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Questions and Answers
What structure is responsible for the identification and classification of pollen grains?
What structure is responsible for the identification and classification of pollen grains?
Which component of the pollen grain is resistant to chemical and biological decomposition?
Which component of the pollen grain is resistant to chemical and biological decomposition?
What is the binomial classification of pollen grains based on germ pores?
What is the binomial classification of pollen grains based on germ pores?
What is the functional role of the vegetative cell in a pollen grain?
What is the functional role of the vegetative cell in a pollen grain?
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Which structure in the pistil receives pollen grains?
Which structure in the pistil receives pollen grains?
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Which of the following describes the structure of the intine in the pollen grain?
Which of the following describes the structure of the intine in the pollen grain?
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What is the first developmental stage of the male gametophyte within the pollen grain?
What is the first developmental stage of the male gametophyte within the pollen grain?
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What type of cells form male gametes in the pollen grain while still within the anther?
What type of cells form male gametes in the pollen grain while still within the anther?
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Where are germ pores found in pollen grains?
Where are germ pores found in pollen grains?
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What happens to the generative cell after pollen has landed on the stigma when it is shed at the two-celled stage?
What happens to the generative cell after pollen has landed on the stigma when it is shed at the two-celled stage?
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Which of the following contributes to the composition of the vegetative cell's cytoplasm?
Which of the following contributes to the composition of the vegetative cell's cytoplasm?
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What is the study of pollen called?
What is the study of pollen called?
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What is the duration of pollen viability in terms of time?
What is the duration of pollen viability in terms of time?
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Which allergen is identified as a significant source of pollen allergies in India?
Which allergen is identified as a significant source of pollen allergies in India?
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What is the function of pollen creams?
What is the function of pollen creams?
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The funiculus connects which two structures in the ovule?
The funiculus connects which two structures in the ovule?
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What characteristics define the endothecium layer of the anther?
What characteristics define the endothecium layer of the anther?
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Which of the following describes the structure of the tapetum?
Which of the following describes the structure of the tapetum?
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What occurs during microsporogenesis?
What occurs during microsporogenesis?
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How are tetrads classified during microsporogenesis?
How are tetrads classified during microsporogenesis?
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What is the function of the outer wall, known as the exine, in pollen grains?
What is the function of the outer wall, known as the exine, in pollen grains?
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What is true about the arrangement of nuclei in a tetrad after meiosis?
What is true about the arrangement of nuclei in a tetrad after meiosis?
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Which type of cytokinesis occurs in some microspores during tetrad formation?
Which type of cytokinesis occurs in some microspores during tetrad formation?
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What happens to the anther when it matures?
What happens to the anther when it matures?
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What structure develops from the integumentary cells in the castor bean at the microplylar region?
What structure develops from the integumentary cells in the castor bean at the microplylar region?
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How many megaspores are produced from one megaspore mother cell during megasporogenesis?
How many megaspores are produced from one megaspore mother cell during megasporogenesis?
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Which stage follows the formation of a two-nucleate embryo sac during embryo sac development?
Which stage follows the formation of a two-nucleate embryo sac during embryo sac development?
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Which cells are found at the micropylar end of the embryo sac?
Which cells are found at the micropylar end of the embryo sac?
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What is the role of the filiform apparatus found in the synergids?
What is the role of the filiform apparatus found in the synergids?
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What typically occurs to the three megaspores that do not become the functional megaspore?
What typically occurs to the three megaspores that do not become the functional megaspore?
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How many cells and nuclei are present in a typical angiosperm embryo sac at maturity?
How many cells and nuclei are present in a typical angiosperm embryo sac at maturity?
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Which part of the integument serves as the outer protective layer?
Which part of the integument serves as the outer protective layer?
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What is self-pollination primarily characterized by?
What is self-pollination primarily characterized by?
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Which of the following is NOT a type of self-pollination?
Which of the following is NOT a type of self-pollination?
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What is one disadvantage of self-pollination?
What is one disadvantage of self-pollination?
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Which of the following correctly defines cross-pollination?
Which of the following correctly defines cross-pollination?
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What is dicliny in terms of pollination?
What is dicliny in terms of pollination?
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What defines protandry in pollination?
What defines protandry in pollination?
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Which of the following is an adaptation for autogamy?
Which of the following is an adaptation for autogamy?
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What is the main benefit of self-pollination?
What is the main benefit of self-pollination?
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Which of the following best describes self-sterility in plants?
Which of the following best describes self-sterility in plants?
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What does prepotency refer to in plant reproduction?
What does prepotency refer to in plant reproduction?
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In which type of heterostyly do plants have two distinct types of flowers?
In which type of heterostyly do plants have two distinct types of flowers?
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What is the main advantage of cross-pollination in plants?
What is the main advantage of cross-pollination in plants?
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What is the role of the germ tube after pollen grains land on the stigma?
What is the role of the germ tube after pollen grains land on the stigma?
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What defines porogamy in the context of pollen tube entry into ovules?
What defines porogamy in the context of pollen tube entry into ovules?
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Which of the following is NOT a disadvantage of cross-pollination?
Which of the following is NOT a disadvantage of cross-pollination?
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What occurs immediately after pollination in the pollen grain?
What occurs immediately after pollination in the pollen grain?
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Study Notes
Sexual Reproduction in Flowering Plants
- Sexual reproduction involves the fusion of male and female gametes from two parents.
- Flowers are the primary reproductive structures in flowering plants.
