Human Reproduction Exercises

HUMAN REPRODUCTION

EXERCISE SOLUTIONS

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Question 1: Fill in the blanks:

(a) Humans reproduce sexually. (asexually/sexually)

(b) Humans are viviparous. (oviparous/viviparous/ovoviviparous)

(d) Male and female gametes are haploid. (diploid/haploid)

(e) Zygote is diploid. (diploid/haploid)

(f) The process of release of the ovum from a mature follicle is called ovulation.

(g) Ovulation is induced by a hormone called the luteinizing hormone (LH).

(h) The fusion of the male and the female gametes is called fertilization.

(i) Fertilization takes place in the ampulla of oviduct.

(j) The zygote divides to form blastocyst, which is implanted in uterus.

(k) The structure which provides vascular connection between the fetus and uterus

is called placenta.

Question 2: Draw a labeled diagram of male reproductive system.

Question 3: Draw a labeled diagram of male reproductive system.

Question 4: Write two major functions each of testis and ovary.

Ans: Functions of the Testis:

(a) Production of sperms or spermatozoa by the process of spermatogenesis.

(b) Production of male sex hormone, called androgen/testosterone, by Leydig cells.

Functions of the ovary:

(a) They produce female gametes called ova by the process of oogenesis.

(b) Production of female sex hormones, estrogen and progesterone. Which are responsible feminine characters.

Question 5: Describe the structure of a seminiferous tubule.

Ans: Seminiferous tubules are highly coiled structure located in the testicular lobule help in the production of sperms. Each seminiferous tubule is lined by germinal epithelium. It is lined on its inner side by two types of cells namely spermatogonia and Sertoli cells respectively.

Spermatogonia are male germ cells which produce primary spermatocytes by meiotic divisions. Primary spermatocytes undergo further meiotic division to form secondary spermatocytes and finally, spermatids. Spermatids later metamorphoses into male gametes called spermatozoa.

Sertoli cells are known as nurse cells of the testes as they provide nourishment to the germ cells. There are large polygonal cells known as interstitial cells or Leydig cells just adjacent to seminiferous tubules. These cells secrete the male hormone called testosterone.

Question 6: What is spermatogenesis? Briefly describe the process of spermatogenesis.

Ans: The process of formation of spermatozoa (sperms) from diploid spermatogonia is called spermatogenesis. 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.

Question 7: Name the hormones involved in regulation of spermatogenesis.

Ans: Gonadotropin releasing hormones (GnRH) secreted from hypothalamus stimulates anterior pituitary gland and stimulates secretion of two gonadotropins - Follicle-stimulating hormones (FSH) and luteinizing hormones (LH). These hormones are involved in the regulation of the process of spermatogenesis.

FSH acts on Sertoli cells, whereas LH acts on Leydig cells of the testis to produce androgen and stimulates the process of spermatogenesis.

Question 8: Define spermiogenesis and spermiation.

Ans: Spermiogenesis: It is the process involving transformation of spermatids into matured spermatozoa or sperms.

Spermiation: It is the process in which sperm heads become embedded in the Sertoli cells and are finally released from seminiferous tubules.

Question 9: Draw a labeled diagram of sperm.

Question 10: What are the major components of seminal plasma?

Ans: The major components of the seminal plasma in the male reproductive system are mucus, spermatozoa, and various secretions of accessory glands. The seminal plasma is rich in fructose, calcium, ascorbic acid, and certain enzymes. It provides nourishment and protection to sperms.

Question 11: What are the major functions of male accessory ducts and glands?

Ans: The male accessory ducts include rete testis, vasa efferentia, epididymis, and vas deferens. They play an important role in the transport and temporary storage of sperms.

Male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands. Secretion of these glands constitute the seminal plasma which is rich in fructose, calcium and some enzymes. The secretion of bulbourethral glands help in the lubrication of the penis.

Question 12: What is oogenesis? Give a brief account of oogenesis.

Answer Oogenesis is the process of the formation of a mature haploid ovum from the diploid oogonia in females. It takes place in the ovaries.

During oogenesis, a diploid oogonium or egg mother cell increases in size and gets transformed into a diploid primary oocyte.

This diploid primary oocyte undergoes first meiotic division i.e., meiosis I or reductional division to form two unequal haploid cells. The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte.

This secondary oocyte undergoes second meiotic division i.e., meiosis II or equational division and gives rise to a second polar body and an ovum.

Hence, in the process of oogenesis, a diploid oogonium produces a single haploid ovum while two or three polar bodies are produced.

Question 13: Draw a labeled diagram of section through ovary?

Question 14: Draw a labeled diagram of a Graafian follicle.

Question 15: Name the functions of the following.

(a) Corpus luteum

(b) Endometrium

(d) Sperm tail

(e) Fimbriae

Ans:

(a) Corpus luteum − Corpus luteum is formed from the ruptured Grafiaan follicle. Acts as an endocrine gland and secretes progesterone hormone during the luteal phase of the menstrual cycle. It is essential for maintenance of the endometrium of the uterus.

