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CBSE Class 12th Biology Notes: Sexual Reproduction in Flowering Plants

Jan 27, 2017 16:48 IST

    In this article we are going to discuss the important points for the Class 12 Biology chapter 2, Sexual Reproduction in Flowering Plants.

    Each definitions and concept is followed by the solved and unsolved questions. You can also find the various categories questions like short, very short and long answer type.

    Have a look on the Highlights of important terminologies and questions:

    Microsporogenesis- The process of formation of microspores from a pollen mother cell through meiosis is called microeporogenesis.

    Vegetative and Generative Cell-The cytoplasm of pollen grain is mature it contains two cells, the vegetative cell and generative cell. The vegetative cell is bigger, has abundant food revenue and a large irregularly shaped nucleus. The generative cell is small and floats in the cytoplasm of vegetative cell.

    The megasporangium (Ovule)- The ovule is a small structure attached to the placenta by means of a stalk called funicle. The body of ovule fuses with funicle.

     In the region called hilum. This hylum represents the junction between ovule and funicle. Each ovule has one or two protective envelopes called integuments encircle the ovule except at the tip where a small opening called the micropyle is organised. Opposite the micropyle end, is the chalaza, representing the based part of the ovule.

    Megasporogenesis- The process of formation of megaspores from the megaspore mother cell is called megasporogenesis. Ovules generally differentiate a single Megaspore Mother Cell (MMC) is the micropylar region of the nucellus.

    Outbreeding Devices-Continued self-pollination result in inbreeding depression. Flowering plant have developed many devices to discourage self-pollination to encourage cross-pollination. In some other species, the anther and stigma are placed at different position. So, that the pollen cannot come in contact with the stigma of the same flowers. Both these devices prevent autogamy. The third device to prevent inbreeding in self in compatibility. In, several species such as Papaya, male and female flowers are present on different plants, that is each plant is either male or female (diocy). This condition prevents both autogamy and geitonogamy.

    Artificial Hybridisation-It is one of the major aproaches of crop improvement pragramme. 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. This is achieved by emasculation and bagging techniques.

    Embryo- Embryo develops at the micropylar end of the embryo sac where the zygote is situated. Most zygotes divides only after certain amount of endosperm is formed. The zygote gives rise to the proembryo and subsequentlu to the globular heart-shaped and mature embryo.

    Parthenocarpu- Parthenocarpq is the formation of fruits without fertilization usually seeds are not produced and hence no new individual is formed. It give rise to seedless fruits e.g.- Pineapple, Banana.

    Abomixis-A few flowering plants such as some species Asteraceal, and grasses, have evolved a special mechanism to produce seeds without fertilisation called apomixis.

    Poly embryony-In such species each ovule contains many embruos. Occurence of more than one embnjo in a seed is referred as polyembryony.

    Pollination-Pollination is the mechanism to achieve this objective. Transfer of pollen grains to the stigma of a pistil is termed pollination :

    Kinds of Pollinations=(i) Autogamy -Pollination is achieved within the same flower. Transfer or. pollen grains from the anther to stigma of the same flower.

    e.g=Chasmogamous flowers Cleistogamous flowers.

    (ii) Geitonogamy- Transfer of pollen grains from the anther to the stigma of another flower of the Same plant.

    (iii) Xenogamy- Transfer of pollen grains from anther to the stigma of a different plant. Agent of pollination - (1) Abiotic agencies (2) Biotic agencies

    (1) Abiotic agencies

    (i) Anemophily - By the wind

    (ii) Hydrophily - By the water.

    (2) Biotic agencies

    (i) Entomophily - By the insects.

    (ii) Orhithophily - By the birds.

    (iii) Chiropterophily - By the bats.

    Very Short Answer Type Questions (1-Mark)

    Q. 1. What is double fertilization.

    Ans. One male gametes fuses with egg (syngamy) to form zygote. Second male gametes fuses with two polar nuclei to form primary endosperm nucleus. All the steps together represent double fertilization.

    Q. 2. Why are cucurbits referred to as monocious.

    Ans. It referred to as monocious because in cucurbits male and female flowers are borne on the same plant.

    Q. 3. How does the mustard inflorescence differ from banana inflorescence in arrangement? Give the technical term for each.

    Ans. In mustard raceme inflorescence is present here, the flowers are borne in acropetal order. In banana spadix inflorescence is present where fleshy axis is enclosed by spathe.

    Q.4. In the following figure of a fruit, label the part which is protective in function and that which is responsible for producing new plants.

    role of seed in the plant

    Ans. Pericarp : Protective in function. Seed is responsible for production new plants.

    plant seed and it's function

    Q. 5. What is the fate of haploid megaspores formed by megaspore mother cell in an angiosperm plant.

    Ans. Out of four megaspores formed due to meiosis in megaspore mother cell, usually upper three degenerate and the functional megaspore embryo sac.

    Q. 6. Name the type of Pollination taking place in Coconut Palm. List five characteristics of the flowers of coconut plant favouring this type of pollination.

    Ans. Type of pollination in coconut plant is Hydrophilly. It is kind of cross pollination carried out by water. Pollen cells from matured anthers drop in water which are carried to 'stigma of another plant by winds (anemophilly). Fertilisation occurs which results in fruits formation.

    Q. 7. Define Parthenocarpy. What are parthenocarpic fruits.

    Ans. Parthenocarpy is the formation of fruits without fertilization. The fruits which are formed without fertilization e.g.-seedless fruits of banana.

