the bud stage.
The calyx may be gamosepolous - united sepals or polysepalous - sepals free.
(2) Corolla
Corolla is composed of petals.
They are usually bright coloured to attract insects for pollination.
Petals may be also united called gamopetalous or polypetalous - petals free.
The shape and colour of corolla vary greatly in plants. Corolla may be tubular, bell - shaped, funnel - shaped or wheel - shaped.
#4 SUB 3M 🖼 1

Question

Describe the structure of the stamen with well labeled diagram.
OR
Explain the structure of microsporophyll in angiosperms with diagram.
OR
Explain the male reproductive part of flowering plant with diagram.

Answer

Structure: Two parts of a typical stamen are (i) Filament and (ii) Anther.
(i) Filament: It is the long and slender stalk of stamen.
The proximal end of the filament is attached to the thalamus or the petal of the flower.
And the distal end of the filament is attached to the anther with the help of connective.
(ii) Anther: It is a terminal part of the stamen.
It is typically a bilobed structure. Each lobe is having two thecal. i.e., Each lobe is dithecous.
Often a longitudinal groove runs lengthwise separating the theca.
Transverse section of an anther: In the transverse section of an anther various types of tissues and their organisation can be clearly observed.
The bilobed nature of an anther is very distinct in the transverse section of an anther.
The anther is tetragonal (four sided) structure consisting of four Microsporangia located at the corners, two in each lobe. The microsporangia develop further and become pollen sacs.
They extend longitudinally all through the length of an anther and are packed with pollen grains.
#5 SUB 2M 🖼 1

Question

Describe the structure of microsporangium with a well labeled diagram
OR
Draw a labelled diagram of enlarged view of one microsporangium showing wall layers.
(March 2025)
OR
Explain the structure of microsporangium.

Answer

The transverse section of a typical microsporangium appears near circular in outline.
It is generally surrounded by four wall layers.
(i) epidermis (ii) endothecium (iii) middle layers and (iv) tapetum.
The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
The innermost wall layer is the tapetum. It nourishes the developing pollen grains.
Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.
When the anther is young, a group of compactly arranged homogenous cells called the sporogenous tissue occupy the centre of each microsporangium.
#6 SUB 2M

Question

Describe the process of microsporogenesis.
OR
Explain microsporogenesis in flowering plants.

Answer

As the anther develops, the cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. The ploidy of the cells of the tetrad is haploid.
As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell.
The process of formation of microspores from a Pollen Mother cell (PMC) through meiosis is called microsporogenesis.
The microspores, as they are formed, are arranged in a cluster of four cells–the microspore tetrad.
As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains.
Inside each microsporangium several thousands of microspores or pollen grains are formed that are released with the dehiscence of anther.
#7 SUB 3M

Question

Explain the representative unit of male gametophyte in angiosperms.
OR
Describe the structure of pollen grains.(Diagram is not required)

Answer

The pollen grains represent the male gametophytes.
Size : about 25-50 micrometers in diameter.
Shape: It is round shaped.
Texture: Smooth or spiky.
It has a prominent two-layered wall. The hard outer layer is called the exine and the inner wall of the pollen grain is called the intine.
(i) Exine
It is made up of sporopollenin which is one of the most resistant organic material known.
It can withstand high temperatures and strong acids and alkali.
No enzyme that degrades sporopollenin is known so far.
Pollen grains are well-preserved as fossils because of the presence of sporopollenin.
The exine exhibits a fascinating array of patterns and designs.
The exine should be hard because it protects pollen grains.
(ii) Intine
The inner wall of the pollen grain is called the intine.
It is a thin and continuous layer made up of cellulose and pectin.
The cytoplasm of pollen grain is surrounded by a plasma membrane.
Cellular structure when pollen grain matures, it contains vegetative cell and generative cell, such structure is called two celled stage.
#8 SUB 2M

Question

Arrange the following terms in correct developmental sequence:
[NCERT Exercise Q.3]
Pollen grain, Sporogenous tissue, Microspore tetrad, Pollen Mother Cell, Male gametes.

Answer

Following is the correct developmental sequence:
#9 SUB 2M

Question

Pollen grains can be stored as fossil- Give scientific reason.

Answer

The hard outer layer-exine is made up of sporopollenin.
It is one of the most resistant organic material known.
It can withstand high temperatures and strong acids and alkali.
No enzyme that degrades sporopollenin is known so far known.
Pollen grains are well preserved as fossils because of the presence of sporopollenin.
#10 SUB 2M

Question

Mention the changes that occurs in the pollen grain before dehiscence.

Answer

Before dehiscence the pollen grain contains two cells, the vegetative cell and the generative cell.
(i) Vegetative cell
It is bigger, has abundant food reserve and a large irregularly shaped nucleus.
(ii) Generative cell
It is small and floats in the cytoplasm of the vegetative cell.
It is spindle shaped with dense cytoplasm and a nucleus.
In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled stage.
In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).
#11 SUB 2M 🖼 1

Question

What is the economic importance of pollen grain ?

Answer

Pollen grains are rich in nutrients. It has become a fashion in recent years to use pollen tablets as food supplements.
In western countries, a large number of pollen products in the form of tablets and syrups are available in the market.
Pollen consumption has been claimed to increase the performance of athletes and race horses.
#12 SUB 3M 🖼 1

Question

Draw a well labelled diagram of a typical anatropous ovule.
OR
Explain the typical anatropous ovule of angiosperms with diagram.
OR
Draw a schematic diagram of typical anatropous ovule and describe structure of megasporangium in detail. (JULY 2023)
OR
With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
[NCERT Exercise Q.4]

Answer

An ovule is a female megasporangium where the formation of megaspores takes place.
The various parts of an ovule are –
(i) Funicle – It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.
(ii) Hilum – It is the point where the body of the ovule is attached to the funicle.
(iii) Integuments – They are the outer layers surrounding the ovule that provide protection to the developing embryo.
(iv) Micropyle – It is a narrow pore formed by the projection of integuments. It marks the point where the pollen tube enters the ovule at the time of fertilization.
(v) Nucellus – It is a mass of the parenchymatous tissue surrounded by the integuments from the outside. The nucellus provides nutrition to the developing embryo. The embryo sac is located inside the nucellus.
(vi) Chalaza – It is the basal part of the ovule in plants, where nucellus and integuments join.
(vii) Embryo sac – An ovule generally has a single embryo sac formed from a megaspore.
#13 SUB 🖼 1 ▦ 1

Question

Differentiate between - Integument and Testa.

Answer

Integument

Testa

(i)

Covers the ovule.

Outer covering of seed.

(ii)

The cells are living.

The cells are dead.

(iii)

Pre-fertilized structure.

Post fertilized structure.

(iv)

Sclereids are absent.

Sclereids are present.

(v)

One or two layered.

One layered.
#14 SUB 2M 🖼 1

Question

How is functional megaspore formed from megaspore mother cell.
OR
Describe megasporogenesis.

Answer

The process of formation of megaspores from the megaspore mother cell is called megasporogenesis.
Ovules generally differentiate a single Megaspore Mother Cell (MMC) in the micropylar region of the nucellus.
It is a large cell containing dense cytoplasm and a prominent nucleus.
The MMC undergoes meiotic division.
Meiosis results in the production of four megaspores.
One of the megaspore is functional while the other three degenerate.
#15 SUB 🖼 1 ▦ 1

Question

Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.

Answer

Microsporogenesis

Megasporogenesis

(i)

It is the process in which a diploid microspore mother cell undergoes meiosis to form haploid microspores.

It is the process of formation of haploid megaspores from the diploid megaspore mother cell.

(ii)

Occurs inside pollen sacs.

Pollens are produced by microsporogenesis.

Occurs inside ovules.

Embryo sacs are produced by megasporgenesis.

(iii)

The arrangement of microspores is tetrahedral.

The arrangement of megaspores is linear.

(iv)

All the four microspores formed are functional.

Only one out of the four megaspores formed is functional.
#16 SUB 2M 🖼 2

Question

Describe the development of female gametophyte in angiosperms. OR
Explain monosporic development of female gametophyte.
OR
Explain the structure of embryo sac.
OR
Draw a well labelled diagram of typical embryo sac and explain in detail.
OR
With a neat diagram explain 7 celled and 8 nucleated nature of female gametophyte. [NCERT Exercise Q.6]

Answer

Monosporic development is the development of female gametophyte from one functional megaspore.
In angiosperms, a single diploid mother megaspore undergoes meiotic division to form four megaspores (haploid).
Female gametophyte:
In a majority of flowering plants, one of the four megaspores is functional while the other three degenerate.
Only the functional megaspore develops into the female gametophyte (embryo sac).
This method of embryo sac formation from a single megaspore is termed monosporic development.
The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac.
Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac.
These mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation.
After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac.
Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.
#17 SUB 2M

Question

Describe the arrangement of cells in a typical embryo sac of an Angiosperm.

Answer

There is a characteristic distribution of the cells within the embryo sac.
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.
The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which plays an important role in guiding the pollen tubes into the synergid.
Antipodal cells: Three cells are at the chalazal end are called the antipodals.
Central cell: The large central cell, as mentioned earlier, has two polar nuclei.
Thus, a typical angiosperm embryo sac, at maturity, though 8-nucleate is 7-celled.
#18 SN 🖼 1

Question

What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reason for your answer.
OR
Write a short note on cleistogamous flower.

Answer

Some plants such as Viola (common pansy), Oxalis, and Commelina produce two types of flowers –
(1) Chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma (like a normal flower), and
(2) Cleistogamous flowers which do not open at all.
In such flowers, the anthers and stigma lie close to each other.
When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination.
Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
Cleistogamous flowers produce assured seed-set even in the absence of pollinators.
#19 SUB 2M 🖼 1

Question

What is pollination? Mention two kinds of pollination.
OR
Briefly mention about any two types of pollination.
OR
Write a note on autogamy. Explain its types.
OR
Briefly mention about autogamy and geitonogamy.
OR
Explain geitonogamy and xenogamy.

Answer

Transfer of pollen grains (from the anther) to the stigma of a pistil is termed pollination.
It is achieved within the same flower or the different flower.
Kinds of Pollination: Depending on the source of pollen, pollination can be divided into following three types.
(i) Autogamy
(ii) Geitonogamy and,
(iii) Xenogamy
(i) Autogamy: Autogamy in flowers requires synchrony in pollen release and stigma receptivity and also, the anthers and the stigma should lie close to each other, so that self-pollination can occur.
(ii) Geitonogamy: Transfer of pollen grains from the anther to the stigma of another flower of the same plant.
Although geitonogamy is functionally cross - pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.
(iii) Xenogamy: Transfer of pollen grains from anther to the stigma of a flower on different plant.
This is the only type of pollination during which pollination brings genetically different type of pollen grains to the stigma.
#20 SUB 4M 🖼 2

Question

Explain pollination in angiosperms by abiotic agents of pollination
OR
Explain pollination by wind (Anemophily).
OR
Explain pollination by water (Hydrophily).
OR
Explain pollination in Vallisneria and Zostera.

Answer

Abiotic agents of pollination are: (1) wind
(2) water
(1) Pollination by wind (Anemophily) is more common amongst abiotic pollinations. Normally, plants bearing unisexual flower shows wind pollination.
Pollens grain are produced in large number to compensate the loss.
The pollen grains are light and non-sticky so that they can be transported by wind currents.
Flowers have well-exposed stamens so that the pollens are easily dispersed into wind currents.
Large, often, feathery stigma to easily trap air borne pollen grains.
Flowers do not show specific shape, colour, fragrant and nectar e.g. corn, grasses and coconut.
Wind-pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence.
(2) Pollination by water (Hydrophily)
Pollination by water is quite rare in flowering plants and is limited to about 30 genera, mostly monocotyledons.
Some examples of water pollinated plants are several marine sea-grasses such as Zostera.
In this group, female flowers remain submerged in water and the pollen grains are released inside the water.
Pollen grains in many such species are long, ribbon like and they are carried passively inside the water.
Some of them reach the stigma and achieve pollination.
In most of the water-pollinated species, pollen grains are protected from wetting by a mucilaginous covering.
Vallisneria:
Some examples of water pollinated plants are Vallisneria and Hydrilla which grow in fresh water.
In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water.
They are carried passively by water currents.
Some of then eventually reach the female flowers and the stigma.
Pollen grains in many such species are long, ribbon like.
#21 SUB 4M

Question

Explain the mechanism of Biotic pollination.

Answer

Majority of flowering plants use a range of animals as pollinating agents.
Bees, butterflies, flies, beetles, wasps, ants, moths, birds (sunbirds and humming birds) and bats are the common pollinating agents.
Insects, particularly bees are the dominant biotic pollinating agents.
Even larger animals such as some primates (lemurs), or even reptiles (gecko lizard and garden lizard) have also been reported as pollinators in some species.
Often flowers of animal pollinated plants are specifically adapted for a particular species of animal.
(A) Floral adaptation:
(1) Majority of insect-pollinated flowers are large, colourful, fragrant and rich in nectar.
(2) When the flowers are small, a number of flowers are clustered into an inflorescence to make them conspicuous.
(3) Animals are attracted to flowers by colour and/or fragrance.
(4) The flowers pollinated by flies and beetles secrete foul odours to attract these animals.
(5) To sustain animal visits, the flowers have to provide rewards to the animals.
(B) Rewards:
In some species, floral rewards are in providing safe places to lay eggs.
(1) For example, the tallest flower of Amorphophallus. The flower itself is about 6 feet in height.
(2) A similar relationship exists between a species of moth and the plant Yucca where both species – Moth and the plant – cannot complete their life cycles without each other.
(3) The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing.
For harvesting the reward(s) from the flower, the animal visitor comes in contact with the anthers and the stigma.
The body of the animal gets a coating of pollen grains, which are generally sticky in animal pollinated flowers. When the animal carrying pollen on its body comes in contact with the stigma, it brings about pollination.
(C) Nectar robbers:
Many insects may consume pollen or the nectar without bringing about pollination. Such floral visitors are referred to as pollen/nectar robbers.
#22 SUB 4M

Question

Describe the different outbreeding devices in detail.
OR
Describe the different devices to discourage self pollination.
OR
Describe the different devices to encourage cross pollination.
OR
Mention two strategies evolved to prevent self-pollination in flowers. [NCERT Exercise Q.8]
OR
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Answer

Majority of flowering plants produce hermaphrodite (bisexual) flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination results in inbreeding depression.
Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.
(i) Dichogamy:
In some species, pollen release and stigma receptivity are not synchronised.
Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen.
(ii) Heterostyly:
In some other species, the anther and stigma are placed at different positions. so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy.
(iii) Self-incompatibility : It inhibits inbreeding.
This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
(iv) Dicliny/Unisexuality:
It is the production of unisexual flowers. If both male and female flowers are present on the same plant such as Castor and maize (monoecious), it prevents autogamy but not geitonogamy.
In several species such as papaya, male and female flowers are present on different plants, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.
#23 SUB 4M 🖼 1

Question

With labeled diagrams, describe the mechanism of Pollen-pistil Interaction.

Answer

All the events from pollen deposition on the stigma until pollen tubes enter the ovule are together referred to as pollen - pistil interaction.
Pollination does not guarantee the transfer of the type of pollen (compatible or non-compatible pollen).
The pistil has the ability to recognise the pollen.
If it is the right type, the pistil accepts the pollen and promotes post - pollination events that leads to fertilization.
If the pollen is of the wrong type, the pistil rejects the pollen by preventing pollen germination on the stigma or the pollen tube growth in the style.
On the basis of pollen, pistil has the ability to accept or reject the pollen. This dialogue is mediated by chemical components of the pollen interacting with those of the pistil.
The pollen grain, germinates on the stigma to produce a pollen tube through one of the germ pores. The contents of the pollen grain move in to the pollen tube.
Pollen tube grows through the tissues of the stigma and style and reaches the ovary. Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergid cells guides the entry of pollen tubes. Pollen pistil interaction is a dynamic process.
#24 SUB 3M 🖼 1

Question

What is artificial hybridisation ? How it can be achieved in a bisexual flower ?
OR
What is meant by emasculation? When and why does plant breeder employ this technique?
OR
What is bagging technique? How is it helpful in a plant breeding programme?
[NCERT Exercise Q.10]
OR
Which Artificial hybridization techniques are used in plant breeding programme?
(JULY 2023)

Answer

A breeder is interested in crossing different species and often genera to combine desirable characters to produce commercially ‘superior’ varieties. Artificial hybridisation is one of the major approaches of crop improvement programme.
In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen).
This is achieved by emasculation and bagging technique.
(i) Emasculation:
If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces, using a pair of forceps (is necessary). This step is referred to as emasculation.
(ii) Bagging:
Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging.
(iii) Rebagging:
When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma, and the flowers are rebagged, and the fruits are allowed to develop.
If the female parent produces unisexual flowers, there is no need for emasculation. The female flower buds are bagged before the flowers open.
When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower is rebagged.
#25 SUB 2M 🖼 1

Question

What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
OR
Explain Primary Endosperm Cell (PEC) formation by pollinated pollen grains.
(MARCH 2023)

Answer

Triple fusion occurs when a male gamete fuses with two polar nuclei within the embryo sac of flowering plants.
The following events take place in triple fusion:
  • The pollen grains get dusted on stigma and germinate giving rise to a pollen tube that enters the ovule.
  • The pollen tube passes into one of the synergids and release two male gametes.
  • One out of the two gametes fuses with the egg nucleus and forms a zygote.
  • The other gamete fuses with the two polar nuclei located in the central cell and forms a triploid endosperm nucleus.
As this involves the fusion of three haploid nuclei, it is termed as triple fusion.
The central cell after triple fusion becomes the Primary Endosperm Cell (PEC) and develops into the endosperm.
#26 SN 3M 🖼 1

Question

Write a short note on Double Fertilization.
OR
Explain double Fertilization in flowering plant (Diagram is not required).

