Q. 24

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Answer :

Pollination- is the transfer of pollen grains from anther to the stigma of pistil.

Wind pollinated plants often posses well exposed stamens , so that the pollens are easily dispersed.


Are large often-feathery stigma to easily trap air-borne pollen grains.


Wind pollinated flowers after have single ovule in each ovary and numerous flowers packed into an inflorescence.


Example of an aquatic plant pollinated by wind is Water hyacinth and lily.


Example of land plant pollinated by wind grasses , the cereal crops, many trees and others. All release billions of pollen grains into the air and only some reach the target.


OR


(a): Menstruation: is the regular discharge of blood and mucous tissue from the inner lining of the uterus through the vagina.


The reproductive cycle starting from the one menstruation till the next one in the female primates is called Menstrual cycle .


The 1st menstruation begins at puberty and is called Menarche.


In human female, menstruation is repeated at an average interval of 28/29 days.


Phases of menstrual cycle:


1. Menstrual phase


2. Follicular phase


3. Luteal phase.


(i): Menstrual phase- it starts from day 1 and lasts for 3 to 5 days.


The endometrial lining of the uterus breaks along with the blood vessels which forms a red fluid and result in menstrual flow.


It occurs when the ovum is not fertilised.


(ii): Follicular phase- occurs between day 6 and fourteen of the menstrual cycle.


in this, the primary follicles mature into the Graffian follicle.


Endometrium regenerates through proliferation.


Both LH and FSH attain a peak level in the middle of the cycle about 14th day.


Rapid secretion of LH leading to its maximum level during the mid-cycle called LH-surge induces rupture ion graffian follicle and thereby the release of ovum known as Ovulation.


(iii): Luteal phase: occurs between day 16 till 28 days.


In this phase, the ruptured part of graffian follicle transforms into yellow body called Corpus luteum.


Corpus luteum secretes large amount of progesterone hormone which maintains the endometrium for implantation of the fertilised ovum.


During pregnancy all events of menstrual cycle stops and there is no menstruation.


In the absence of fertilisation, the corpus luteum degenerates hence causes disintegration of the endometrium leading to menstruation and a new cycle begins.


In humans, menstrual cycle ceases around the age of 50 and is called Menopause.



(b): The hormones that influences menstrual cycle are FSH(follicle stimulating hormone) and LH( Lutenizing hormone).


FSH stimulates follicular growth in ovaries, also stimulates oestrogen secretion.


LH surge causes ovulation, it results in formation of a corpus luteum.


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