Exam-ready answers to all 21 exercises of Chapter 2, Human Reproduction (NCERT Class 12 Biology, 2026-27): male and female reproductive systems, seminiferous tubules, spermatogenesis and its hormones, spermiogenesis and spermiation, semen, oogenesis, the Graafian follicle, the menstrual cycle, parturition, sex determination, and twins. All 21 questions are answered, with the key answer highlighted.
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) (e) Zygote is ______ (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 ______.
Solution
(a) sexually
(b) viviparous
(c) internal
(d) haploid
(e) diploid
(f) ovulation
(g) luteinising hormone (LH)
(h) fertilisation (syngamy)
(i) the ampullary region of the fallopian tube (oviduct)
Draw the pelvic view and label the testes in the scrotum, epididymis, vas deferens, seminal vesicle, ejaculatory duct, prostate, Cowper's gland, urethra and penis.
Draw a labelled diagram of female reproductive system.
Solution
The female reproductive system has a pair of ovaries, a pair of oviducts (fallopian tubes), the uterus, cervix, vagina and the external genitalia, with mammary glands as accessory organs.
Labels to show: ovary, fimbriae, infundibulum, ampulla, isthmus (parts of the fallopian tube), uterus (with perimetrium, myometrium, endometrium), uterine cavity, cervix, cervical canal, vagina.
Draw the front view and label the ovaries, fallopian tubes (fimbriae, infundibulum, ampulla, isthmus), uterus with its three layers, cervix and vagina.
Each testis has about 250 lobules, and each lobule has one to three highly coiled seminiferous tubules, where sperms are produced.
The tubule is lined on its inside by two kinds of cells: male germ cells (spermatogonia), which divide by meiosis to form sperms, and Sertoli cells, which nourish the germ cells.
Outside the tubules, in the interstitial spaces, lie blood vessels and interstitial (Leydig) cells, which secrete androgens (testosterone), and some immunocompetent cells.
A coiled tubule lined by germ cells (spermatogonia → sperms) and Sertoli cells (nourishment); Leydig cells lie outside, secreting androgens.
Spermiogenesis: the transformation of spermatids into spermatozoa (sperms).
Spermiation: the release of sperms from the seminiferous tubules (after spermiogenesis, the sperm heads are embedded in the Sertoli cells and are then released).
Spermiogenesis: spermatids → sperms. Spermiation: release of sperms from the seminiferous tubules.
Seminal plasma is secreted by the seminal vesicles, prostate and bulbourethral glands. It is rich in fructose, calcium and certain enzymes; the bulbourethral glands also add mucus that lubricates the penis.
Fructose, calcium and certain enzymes (plus mucus).
What are the major functions of male accessory ducts and glands?
Solution
Accessory ducts (rete testis, vasa efferentia, epididymis and vas deferens) store and transport sperms from the testis to the outside through the urethra. Sperms also mature in the epididymis.
Accessory glands (seminal vesicles, prostate and bulbourethral glands) secrete seminal plasma, which nourishes and activates the sperms and provides a fluid medium; the bulbourethral secretion also lubricates the penis.
Ducts store and carry sperms; glands secrete seminal plasma, which nourishes and carries sperms and lubricates the penis.
What is oogenesis? Give a brief account of oogenesis.
Solution
Oogenesis is the formation of a mature female gamete (ovum) in the ovary. It begins during embryonic development.
Millions of oogonia (egg mother cells) form in each foetal ovary; no more are formed after birth.
They enter meiosis I and stop at prophase I as primary oocytes, each surrounded by granulosa cells (a primary follicle). Many follicles degenerate; about 60,000–80,000 remain at puberty.
Follicles grow into secondary and then tertiary follicles (with a fluid-filled cavity, the antrum).
In the tertiary follicle, the primary oocyte completes meiosis I, forming a large secondary oocyte and a tiny first polar body (unequal division).
The tertiary follicle becomes the mature Graafian follicle, which ruptures at ovulation to release the secondary oocyte (ovum).