(b) Endometrium − It is the innermost lining of the uterus, richly supplied with blood vessels responsible for nutrition and development of the foetus. It undergoes cyclic changes during menstrual cycle. Implantation of blastocyst takes place here

(c) Acrosome − It is a cap-like structure present at the tip of sperm. It contains hydrolytic enzymes (hyaluronidase enzyme) that help in dissolving membranes of the ovum during fertilisation.

(d) Sperm tail − It is the longest region of the sperm that facilitates the movement of the sperm inside the female reproductive tract.

(e) Fimbriae − They are finger-like projections present at the opening of oviduct. They help in the collection of the ovum (after ovulation), which is facilitated by the beating of the cilia.

Question 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)

(d) Leydig cells synthesise androgens. (True/False)

(e) Oogenesis takes place in corpus luteum. (True/False)

(f) Menstrual cycle ceases during pregnancy. (True/False)

(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)

Answer:

(a) False - Androgens are produced by Leydig cells or interstitial cells.

(b) True - Spermatozoa get nutrition from Sertoli cells.

(d) True - Leydig cells synthesise androgens.

(e) False - Oogenesis takes place in the ovary.

(f) True - Menstrual cycle ceases during pregnancy.

(g) True - Presence or absence of the hymen is not a reliable indicator of virginity or sexual experience.

Question 17: What is menstrual cycle? Which hormones regulate menstrual cycle?

Ans: The menstrual cycle is a rhythmic series of physiological changes that occur in the female reproductive tract in primates. It is repeated at an average interval of about 28/29 days.

During menstruation the soft tissues present in the endometrium wall of the uterus breakdown and oozes pit along with blood and unfertilised egg through the vagina. This is known as menses.

The follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone are the various hormones that regulate the menstrual cycle.

The level of FSH and LH secreted from the anterior pituitary gland increases during the follicular phase. FSH secreted under the influence of RH (releasing hormone) from the hypothalamus stimulates the conversion of a primary follicle into a graafian follicle.

The level of LH increases gradually leading to the growth of follicle and secretion of estrogen. Estrogen inhibits the secretion of FSH and stimulates the secretion of luteinizing hormone. It also causes the thickening of the uterine endometrium. The increased level of LH causes the rupturing of the Graafian follicle and release the ovum into the fallopian tube (Ovulation). The ruptured Graafian follicle changes to corpus luteum and starts secreting progesterone hormone during the luteal phase.

Progesterone hormone helps in the maintenance and preparation of endometrium for the implantation of the embryo. High levels of progesterone hormone in the blood decrease the secretion of LH and FSH, therefore inhibiting further ovulation.

Question 18: What is parturition? Which hormones are involved in induction of parturition?

Ans: The act of expelling the full-term foetus from the mother’s uterus at the end of gestation period is called parturition. The hormones involved in this process are oxytocin and relaxin.

Oxytocin helps in contraction of smooth muscles of myometrium of the uterus, which directs the full-term foetus towards the birth canal.

Relaxin hormone causes relaxation of the pelvic ligaments and prepares the uterus for child birth.

Question 19: In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?

Answer It is not correct to blame women for giving birth to daughters.

All human beings have 23 pairs of chromosomes. Human males have 22 pairs of autosomes and contain one or two types of sex chromosome. They are either X or Y. On the contrary, human females have 22 pairs of autosomes and contain only the X sex chromosome.

The sex of an individual is determined by the type of the male gamete (X or Y), which fuses with the X chromosome of the female. If the fertilizing sperm is X, then the baby will be a girl and if it is Y, then the baby will be a boy.

Question 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: An ovary releases an egg every month. When two babies are produced in succession, they are called twins. Generally, twins are produced from a single egg by the separation of early blastomeres resulting from the first zygotic cleavage. As a result, the young ones formed will have the same genetic make- up and are thus, called identical twins.

If the twins born are fraternal, then they would have developed from two separate eggs. This happens when two eggs (one from each ovary) are released at the same time and get fertilized by two separate sperms. Hence, the young ones developed will have separate genes and are therefore, called non-identical or fraternal twins.

Question 21: How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?

Answer Six eggs release by the ovary of a female dog if it gave birth to sex puppies.

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IMPORTANT QUESTIONS

What is implantation? (1-mark)
Draw a neat labelled, diagrammatic sectional view of female reproductive system. (5-marks)
During which month of pregnancy the first movement of foetus is observed? (1-mark)
Draw a neat labelled diagram of human male reproductive system. (5-marks)
Define menopause. (1 mark)
Assign the functions for the following structures. a. Acrosome b. Endometrium c. Corpus luteus. (3 marks)
With the graphical representation explain the role of hormones in menstrual cycle. (5-marks)
What is menarche? (1-mark)
Name three hormones produces in pregnant women. (3-marks)
Name the hormones secreted by Leydig cells and corpus luteum (2-marks)
Name any two hormones secreted by ovary. (2-marks)
Give a schematic representation of spermatogenesis. (5-marks)
Mention the functions of placenta. (3-marks)
Draw a neat labeled diagram of human sperm. (5-marks)
Explain the process of oogenesis with schematic representation. (5-marks)