Question

a) How does megaspore mother cell develop into 7 celled 8 nucleate embryosac in an angiosperm. Explain with diagram.
b) Mention two outbreeding devices that flowering plant have developed & explain how they help to encourage cross pollination?​

Answer 1

Answer:

The megaspore mother cell produces two nuclei by the mitotic division which moves to opposite poles and forms 2- nucleate embryo sac. Further mitosis produces 4 nucleate and then 8 nucleate stage of the embryo sac. After 8 nucleate stage, the cell wall is laid down and typical embryo sac is formed. Among 8, 6 nuclei are organised into cells, remaining two are in the large central cell. Out of 6, 3 are at the micropylar end, 2 cells are synergids while one is egg cell. Other 3 are at the chalazal base called as antipodal cells. Thus, the angiosperm embryo sac is 8 nucleated and 7 celled

Answer 2

Answer:

megaspore mother cell undergoes meiosis to form 4 megaspores,from which 3 are non functional but 1 is functional.

outbreeding devices 1.dicliny-production of unisexual flowers

                                  2.dicogamy-in some species pollens are released much                

                                     before stigma gets receptive or vice-versa thus

                                     maturation time of stigma and release of pollen are

                                    different.

Explanation: