MP Board Class 12th Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants
Sexual Reproduction in Flowering Plants NCERT Textbook Questions and Answers
Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Development of male gametophyte takes place in anther and female gametophyte in ovary.
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.
Differences between Microsporogenesis and Megasporogenesis:
|1.||In this process haploid microspores are formed from diploid microspore motto’cell.||In this process, haploid megaspores are formed from diploid megaspore mother cell.|
|2||The four microspores formed from a single microspore mother cell are generally aranged in a tetrahedral structure.||The four megaspores formed from a megaspore mother cell are arranged in die from of a linear tetrad.|
|3.||All the four microspores arranged in a tetrahedral tetrad are functional.||Only one megaspore remain functional while the other three degenerates.|
Meiosis Occurs during micro and megasporogenesis microspores (Pollen grain) are formed at the end of micro sporogenesis and female gametophyte (enibro sac) are formed at the end of megasporogenesis.
Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male garnets.
Sporogenous tissue → Pollen mother cell → Microspore → Tetrad → Pollen grain → Male garnets.
With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
Structure of Ovule: Each ovule consists of the following parts as visible in a longitudinal section:
- Funicles: It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.
- Hilum: It is the point where the body of the ovule is attached to the funicles.
- Integuments: They are the outer layers surrounding the ovule that provide protection to the developing embryo.
- Micropyle: It is a narrow pore formed by the projection of integuments. It makes the point where the pollen tubes enter the ovule at the time of fertilization.
- 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.
- Chalazal: It is the based swollen part of the nucellus from where the integuments originate.
What is mean by monosporic development of a female gametophyte?
Out of theTour megaspores, three degenerate and only one remains functional which develops in to a female gametophyte or embryo sac. This is called monosporic development, i.e., when embryosac develops from one single megaspore it is called monosporic embryo sac.
A neat diagram explains the 7-celled, 8-nucleate nature of the female gametophyte.
Explanation: Nucleus of the functional megaspore undergoes mitosis resulting in 2-nuclei that move to two opposite poles forming 2-nucleate embryo sac.
Two more mitotic nuclear divisions result in 4-nucleate and later 8-nucleate stages of the embryo sac. so, far no cytokinesis (cytoplasmic division) has taken place.
Now cell walls start to build leading to the organisation of female gametophyte or embryo sac.
Six of the 8-nuclei are bound by cell wall and the remaining 2-celled polar nuclei lie below the egg apparatus in the large central cell.
Three cells are grouped together at the micropylar end and constitute the egg appara¬tus, which is constituted of two synergids and one egg cell.
Three cells at the chalazal end are called antipodals. The large central cell has 2-polar nuclei.
Thus, a typical angiosperm embryo sac at maturity is 7-celled but 8-nucleated as the central cell has 2-nuclei
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons to your answer.
Chasmogamous flowers are open flowers with exposed stamens and stigma which facilitate cross-pollination.
No cross-pollination occurs in cleistogamous flowers. As these flowers are closed and never open and thus no transfer of pollen from outside to the stigma of the flower is possible. So there is no occurs cross-pollination.
Mention two strategies evolved to prevent self-pollination in flowers.
Self-pollination involves the transfer of pollen from the stamen to the pistil of the same flower. Two strategies that 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 androecium 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.
What is self-incompatibility? Why does self-pollination not lead to seed forma¬tion in self-incompatible species?
Self-incompatibility is a genetic mechanism to prevent self-pollen from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
In these cases, self-pollination does not lead to seed formation because fertilization is inhibited.
What is the bagging technique? How is it useful in a plant breeding programme?
Various artificial hybridization techniques (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.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion?
Triple fusion refers to the process of fusion of three haploid nuclei. It takes place in the embryo sac.
The 3-nuclei that fuse together are the nucleus of the male gamete and 2-polar nuclei of the central cell to produce a triploid primary endosperm nucleus.
Why do you think the zygote is dormant for some time in a fertilized ovule?
The zygote is formed by the fusion of the male gamete with the nucleus of the egg cell. The zygote remains dormant for some time 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.
