question_answer

Describe the function of two pituitary and two ovarian hormones in the menstrual cycle of human female.

Or

Explain by giving reasons for the following.

(i) Most zygotes in angiosperms divide only after certain amount of endosperm is formed.

(ii) Groundnut seeds are exalbuminous and castor seeds are albuminuous.

(iii) Micropyle remains as a small pore in the seed coat of a seed.

(iv) Integuments of an ovule harden and the water content is highly reduced as the seed matures.

(v) Apple and cashewnuts are called false fruits.

Answer:

The menstrual cycle is controlled by rhythmic synthesis and release of ovarian hormones under feedback control from the hormones of anterior pituitary. These are discussed below

(i) Pituitary hormones The gonadotroph cells of anterior pituitary secrete FSH and LH in females. Their role in menstrual cycle are

(a) Follicle Stimulating Hormone (FSH) It is secreted during the follicular phase of the cycle and is responsible for follicular phase of the cycle and is responsible for follicular development on induction of LH receptors on granulosa cells of the ovary.

(b) Luteinising Hormone (LH) Its primary function is to stimulate the formation of corpus luteum and secretion of estradiol and progesterone from ovary.

(ii) Ovarian hormones Ovary secrets the following hormones under the effect of FSH and LH.

(a) Oestrogen It influences proliferation of the uterine endometrium to prepare for implantation of the fertilised oocyte. Ovulation occurs and the ruptured follicles develop into corpus luteum. Secretion of LH is inhibited.

(b) Progesterone secreted from corpus luteum under LH influence/maintains endometrium for implantation. It rising levels inhibits LH.

Or

(i) Zygote in angiosperms mostly divides only after a certain amount of endosperm is formed as an adaptation strategy to assure nutrition for the developing embryo.

(ii) (a) Groundnut seeds are exalbuminous because the developing embryo utilises the endosperm completely. So, there is no endosperm left in the seed.

(b) Castor seeds are albuminous because endosperm is not completely used up by the developing embryo. There is some amount of endosperm left in the seeds always.

(iii) Micro Pyle allows entry of water and oxygen during seed germination.

(iv) During unfavorable conditions, seeds become dormant. The loss of water reduces the metabolic activity of seeds and hardens the integuments.

(v) The fruit derived from ovary along with other accessory floral parts is called false fruit. In apple and cashewnuts thalamus contributes in the fruit formation. So, they are not called as true fruits.