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प्रश्न
Sketch and label stages in the development of the angiospermic female gametophyte from the functional megaspore.
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उत्तर
In angiosperms, the female gametophyte, also known as the embryo sac, develops from the functional megaspore through a process called megagametogenesis.
Stages of development:
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Functional megaspore (Haploid): Out of the four megaspores formed after meiosis of the megaspore mother cell, only one (usually the chalazal one) remains functional, while the other three degenerate.
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Two-nucleate stage: The nucleus of the functional megaspore divides mitotically to form two haploid nuclei, which migrate to opposite poles of the cell.
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Four-nucleate stage: Both nuclei divide again mitotically to form four nuclei, two at each pole.
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Eight-nucleate stage (Mature embryo sac): A final mitotic division produces eight nuclei, four at each pole.
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The egg apparatus is made up of three nuclei at the micropylar end: one egg cell and two synergids.
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Three nuclei at the chalazal end make up antipodal cells.
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Two nuclei move to the center and fuse to form the secondary (polar) nucleus.
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Thus, the mature embryo sac becomes seven-celled and eight-nucleate.
Development of Female Gametophyte (Embryo Sac)
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संबंधित प्रश्न
In a flowering plant a microspore mother cell produces four male gametophytes, while a megaspore mother cell forms only one female gametophyte. Explain.
Read the statement and answer the questions that follow.
A flower of brinjal has 520 ovules in its ovary. However, it produces a fruit with only 480 viable seeds.
(a) What could have prevented the rest of the 40 ovules from maturing into viable seeds? Explain giving a reason.
(b) Describe the development of a dicot embryo in a viable seed.
(c) Why certain angiospermic seed albuminous while others are exalbuminous? Explain.
A capsicum flower has 240 ovules in its ovary. But, it produces a fruit with only 180 viable seeds.
Define Racemose inflorescence
Name the terminal stage of ageing in the life cycle of plants.
Explain the events upto double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm.
Sketch and label ‘structure of a pea flower’.
Science of cultivation, breeding, marketing and arrangement of flowers is called ______.
Pollen grains are well preserved as fossils because of the presence of ______
Which of the following statement is incorrect?
