Human Reproduction Class 12: NCERT Chapter 2 PDF and Guide

Human Reproduction is Chapter 2 of the NCERT Class 12 Biology book. The official human reproduction class 12 NCERT chapter PDF is right below, followed by a section-by-section guide to what the chapter teaches — so the book makes sense on a first read. The chapter opens on page 25 and spans 15 printed pages in the current NCERT edition.

Download the human reproduction class 12 NCERT chapter PDF

This is the same PDF NCERT publishes on its official portal, in the edition used across schools. Open the official human reproduction class 12 NCERT chapter PDF to read the full chapter with its figures and exercises exactly as NCERT prints them.

Chapter 2 at a glance

The table below gives the chapter’s shape — how many sections, captioned figures and exercise questions it holds. Use the numbers to judge the size of the task; the explanation of what each section teaches follows on this page.

What Chapter 2 covers: from gametes to childbirth

The chapter is arranged like the events it describes. Anatomy comes first because every later event needs a site; then one ovum is followed from its formation in the ovary to the birth of a baby and the first feed. The table maps each numbered section 2.1 to 2.7 in one line.

Notice the logic. Sections 2.1 and 2.2 give the structures; 2.3 makes the gametes; 2.4 synchronises the female organs through the menstrual cycle; 2.5 joins the gametes and implants the embryo; 2.6 grows the embryo into a foetus; 2.7 delivers it and feeds the newborn. Learn the sequence once and the chapter’s argument is memorised.

Key concepts in Human Reproduction

This section follows the book’s own order: first the anatomy that hosts everything, then the making of gametes, the monthly cycle, and the chain of events from fertilisation to childbirth. Each subsection below matches one section of the chapter (pp. 26-38).

The male reproductive system: testes, ducts and glands

The male system exists to make sperms, store them and deliver them into the female tract. Every part below serves one of those three jobs, and the sperms’ route ties them together.

• