NCERT Solutions for Class 12 Biology Chapter 2: Human Reproduction (NCERT 2026–27)
These Class 12 Biology Chapter 2 solutions cover Human Reproduction, including the male and female reproductive systems, gametogenesis, the menstrual cycle, fertilisation, implantation, pregnancy, parturition and lactation. Every question from the NCERT Exercises is reproduced verbatim and answered in clear, exam-ready prose for the 2026–27 session.
Class: 12Subject: BiologyChapter: 2Title: Human ReproductionExercises: 21 questionsSession: 2026–27
Chapter 2, Human Reproduction, explains how humans — being sexually reproducing and viviparous — produce offspring. The reproductive events include gametogenesis (sperm formation in males, ovum formation in females), insemination, fertilisation forming a zygote, implantation of the blastocyst, gestation (embryonic development) and parturition (delivery). The chapter describes the male reproductive system (testes, accessory ducts and glands, external genitalia), the female reproductive system (ovaries, oviducts, uterus, vagina, mammary glands), spermatogenesis and oogenesis, the hormonally controlled menstrual cycle, fertilisation and early development, the role of the placenta, and finally parturition and lactation. These events occur after puberty and are controlled by a network of hypothalamic, pituitary and gonadal hormones.
Key Concepts & Terms
Spermatogenesis: formation of haploid sperms from diploid spermatogonia in the seminiferous tubules, beginning at puberty.
Oogenesis: formation of a mature ovum; initiated during embryonic life, arrested at prophase-I, and completed only after fertilisation.
Spermiogenesis: transformation of spermatids into mature spermatozoa (sperms).
Spermiation: release of mature sperms from the seminiferous tubules.
Menstrual cycle: the ~28-day reproductive cycle of female primates, regulated by GnRH, LH, FSH, estrogen and progesterone.
Fertilisation: fusion of a haploid sperm with a haploid ovum in the ampullary region of the fallopian tube, forming a diploid (2n = 46) zygote.
Implantation: attachment and embedding of the blastocyst in the endometrium of the uterus, leading to pregnancy.
Placenta: the structural and functional unit connecting the foetus to the uterine wall; exchanges nutrients/gases and acts as an endocrine organ.
NCERT Exercises — Complete Solutions
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)(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 _____________
ANSWER(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)(j) blastocyst(k) placenta
2. Draw a labelled diagram of male reproductive system.
ANSWERIn the exam draw a neat sectional diagram and label these parts in correct sequence. The male reproductive system consists of a pair of testes lying in the scrotum; inside each testis are seminiferous tubules that open via the rete testis into the vasa efferentia, which lead to the epididymis (along the posterior surface of the testis).The epididymis continues as the vas deferens, which ascends to the abdomen, loops over the urinary bladder, receives a duct from the seminal vesicle, and opens into the urethra as the ejaculatory duct. The accessory glands — paired seminal vesicles, a single prostate gland and paired bulbourethral glands — and the penis (with the glans penis covered by foreskin) complete the diagram.
3. Draw a labelled diagram of female reproductive system.
ANSWERDraw a neat sectional diagram showing a pair of ovaries located on either side of the lower abdomen, each connected to the pelvic wall and uterus by ligaments. From near each ovary extends a fallopian tube (oviduct) with its funnel-shaped infundibulum bearing finger-like fimbriae, then the wider ampulla, and finally the narrow isthmus that joins the uterus.Label the uterus (womb) with its three layers (perimetrium, myometrium, endometrium), the narrow cervix with its cervical canal, the vagina, and the external genitalia. Adding a labelled mammary gland showing mammary lobes, alveoli, tubules and ducts strengthens the answer.
4. Write two major functions each of testis and ovary.
ANSWERTestis: (i) produces the male gametes — sperms — by spermatogenesis in the seminiferous tubules; (ii) secretes male sex hormones (androgens, mainly testosterone) from the Leydig cells, which control male secondary sexual characters and the functioning of accessory ducts and glands.Ovary: (i) produces the female gamete — the ovum — by oogenesis; (ii) secretes female steroid hormones (ovarian hormones such as estrogen and progesterone) that regulate the menstrual cycle, secondary sexual characters and pregnancy.
5. Describe the structure of a seminiferous tubule.
ANSWEREach testis has about 250 compartments called testicular lobules, and each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced. The inner lining of each tubule has two types of cells: male germ cells (spermatogonia), which undergo meiotic divisions to form sperms, and Sertoli cells, which provide nutrition to the developing germ cells.The regions outside the seminiferous tubules, called interstitial spaces, contain small blood vessels and interstitial (Leydig) cells that synthesise and secrete androgens, along with other immunologically competent cells.
6. What is spermatogenesis? Briefly describe the process of spermatogenesis.
ANSWERSpermatogenesis is the process by which immature male germ cells (spermatogonia) produce sperms; it begins at puberty in the seminiferous tubules.The diploid spermatogonia (46 chromosomes) on the inner wall multiply by mitosis. Some, called primary spermatocytes, undergo the first meiotic (reduction) division to form two haploid secondary spermatocytes (23 chromosomes each). These complete the second meiotic division to give four haploid spermatids. The spermatids are then transformed into spermatozoa (sperms) by spermiogenesis, after which they are released by spermiation. The process is initiated by GnRH from the hypothalamus, which stimulates LH and FSH from the pituitary; LH triggers androgen secretion (driving spermatogenesis) while FSH acts on Sertoli cells to aid spermiogenesis.
7. Name the hormones involved in regulation of spermatogenesis.
ANSWERThe hormones are: Gonadotropin Releasing Hormone (GnRH) from the hypothalamus; the two gonadotropins from the anterior pituitary — Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH); and androgens (testosterone) secreted by the Leydig cells. LH stimulates the Leydig cells to secrete androgens that drive spermatogenesis, while FSH acts on Sertoli cells to support spermiogenesis.
8. Define spermiogenesis and spermiation.
ANSWERSpermiogenesis: the process by which the haploid, non-motile spermatids are transformed into mature, motile spermatozoa (sperms).Spermiation: the process by which the mature sperms, after spermiogenesis, are released from the Sertoli cells into the lumen of the seminiferous tubules.
9. Draw a labelled diagram of sperm.
ANSWERDraw the sperm as a microscopic structure with four parts, all enclosed by a plasma membrane: a head containing an elongated haploid nucleus whose anterior portion is covered by a cap-like acrosome (filled with enzymes that help fertilisation); a short neck; a middle piece containing numerous mitochondria that supply energy for movement; and a long tail that provides motility.
10. What are the major components of seminal plasma?
ANSWERSeminal plasma is the fluid formed by secretions of the seminal vesicles, prostate and bulbourethral glands. Its major components are fructose, calcium and certain enzymes. The fructose provides energy for sperms, while other constituents help nourish, activate and transport them. (Seminal plasma together with sperms constitutes the semen.)
11. What are the major functions of male accessory ducts and glands?
ANSWERAccessory ducts (rete testis, vasa efferentia, epididymis, vas deferens): they store and transport the sperms from the testis to the outside through the urethra, and their secretions help in the maturation and motility of sperms.Accessory glands (seminal vesicles, prostate, bulbourethral glands): their secretions form the seminal plasma, rich in fructose, calcium and enzymes, which nourishes and activates the sperms; the bulbourethral secretion also lubricates the penis to facilitate insemination.
12. What is oogenesis? Give a brief account of oogenesis.
ANSWEROogenesis is the process of formation of a mature female gamete (ovum) in the ovary. It is initiated during embryonic development, when a couple of million gamete mother cells (oogonia) form in each fetal ovary; no new oogonia are added after birth.The oogonia enter meiosis but are arrested at prophase-I as primary oocytes, each surrounded by granulosa cells to form a primary follicle. Many degenerate, leaving 60,000–80,000 per ovary at puberty. The follicle develops into a secondary follicle, then a tertiary follicle with a fluid-filled antrum; here the primary oocyte completes meiosis-I unequally to form a large secondary oocyte and a tiny first polar body. The tertiary follicle matures into a Graafian follicle, which ruptures to release the secondary oocyte at ovulation. The second meiotic division is completed only after a sperm enters, forming the haploid ovum and a second polar body.
13. Draw a labelled diagram of a section through ovary.
ANSWERDraw an oval ovary covered by a thin germinal epithelium enclosing the ovarian stroma, which is divided into a peripheral cortex and an inner medulla. In the cortex, show the developmental sequence of follicles: primary follicle → secondary follicle → tertiary follicle (with antrum) → mature Graafian follicle, the released secondary oocyte (ovum) at ovulation, and the corpus luteum formed afterwards. Also label blood vessels in the medulla.
14. Draw a labelled diagram of a Graafian follicle?
ANSWERDraw the mature Graafian follicle and label: the large fluid-filled cavity called the antrum; the surrounding granulosa cells; the two theca layers — inner theca interna and outer theca externa; the secondary oocyte placed eccentrically; the zona pellucida (a new membrane around the oocyte); and the corona radiata (granulosa cells surrounding the oocyte).
15. Name the functions of the following:
(a) Corpus luteum (b) Endometrium(c) Acrosome (d) Sperm tail(e) Fimbriae
ANSWER(a) Corpus luteum: secretes large amounts of progesterone, which maintains the endometrium for implantation of the fertilised ovum and for the other events of pregnancy.(b) Endometrium: the inner glandular lining of the uterus; it undergoes cyclical changes during the menstrual cycle and is necessary for implantation of the blastocyst and nourishment of the embryo.(c) Acrosome: the cap-like anterior structure of the sperm head, filled with enzymes that help the sperm penetrate the zona pellucida and plasma membrane of the ovum during fertilisation.(d) Sperm tail: provides motility to the sperm, enabling it to swim towards and reach the ovum for fertilisation.(e) Fimbriae: the finger-like projections at the edge of the infundibulum that help in the collection of the ovum after ovulation.
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 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. Correction: Androgens are produced by the Leydig (interstitial) cells, not Sertoli cells.(b) True. Sertoli cells provide nutrition to the developing germ cells/sperms.(c) False. Correction: Leydig cells are found in the testis (interstitial spaces), not in the ovary.(d) True. Leydig cells synthesise and secrete androgens.(e) False. Correction: Oogenesis takes place in the ovary; the corpus luteum only secretes progesterone.(f) True. During pregnancy all events of the menstrual cycle stop, so there is no menstruation.(g) True. The hymen may be absent or torn for many non-sexual reasons, so it is not a reliable indicator of virginity or sexual experience.
17. What is menstrual cycle? Which hormones regulate menstrual cycle?
ANSWERThe menstrual cycle is the reproductive cycle in female primates (monkeys, apes and humans), repeated at an average interval of about 28–29 days. The cycle of events from one menstruation till the next includes the menstrual phase, follicular phase, ovulation and luteal phase; one ovum is released around the middle of each cycle.It is regulated by the pituitary gonadotropins — LH and FSH — and the ovarian hormones — estrogen (secreted by growing follicles) and progesterone (secreted by the corpus luteum). The mid-cycle LH surge induces ovulation. (GnRH from the hypothalamus controls the release of LH and FSH.)
18. What is parturition? Which hormones are involved in induction of parturition?
ANSWERParturition is the process of delivery of the fully developed foetus (childbirth) at the end of pregnancy, caused by vigorous contractions of the uterus. It is induced by a complex neuroendocrine mechanism.Signals from the fully developed foetus and the placenta produce mild uterine contractions (the foetal ejection reflex), which trigger release of oxytocin from the maternal pituitary. Oxytocin causes stronger uterine contractions, stimulating still more oxytocin secretion until the baby is expelled. Hormones involved include oxytocin, along with estrogens and cortisol.
19. In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
ANSWERThe sex of a baby is determined by the sperm (father), not the mother. A human female has the sex-chromosome pattern XX, so every ovum carries an X chromosome. A male is XY, so half his sperms carry X and half carry Y.If an X-bearing sperm fertilises the ovum, the zygote is XX — a girl; if a Y-bearing sperm fertilises it, the zygote is XY — a boy. Since the mother can supply only an X chromosome, she cannot influence whether the child is a boy or a girl. Therefore, blaming a woman for giving birth to daughters is scientifically wrong.
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?
ANSWERA human ovary releases one egg (ovum) per month (during ovulation in the menstrual cycle).For identical (monozygotic) twins, only one egg is released; it is fertilised by one sperm to form a single zygote which then splits into two embryos, so a single egg gives both twins.Yes, the answer changes for fraternal (dizygotic) twins: two eggs are released and each is fertilised by a separate sperm, producing two genetically different zygotes.
21. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
ANSWERAssuming each puppy developed from a separate fertilised egg, the ovary (ovaries) of the dog must have released 6 eggs, each fertilised by a different sperm to form 6 zygotes and hence 6 puppies.
Extra Practice Questions
Short Answer Type Questions
Q1. Why is the scrotum located outside the abdominal cavity?
ANSWERThe scrotum keeps the testes at a temperature about 2–2.5°C lower than the normal internal body temperature, which is necessary for normal spermatogenesis (sperm formation).
Q2. Name the three layers of the uterine wall and state which one undergoes cyclical changes.
ANSWERThe three layers are the outer perimetrium, the middle muscular myometrium and the inner glandular endometrium. The endometrium undergoes cyclical changes during the menstrual cycle, while the myometrium contracts strongly during delivery.
Q3. What is the significance of the LH surge during the menstrual cycle?
ANSWERThe rapid rise of LH to its maximum (the LH surge) around the 14th day of the cycle induces rupture of the Graafian follicle and the release of the ovum, i.e. it triggers ovulation.
Q4. What is colostrum and why is it important for a newborn?
ANSWERColostrum is the milk produced during the initial few days of lactation. It contains several antibodies that are absolutely essential to develop resistance (immunity) in the newborn baby.
Q5. List two endocrine functions of the placenta.
ANSWERThe placenta produces hormones such as human chorionic gonadotropin (hCG) and human placental lactogen (hPL), as well as estrogens and progestogens, which help maintain pregnancy and support foetal growth.
Long Answer Type Questions
Q1. Describe the major events of the human menstrual cycle along with the hormonal changes.
ANSWERThe ~28-day menstrual cycle has four phases. (1) Menstrual phase (days 1–5): the endometrium and its blood vessels break down and pass out as menstrual flow, occurring only if the ovum was not fertilised. (2) Follicular (proliferative) phase: primary follicles develop into a mature Graafian follicle and the endometrium regenerates; gonadotropins (LH and FSH) rise gradually, stimulating follicular growth and estrogen secretion. (3) Ovulatory phase: LH and FSH peak around day 14, and the mid-cycle LH surge ruptures the Graafian follicle, releasing the ovum (ovulation). (4) Luteal (secretory) phase: the remaining follicle becomes the corpus luteum, which secretes large amounts of progesterone to maintain the endometrium for possible implantation. If fertilisation does not occur, the corpus luteum degenerates, the endometrium disintegrates, and menstruation begins, marking a new cycle. The cycle operates between menarche and menopause.
Q2. Explain the process of fertilisation and the events leading to implantation.
ANSWERAfter insemination, motile sperms pass through the cervix and uterus and reach the ampulla of the fallopian tube, where the ovum is also transported; fertilisation occurs only if both arrive simultaneously. A sperm contacts the zona pellucida, and acrosomal enzymes help it penetrate the zona pellucida and plasma membrane; this entry blocks additional sperms, ensuring monospermy and inducing completion of the secondary oocyte’s second meiotic division (forming the ovum and a second polar body). The haploid sperm and ovum nuclei fuse to form a diploid zygote (2n = 46). The sex of the baby is decided here, by whether an X- or Y-bearing sperm fertilises the ovum. As the zygote moves through the isthmus by cleavage, it forms 2, 4, 8, 16 blastomeres; the 8–16 celled stage is the morula, which develops into a blastocyst (with an outer trophoblast and inner cell mass). The trophoblast attaches to the endometrium and the blastocyst becomes embedded in it — this is implantation, which leads to pregnancy.
Q3. Compare spermatogenesis and oogenesis with respect to site, timing, number and size of gametes formed.
ANSWERSite: spermatogenesis occurs in the seminiferous tubules of the testis, oogenesis in the ovary. Timing of onset: spermatogenesis begins at puberty and continues even in old age; oogenesis is initiated during embryonic life, arrested at prophase-I, resumes at puberty and ceases at menopause. Completion: spermatogenesis is completed within the testis before release, whereas oogenesis is completed only after a sperm enters the secondary oocyte. Number of gametes per cell: each primary spermatocyte forms four functional sperms, while each primary oocyte forms one functional ovum plus polar bodies (which degenerate). Equality of division: meiosis in spermatogenesis gives equal cells, while in oogenesis the divisions are unequal so the ovum retains most of the cytoplasm. Size: sperms are small and motile; the ovum is large and non-motile.
MCQs & Answer Key
1. In humans, fertilisation normally takes place in the:
(a) uterus (b) ampulla of the fallopian tube (c) ovary (d) cervix
For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.
A-R 1. Assertion: The scrotum keeps the testes at a lower temperature than the body core.
Reason: A temperature 2–2.5°C below body temperature is necessary for normal spermatogenesis.
A-R 2. Assertion: Each primary oocyte ultimately gives rise to a single functional ovum.
Reason: The meiotic divisions in oogenesis are unequal, producing one large ovum and polar bodies that degenerate.
A-R 3. Assertion: The sex of a human baby is determined by the mother.
Reason: All ova produced by the female carry an X chromosome.
A-R 4. Assertion: Menstruation does not occur during pregnancy.
Reason: During pregnancy all events of the menstrual cycle stop.
A-R 5. Assertion: The corpus luteum is essential for maintaining the endometrium after ovulation.
Reason: The corpus luteum secretes large amounts of estrogen that stimulates ovulation.
Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(C).
Common Mistakes to Avoid
Watch out for these
Confusing Sertoli cells (nutrition to germ cells, FSH target) with Leydig cells (secrete androgens, LH target).
Writing that fertilisation occurs in the uterus — it occurs in the ampulla of the fallopian tube.
Saying ovulation is triggered by FSH — it is the LH surge that induces ovulation.
Stating that oogonia are added after birth — no new oogonia form after birth; the primary oocytes are merely arrested.
Claiming each primary oocyte forms four ova — it forms one ovum and polar bodies (unlike spermatogenesis, which gives four sperms).
Mixing up identical (one egg, one sperm) and fraternal (two eggs, two sperms) twins.
How to score full marks in this chapter
Memorise the correct sequence of male ducts (rete testis → vasa efferentia → epididymis → vas deferens) and the follicle sequence (primary → secondary → tertiary → Graafian). For diagram questions (Q2, Q3, Q9, Q13, Q14) draw neat, labelled figures — labels often carry the marks. Always link the right hormone to the right event (LH→Leydig cells/ovulation; FSH→Sertoli cells/follicle growth; progesterone→endometrium; oxytocin→parturition). Use exact chromosome numbers (spermatogonium 46, secondary spermatocyte 23, zygote 46) to gain quick marks.
Frequently Asked Questions
What is Class 12 Biology Chapter 2 Human Reproduction about?
It explains how humans reproduce sexually and viviparously — covering the male and female reproductive systems, gametogenesis (spermatogenesis and oogenesis), the menstrual cycle, fertilisation, implantation, pregnancy and embryonic development, and finally parturition and lactation, all controlled by hypothalamic, pituitary and gonadal hormones.
Where does fertilisation take place in humans?
Fertilisation takes place in the ampullary region of the fallopian tube (oviduct), only when the ovum and sperms reach it simultaneously. The fusion of a haploid sperm with a haploid ovum forms a diploid zygote (2n = 46).
How is the sex of a baby determined?
By the father’s sperm. Every ovum carries an X chromosome, while sperms carry either X or Y. An X-bearing sperm gives an XX (girl) zygote and a Y-bearing sperm gives an XY (boy) zygote, so the father, not the mother, determines the sex.
Are these Class 12 Biology Chapter 2 solutions free?
Yes. All solutions are free and follow the official NCERT Biology textbook for session 2026–27, with every Exercises question answered.