Answer

After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid.
One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of a diploid cell, the zygote.

Then,

  • The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid Primary Endosperm Nucleus (PEN).
  • As this involves the fusion of three haploid nuclei, it is termed as triple fusion.
  • Since two types of fusions, syngamy and triple fusion take place in an embryo sac, the phenomenon is termed double Fertilization, an event unique to flowering plants.
#27 SUB 🖼 1

Question

Why do you think the zygote is dormant for sometime in a fertilised ovule?

Answer

Fusion of male gamete with an egg in embryo sac results in zygote.
The zygote (2n), now remains in resting period and waits for endosperm.
The endosperm is formed from the primary endosperm nucleus which was a product of triple fusion.
After formation of endosperm, embryonic development starts from zygote.
Endosperm provides nutrition to the developing embryo.
#28 SUB 2M

Question

Explain : Endosperm.
OR
Discuss about the structure which is the product of triple fusion at the end of double fertilisation.

Answer

Endosperm development precedes embryo development.
The primary endosperm cell (PEC) divides  repeatedly and forms a triploid endosperm tissue.
The cells of this tissue are filled with reserve food materials and are used for the nutrition of the developing embryo.
In the most common type of endosperm development, the PEN undergoes successive nuclear divisions to give rise to free nuclei.
This stage of endosperm development is called free-nuclear endosperm.
Subsequently, cell wall formation occurs and the endosperm becomes cellular.
The number of free nuclei formed before cellularisation varies greatly.
The coconut water from tender coconut (that is present inside) is nothing but free-nuclear endosperm (made up of thousands of nuclei) and the surrounding white kernel is the cellular endosperm.
#29 SUB 3M 🖼 1

Question

Explain the structure of typical dicotyledonous embryo with diagram.

Answer

Dicotyledonous embryo: A typical dicotyledonous embryo, consists of an embryonal axis and two cotyledons.
(i) Epicotyl: The portion of embryonal axis above the level of cotyledons is the Epicotyl, which terminates with the plumule or stem tip.
(ii) Hypocotyl: The cylindrical portion below the level of cotyledons is Hypocotyl that terminates at its lower end in the radicle or root tip. The root tip is covered with a root cap.
#30 SUB 3M 🖼 1

Question

Explain L.S. of grass embryo with diagram.
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Answer

Monocotyledonous embryo: Embryos of monocotyledons possess only one cotyledon.
(i) Scutellum: In the grass family, the cotyledon is called scutellum that is situated towards one side (lateral) of the embryonal axis.
(ii) Coleorhiza: At its lower end of the embryonal axis, has the radicle and root cap enclosed in an undifferentiated sheath called Coleorhiza.
(iii) Coleoptile: The portion of the embryonal axis above the level of attachment of scutellum is the epicotyl. Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure, the Coleoptile.
#31 SUB 2M ▦ 1

Question

Differentiate between Epicotyl and hypocotyl.[NCERT Exercise Q.13(a)]

Answer

Hypocotyl

Epicotyl

(1)

The cylindrical portion of embryonal axis below the level of cotyledons is called hypocotyl.

(1)

The portion of embryonal axis above the level of cotyledons is called epicotyl.

(2)

Hypocotyl terminates at its lower end in the radicle or root tip

(2)

The epicotyl

terminates with the plumule or stem tip.
#32 SUB 2M ▦ 1

Question

Differentiate between coleoptile and coleorhiza.[NCERT Exercise Q.13(b)]

Answer

Coleoptile

Coleorhiza

(1)

Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure, the coleoptile.

(1)

The embryonal axis has the radicle and root cap enclosed in an undifferentiated sheath called

coleorhiza.

(2)

It protects the plumule.

(2)

It protects the radicle.

(3)

Emerges above the soil while seed germination.

(3)

It stays below the soil while seed germnation.

(4)

It grows for some period of time after emerging out of seed.

(4)

It's growth stops after emerging out of seed.
#33 SUB 3M

Question

Describe the Structure of typical angiospermic seed. OR
Describe the final product of sexual reproduction of an angiospermic plant.

