Explain the ovarian and uterine events that occur during a menstrual cycle in a human female, under the influence of Pituitary and Ovarian hormones respectively.
OR

(a) Why does endosperm development precede embryo development in angiosperm seeds? State the role of endosperm in mature albuminous seeds.

(b) Describe with the help of three labelled diagrams the different embryonic stages that include mature embryo of dicot plants.

1. Menstrual cycle is the reproductive cycle in female primates which begins when puberty (12-16 years) is reached. The beginning of menstrual cycle is known as Menarche and the end of menstrual cycle is known as menopause (between 45-50 years).

2. In a female primate menstrual cycle takes place once in every 28-29 days.

3. The cycle includes uterine and ovarian phases.

Events in a Menstrual cycle:

OVARIAN CYCLE:

The ovarian cycle consists of Follicular phase, Ovulation and Luteal phase

FOLLICULAR PHASE:

1. It is the initial phase in the ovarian cycle. In this phase as the follicle stimulating hormone level increases, ovarian follicles mature and get ready to release an egg.

OVULATION:

1. This is the second phase.In this phase mature egg is released from the follicle into the oviduct.

2. In this phase estradiol decreases the production of Leutinising Hormone (LH) from the anterior pituitary gland.

3. After the maturation of the egg, estradiol reaches threshold and its effect reverses. Estrogen level also increases the amount of LH which is also known as the LH surge. It starts at day 12 and remains till 48 hours.

LUTEAL PHASE :

1. It is the final stage of the ovarian cycle.In this phase LH ans FSH makes the remaining part of the dominant follicle into Corpus Luteum which releases in turn produces progesterone.

2. Progesterone in turn increases the production of estrogen.

3. The hormones present in the corpus luteum also suppress the production of LH and FSH to maintain the corpus luteum.

4. Consequently the level of FSH and LH fall.

UTERINE CYCLE:

The uterine cycle consists of the Menstrual phase, Secretary phase and proliferative phase.

Menstrual Phase:

1. The menstrual phase lasts for around 3-7 days in which blood flow takes place due to the shedding of the endometrium lining prepared for the fertilised egg.

PROLIFERATIVE PHASE:

1. In this phase estrogen causes the uterus lining to grow.

SECRETARY PHASE:

1. In this phase corpus luteum produces progesterone which makes the endometrium lining thicken.

OR

(a) Function of Endosperm: It is a storage tissue which mainly stores food,starch,proteins and many other nutrients .

Hence, endosperm development precede embryo development in angiosperm seeds because endosperm provides the developing embryo with nutrition and helps in its growth.

(b)

Formation of an Embryo :

1. After the formation of an endosperm embryo starts forming.

2. The zygote divides by mitosis to form pro-embryo.

3. Now, a globular and heart shaped embryo are formed which in turn matures into shoe shaped embryo.

4. In dicots the embryo has two cotyledons and an embryonal axis between both the cotyledons.

5. The portion of embryonal axis above the level of attachment of cotyledons is epicotyl. It contains the pumule (shoot tip).

6. The portion of embryonal axis below the level of attachment of cotyledons is hypocotyl. It consists of the radicle (root tip).

Embryonic stages that include mature embryo of dicot plants are:

1. Fertilised embryo having zygote and Primary Endosperm Nucleus (PEN)

2. Formation of heart shaped and globular embryo.

3. Formation of mature shoe shaped embryo.