Q. 295.0( 1 Vote )

The following is

Answer :

(i) Figure 'F' illustrates ovulation.


The stage of oogenesis that it represents is the ovulatory stage.


(ii) The ovarian hormone and the pituitary hormone that have caused the above mentioned event are Progesterone (Ovarian hormone) and Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH) - pituitary hormone.


(iii) The changes that occur in the uterus simultaneously in anticipation is that the endometrium lining of the uterus gets thickened as well as there is a increase in blood supply to the endometrium.


(iv) 'C' represents the secondary follicle while 'H' represents the corpus luteum.


Difference between the two is as follows:


a) The secondary follicle has the theca layer while the corpus luteum does not have it.


b) Layer of granulosa cells are present in the secondary follicle but absent in the corpus luteum.


(v) Labelled sketch of the structure of a human ovum prior to fertilization is as follows -



OR


(a) The megaspore mother cell develop into 7-celled, 8 nucleate embryo sac in an angiosperm in the following way:


i) The nucleus of the functional megaspore divides mitotically forming two nuclei that move to the opposite poles, forming the 2-nucleate embryo sac.


ii) Two more mitotic nuclear divisions result in the formation of 4-nucleate and then 8-nucleate stages of the embryo sac.


iii) After the 8-nucleate stage, cell walls are laid down leading to the formation of the typical female gametophyte or embryo sac.


The diagram below shows the nucleate stages of the embryo sac.



(b) Located in the nucellus, is the embryo sac or known as the female gametophyte.


An ovule generally has a single embryo sac formed from a megaspore.


Labelled diagram of a mature embryo sac is as follows:



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