Q. 25

(a) Draw the embr

Answer :

a)



b)The nucleus of the megaspore divides mitotically to form two nuclei, that move on the opposite poles and forms 2 nucleate embryo sac.


c)The development of endosperm in coconut takes place by the following steps:


1.The nucleus of the primary endosperm gets divided bby free nuclear division.


2.The nucleus first divides into 2 and so on till 128 nuclei are formed.


3.By the process of cytokinesis (the process of physical cell division into daughter cells) it finally converts into cellular endosperm.


Function of endosperm:


It provides nutrition to the growing embryo.


OR


Menstrual cycle is the natural changes that occur in a female reproductive system. It marks the beginning of the female reproductive phase.


Menstrual cycle has two main cycles:


1.Ovarian cycle


2. Uterine cycle


OVARIAN CYCLE:


It mainly includes three phases Follicular Phase, Ovulation and Luteal phase.


1. Follicular Phase:


In this phase FSH (Follicle Stimulating Hormone) causes the ovarian follicle to mature causes the release of an egg.


2.Ovulation:


In this phase mature egg is released from the ovarian follicle into the oviduct.


This takes place when LH (Lutenising Hormone) is released, this causes the follicular wall to get weaken and causes the release of mature egg from it.


3.Luteal Phase:


a)It is the final stage of the ovarian cycle.


b)During this phase LH and FSH causes the remaining part of the c)follicle to convert into Corpus Luteum which in turn releases progesterone.


d)Progesterone in turn decreases LH and FSH which in turn is required by corpus luteum.


UTERINE CYCLE:


1.Menstruation:


a) It is the first phase of the uterine cycle.


b)In this phase bleeding takes place.


2.Proliferative Phase:


During this phase level increases causing the uterus lining to proliferate (grow).


3.Secretory Phase:


a)It is the final phase of the uterine cycle.


b)Corpus luteum produces progesterone which makes the endometrium receptive of blastocysts.



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