Q. 24

(a) Plan an exper

Answer :

(a) Artificial hybridisation can be opted to ensure that the seeds are formed only from the desired sets of pollen grains. The steps taken are the following -



If there is unisexual female flower involved then there is no need for emasculation.


(b) Importance of artificial hybridisation –


• Helps to produce good yield.


• Helps to produce commercially superior varieties.


• Helps to produce varieties with desired characters.


OR


In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.



i. The cycle begins with the menstrual phase followed by the follicular phase. In the follicular phase, the primary follicles mature into the Graafian follicle and simultaneously the endometrium of uterus regenerates. These changes are caused due to the change in levels of pituitary and ovarian hormones. During this phase, the levels of LH and FSH increase gradually. It causes follicular development which causes secretion of estrogens.


ii. Both LH and FSH attain peak level during the middle of the cycle (14th day). Rapid secretion of LH leads to its peak level at about 14th day called the LH surge. This induces the Graafian follicle to rupture and thereby release of ovum. This is ovulatory phase.


iii. The next phase is luteal phase. During this phase, the remaining parts of luteal phase Graafian follicle transform as the corpus luteum which secretes large amounts of progesterone. It is essential for maintenance of the endometrium.


iv. In the absence of fertilisation, the corpus luteum degenerates which causes disintegration of endometrium. This leads to a new cycle.


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