Answer

In angiosperms, the seed is the final product of sexual reproduction. Seeds are formed inside fruits. A seed, typically, consists of seed coat, cotyledons and embryo axis.
(i) The cotyledons: The cotyledons of the embryo are simple structures, generally thick and swollen due to storage of food reserves (as in legumes).
Mature seeds may be non-albuminous or
ex-albuminous.

(a) Non albuminous seeds: Non albuminous seeds have no residual endosperm as they are completely consumed during embryo development (e.g., pea, groundnut).

(b) Albuminous seeds: Albuminous seeds retain a part of endosperm as they are not completely used up during embryo development
(e.g., wheat, maize, barley, castor).

(c) Perisperm: Occasionally, in some seeds such as black pepper and beet, remnants of nucellus are also persistent. This residual, persistent nucellus is the Perisperm.

(ii) Integuments: Integuments of ovules harden as tough protective seed coats.
Dicotyledonous seeds have two layers. The outer tough and yellowish layer is called testa. The inner thin and transparent layer is called the tegmen.
(iii) Micropyle: The micropyle remains as a small pore in the seed coat. This facilitates the entry of oxygen and water into the seed during germination.
Mature seed: Its water content is reduced and become relatively dry (10-15 percent moisture by mass). The general metabolic activity of the embryo slows down. The embryo may enter a state of inactivity called dormancy. If favourable conditions are available (adequate moisture, O2 and Suitable temperature), they germinate.
#34 SUB 2M 🖼 1 ▦ 1

Question

Differentiate between perisperm and pericarp.

Answer

Perisperm

Pericarp

(1)

In some seeds, remnants of nucellus are also persistent. This residual, persistent nucellus is called

perisperm.

(1)

It is the wall of fertilized and mature ovary which develops into fruit wall called pericarp.

(2)

It is a part of seed.

(2)

It is a part of fruit.

(3)

It is usually dry.

(3)

It can be dry or fleshy.

(4)

Example: black pepper and beet.

(4)

It is found in every fruit.
#35 SN 3M

Question

Write a short note on advantages of seeds.

Answer

Seeds offer several advantages to angiosperms.
(i) Firstly, since reproductive processes such as pollination and Fertilization are independent of water, seed formation is more dependable.
(ii) Seeds have better adaptive strategies for dispersal to new habitats and help the species to colonise in other areas.
(iii) As they have sufficient food reserves, young seedlings are nourished until they are capable of photosynthesis on their own.
(iv) The hard seed coat provides protection to the young embryo.
(v) Being products of sexual reproduction, they generate new genetic combinations leading to variations.
(vi) Seed is the basis of our agriculture. Dehydration and dormancy of mature seeds are crucial for storage of seeds which can be used as food by human beings throughout the year and also to raise crop in the next season.
#36 SUB 2M

Question

Seed is a basis of our agriculture : Explain.

Answer

Dehydration and dormancy of mature seeds are crucial for storage of seeds.
It can be used as food throughout the year and also to raise crop in the next season.
The presence of seed coat protects embryo which will germinate in a suitable conditions.
Germination of seed is a basis of our agriculture.
#37 SUB 3M 🖼 1

Question

Describe the types of fruits. OR
Why apple is known as false fruit ? Which parts of flower participate in the formation of fruits? [NCERT Exercise Q.14]
OR
Explain term : Parthenocarpic fruit.

Answer

The fertilized ovary is called fruit.
(i) Parthenocarpic fruits
Although in most of the species, fruits are the results of fertilization, there are a few species in which fruits develop without fertilization. Such fruits are called parthenocarpic fruits. eg. Banana.
(ii) True fruits
Develop only from the ovary. In most plants, by the time the fruit develops from the ovary, other floral parts degenerate and fall off.
(iii) False fruits
The thalamus of flower also contributes to fruit formation. Can be observed in a few species such as apple, strawberry, cashew, etc.
#38 SUB 3M

Question

If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why ?

Answer

Production of fruit without fertilization is called parthenocarpy. Seed formation does not take place here (seedless fruit). An unfertilised ovary is converted into fruit.
Plant growth regulaters such as auxin - 2, 4, D (2, 4 dichlor phenoxy acetic acid) is used here.
Banana, grapes, pineapple, watermelon etc. can be obtained as parthenocarpic fruit with great economic importance.
Here, the uncertainty of survival of sexual reproduction can be avoided.
The seeds of fruit which is used as food for this type of fruits, this method is not applicable.
e.g. pomegranate.
#39 SUB 2M 🖼 1

Question

What is apomixis and what is its importance?
OR
Explain the mechanism of production of seed without fertilisation.
OR
Explain the term Apomixis.

