2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants

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Karnataka 2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants

2nd PUC Biology Sexual Reproduction in Flowering Plants NCERT Text Book Questions and Answers

Question 1.
Name the parts of an angiosperm flower in which the development of male and female gametophyte takes place.
Answer:
Development of male gametophyte takes place from microspore or pollen grains which develop inside the microsporangium or pollen sac of an anther.
Development of female gametophyte takes place in the nucellus of the ovule.

Question 2.
Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structure formed at the end of these two events.
Answer:
The development of microspore from the microspore mother cell is called microsporogenesis. The development of the megaspore from the megaspore mother cell is called megasporogenesis. In both these developments, the mother cell undergoes meiotic division or reduction division to produce spores. At the end of these divisions, microspores or pollen grains are produced inside the pollen sac, and megaspores are produced inside the ovary.

Question 3.
Arrange the following terms in the correct developmental sequence. Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gamete.
Answer:
Sporogenous tissue – pollen mother cell – microspore tetrad – pollen grains – male gametes.

Question 4.
With a neat and labelled diagram, describe the parts of a typical angiosperms ovule.
Answer:
An ovule is a female megasporangium where the formation of megaspores takes place.

2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 1
The various parts of an ovule are:

  • A small stalk or funicle by which the ovule remains attached with the placenta of the ovary.
  • Hilum is the point at which it is attached with the ovule. In the inverted ovule the funicle fuses with the main body of the ovule and is called as raphe.
  • The ovule is surrounded on all sides by two integuments but not at the apex where an aperture called micropyle is present. This end of the ovule is called a micropylar, while the end of the ovule opposite to it is called a chalazal end.
  • The embryo sac is situated inside the nucellus.
  • Towards the micropyle end of the embryosac, one egg or oospore and two synergids are found, and towards the chalaza end of embryosac, three antipodal cells are found. At the center secondary nuclei are found.

KSEEB Solutions

Question 5.
What is meant by the monosporic development of female gametophyte?
Answer:
In many flowering plants, only one out of the four megaspores enlarges and develops into a female gametophyte or embryo sac. The other three megaspores degenerate. This type of embryo sac formation is called a monosporic type of development.

Question 6.
With a neat labelled diagram, explain the 7 celled, 8 nucleate nature of the female gametophyte.
Answer:
2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 2

Embryo sac is an oval multicellular structure. It is covered by a thin membrane derived from the parent megaspore wall. The typical or Polygonum type of embryo sac contains 8 nuclei but 7 cells – 3 micropylar, 3 chalazal and one central. The three micropylar cells are collectively known as egg apparatus. One cell is larger and is called egg or oosphere. It bears a central or micropylar vacuole and a nucleus towards the chalazal end. The remaining two cells are called synergids or help cells.

Each of them bears a filiform apparatus in the micropylar region, a lateral hook, chalazal vacuole and a central nucleus. The egg or oosphere represents the single female gamete of the embryo sac. The synergids help in obtaining nourishment from the outer nucellar cells, guide the path of pollen tube by their secretion and function as shock absorbers during the penetration of the pollen tube into the embryo sac.

The three chalazal cells of the embryo sac are called antipodal cells. They are the vegetative cells of the embryo sac which may degenerate soon or take part in absorbing nourishment from the surrounding nucellar cells. Internally, they are connected with central cell by means of plasmodesmata.

The central cell is the largest cell of the embryo sac. It has a highly vacuolated cytoplasm which is rich in reserve food and Golgi bodies. In the middle, the cell contains two polar nuclei which often fuse to form a single diploid secondary nucleus. Thus, all the cells of the embryo sac are haploid except the central cell which becomes diploid due to fusion of polar nuclei.

Question 7.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give a reason for your answer.
Answer:
Chasmogamous flowers are the normal type of flowers, which are similar I to flowers of other species with exposed anthers and stigma, usually found in Commelina. Naturally, cross-pollination cannot occur in cleistogamous flowers because they are usually seen below the soil surface.

