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 development of male and female gametophyte takes place.
Answer:
Inside the anther, the cells of microsporangia develop as male gamete. Inside the ovary megasporangial cells develop as female gametes.

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:

Microsporogenesis Megasporogenesis
  1. The process of formation of microspores from pollen mother cell through meiosis is called microsporo­genesis.
  2. Pollen grains are formed at the end of this event. Occurs inside the pollensac of the anther.
1. The process of formation of megaspores from megaspore mother cells through meiosis is called megaspore -genesis.

2.  Egg is, produced inside the embryo sac at the end of this event.

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 grain → male gamete.

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 piaee.

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

1. Funicles: It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.

2. Hilum: It is the point where the body of the ovule is attached to the funicles.

3. Integuments: They are the outer layers surrounding the ovule that provide protection to the developing embryo.

4. Micropyle: It is a narrow pore formed by the projection of integuments. It makes the point where the pollen tubes enters the ovule at the time of fertilization.

5. Nucellus: It is a mass of 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.

6. Chalazal: It is the based swollen part of the nucellus from where the integuments originate.

KSEEB Solutions

Question 5.
What is meant by monosporic development of female gametophyte?
Answer:
The female gametophyte or the embryo sac develops, from a single functional megaspore. This is known as monosporic development of the female gametophyte. In most flowering plants, a single megaspore mother cell present at the micropylar pole of the nucellus region of the ovule undergoes meiosis to produce four haploid megaspores. Later out of these 4 megaspores, only one functional megaspore develops into female gametophyte, while the remaining 3 degenerates.

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
The female gametophyte (embryo sac) develops from a single functional megaspore. Thus, megaspore undergoes three successive mitotic divisions to form 8 nucleate embryo sac. The first mitotic division in the megaspore forms 2 nuclei. One nucleus moves towards the micropylar end while the other nucleus moves towards the chalazal end. Then these nuclei divide at their respective ends and redivide to form 8 nucleate stages.

As a result there are 4 nuclei each at both the ends i.e., at the micropylar and the chalazal end in the embryo sac. At the micropylar end, out of 4 nuclei only 3 differentiate into 2 synergids and one egg cell. Together they are known as egg apparatus. Similarly, at the chalazal end 3 out of 4 nuclei differentiates as antipodal cells. The remaining 2 cells (of the micropylar and chalazal end) move towards the centre and are known as the polar nuclei, which are situated in the centre of embryo sac. Hence, at maturity, the female gametophyte appears as a 7 celled structure, though is has 8 nucleate.

Question 7.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous
flowers ? Give a reason for your answer.
Answer:
There are 2 types of flowers present in plants namely oxalis and viola chasmogamous and cleistogamous flowers. Chasmogamous flowers have exposed anthers and stigma similar to the flowers of other species.

Cross pollination cannot occur in cleistogamous flowers. This is because cleistogamous flowers never open at all. Also, the anther and the stigma lie close to each other in these flowers. Hence only self pollination is possible in these flowers.

Question 8.
Mention two strategies evolved to prevent self pollination in flowers.
Answer:
Self pollination involves the transfer of pollen from the stamen to the pistil of the same flower. Two strategies have evolved to prevent self pollination in flowers are as follows.

(a) In certain plants, the stigma of the flower has the capability to prevent the germination of pollen grains and hence, prevent the growth of the pollen tube. It is a genetic mechanism to prevent self pollination called self incompatibility. This may be between the individuals of the same species or between individuals of different species. Thus, incompatibility prevents breeding.

(b) In some plants, the gynoecium matures before the androeicum or vice – versa. This phenomenon is known as protogyny or protandry respectively. This prevents the pollen from coming in contact with the stigma of the same flower.

Question 9.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self incompatible species ?
Answer:
Self-incompatibility is a genetic mechanism in angiosperm that prevents self-pollination. It develops genetic incompatibility between individuals of the same species or between the individuals of different species.

The plants which exhibits this phenomenon have the ability to prevent germination of pollen grains and thus prevents the growth of the pollen tube on the stigma of the flower. This prevents the fusion of the gametes along the development of the embryo. As a result no seed formation takes place.

Question 10.
What is bagging techniques? How is it useful in a plant breeding programme.
Answer:
Various artificial hybridization technique (various crop improvement programmes involve the removal of the anther from bisexual flowers without affecting the female reproductive part (pistil) through the process of emasculation. Then, these emasculated flowers are wrapped in bags to prevent pollination by unwanted pollen grains. This process is called bagging.

This technique is an important part of the plant breeding programme as it ensures that pollen grains of only desired plants are used for fertilization of the stigma to develop the desired plant variably.

Question 11.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer:
Triple fusion is the fusion of the male gamete with 2 polar nuclei inside the embryo sac of the angiosperm. When pollen grains fall on the stigma, they germinate and give rise to the pollen tube that passes through the style and enters into the ovule.