Meiosis II is completed only after a sperm enters, forming the ovum and a second polar body.
Oogonia → primary oocytes (arrested in prophase I) in follicles → secondary oocyte and first polar body (meiosis I) in the Graafian follicle → released at ovulation; meiosis II completes after sperm entry.
Draw a labelled diagram of a section through ovary.
Solution
The section shows follicles at different stages in the stroma.
Labels to show: germinal epithelium, primary follicle, secondary follicle, tertiary follicle (with antrum), Graafian follicle, ovum (secondary oocyte), ovulation (released ovum), corpus luteum, corpus albicans, blood vessels, stroma.
Show the follicles in sequence (primary → secondary → tertiary → Graafian), ovulation, the corpus luteum and corpus albicans, with the germinal epithelium and stroma.
Identify True/False statements. Correct each false statement to make it true. (a) Androgens are produced by Sertoli cells. (b) Spermatozoa get nutrition from Sertoli cells. (c) Leydig cells are found in ovary. (d) Leydig cells synthesise androgens. (e) Oogenesis takes place in corpus luteum. (f) Menstrual cycle ceases during pregnancy. (g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
Solution
(a) False. Androgens are produced by Leydig cells.
(b) True.
(c) False. Leydig cells are found in the testis.
(d) True.
(e) False. Oogenesis takes place in the ovary (in the follicles).
(f) True.
(g) True.
True: (b), (d), (f), (g). False: (a) Leydig cells make androgens; (c) Leydig cells are in the testis; (e) oogenesis is in the ovary.
What is menstrual cycle? Which hormones regulate menstrual cycle?
Solution
The menstrual cycle is the cyclical series of changes in the ovary and the uterus of primate females, repeated about every 28–29 days. It begins at puberty (menarche) and ends at menopause. It has four phases: menstrual (days 1–5, shedding of the endometrium), follicular (follicles grow and the endometrium regenerates), ovulatory (about day 14, LH surge causes ovulation) and luteal (corpus luteum secretes progesterone).
Hormones: pituitary FSH and LH (under the control of hypothalamic GnRH) and ovarian oestrogen and progesterone.
A ~28-day cycle of changes in the ovary and uterus (menstrual, follicular, ovulatory, luteal phases), regulated by FSH, LH, oestrogen and progesterone.
What is parturition? Which hormones are involved in induction of parturition?
Solution
Parturition is the process of delivery (birth) of the foetus at the end of pregnancy, by vigorous contractions of the uterus.
It is induced by a neuroendocrine mechanism. Signals from the fully developed foetus and placenta cause mild uterine contractions (the foetal ejection reflex), which trigger the release of oxytocin from the maternal pituitary. Oxytocin causes strong contractions of the uterine muscles. Other hormones involved are cortisol (from the foetus), oestrogens and relaxin (which softens the pelvic ligaments).
Birth of the baby by uterine contractions; mainly oxytocin, with cortisol, oestrogens and relaxin.
In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
Solution
Sex is decided by the sperm, not the egg. A woman has XX chromosomes, so all her eggs carry X. A man has XY, so half his sperms carry X and half carry Y. If an X-carrying sperm fertilises the egg, the child is a girl (XX); if a Y-carrying sperm fertilises it, the child is a boy (XY). So the sex of the baby depends on the father's sperm, and blaming the mother is wrong.
The father's sperm (X or Y) decides the child's sex; all eggs carry X.
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?
Solution
Normally one egg is released each month (by one of the two ovaries).
Identical twins:one egg, because identical twins develop from a single fertilised egg whose early embryo splits into two.
Fraternal twins: yes, the answer changes: two eggs are released and fertilised by two different sperms.
One egg per month; identical twins: one egg; fraternal twins: two eggs.
How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Solution
At least six eggs: dogs are polyovulatory, and normally each puppy develops from a separate fertilised egg. (More may have been released, as some eggs may not be fertilised.)
At least six.
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For NCERT Biology Class 12 (2026-27 edition) - all 13 chapters, CBSE board 2027
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