Answer

Apomixis is a special mechanism of reproduction. Production of seeds without Fertilization is called apomixis.
Importance:
(1) There is no meiosis during apomixis which does not involve separation of chromosomes.
(2) The desirable characters can be maintained for indefinite time period.
(3) In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilization.
#40 SN 3M

Question

Write a short note on polyembryony with example.

Answer

Occurrence of more than one embryo in a seed is referred to as polyembryony. It is found in conifers and it is very common.
In angiosperms such as lemon, orange, onion, peanut and mango polyembryony is found.
When there is presence of more than one ovule in the embryo sac, results in the polyembryony.
Sometimes, antipodal cells, synergid cell or cells from the integuments are developed into embryo.
Polyembryony is significantly used in crop production and garden.
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#43 CS

Question

Fruit : In most plants, by the time the fruit develops from the ovary, other floral parts degenerate and fall off. However, in a few species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit formation. Such fruits are called false fruits. Most fruits, however, develop only from the ovary and are called true fruits. Although in most of the species, fruits are the results of Fertilization, there are a few species in which fruits develop without Fertilization. Such fruits are called parthenocarpic fruits. Banana is one such example. Parthenocarpy can be induced through the application of growth hormones and such fruits are seedless.
(i) What is false fruit? How does it differ from true fruit?

(ii) What is parthenocarpic fruit? Give one example.

(iii) Give examples of false fruit and true fruit each.
(iv) From where fruit is developed?


Answer

(i) The Fruit which is developed from other part of flower along with ovary, is called false fruit. True fruit develops from ovary only. (ii) In some species, formation of a fruit without fertilization takes place. This type of fruit is called parthenocarpic fruit. Example: Banana. (iii) Example: False Fruit Cashew, Apple
True Fruit: Mango, Coconut (iv) In most of the plants, the fruit develops from the ovary.
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#44 CS

Question

Microsporangium : A typical angiosperm anther is bilobed with each lobe having two thecae, i.e., they are dithecous. Often a longitudinal groove runs lengthwise separating the theca. Let us understand the various types of tissues and their organisation in the transverse section of an anther. The bilobed nature of an anther is very distinct in the transverse section of the anther. The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe.
The microsporangia develop further and become pollen sacs. They extend longitudinally all through the length of an anther and are packed with pollen grains.
In a transverse section, a typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers: the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen. The innermost wall layer is the tapetum. It nourishes the developing pollen grains.
(i) Bilobed anther contains ________________ microsporangium, in which each lobe contains ____________thecae.

I

II

(a)

Four

Three

(b)

Two

Four

(c)

Four

Two

(d)

Two

Two
(ii) What are the four layers of the wall of microsporangium from outside to inside?
(iii) The developed microsporangium is called____.
(iv) Name the layers that help in the dehiscence of anther.

Answer

(i) (c) four, two (ii) Epidermis → Endothecium → Middle layers →Tapetum 
(iii) The developed microsporangium results in pollen sac. (iv) The outer three walls epidermis, endothecium, middle layer help in dehiscence of anther.
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#45 CS

Question

Embryo-sac in angiosperm : The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2- nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. It is of interest to note that these mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac. Observe the distribution of cells inside the embryo sac. Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell. There is a characteristic distribution of the cells within the embryo sac. 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. 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. Three cells are at the chalazal end and are called the antipodals. The large central cell, as mentioned earlier, has two polar nuclei. Thus, a typical angiosperm embryo sac, at maturity, though 8-nucleate is 7-celled.
(i) The embryo sac of angiosperm is _____ celled and _____ Nucleate at maturity.
(ii) _____out of the eight nuclei are surrounded by cell walls.
(iii) Which cells are included in egg apparatus?
(iv) How many sequential cell division take place for the formation of 8 nuclei of embryo sac?