(a) Hypocotyl and Epicotyl
(b) Colcoptile and Coleorhiza
(c) Integument and Testa
(d) Perisperm and Pericarp.
(a) Differences between Hypocotyl and Epicotyl:
|1.||lies between the radicle and the point lie between the radicle and the point of attachment of cotyledons is called the hypocotyl.||The region of the embryonal axis that lies between the plumule and cotyledons is called epicotyl.|
|2.||Hypocotyl pushes the seed above the soil in epigeal germination||Epicotyl pushes the plumule above the soil in hypogeal germination.|
|3.||It is an important component of the embryonic root system.||It is an important component of the embryonic shoot system.|
(b) Differences between Coleoptile and Coleorhiza:
|1.||The shoot apex and few leaf primordia are enclosed in the epicotyl region is called coleoptile||The ridicule and rootcap are situated at the lower end of the embryonal axis are enclosed by a protective sheath called coleorhiza.|
|2||It comes out of the soil.||It remains inside the soil.|
(c) Differences Between Integument and Testa:
|1.||It is the protective covering of the ovule||It is the protective covering of the seed|
|2.||It is part of pre fertilisation||It is a part of post fertilisation.|
(d) Differences between Peris perm and Pericarp:
|1.||It is the part of the nucellus which remains in||The ovary is converted into a pericarp after|
|2||It is a part that belongs to the seed||It is a part that belongs to fruit.|
|3.||It is usually dry.||It can be dry and fleshy.|
Why is apple called a false fruit? Which parts of the flower form the fruit?
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 parts develop from an ovary but don’t consist 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.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Emasculation means the removal of anthers, with forceps, from the flower bud before dehiscence.
Plant breeder employs this technique to prevent contamination of stigma with the undesired pollen. This is useful in artificial hybridisation, where desired pollen is required.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
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.
Explain the role of tape turn in the formation of pollen grain walls.
Tapetum is the innermost layer of the microsporangium. It produces the exine layer of the pollen grains, which is composed of sporopollenin, the most resistant fatty, substance.
During microsporogenesis, the cells of the tapetum produce various enzymes, hormones, amino acids, and other nutritious materials required for the development of pollen grains.
What is apomixis and what is its importance?
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.
Sexual Reproduction in Flowering Plants Other Important Questions and Answers
Sexual Reproduction in Flowering Plants Objective Type Questions
1. Choose the Correct Answers:
Fertilization process is:
(a) Fusion of male gamete with egg
(b) Transference of pollengrains to stigma
(c) Fusion of polar nucleus with male gamete
(d) Formation of seed from ovule.
(a) Fusion of male gamete with egg
Female gametophy te of angiosperms is:
(a) Megaspore mother cell
Effect of nector demonstrate by Xenia word on:
(a) Morphological tissue
In a diploid flowering plant, no. of chromosomes are 12, then 6 chromosomes will be present in:
(a) Cotyledons cells
(b) Endospermic cells
(c) Synergids cells
(d) Leaf cells.
(c) Synergids cells
Seed coats of seed after fertilization develop from:
(a) Degenerative secondary nucleus
(c) Peripheral part of endosperm
Development of ovary into fruit from ovule without fertilization, the process is called:
(a) Parthenio ovule
Mitotic cell division in an ovule takes place in:
(b) Megaspore mother cell
(b) Megaspore mother cell
Development of sporophyte without the fusion of a gamete is called:
Male gametes are found in angiospermic plants :
(a) In pollengrain
(b) In anther
(c) In ovule
(d) All of these
(a) In pollengrain
The function of pollentube is:
(a) Help in pollination
(b) Protection of stigma
(c) Male gamete carrier
(d) All of these
(c) Male gamete carrier
Tapetum is a part of:
(a) Male gametophyte
(b) Female gametophyte
(c) Ovary wall
(d) Anther wall.
(d) Anther wall.
Cotyledons is situated in monocots:
(d) In Any Position
Which type of pollination found in sunflower:
(a) Self pollination
(b) Cross pollination
(c) All of the above
(d) None of these.
(c) All of the above
Endospermic nucleus are :
(d) None of these.
Double fertilization is discoverd by: :
(a) By Navaschin
(a) By Navaschin
The type of pollination in which genetically different pollen grains are brought to
stigma is : (AMU 2012)
(d) Dichogamy. ,
If the number of chromosome in root cell is 14 then what will be the number of chromosome in synergid cell of in ovule of that parent (BHU2012)
Presence of many embryo (Polyembryony) is characters tic feature of: (BHU2012)
(d) None of these.
Sporopollenin is formed by the polymerisation of : (BHU2012)
(a) Fat and Phenol
(b) Carotenoid and Fat
(c) Fat and Ester
(d) Carotenoid and Ester.
(a) Fat and Phenol
2. Fill in the Blanks:
- The main function of endosperm in a seed is the storage of ………………
- Pollination takes place by the agency of bird is called ………………
- Apple is an example of fruit. ………………
- Tissue on which ovules are attached is called ………………
- ……………… types stamens are found in sunflower.
- In plants development of fruit takes place from ………………
- One cotyledon of maize is called ………………
- Tetradynamous stamens are found in ………………
- ………………is thin in endospermic seed.
- In ovule …………….. is joined with funiculus.
- Anther is ……………… in angiospermic plants.
- ……………… type of pollination are found in Typha.
- ……………… pollination is occurs in Salvia.
- Outer wall of pollen grain is called ………………
- Process of seedless fruit is called ………………
- Food material
- Cell wall
- Reproductive organ
3. Match the Following:
4. Answer in One Word/Sentence:
- Name the four whorls of flower.
- Give the term for plants which produce flower and fruits many times.
- Name the outer coat of the seed.
- Give example of plant in which flowers are pollinated by bat.
- Give the term used for similar calyx and corolla.
- What parts of the plant produce seed and fruit after fertilization?
- Name the type of pollination carried out of bat.
- Give the term for fruit development without fertilization.
- Calyx, Corolla, Androecium and Gynoecium
- Perrenial plants
- Seed coat
Sexual Reproduction in Flowering Plants Very Short Answer Type Questions
Development of female gametophyte occurs in which cell?
By functional megaspore mother cell.
What is the other name of female gametophyte?
Ovule derives nourishment from which part of the carpel?
Ovule derives nourishment from placenta.
What are cleistogamous flowers ? Give an example.
The flowers which do not open are called cleistogamous flowers, e.g. Commelina
What is the substance found on the exine of pollen grains?
Give the characters of wind pollinated flowers.
White in colour, small in size and pollengrains are formed in large number.
What is the ploidy of angiospermic endosperm?
Give an example of a monocotyledonous endospermic seed.
Give example of two false fruit.
What are monocious plants?
Plants which has both male and female flower.
Sexual Reproduction in Flowering Plants Short Answer Type Questions
What is parthenogenesis ?
Parthenogenesis : It is the method of reproduction in which ovum develops into embryo and forms a new plant without fertilization. It has been observed that pollination is necessary for parthenogenesis. It stimulates the process. Ulothrix, Spirogyra and Solan- aceae and Malvaceae family plants reproduce by this method.
Sometimes in some plants ovary also develops into fruit during this process. Such fruits are called as parthenocarpic fruits.
Example: Banana, Apple, Grapes, Guava etc. shows parthenocarpic fruits.
What is Polyembryony?
Polyembryony : When more than one embryo develops in one seed then this condition is called as Polyembryony. It is generally found in citrus family. It is also found in Nicotiana, conifers, rice, wheat. It occurs when fertilization occurs in all embryo sacs found in the ovule.
Describe structure of anther with labelled diagram.
Structure of Anther : Transverse section of anther shows that it consists of 2 lobes which are connected by connective. Each lobe contains two Pollen sacs. Innermost layer of pollen sac is called as Tapetum.
Tapetum is a layer rich in nutritive contents which supplies food material for the developing pollen grains. At first many Pollen mother cells are formed in them which divides meiotically to form haploid pollen grains.
Give four contrivances for self pollination.
Contrivances for self-pollination:
(1) Bisexuality : When male and female parts are found in same flower then possibility of self-pollination increases.