Question 8.
Mention two strategies evolved to prevent self-pollination in flowers.
Answer:
Continued self-pollination results in inbreeding depression. So flowering plants have developed the following devices to discourage self-pollination and to encourage cross-pollination:

  1. Dicliny (unisexuality): Flowers are unisexual so that self-pollination is not possible. The plants may be monoecious (bearing both male and female flowers, e.g., maize) or dioecious (bearing male and female flowers on different plants, e.g., mulberry, papaya).
  2. Dichogamy: Anthers and stigmas mature at different times in a bisexual flower so as to prevent self-pollination.
  • Protandry – Anthers mature earlier than the stigma of the same flower. Their pollen grains become available to stigmas of the older flowers,
    e.g., sunflower, Salvia.
  • Protogyny – Stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e.g., Mirabilis jalapa (four o’clock), Gloriosa, Plantago.

Question 9.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer:
In some flowers, the pollen grains do not germinate on the pistil of the same flower. This is called self-incompatibility. In such cases, the pollen grains do not germinate and produce male gametes and hence fertilisation does not occur. So seeds are not produced in self-incompatible flowers.

Question 10.
What are bagging techniques? How is it useful in a plant breeding programme.
Answer:
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. 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. When the stigma of the 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 allowed to develop. This process allows plant breeders to use desired varieties of pollen to obtain desired seeds.

Question 11.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer:
One of the male gametes fuses with the secondary nucleus is called triple fusion. It takes place in the embryo sac. After the normal fertilization i.e., syngamy, (fusion of male gamete with egg), the other male gamete fuses with secondary nucleus or endosperm nucleus. The nuclei involved in triple fusion are the secondary nucleus or endosperm nucleus. They are diploid;

Question 12.
Why do you think the zygote is dormant for some time in a fertilized ovule?
Answer:
Fertilised egg is known as zygote which gives rise to embryo. Before development, the zygote undergoes a resting period. This is because the zygote waits for the formation of certain amount of endosperm for the nourishment of embryo. This is an adaptation to provide assured nutrition to the developing embryo.

Question 13.
Differentiate between
(a) Hypocotyl and epicotyl
(b) Coleoptile and coleorhiza
(c) Integument and testa
(d) Perisperm and pericarp
Answer:
(a) Hypocotyl and epicotyl

Hypocotyl Epicotyl
1.   The portion of the embryonal axis which lies below the cotyledon in a dicot embryo is known as hypocotyl.
2.  It terminates with the radicle.
1.   The portion of the embryonal axis which lies above the cotyledon in a dicot embryo is known as epicotyl.
2.  It terminates with the plumule.

(b) Coleoptile and coleorhiza

Coleoptile Coleorhiza
It is a conical protective sheath that encloses the plumule in a monocot seed. It is an undifferentiated sheath that encloses the radicle and the root cap in a monocot seed.

(c) Integument and testa

Integument Testa
It is the outermost covering of an ovule. It provides protection to it. It is the outermost covering of a seed.

(d) Perisperm and pericarp

Perisperm Pericarp
It is the residual nucellus which persists. It is present in some seeds such as beet. It is the ripened wall of a fruit, which develops from the wall of an ovary.

Question 14.
Why is apple called a false fruit? Which part(s) of the flower forms fruit?
Answer:
Most fruits develop only from the ovary and are called true fruits. When fruit develops from other floral parts other than ovary it is called false fruit. Apple is a false fruit where the thalamus contributes to fruit formation.

Question 15.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer:
It is the removal of anthers before anthesis from the bisexual flower which is used as a female parent. During hybridization, the plant breeder uses this technique to prevent self-pollination.

KSEEB Solutions

Question 16.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer:
Parthenocarpic fruits are fruits which develop without fertilisation and hence are seedless. Parthenocarpy can be induced through the application of growth hormones. Important fruits like banana, papaya, orange, grapes, guava, watermelon etc. can be made seedless by applying growth substances as they are economically important fruits and if made seedless they will be more valuable.

Question 17.
Explain the role of the tapetum in the formation of pollen grain walls.
Answer:
Tapetum is the innermost layer of microsporangium. It provides nourishment to the developing pollen grains. During microsporogenesis, the cells of the tapetum produce various enzymes, hormones, amino acids, and other nutritious material required for the development of pollen grain. It also produces the exine layer of the pollen grains, which is composed of sporopollenin.

Question 18.
What is apomixis and what is its importance?
Answer:
Normal type of sexual reproduction having two regular features i.e., meiosis and fertilisation is called amphimixis. But in some plants, this normal sexual reproduction is replaced by some abnormal type of sexual reproduction called apomixis.