After this, the pollen tube enters between one of the synergids and releases 2 male gametes there. Out of these 2 male gametes, one gamete fuses with nucleus of the egg cell and forms zygote (syngamy). The other male gametes fuses with 2 polar nuclei in the centre form a triploid primary endosperm nucleus. Since this process involves the fusion of 3 haploid nuclei, it is known as triple fusion. It results in the formation of endosperm.

Question 12.
Why do you think the zygote is dormant for some time in a fertilized ovule ?
Answer:
The zygote is formed by the fusion of the male gamete with the nucleus of the egg cell. The zygote remains dormant for sometime and waits for the endosperm to form, which develops from the primary endosperm cell resulting from triple fusion. The endosperm provides food for the developing embryo and after the formation of endosperm, further development of the embryo from the zygote starts.

Question 13.
Differentiate between
(a) Hypocotyl and epicotyl
(b) Coleoptile and coleorrhiza
(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:
Fruits derived not from the ovary but from other accessory floral parts are called false fruits. On the contrary, true fruits are those fruits in which fleshy part develop from ovary, but don’t consists of the thalamus or any other floral parts. In an apple the fleshy receptacle forms the main edible part. Hence it is a false fruit.

Question 15.
What is meant by emasculation ? When and why does a plant breeder employ this technique?
Answer:
Emasculation is the process of removing anthers from bisexual flowers without affecting the female reproductive part (pistil). Emasculation is performed by plant breeders in bisexual flowers to obtain the desired variety of a plant by crossing a particular plant with the desired pollen grain. After removing the anthers, the flowers are covered with a bag before they open. This ensures that the flower is pollinated by pollen grains obtained from desirable varieties only. Later, the mature, viable and stored pollen grains are dusted on the bagged stigma by breeders to allow artificial pollination to take place and obtain the desired plant variety.

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:
Parthenocarpy is the process of developing fruits without involving the process of fertilization or seed formation. Therefore the seedless varieties of economically important fruits such as orange, lemon, grapes etc. are produced using this technique. This technique involves inducing fruit formation by the application of plant growth hormone such as auxins.

Question 17.
Explain the role of tapetum in the formation of pollen grain wall.
Answer:
Tapetum is the innermost layer of microsporangium. It provides nourishment to the developing pollen grains. During micro sporogenesis, the cells of 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 the sporopollenin.

Question 18.
What is apomixos and what is its importance ?
Answer:
Apomixis in the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production. The method of producing hybrid seeds by cultivation is very expensive for farmers. Also by sowing hybrid seeds, it is difficult to maintain hybrid . characters that segregate during meiosis. Apomixis prevents the loss of specific characters in the hybrid. Also it is a cost effective method for producing seeds.

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.
Name the protective substance present on the pollen envelop to tide over adverse condition. [CBSE 98]
Answer:
Sporopollenin.

Question 2.
Name some water pollinated plats.
Answer:

  • Fresh water – vallesneria
  • Hydrolla Aquatic – Zostera

Question 3.
What technical term is applied to fruits formed without fertilization ?
Answer:
Parthenocarpy

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

KSEEB Solutions

Question 5.
List the general characteristics of the pollen grains of wind pollinated plants.
Answer:
The pollen grains are smooth, dry, light, non-sticky and may be winged. [CBSE – 2K]

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.
State the function of a suspensor.
Answer:
Pushes the developing embryo into the endosperm for absorption of nutrients.

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 egg cell and second gamete with polar nuclei in angiosperm. [CBSE – 99]

Question 12.
State the difference between the endosperm of gymnosperms and angiosperms.
Answer:
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:
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 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 ?
Ans:
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 where as parthenogenesis is the formation of embryo from unfertilized egg.

Question 2.
Draw a labelled diagram of 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 favourable for active growth.
Two advantages of dormancy:

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

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 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.
Differentiate between non-albuminous and albuminous seeds with examples.
Answer:

  • Non albuminous seeds have no residual endosperm as it is completely consumed during embryo development. Eg: Pea, ground nut.
  • Albuminous seeds retain, a part of endosperm as it is not completely used up during embryo development. Eg: Wheat, maize, barley, castor.

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

  • In the monocot seed, the region of embryonic axis below the cotyledon is the radicle covered with protective sheath is coleorrhiza.
  • 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 dicotyledonous embryo.
Ans:
The process of development of mature embryo from 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 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 cotyledon. 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 protrubrance through one of the germ pore. This out growth continues to grow as 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 enzyme to digest the tissues of the style and enters the ovule through micropylar end and discharges the two male gametes into one of the synergfds 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 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.
Describe the structure of a typical embryo sac found in flowering plant. Why is it generally referred to as monosporic ?
Answer:
A typical embryo sac is 8 nucleate and 7 celled. Six of the eight nuclei become surrounded by cell wall and are organised into cells. Two of the nuclei, called polar nuclei remain in the centre of the large central cell. Three cells are grouped together at the micropylar end forming the egg apparatus. Of these, one is the female gamete and two are synergids; the synergids have special cellular thickening called filiform apparatus at the micropylar tip.

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.