Microsporogenesis and Pollen Grain Structure
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Microsporogenesis and Pollen Grain Structure

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Questions and Answers

What type of pollination brings genetically different types of pollen grains to the stigma?

  • Self-pollination
  • Water pollination
  • Cross-pollination (correct)
  • Wind pollination

    • Majority of plants use abiotic agents for pollination.

    False

    What are the two types of abiotic agents used for pollination?

    Wind and water

    Wind-pollinated flowers often have a ______ ovule in each ovary.

    <p>single</p> Signup and view all the answers

    Match the following types of pollination with their characteristics:

    <p>Wind pollination = Requires light and non-sticky pollen grains Water pollination = Rare and limited to few genera Cross-pollination = Brings genetically different pollen grains Self-pollination = Pollen comes from the same plant</p> Signup and view all the answers

    Which of the following plants is a familiar example of wind-pollination?

    <p>Corn</p> Signup and view all the answers

    Pollination by water is more common than pollination by wind.

    <p>False</p> Signup and view all the answers

    What type of flowers produce an enormous amount of pollen compared to the number of ovules?

    <p>Wind-pollinated flowers</p> Signup and view all the answers

    What is the process of formation of microspores from a pollen mother cell called?

    <p>Microsporogenesis</p> Signup and view all the answers

    Pollen grains have a soft outer layer that protects them from environmental factors.

    <p>False</p> Signup and view all the answers

    What are the two cells found in a mature pollen grain?

    <p>Vegetative cell and generative cell</p> Signup and view all the answers

    The outer layer of the pollen grain, made up of sporopollenin, is called the ______.

    <p>exine</p> Signup and view all the answers

    Match the parts of the pollen grain with their descriptions:

    <p>Exine = Hard outer layer made of sporopollenin Intine = Thin inner wall made of cellulose and pectin Germ pore = Apertures where sporopollenin is absent Cytoplasm = Surrounds the plasma membrane of the pollen grain</p> Signup and view all the answers

    What happens to microspores as the anthers mature?

    <p>They dissociate and develop into pollen grains.</p> Signup and view all the answers

    Pollen grains are always uniformly shaped across species.

    <p>False</p> Signup and view all the answers

    Pollen grains typically measure about ______ micrometers in diameter.

    <p>25-50</p> Signup and view all the answers

    Which of the following are characteristics of pollen/nectar robbers?

    <p>They consume pollen or nectar.</p> Signup and view all the answers

    Self-incompatibility is a mechanism that promotes self-pollination.

    <p>False</p> Signup and view all the answers

    What is the primary effect of inbreeding depression in flowering plants?

    <p>Reduced viability and fitness of offspring.</p> Signup and view all the answers

    Pollen is released before the stigma becomes receptive or the stigma becomes receptive much before the release of pollen is known as __________.

    <p>dichogamy</p> Signup and view all the answers

    Match the following devices to their function in preventing self-pollination:

    <p>Dichogamy = Pollen release and stigma receptivity not synchronized Unisexual flowers = Flowers of only one sex on each plant Dioecy = Male and female flowers on different plants Self-incompatibility = Inhibition of self-pollen fertilization</p> Signup and view all the answers

    What method do some flowering plants use to prevent autogamy by placing anthers and stigma at different positions?

    <p>Heterostyly</p> Signup and view all the answers

    In monoecious plants, male and female flowers are present on separate plants.

    <p>False</p> Signup and view all the answers

    Describe the role of the pistil in pollen-pistil interaction.

    <p>The pistil recognizes whether the pollen is compatible or incompatible.</p> Signup and view all the answers

    What is the process called when both syngamy and triple fusion occur in flowering plants?

    <p>Double fertilisation</p> Signup and view all the answers

    The development of the embryo occurs before the development of the endosperm.

    <p>False</p> Signup and view all the answers

    What happens to the central cell after triple fusion?

    <p>It becomes the primary endosperm cell (PEC).</p> Signup and view all the answers

    The term for the fusion of one male gamete with the egg cell nucleus is __________.

    <p>syngamy</p> Signup and view all the answers

    What is bagged before the flowers open during the pollination process?

    <p>The female flower buds</p> Signup and view all the answers

    Match the following processes to their descriptions:

    <p>Syngamy = Fusion of male gamete with egg cell nucleus Triple Fusion = Fusion of male gamete with two polar nuclei Primary Endosperm Cell (PEC) = Develops into endosperm Zygote = Develops into embryo</p> Signup and view all the answers

    Emasculation is necessary when the female parent produces unisexual flowers.

    <p>False</p> Signup and view all the answers

    What is the main role of the primary endosperm nucleus (PEN)?

    <p>To provide nutrition to the developing embryo.</p> Signup and view all the answers

    What is polyembryony?

    <p>The occurrence of more than one embryo in a seed</p> Signup and view all the answers

    Hybrid seeds maintain their characteristics when grown from collected seeds.

    <p>False</p> Signup and view all the answers

    What is the primary function of the androecium in flowers?

    <p>It represents the male reproductive organs.</p> Signup and view all the answers

    The __________ develops inside the microsporangia and matures into pollen grains.

    <p>microspores</p> Signup and view all the answers

    Match the following parts of the flower with their functions:

    <p>Androecium = Male reproductive organs Gynoecium = Female reproductive organs Anther = Pollen production Pollen grains = Male gametophytes</p> Signup and view all the answers

    What is a significant benefit of apomixis in hybrid seed production?