(2) Cieistogamy : In Commelina benghalensis both cleistogamous and chasmogamous flowers are produced. The former are the underground flowers and the latter are the aerial ones developed on branches. In the small, inconspicuous cleistogamous flowers the pollen are shed within the closed flowers so that self-pollination is a must. This is also observed in Impatiens, Oxalis, Viola, Portulaca etc.
(3) Homogamy : Here the stamens and carpels mature at the same time. So, there is a greater chance of self-pollination as compared to cross-pollination, e.g., Mirabilis, Argemone etc.
(4) Failure of cross pollination : In some flowers generally cross pollination occurs but if they fails to do cross pollination then self-pollination occurs.
What do you mean by micropropagation?
Micropropagation : It is a modern method of reproduction. By this process thousands of new plants can be obtained from few tissues of mother plant. This method is based on tissue and cell culture technique.
In this process a small part of tissue is separated from the plant and then it is grown in nutrient medium in aseptic condition. The tissue develops to form a cluster of cells which is called as callus. This callus can be preserved for long time for multiplication. A small part of the callus is transferred to nutrient medium, where it grows into a new plant. This plant is then transferred to the field. By this process Orchids, Carnations, Chrysanthemum plants can be grown successfully.
What are the advantages of cross-pollination ?
Advantages of cross-pollination:
- The weaker characteristics of the race elimi¬nated and replaced by better character of nature.
- New improved varieties cap be produced by cross-pollination. ‘
- It increases the adaptability of the offsprings.
- Seeds are more vigorous.
What is fertilization? Draw labelled diagram showing path of pollen tube during fertilization.
What do you mean by sexual reproduction? Describe the process of fertilization in plants with the help of diagram or sexual reproduction.
Fertilization : The process of fusion of male and female gamete is called as fertilization or sexual reproduction. As a result of this process a diploid zygote is formed.
Differences between self and cross pollination
Differences between Self and Cross poltination :
|No.||Self pollination||Cross pollination|
|1.||It is the process of transfer of pollen grains from one flower to the stigma of same flower of same plant.||Transfer of pollen grains from one flower to the stigma of flower of another plant.|
|2.||Medium is not reqired||Medium is required|
|3.||Plants do not show any special chara cter.||Attractive, coloured,scent or honey bearing flowers are produced to attract insect.|
|4.||Less number of pollen grains are produced.||More number of pollen grains are produced.|
Sexual Reproduction in Flowering Plants Long Answer Type Questions
What is self-pollination ? Give advantages and disadvantages of self pollination.
Self-pollination : When the pollen grain of one flower are transferred to the stigma of the same flower then the process is called as self-pollination.
Advantages of self-pollination:
These are the advantages of self pollination:
- Parental characters can be preserved indefinitely in several generations.
- Self-pollination helps in maintaining pure lines for experimental hybridization.
- It is most economical method of pollination. The plants do not consume their energies in the production of
- large number of pollen grains, nectar and coloured corolla.
- It ensures seed production and flowers do not take chances of the failure of fertilization.
Disadvantages of self-pollination:
These are the disadvantages of self-pollination :
- The weaker characteristics or defects of the plant can never be eliminated from the race.
- No useful characters can be introduced in the race.
- The immunity of race towards diseases falls and ultimately it falls prey to many diseases.
What is double fertilization?
Explain double fertilization in angiosperms.
Double fertilization : It is found in all angiospermic plants. It was first discovered by S.N. Navaschin (1899) in Lilium and Fritillaria. When pollen tube come in contact of embryo sac then the tip of the pollen tube disintegrate and release two male gametes into the embryo sac. Out of which one male gamete (x) fuses with egg cell (x) to form a diploid zygote. This process is called as fertilization. The second male gamete (x) fuses with secondary nuclei (2x) to form a triploid body.
The act of two nuclear fusion is called as double fertilization.
Describe development of embryo sac or Female gametophyte in angiosperms.
