Q.1 Fill in the blanks:
(a) Humans reproduce …………. (asexually/sexually)
(b) Humans are …………. (oviparous/viviparous/ovoviviparous)
(c) Fertilization is …………. in humans (external/internal)
(d) Male and female gametes are …………. (diploid/haploid)
(e) Zygote is …………. (diploid/haploid)
(f) The process of release of ovum from mature follicle is called ………….
(g) Ovulation is induced by a hormone called ………….
(h) The fusion of male and female gametes is called ………….
(i) Fertilization takes place in ………….
(j) Zygote divides to form …………. which is implanted in uterus
(k) The structure which provides vascular connection between foetus and the uterus is called ………….
Ans. Functions of testis: The testis are, in fact, heterocrine structures. The have both exocrine and endocrine regions. The exocrine region includes seminiferous tubules. The latter produce spermatozoa (male gamete). The endocrine region has Leydig cells which secrete male sex hormones, commonly termed androgens.
Functions of ovaries: The ovaries, like the testis, have both an exocrine fucntion (i.e., production of ova)and an endocrine role (i.e., secretion of female sex hormones commonly termed estrogens)
Each testicular lobule has tightly coiled seminiferous tubules which are packed with cells undergoing spermatogenesis (spermatogonia) and Sertoli cells. A germinal epithelium of delicate connective tissue surrounds the seminiferous tubules. The large sustentacular cells that extend from the capsule to the lumen of the seminiferous tubule are called Sertoli cells. They serve to support, nourish and regulate the development of cells undergoing spermatogenesis. The endocrine cells present in the space between seminiferous tubules are termed as interstitial cells of Leydig. They serve to secrete androgen, testosterone.
Ans. Spermatogenesis is the process of the production of sperms from the immature germ cells in males. It takes place in seminiferous tubules present inside the testes. During spermatogenesis, a diploid spermatogonium (male germ cell) increases its size to form a diploid primary spermatocyte. This diploid primary spermatocyte undergoes first meiotic division (meiosis I), which is a reductional division to form two equal haploid secondary spermatocytes. Each secondary spermatocyte then undergoes second meiotic division (meiosis II) to form two equal haploid spermatids. Hence, a diploid spermatogonium produces four haploid spermatids. These spermatids are transformed into spermatozoa (sperm) by the process called spermiogenesis.
Ans. Spermiogenesis: The process involving transformation of spermatids into mature spermatozoa is called spermiogenesis.
Spermiation: the process by which mature spermatids are released from Sertoli cells into the seminiferous tubule lumen prior to their passage to the epididymis is called spermiation.
Ans. Major components of seminal plasma are:
(i) Secretions of accessory sex glands (ii) Mucus (iii) Spermatozoa
The seminal plasma is rich in fructose, ascorbic acid, citrate, prostaglandins calcium and certain enzymes.
Ans. Major functions of male accessory ducts are:
(i) aid in sperm transport (ii) temporary storage of spermatozoa
Major functions of male accessory glands are:
Male accessory glands secrete various secretions that constitute the part of seminal plasma. These secretions are rich in fructose, ascorbic acid, citrate, prostaglandins and some enzymes. These secretions nourish and activate the spermatozoa to swim.
Q.15 Name the functions of the following:
(a) Corpus luteum (b) Endometrium (c) Acrosome (d) Sperm tail (e) Fimbriae
Ans. (a) Corpus luteum: Its major function is the secretion of progesterone hormone. If fertilization occurs, the progesterone secretion, through feedback control, inhibits the secretion of FSH-RH from hypothalamus. This prevents the onset of next menstrual cycle.
(b) Endometrium: It is the inner layer of uterus. It undergoes cyclic changes during different phases of menstrual cycle in anticipation for the implantation of blastocyst.
(c) Acrosome: It is the anterior part of head of sperm. It contains hydrolytic enzymes and is used to contact and penetrate the egg in fertilization.
(d) Sperm tail: It helps in the movement of spermatozoon in a fluid medium.
(e) Fimbraie: The motile, finger-like processes present on the margins of infundibulum (broad, funnel-shape proximal part of fallopian tubes) are termed fimbraie. These bear cilia which beat towards the ostium to direct the egg into the infundibulum.
Q.16 Identify true/false statements. Correct each false statement to make it true.
(a) Androgens are produced by Sertoli cells. (True/False)
(b) Spermatozoa get nutrition from Sertoli cells.(True/False)
(c) Leydig cells are found in ovary. (True/False)
(d) Leydig cells synthesize androgens. (True/False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(f) Menstrual cycle ceases pregnancy. (True/False)
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)
Ans. (a) False (b) True (c) False (d) True (e) False (f) True (g) True
Corrected false statements: (a) Androgens are produced by leydig cells
(c) Leydig cells are found in testis
(e) Oogenesis takes places in ovaries
Ans. Menstrual cycle occurs only in primates (monkeys, apes and man). It involves cyclic activity of gamete formation in females that takes about 28 days and involves changes in the structure and function of the entire reproductive system.
The hormones that regulate menstrual cycle are : (i) Follicle stimulating hormone (FSH) (ii) Luteinizing hormone (LH) (iii) Estradiol (iv) Prolactin (v) Progesterone
Ans. Human ovary produces only one egg in a month.
As the identical twins are monozygotic and are produced from two parts of same zygote so only one egg was released from the ovary.
As the fraternal twins are dizygotic and are produced from two different zygotes which is possible only if two eggs are released from the ovaries in a month.