    <p>It ensures consistent traits in the next generation.</p> Signup and view all the answers

    Pollen grains consist of a single-layered wall.

    <p>False</p> Signup and view all the answers

    What surrounds the microsporangium in a typical anther?

    <p>Four wall layers: epidermis, endothecium, middle layers, and tapetum.</p> Signup and view all the answers

    Study Notes

    Microsporogenesis

    • During microsporogenesis, pollen mother cells (PMCs) undergo meiosis to form microspores.
    • Four microspores form a microspore tetrad.
    • Microspores dissociate as the anther matures, developing into pollen grains.
    • Each microsporangium produces thousands of pollen grains.
    • The pollen grain is the male gametophyte.

    Pollen Grain Structure

    • Pollen grains are typically spherical, measuring 25-50 micrometers in diameter.
    • The outer layer of the pollen grain is called the exine, composed of sporopollenin.
    • Sporopollenin is highly resistant to degradation and can survive extreme conditions.
    • The exine has apertures called germ pores, where sporopollenin is absent.
    • The inner wall of the pollen grain is called the intine, made up of cellulose and pectin.
    • A mature pollen grain contains two cells:
      • The vegetative cell: larger, contains food reserves, and has a large nucleus.
      • The generative cell: smaller, will divide to form sperm cells.

    Pollination

    • Pollination is the transfer of pollen from the anther to the stigma.
    • Different pollination methods exist:
      • Wind Pollination: Common in grasses and other wind-pollinated plants.
        • Pollen is light and non-sticky for easy wind dispersal.
        • Stamens are often exposed and stigmas are feathery, trapping windborne pollen.
      • Water Pollination: Rare in flowering plants, limited to a few genera.
        • Pollen is released into water to reach the stigma.
      • Animal Pollination: The most common form in plants.
        • Animals like insects, birds, mammals can act as pollinators.
        • Flowers often have adaptations for attracting pollinators, such as colors, scents, and nectar.

    Outbreeding Devices

    • Outbreeding devices are mechanisms that promote cross-pollination and discourage self-pollination.
    • These mechanisms help prevent inbreeding depression.
    • Outbreeding devices include:
      • Asynchronous Maturation of Anther and Stigma: Pollen is released before the stigma is receptive or vice versa.
      • Spatial Separation of Anther and Stigma: Anther and stigma are positioned differently in the flower, preventing self-pollination.
      • Self-Incompatibility: A genetic mechanism where the pollen from the same plant or flower cannot fertilize the ovules, blocking pollen germination or pollen tube growth.
      • Unisexual Flowers:
        • Monoecious: Both male and female flowers present on the same plant (e.g., castor, maize).
        • Dioecious: Male and female flowers are on separate plants (e.g., papaya), preventing both autogamy and geitonogamy.

    Pollen-Pistil Interaction

    • The pistil can recognize compatible pollen from the same species and incompatible pollen from other species or the same plant.
    • Only compatible pollen will germinate and grow a pollen tube towards the ovule.

    Double Fertilization

    • Double fertilization is a unique event in flowering plants.
    • After pollination, two male gametes travel through the pollen tube.
    • Syngamy: One male gamete fuses with the egg cell to form the diploid zygote.
    • Triple Fusion: The other male gamete fuses with the two polar nuclei in the central cell, forming the triploid primary endosperm nucleus (PEN).
    • The fusion of the three haploid nuclei is called triple fusion.

    Post-Fertilization: Endosperm Development

    • Endosperm development often precedes embryo development.
    • The primary endosperm cell (PEC) divides repeatedly to form the triploid endosperm tissue, providing nourishment to the developing embryo.

    Post-Fertilization: Embryo Development

    • The zygote divides mitotically to form an embryo, which develops into a young plant.

    Polyembryony

    • Polyembryony is the occurrence of more than one embryo in a seed.
    • It can occur when nucellar cells surrounding the embryo sac divide and form embryos.
    • Example: Citrus and Mango.

    Apomixis

    • Apomixis is a form of asexual reproduction in flowering plants where seeds are produced without fertilization.
    • Apomictic embryos are genetically identical to the parent plant and can be called clones.
    • Apomixis has potential in agriculture for maintaining desirable hybrid characters in plants.

    Summary of Sexual Reproduction in Flowering Plants:

    • The flower is the reproductive organ in flowering plants, containing the male reproductive organ (androecium) and female reproductive organ (gynoecium).
    • The anther produces pollen grains by a process called microsporogenesis.
    • Pollen grains act as male gametophytes, and they have a resistant outer layer called the exine made of sporopollenin.
    • Pollination is the transfer of pollen to the stigma.
    • There are different pollination mechanisms (wind, water, and animal pollination).
    • Outbreeding devices prevent self-pollination and promote cross-pollination.
    • Double fertilization occurs in flowering plants, involving syngamy and triple fusion.
    • Following fertilization, the zygote develops into an embryo, and the endosperm provides nourishment for the developing embryo.

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    Description

    This quiz covers the process of microsporogenesis, including the formation of microspores and their development into pollen grains. It also delves into the structure of pollen grains, detailing the exine, intine, and the cells within. Test your understanding of these fundamental concepts in plant reproduction.

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