Development of embryo sac or Female gametophyte in angiosperms :
During the initial stage of development of ovule primary archesporial cell gets demarcated at the apex of the nucellus below the epidermis. It divides periclinally into a outer primary parietal cell or primary wall cell and an inner primary sporogenous cell. The later acts as a megaspore mother cell which enlarges in size and divide meiotically to form a row of four megaspores. Of the four cells the upper three cells degenerate and appear as dark caps while the lowest one functions arid is called the functional megaspore. The latter greatly enlarges and forms the embryo sac.
Describe development of Endosperm.
Development of Endosperm : It develops from the triploid tissue of the fertilized embryo sac after the act of double fertilization. It is of the following three types:
- Free nuclear endosperm.
- Cellular type of endosperm.
- Helobial type of endosperm.
The name refers to the type of nuclear divisions of the endosperm nucleus. If triploid nucleus divides by free nuclear division the endosperm produced contains many nuclei lying freely in it and hence it is termed as free nuclear endosperm. If the nuclear division is followed by wall formation it is called as cellular type. If endosperm is intermediate between the two types it is called as helobial type.
What is male gametogenesis ? Describe male gametogenesis in plants.
Describe development of pollen grain.
Male gametogenesis: The process of formation of male gametes is called as male gametogenesis or microsporogenesis.
Each anther usually consists of two lobes, connected together by a connective. Each lobe contains two sacs called as Pollen sac. In the early stage of development the anther comprises of a homogenous mass of cells limited by a well demarcated epidermis. During the course of development the anther gets four lobed. Each lobe exhibits a hypodermal lining, few cells thick with distinct nuclei. These hypodermal cells constitute the archesporium. The cell of archesporium divide periclinally, cutting of parietal cells towards the periphery and sporogenous cells within it two chambers or loculi, which are termed as pollen sacs or microsporangia.
Fig. Development of Pollen grain : (A) Formation of Pollen lobes, (B) Archesporial cell, (C) and (D) Division in Parietal cell, (E) and (F) Parietal layer : Tapetum sporogenous tissue (G), (H) and (I) Pollen mother cell, (J) Pollen grain, (K) Outer layer Degenerate, (L) Four free Pollen grains.
Besides the above changes in the wall layers the sporogenous layer comprising of primary sporogenous cells also undergo several divisions to form microspore mother cells or pollen mother cells. In the initial stage the microspore mother cells are closely packed but as the anther enlarges the pollen sac becomes spacious and the pollen mother cells assume spherical shape and get loosely arranged.
In many cases some of the sporogenous cells are nonfunctional and serve only as the nutritive material for the functional microspore mother cells. Each microspore mother cell is diploid in nature and by a single meiotic division give rise to four haploid nuclei. The four nuclei so formed are arranged tetrahedrally, and called as Tetrad. Innermost layer of pollen sac is called as Tapetum. Outer to which endothecium layer is formed. In outer most layer of pollen sac epidermis is formed. Surrounding each nuclei exine and intine are formed, now each structure is called as Pollen grain. Pollen grains are liberated during the dehiscence of anthers through stomium.
(i) Embryo sac and Endosperm
(ii) Seed and Ovule
(i) Difference between Embryosac and Endosperm:
|1.||It is haploid structure.||It is triploid structure.|
|2.||It is found in ovule.||It is found in seed.|
|3.||It is formed before fertilization.||It is formed after fertilization.|
|4.||Nutritive materials are stored.||Nutritive materials are not stored.|
|5.||It consists antipodal cells, egg cell, synergid cells and two polar nuclei.||Antipodal cells, egg cell, synergid cells are absent and all cells are similar.|
(ii) Difference between Seed and Ovule
|1.||It is formed in the fruit seed is formed after fertilization of ovule.||Before fertilization ovule is found into the ovary called mega sporangium.|
|2.||Seed is surrounded by integument. Outer covering is called outer integument and inner covering is called inner integument.||Nucellus is present below the ovule and is surrounded by inner and outer covering.|
|3.||Embryosac is absent in seed.||Embryosac is present in ovule.|
|4.||Embryo is present in seed||Embryo is absent in ovule.|
|5.||Endosperm may be found in seed||Endosperm is not found in ovule.|
|6.||Seed make a new plant||Ovule is not germinate.|