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NCERT Solutions · Class 12 Biology Human Reproduction

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Exercises 2.1–2.10 (part 1 of 2)

  1. Exercise 2.1

    Fill in the blanks:
    (a)
    Humans reproduce _____________ (asexually/sexually)
    (b)
    Humans are _____________ (oviparous, viviparous, ovoviviparous)
    (c)
    Fertilisation is _____________ in humans (external/internal)
    (d)
    Male and female gametes are _____________ (diploid/haploid) (f) The process of release of ovum from a mature follicle is called _____________ (g) Ovulation is induced by a hormone called _____________ (h) The fusion of male and female gametes is called _____________ (i) Fertilisation takes place in _____________ (j) Zygote divides to form _____________which is implanted in uterus. (k) The structure which provides vascular connection between foetus and uterus is called _____________

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    (a) sexually
    (b) viviparous
    (c) internal
    (d) haploid
    (e) diploid
    (f) ovulation
    (g) luteinising hormone (LH) — the mid-cycle LH surge ruptures the Graafian follicle
    (h) fertilisation
    (i) the ampullary region of the fallopian tube (oviduct)
    (j) blastocyst
    (k) placenta

  2. Exercise 2.2

    Draw a labelled diagram of male reproductive system.

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    ncert_XII_Biology_fig_2-2
    Draw a sectional view of the male pelvis showing the testes, the accessory ducts, the accessory glands and the penis in one continuous path.
    Show the paired testes hanging outside the abdominal cavity inside a pouch, the scrotum; open one testis to show its testicular lobules with coiled seminiferous tubules.
    From the tubules, lead a line into the rete testis, then out through the vasa efferentia into the epididymis, drawn as a coiled body along the posterior surface of the testis.
    Continue the epididymis into the vas deferens, which ascends into the abdomen and loops over the urinary bladder.
    Show the duct of the seminal vesicle joining the vas deferens; the common duct beyond that junction is the ejaculatory duct, opening into the urethra.
    Draw the prostate encircling the urethra just below the bladder, and the paired bulbourethral glands below the prostate.
    Carry the urethra through the penis to its external opening, the urethral meatus; mark the enlarged tip as the glans penis and the loose fold of skin over it as the foreskin.
    Labels required: scrotum, testis, testicular lobule, seminiferous tubules, rete testis, vasa efferentia, epididymis, vas deferens, seminal vesicle, ejaculatory duct, urinary bladder, prostate, bulbourethral gland, urethra, penis, glans penis, foreskin, urethral meatus.

  3. Exercise 2.3

    Draw a labelled diagram of female reproductive system.

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    ncert_XII_Biology_fig_2-3
    Draw a sectional view of the female pelvis showing a pair of ovaries, the oviducts, the uterus, the cervix, the vagina and the external genitalia.
    Place the paired ovaries, one on each side of the lower abdomen, each about $\displaystyle 2$–$\displaystyle 4$ cm long and tied to the pelvic wall and uterus by ligaments.
    From each ovary run a fallopian tube (oviduct), $\displaystyle 10$–$\displaystyle 12$ cm long, drawn in three parts: the funnel-shaped infundibulum nearest the ovary, its edge fringed with finger-like fimbriae; then the wider ampulla; then the narrow isthmus joining the uterus.
    Draw the single uterus (womb) as an inverted pear, and cut its wall open to show the three layers from outside in — the thin membranous perimetrium, the thick smooth-muscle myometrium, and the inner glandular endometrium lining the uterine cavity.
    Narrow the uterus below into the cervix, label its cavity the cervical canal, and open it into the vagina (cervical canal plus vagina form the birth canal).
    Label the external genitalia: mons pubis, labia majora, labia minora, hymen and clitoris, with the urethral opening between the clitoris and the vaginal opening.
    Labels required: ovary, ligament, infundibulum, fimbriae, ampulla, isthmus, uterus, perimetrium, myometrium, endometrium, cervix, cervical canal, vagina, mons pubis, labia majora, labia minora, hymen, clitoris.

  4. Exercise 2.4

    Write two major functions each of testis and ovary.

