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Questions and Answers
Which of the following mechanisms is a form of asexual reproduction that mimics sexual reproduction?
In which type of endosperm do the cells undergo successive nuclear divisions to give free nuclei?
What is the function of the reserve food materials in the cells of triploid endosperm?
Which part of the embryo develops at the micropylar end of the embryo sac?
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What is the characteristic of the zygote in dicotyledons?
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Which part of the seed is formed inside fruits?
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What is the function of the root cap in monocotyledons?
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What is the characteristic of the embryo axis in dicotyledons?
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Which of the following is a characteristic of polyembryony?
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What is the adaptation that provides assured nutrition to the developing embryo?
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Study Notes
Sexual Reproduction in Flowering Plants
Structure of Anther and Microsporangium
- The androecium consists of a whorl of stamens, representing the male reproductive organ.
- The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe.
- Each microsporangium appears near circular in cross-section, surrounded by four wall layers.
Microsporogenesis and Pollen Grain
- Microsporogenesis is the process of formation of microspores from PMC (Pollen Mother Cell).
- As anthers mature and dehydrate, microspores dissociate from each other and develop into pollen grains.
- A pollen grain has a prominent two-layered wall - exine and intine, and represents the male gametophyte.
Pollen Grain Structure
- The exine is the outer hard layer, made of sporopollenin, with germ pores where sporopollenin is absent.
- The intine is the inner wall layer, thin and continuous, made of cellulose and pectin.
- The vegetative cell is larger, has abundant food reserves, and a large irregularly shaped nucleus.
- The generative cell is smaller, floats in the cytoplasm of the vegetative cell, and has dense cytoplasm and a nucleus.
Pollination
- Pollination is the transfer of pollen shed from an anther to the stigma of a pistil.
- Types of pollination: autogamy (within the same flower), geitonogamy (between flowers of the same plant), and xenogamy (between different plants).
Agents of Pollination
- Abiotic agents: wind and water.
- Wind pollination requires light, non-sticky pollen and is common in grasses.
- Water pollination is rare, limited to 30 genera of monocotyledons, and is more common among abiotic pollinations.
Pistil, Megasporangium (Ovule), and Embryo Sac
- The gynoecium represents the female reproductive part.
- The pistil consists of stigma, style, and ovary, containing the ovule.
Pollen-Pistil Interaction
- The ability of the pistil to recognize the pollen, followed by its acceptance or rejection, is a dynamic process mediated by chemical components.
- Compatible pollination leads to pollen tube growth, and the contents of the pollen grain move into the pollen tube.
Double Fertilisation
- One male gamete fuses with the egg to form the diploid zygote (syngamy).
- The other male gamete fuses with the polar nuclei of the central cell to produce the triploid primary endosperm nucleus (triple fusion).
Post-Fertilisation: Structure and Events
- Endosperm development precedes embryo development.
- The central cell after triple fusion becomes the primary endosperm cell (PEC) and develops into endosperm.
- Embryo develops at the micropylar end of the embryo sac, where the zygote is situated.
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Description
This quiz covers the basics of sexual reproduction in flowering plants, including the structures and events involved in pre-fertilization.