The term apomixis was first given by Winkler (1908). Apomixis may be defined as, abnormal kind of sexual reproduction in which an egg or other cells associated with an egg (synergids, antipodals, etc.) develop into an embryo without fertilisation and with or without meiosis. Hybrid varieties of several food and vegetable crops are being extensively cultivated. The cultivation of hybrids tremendously increased productivity.

One of the problems of hybrids is that hybrid seeds have to be produced every year. If the seeds collected from hybrids are sown, the plants in the progeny will segregate and do not maintain hybrid characters. Production of hybrid seeds is costly and hence the cost of hybrid seeds becomes too expensive for the farmers. If these hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. Then the farmers can keep on using the hybrid seeds to raise new crops year after year and do not have to buy hybrid seeds every year. Embryos formed through apomixis are generally free from infections.

2nd PUC Biology Sexual Reproduction in Flowering Plants Additional Questions and Answers

2nd PUC Biology Sexual Reproduction in Flowering Plants One Mark Questions

Question 1.
Find the odd one out
b. Endothecium, Tapetum, Middle layers, Nucellus
c. Exine, Tube nucleus, Synergids, Generative cell
d. Egg, Intine, Antipedals, Secondary nucleus
Answer:
b. Nucellus
c. Synergids
d. Intine

Question 2.
Name some water-pollinated plats.
Answer:

  • Freshwater – Vallisneria
  • Hydrilla Aquatic – Zostera

Question 3.
Some flowers are highly modified for insect pollination. They have many features which help this kind of pollination.
a. What are these flowers called?
b. Explain the characters which make them suitable for this type of pollination.
Answer:
a. Entamophilous flowers
b. Brightly coloured, fragrant, nectary, sticky pollen grains.

Question 4.
What is a false fruit? Give an example.
Answer:
The fruit is formed by any floral parts of the flower other than the ovary, eg. apple, pear, cashew nut, etc. [CBSE – 95]

KSEEB Solutions

Question 5.
Angiosperms produce male and female reproductive structures in which male and female gametophytes and gametes are produced.
a. Name the male and female reproductive structure.
b. Name the male and female gametophytes.
Answer:
a. The male reproductive structure is another and the female reproductive structure is the pistil.
b. The male gametophyte is the mature pollen grain and the female gametophyte is embryosac.

Question 6.
Which nuclei fuse to give endosperm?
Answer:
Polar nuclei.

Question 7.
Name the stage of the occurrence of more than one embryo in a seed.
Answer:
Polyembryony.

Question 8.
The term for the early stages of embryo development.
Answer:
Embryogeny

Question 9.
The formation of the primary endosperm nucleus is called triple fusion. Why is it called so?
Answer:
The primary endosperm nucleus is formed by the fusion of the secondary nucleus and a male gamete and the secondary nucleus is formed by the fusion of two haploid polar nuclei. As three fusions are taking place in the formation of the primary endosperm nucleus, it is called triple fusion.

Question 10.
Define parthenocarpy.
Answer:
These are seedless fruits which are formed without pollination and fertilization.

Question 11.
What is fertilization?
Answer:
It is the fusion of one male gamete with the egg cell and a second gamete with polar nuclei in angiosperm. [CBSE – 99]

Question 12.
State the difference between the endosperm of gymnosperms and angiosperms.
Answer:
The endosperm of gymnosperms is haploid gametophyte but in angiosperms, it is triploid as it is formed after double fertilization.

Question 13.
What is epicotyl?
Answer:
A portion of an embryonic axis between the plumule and cotyledon.

Question 14.
Define the term geitonogamy.
Answer:
A condition where pollen from one flower deposited on the stigma of another flower borne on the same plant.

Question 15.
What is the fate of the secondary nucleus after fertilization?
Answer:
It forms the endosperms.

Question 16.
What is allogamy?
Answer:
It is the transfer of pollen from one flower to the stigma of another flower on a separate plant of the same species.

Question 17.
What develops into a microspore mother cell in a flower?
Answer:
Sporogenous cells.

KSEEB Solutions

Question 18.
What is coleorrhiza ? [CBSE – 97]
Answer:
It is the protective cap over the radicle of maize.

Question 19.
What is scutellum?
Answer:
It is the single cotyledon of maize.

Question 20.
What is funiculus?
Answer:
The stalk of the ovule by which it is attached to the placenta.