- Sporophylls are the reproductive organs within the flowers, classified into:
- Microsporophylls (stamens)
- Megasporophylls (carpels)
- A carpel contains:
- Ovule
- Style
- Stigma
- Stamens consist of:
- Filament
- Anther
- Connective
- Sexual reproduction in flowering plants has three steps:
- Pre-fertilization
- Double fertilization
- Post-fertilization
Pre-Fertilization: Structure and Events
- Pollen grain formation
- Embryo sac formation
Pollen Grain Formation
- Stamen: The male reproductive unit, composed of an anther and a filament.
- Anther: Bilobed, with each lobe containing four pollen sacs (microsporangia).
- Pollen sacs contain numerous pollen grains.
- Anther wall: Composed of four layers of cells.
- Anther dehiscence: Release of pollen grains through slits.
- Anther development: Begins with homogeneous meristematic cells, forming four lobes and four layers of archesporial cells.
- Archesporial cells: Divide to form primary parietal cells and primary sporogenous cells.
- Parietal cells: Form the anther wall.
- Sporogenous cells: Form microspores or pollen mother cells (PMCs).
- Tapetum: Innermost wall layer that feeds the growing spores.
- Microspores development (Microsporogenesis):
- PMCs undergo meiosis, forming tetrahedral tetrads.
- Cytokinesis: Sequential or simultaneous.
- Tetrads: Classified into five types (tetrahedral, isobilateral, decussate, T-shaped, linear).
- Cell wall formation after meiosis I and II.
- Pollen grains: Male gametophyte's first cells
- Anther dehiscence: Pollen liberation
- Pollen grains: Vary in shape and size. Typically 25-30 micrometers in diameter. Have a double-layered exterior wall (sporoderm):
- Exine: Outer layer, thick, sporopollenin-composed.
- Intine: Inner layer, thin, composed of pectin and cellulose.
- Microspores: Present as pollinium in some families (Asclepiadaceae and Orchidaceae).
Pollen Viability
- Pollen viability: Time pollen grains remain functional; estimated by temperature and humidity.
- Pollen grains are viable for 30 minutes.
Pollen Allergy
- Pollen grains cause various respiratory disorders (asthma, bronchitis), allergies.
- Carrot grass is a significant allergen.
Female Reproductive Unit (Pistil)
- The female reproductive unit is the pistil (gynoecium).
- Pistil/carpel: Composed of stigma, style, and ovary.
- Stigma: Part that receives pollen grains.
- Style: Connects stigma to the ovary.
- Ovary: Swollen base containing one or more ovules (megasporangium surrounded by integuments).
- Ovule develops into a seed after fertilization
- Funiculus: Stalk that attaches ovule to placenta.
- Hilum: Point where funicle attaches to the ovule.
- Nucellus: Parenchymatous tissue equivalent to the megasporangium.
- Micropyle: Pore at the opposite end of the integuments from the chalaza.
- integuments: layers surrounding the nucellus.
- Endothelium may nourish the developing embryo sac.
- Cuticle: Layer covering the integuments and nucellus.
Megasporogenesis
- Megasporogenesis: Process of producing megaspores from the megaspore mother cell (MMC).
- MMC is located in the nucellar micropylar region of the ovule.
- MMC undergoes meiosis, producing four megaspores.
- In most flowering plants, only one megaspore survives, developing into the female gametophyte (embryo sac).
Embryo Sac Formation
- Mitosis in the functional megaspore forms a two-nucleate embryo sac.
- Subsequent mitotic divisions result in a four-nucleate, then eight-nucleate embryo sac.
- Cell walls develop after the eight-nucleate stage, establishing a multicellular structure (female gametophyte).
- Embryo sac: Contains cells like the egg apparatus (egg cell + synergids), central cell (two polar nuclei), and antipodal cells.
Double Fertilization
- Fusion of two male gametes with different structures within the embryo sac.
- One sperm fertilizes the egg cell, forming the zygote (2n).
- The other sperm fuses with the two polar nuclei, forming the triploid primary endosperm nucleus (3n).
- Results in the formation of the diploid zygote and the triploid endosperm.
Post Fertilization
- Endosperm: Nutritive tissue resulting from the triple fusion (3n) that nourishes the embryo.
- Endosperm development follows a variety of patterns.
- It may be either cellular or nuclear or a combination both.
- Endosperm nourishes the developing embryo and seedlings.
Importance of Seeds
- Evolutionary success: Encloses the embryo to prevent harm and provide food reserves.
- Seed dispersal: Colonization and propagation to new areas.
- Genetic variation: Adaptability to diverse environments.
- Agriculture and civilization: Crucial for food production and human development.
Seed Viability
- The period during which seeds retain the ability to germinate.
- Affected by genetic and environmental factors (humidity, temperature).
- Viability may last from a few days to over a century.
Apomixis
- Asexual reproduction that mimics sexual reproduction in seed plants, forming seeds without fertilization.
- Controlled by genes, resulting in genetically identical offspring (clones).
Polyembryony
- Presence of more than one embryo in a seed.
- May be true polyembryony (fertilization of more than one egg) or false polyembryony (embryos formed from parts of the ovule other than the egg).
- Examples: Citrus, groundnut.
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Description
This quiz covers the key concepts of sexual reproduction in flowering plants, focusing on the structures and events involved, including the reproductive organs, fertilization processes, and pollen grain formation. Test your knowledge on the roles of male and female gametes and the intricacies of flowers in plant reproduction.