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    Testis
    Produces the male gametes — sperms — by spermatogenesis inside the seminiferous tubules.
    Its Leydig (interstitial) cells synthesise and secrete the testicular hormones, the androgens, which drive spermatogenesis and maintain the male accessory ducts and glands.
    Ovary
    Produces the female gamete, the ovum, and releases it at ovulation.
    Secretes the ovarian hormones — steroid hormones such as estrogen (from the growing follicles) and progesterone (from the corpus luteum).

  5. Exercise 2.5

    Describe the structure of a seminiferous tubule.

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    The seminiferous tubule is the highly coiled tubule inside the testis in which sperms are produced.
    Each testis has about $\displaystyle 250$ compartments called testicular lobules, and each lobule contains one to three such tubules.
    Each tubule is lined on its inside by two types of cells — the male germ cells (spermatogonia) and the Sertoli cells.
    The male germ cells undergo meiotic divisions that finally lead to sperm formation.
    The Sertoli cells provide nutrition to the germ cells; the sperm heads stay embedded in them until spermiation.
    The regions outside the tubules, the interstitial spaces, contain small blood vessels and the interstitial cells (Leydig cells), which secrete androgens; immunologically competent cells are also present there.
    The seminiferous tubules of the testis open into the vasa efferentia through the rete testis.

  6. Exercise 2.6

    What is spermatogenesis? Briefly describe the process of spermatogenesis.

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    Spermatogenesis is the process by which the immature male germ cells (spermatogonia) in the testis produce sperms; it begins at puberty.
    The spermatogonia lie on the inside wall of the seminiferous tubules and multiply by mitotic division to increase in number; each is diploid with $\displaystyle 46$ chromosomes.
    Some of the spermatogonia, called primary spermatocytes, periodically undergo meiosis.
    A primary spermatocyte completes the first meiotic (reduction) division to give two equal, haploid secondary spermatocytes, with $\displaystyle 23$ chromosomes each.
    Each secondary spermatocyte undergoes the second meiotic division, so that four equal, haploid spermatids are formed.
    The spermatids are transformed into spermatozoa (sperms) by spermiogenesis.
    The sperm heads then become embedded in the Sertoli cells and are finally released from the seminiferous tubule by spermiation.

  7. Exercise 2.7

    Name the hormones involved in regulation of spermatogenesis.

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    Gonadotropin releasing hormone (GnRH) — a hypothalamic hormone whose secretion rises sharply at puberty and acts on the anterior pituitary.
    Luteinising hormone (LH) — a pituitary gonadotropin that acts on the Leydig cells and stimulates synthesis and secretion of androgens.
    Follicle stimulating hormone (FSH) — the other pituitary gonadotropin; it acts on the Sertoli cells and stimulates secretion of factors that help spermiogenesis.
    Androgens — secreted by the Leydig cells, they in turn stimulate the process of spermatogenesis itself.

  8. Exercise 2.8

    Define spermiogenesis and spermiation.

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    Spermiogenesis is the transformation of the spermatids into spermatozoa (sperms).
    Spermiation is the release of the sperms from the seminiferous tubules; until then their heads lie embedded in the Sertoli cells.

  9. Exercise 2.9

    Draw a labelled diagram of sperm.

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    Draw the sperm as a long, slender cell in four parts placed end to end: head, neck, middle piece and tail, with a plasma membrane enveloping the whole body.
    Draw the head as an oval containing an elongated haploid nucleus, and cap its anterior portion with the acrosome, a cap-like structure filled with enzymes that help fertilisation of the ovum.
    Show a short neck immediately behind the head.
    Draw the middle piece as a slightly thicker segment packed with mitochondria, which produce the energy for movement of the tail.
    Draw the tail as the longest part, a fine whip-like process that gives the sperm its motility.
    Labels required: plasma membrane, acrosome, nucleus, head, neck, middle piece, mitochondria, tail.

  10. Exercise 2.10

    What are the major components of seminal plasma?

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    Seminal plasma is rich in fructose, calcium and certain enzymes.
    It is made of the secretions of the male accessory glands — the paired seminal vesicles, the prostate and the paired bulbourethral glands; the bulbourethral secretion also lubricates the penis.
    Seminal plasma together with the sperms constitutes the semen.