    Short Answer Type Questions (2-Marks)

    Q.1. Explain the role of tapetum in the Pollen-grain wall formation.

    Ans. It nourishes the developing pollen grains. The tapetal cells provide nourishment to young microspore (amoeboid) or through diffusion parietal or secretory type.

    Q. 2. Draw a longitudinal section of a flower showing pollen tube. With their labels.

    Ans.

    pollen tube and its functions

    Q. 3. Why do you think, the zygote does not for sometime in a fertilized ovule.

    Ans. Zygote start formation of embryo only when certain amount of endosperm is formed . This is an adaptation to provide assured nutrition to the developing embryo .

    Q. 4. Define with the draw chasmogamous and cleisto gamous flowers.

    Ans.

    Chasmogamous

    flowers

    Cleistogamous

    flowers

    Those flowers which are similar to flowers of other species with exposed anther and stigma.

    Those flowers which do not open at all, and the anthers and stigma lie close to each other.

    types of flower

    Q. 6. Give a labelled diagram of a typical dicot embryo.

    Ans.

    structure of typical dicot embryo

    Q. 7. Give a view of microsporangium wall formation with their labells.

    Ans.

    microsporangium wall formation

    Q. 8. Write the difference between Microsporogenesis and megasporogenesis.

    Ans.

    Microsporogenesis

    Megasporogenesis

    1. This is the formation of microspores in

    sporogenous tissue due to meiosis.

    2. Microspore leads to development of male gametophyte.

     

    1. This is the formation of megaspores in megaspore mother cell due to meriosis.
    2. Leads to formation of female gametophyte (embryo sac).

    Q. 9. Differentiate between

    (i) Hypocotyl and Epicotyl

    (ii) Perisperm and Pericarp.

    Ans. (i)

    Hypocotyl

    Epicotyl

    The cylindrical position below the level of cotyledons is called hvpocotyl.

     

    The portion of embryonal axis above the level

    of cotyledons is called epicotyl.

    (ii)

    Perisperm

    Peri carp

    It is the residual persistent nucellus.

     

    Covering of fruit.

    Short Answer Type Questions (3-Marks)

    Q. 1. Write the differences between self-pollination and cross pollination.

    Ans.

    Self Pollination

    Cross Pollination

    1. It is migration of pollen grains from anther to the stigma of the same flower.

    2. Self-pollination always occur through touch

       or wind. 

    3. Both anthers and stigmas matures at the

       same time.

    4. It can occur in closed flower homozygous.

    5. It preserves the parental characters. Origin

       of new species is not possible.

    1. It is migration of pollen grains from anther to the stigma of another flower of anther plants.

    2. It always occurs through an external agents e.g. air, wind, insects.

    3. The anthers and stigmas mature at different time.

    4. It can occur in open flower and it always heterozygous.

    5. It does not preserve the parental characters, produces new races and varieties.

    Q. 2. Define wind pollination, Write their significant with draw.

    Ans. Pollination brought about through the agency of wind in plants.

    Significance-

    (i) They are devoid of scent, necter etc.

    (ii) The pollen grains are dry and unwettable.

    (iii) To catch the pollen grains, the stigma becomes stick)" hairy, feathery or branched.

    Anemophilous flower (wind pollinated flower) usually bear single ovule in each ovary.

    e.g. Coconut palm, Date palm, Cannabis, Zea mays, Grasses.

    wind pollination and its effects

    Long Answer Type Questions (5-Marks)

    Q. 1. (a) How do the male gametes that are present in the pollen grains reach the site mentioned by you in part (a) to cause double fertilization ?

    (b) Draw a longitudinal sectional view of a typical anatropus ovule to show the site where double fertilization. takes place. Lable any four major parts of the ovule.

    Ans. (a) The pollen tube releases the male gametes into the cytoplasm of the synergid. The fusion of three haploid nuclei it is termed triple fusion and in it is two types of fusions, syngamy and triple fusion lake is an embryo sac the phenomenon is termed double fertilisation.

    (b) In Embryo sac double fertilization takes place.

    a typical anatropus ovule

    Q. 2. (a) Describe the stages in embryo development in a dicot plant.

    (b) Draw a schematic labelled diagram of a fertilised embryo sac of an Angiosperm.

    Ans. (a) Embryo develops at the micropylar end of the embryo sac where the zygote is situated. Most zygotes divide only after certain amount of endosperm is formed. This adaptation provide assured nutrition to the dezeloping embryo the large stages of Embryo development (embryogeny) are similar in monocotyledons and dicotyledone.

    The stages of embryogeny in a dicotyledonous embryo. The zygote gives rise to the preembryo and subsequently to the globular, heart-shaped and mature embryo.

    In the dicot stem the embryo consists of an embryonal axis, two cotyledons, Plumule, radical or root tip. The root tip is covered with root cap.

     a fertilised embryo sac of an Angiosperm

    Structure of  a fertilised embryo sac of an Angiosperm

    megaspore tetrad and micropyler end

    A diagrammatic representation of the mature embryo sac

    Part of the ovule showing a large megaspore mother cell, a dyad and a tetrad of megaspores; (b) 2/ 4 and 8-nucleate stages of embryo sac and a mature embryo sac; (c) A diagrammatic representation of the mature embryo sac.

    DISCLAIMER: JPL and its affiliates shall have no liability for any views, thoughts and comments expressed on this article.

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