Answer

(i) 7 and 8 Nucleate (ii) 6 - Nuclei (iii) Egg apparatus contains one egg and two synergid cells. (iv) 3 mitosis
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#46 CS 🖼 2

Question

Transfer of pollen grains: Transfer of pollen grains (shed from the anther) to the stigma of a pistil is termed pollination. Pollen are non motile structure which are transferred by pollinating agents. There are three types of pollination seen, Autogamy, Geitonogamy and Xenogamy. Transfer of pollen grains from the anther to the stigma of the same flower. Geitonogamy is one type of self pollination but transfer of pollen grains from the anther to the stigma of another female flower of the same plant.
Pollinating agents can be biotic or abiotic, biotic pollinating agents. Bees, butterflies, flies, beetles, wasps, ants, moths, sunbirds, humming birds, bats, gecko lizard are the common pollinating agents. Among the animals, insects, particularly bees are the dominant biotic pollinating agents. Water and wind are abiotic pollinating agents. Pollination by wind is more common amongst abiotic pollinations. Pollination by water is quite rare in flowering plants and is limited to about 30 genera.
(i) Which type of pollination is seen in a given diagram? (both the flowers belong to different plants)
(ii) Which are the most dominant pollinating agents on the earth?
(iii) What are the biotic and abiotic pollinating agents?
(give two examples of each)
(iv) Explain about the pollination shown in the given diagram.

Answer

(i) Transfer of pollen grains from anther to the stigma of another flower of the different plant. (ii) Honey bees are the most dominant pollinating agents. (iii) Biotic Honey bee, Butterfly Abiotic Wind, Water (iv) Pollen grains are transported from the anther to stigma of a same flower which shows autogamy.
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#47 CS

Question

Artificial hybridisation : This is one of the major approaches of crop improvement programme. In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen). This is achieved by emasculation and bagging techniques.
(i) If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps is necessary. This process is referred to as _________.
(a) Collection (b) Selection
(c) Emasulation (d) Bagging
(ii) In artificial hybridisation it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination from unwanted pollen. So, what processes are included in this type of crossing ?
(i) Emasculation (ii) Bagging
(iii) Selection (iv) Rebagging
(a) i, ii, iii (b) i and iii
(c) i, ii and iv (d) ii and iv
(iii) If the female parent produces unisexual flowers then which step is not required ?
(a) Emasculation (b) Bagging
(c) Rebagging (d) (a) and (b) both
(iv) Why bagging is important ?
(a)To protect stigma from desirable pollen grains.

(b) To protect stigma from contamination from unwanted pollen.
(c) Both of the above

(d) None of the above

Answer

(i) (c) Emasculation (ii) (c) i, ii and iv (iii) (a) Emasculation (iv) (b) to protect stigma from contamination from unwanted pollen.
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#48 CS

Question

(Double fertillisation is characteristic of flowering plants : After entering one of the synergids, the pollen tube releases the two male gametes into to cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN). As this involves the fusion of three haploid nuclei it is termed triple fusion. Since two types of fusions, syngamy and triple fusion take place in an embryo sac the phenomenon is termed double fertilisation, an event unique to flowering plants. The central cell after triple fusion becomes the primary endosperm cell (PEC) and develops into the endosperm while the zygote develops into an embryo.
(i) Choose correct option regarding product formed after double fertilisation.
(a) Diploid embryo (b) Triploid endosperm
(c) Both of the above (d) None of the above
(ii) _________ gametes and _____________ cells take part in the double fertilisation.
(a) 2, 4 (b) 3, 4
(c) 4, 5 (d) 6, 7
(iii) The unique phenomenon seen in double fertilisation is _____________
(a) Syngamy (b) Triple fusion
(c) a and b both (d) None of the above
(iv) Primary Endosperm Nucleus (PEN) is ________ Structure.
(a) haploid (b) Diploid
(c) Triploid (d) None of the above

Answer

(i) (c) Both of the above (ii) (b) 3, 4 (iii) (c) (a) and (b) both (iv) (c) Triploid
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#49 CS

Question

As the anther develops, the cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. (As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. The mircrospores, as they are formed, are arranged in a cluster of four cells-the microspore tetrad, As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. Inside each microsporangium several thousands of microspores or pollen grains are formed that are released with the dehiscence of anther.)
(i) How many pollen grains are formed from one pollen Mother Cell (PMC)?
(a) Two (b) Three (c) Four (d) One
(ii) How many pollen tetrad forms from 100 pollen Mother cell ?
(a) 400 (b) 25 (c) 100 (d) 200
(iii) How many meiosis occurs in PMC to form 100 pollen grain ?
(a) 25 (b) 50 (c) 75 (d) 100
(iv) The process of pollen grain formation from Pollen Mother cell is called ________.

Answer

(i) (c) Four (ii) (c) 100 (iii) (a) 25 (iv) (b) Microsporogenesis

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