Biology Human Reproduction Chapter 3 – Exercise

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. (a) sexually (b) viviparous (c) internal (d) haploid (e) diploid (f) ovulation (g) Luteinizing hormone (LH) (h) fertilization (i) ampullary-isithmic function of fallopian tube (j) blastocyst (k) placenta
Q.2 Draw a labelled diagram of male reproductive system.

Ans.

male-reproductive

Q.3 Draw a labelled diagram of female reproductive system.

Ans.

female-reproductive

Q.4 Write two major functions each of testis and ovary.

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)

Q.5 Describe the structure of a seminiferous tubule.

Ans.

seminiferous

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.

Q.6 What is spermatogenesis? Briefly describe the process of spermatogenesis.

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.

spermatogenesis

Q.7 Name the hormones involved in regulation of spermatogenesis.
Ans. Follicle stimulating hormone (FSH) and Interstitial cells stimulating hormone (ICSH)
Q.8 Define spermiogenesis and spermiation.

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.

Q.9 Draw a labelled diagram of sperm.

Ans.

sperm

Q.10 What are the major components of seminal plasma?

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.

Q.11 What are the major functions of male accessory ducts and glands?

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.12 What is oogenesis? Give a brief account of oogenesis.
Ans. The process of formation of mature female gametes is called oogenesis. It starts during embryonic development stage when millions of oogonia (gamete mother cells) are formed in each fetal ovary. The gamete mother cells start division and enter into prophase-I of meiotic division and get temporally arrested. At this stage, they are called primary oocytes. Each primary oocyte gets surrounded by a layer of granulosa cell than it is called the primary follicle. The primary follicle gets surrounded by more layers of granulosa cells called secondary follicle that transform into tertiary follicle that contains a fluid filled cavity called antrum. The tertiary follicles further change into the mature follicle called Graafian follicle, which rapture to release secondary oocytes (ovum) from the ovary by the process of ovulation.

oogenesis

Q.13 Draw a labelled diagram of section through ovary.
Ans. section-through
Q.14 Draw a labelled diagram of Graafian follicle.

Ans.

graapian

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

Q.17 What is menstrual cycle? Which hormones regulate menstrual cycle?

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

Q.18 What is parturition? Which hormones are involved in induction of parturition?
Ans. Parturition is the act of expelling the full-term youngone from the mother’s uterus at the end of gestation. The hormones involved in the induction of parturition are oxytocin and relaxing.
Q.19 In our society, the women are often blamed for giving birth to daughters. Can you explain why this is not correct.
Ans. Females produces only one type of gametes, each carrying X chromosome. However, male produces two types of gametes, 50% carrying X chromosome and 50% carrying Y chromosome. Sex of the child, in human beings, is determined depending upon which kind of male gamete fertilizes the female gamete. If male gamete carrying X chromosome fertilizes the female gamete, the child will be female. However, if male gamete carrying Y chromosome fertilizes the female gamete, the child will be male. Therefore, women should not be blamed for giving birth to daughters.
Q.20 How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?

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.

Q.21 How many eggs do you think were released by the ovary of a female dog which gave birth to six puppies?
Ans. Six eggs

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