explain the development of monospiric and disporic embryo
Answers
Answer:
The formation of the female gametophyte from a single functional megaspore is called as monosporic development.
The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles. This forms a two-nucleate embryo sac.
Two more sequential mitotic nuclear divisions result in the formation of four-nucleate and eight-nucleate stages of embryo sac.
These mitotic divisions are free nuclear type in which karyokinesis is not followed immediately by cytokinesis.
After the eight-nucleate stage, the walls are laid down leading to the organization of the typical female gametophyte. Six of eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.
A typical angiosperm embryo sac at maturity is eight nucleate and seven cells. Three cells lie at micropylar end forming egg apparatus. Three ends at chalazal end called as antipodal cells. A single large central cell which has two polar nuclei.
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Answer:
There are three types of embryo sacs, monosporic, bisporic and tetrasporic. ... In the monosporic embryo sac, out of the four megaspores, one megaspore at the chalazal end takes part in the formation of the embryo sac. ... In the bisporic embryo sac, two megaspores take part in the formation of the embryo sac.
Explanation:
The formation of the female gametophyte from a single functional megaspore is called as monosporic development.
The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles. This forms a two-nucleate embryo sac.
Two more sequential mitotic nuclear divisions result in the formation of four-nucleate and eight-nucleate stages of embryo sac.
These mitotic divisions are free nuclear type in which karyokinesis is not followed immediately by cytokinesis.
After the eight-nucleate stage, the walls are laid down leading to the organization of the typical female gametophyte. Six of eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.
A typical angiosperm embryo sac at maturity is eight nucleate and seven cells. Three cells lie at micropylar end forming egg apparatus. Three ends at chalazal end called as antipodal cells. A single large central cell which has two polar nuclei.
Bisporic development results from failure of cytokinesis after meiosis II. As a result, the megaspore tetrad is comprised of two cells each containing two megaspore nuclei. The embryo sac develops from one of these dyad cells by two rounds of mitotic division and the other dyad cell is suppressed.
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