2nd PUC Biology Sexual Reproduction in Flowering Plants Two Marks Questions

Question 1.
Differentiate between parthenocarpy and parthenogenesis.
Answer:
Parthenocarpy is .the formation of fruit without fertilization whereas parthenogenesis is the formation of an embryo from an unfertilized egg.

Question 2.
Draw a labelled diagram of the mature pollen grain. [CBSE – 90]
Answer:
2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 3
Question 3.
What is seed dormancy? Give any 2 advantages. [CBSE – 94]
Answer:
Seed dormancy is the condition of the seed when it fails to germinate even though the environmental conditions are favorable for active growth.
Two advantages of dormancy:

  • It helps the seed to disseminate in time and space in order to achieve a maximum cooperative environment for the survival of species.
  • To ensure successful seed germination under the most favourable conditions.

Question 4.
What are false fruits? Give example.
Answer:
The fruits which develop from parts other than ripened ovary are called false fruits.
Eg: fruits of apple and pear develop from the fleshy thalamus. [CBSE – 95]

Question 5.
Write the significance of double fertilization.
Answer:
Double fertilization leads to the development of triploid endosperm which provides nourishment to the developing healthy seed and this triploid endosperm compensates for the extreme reduction of female gametophyte in angiosperms.

Question 6.
Arrange the following terms in a correct developmental sequence.
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Answer:
The correct development sequence for the above terms is sporogenous tissue, microspore tetrad, pollen mother cell, pollen grain, male gametes.

Question 7.
Write the difference between coleoptile and coleorhiza.
Answer:

  • In the monocot seed, the region of the embryonic axis below the cotyledon is the radicle covered with a protective sheath is coleorhiza.
  • Above the point of attachment of the cotyledon, the embryonic axis becomes the plumule which is enclosed by a leaf-like covering called coleoptile.

2nd PUC Biology Sexual Reproduction in Flowering Plants Five Marks Questions

Question 1.
Describe the process of development of a dicotyledonous embryo.
Answer:
The process of development of a mature embryo from a diploid zygote is called embryogenesis. After fertilization, the zygote of the ovule divides transversely into two cells – a small apical cell and a large basal cell. The basal cell lying towards the micropyle divides in one direction into a row of cells called a suspensor. It pushes the developing embryo into the endosperm for the absorption of nutrients.

The apical cell located towards the antipodal end of the zygote undergoes two vertical divisions and one transverse division to form the embryonal mass. The cells of the embryonal mass divide repeatedly and the various parts of the embryo are formed. The anterior cells of the embryonal mass form plumule and two cotyledons. The main part of the radicle and the hypocotyl are formed from the posterior embryonal mass cells.
2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 4

Question 2.
Trace the events that would take place in a flower from the time the pollen grain of the same species falls on the stigma up to the completion of fertilization.
Answer:
2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 5
The pollen grain develops on the stigma stimulated by the secretion of the stigma. The intine grows out as a protuberance through one of the germ pores. This outgrowth continues to grow as a pollen tube. The nucleus of the vegetative cell moves into it followed by the generative cell. The generative cell divides into two male gamete and moves to the tip of the pollen tube.

The pollen tube secretes enzymes to digest the tissues of the style and enters the ovule through the micropylar end and discharges the two male gametes into one of the synergies of the embryo sac. One of the male gametes fuses with the ovum to form a zygote. This process is called syngamy. The other male gamete fuses with the secondary nucleus to form the primary endosperm nucleus.

This process is called triple fusion. Since there are two fusions (syngamy and triple fusion) inside the ovule during fertilization, it is known as double fertilization.

KSEEB Solutions

Question 3.
Draw a labelled diagram of a T.S of a dehisced anther.
Answer:
2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants 6

Question 4.
The flower of brinjal is referred to as chasmogamous while that of beans is cleistogamous. How are they different from each other?
Answer:

  • Chasmogamous flowers: Chasmogamous flowers are similar to flowers of other species with exposed anthers and stigma.
  • Cleistogamous flowers: Cleistogamous flowers never open to ensure self-pollination. They remain closed so that cross-pollination does not occur.

Three cells are grouped at the clealazal end; they are called antipodals. The large cell in the centre of the embryo sac is the central cell. Later 2 polar nuclei in the centre cell fused to form a depolid secondary nucleus or endosperm nucleus. Thus the embryo sac of flowering plants is 8 nucleate 7 celled at maturity. This type of embryo sac is called monosporic because it is formed from only one of the 4 megaspores.

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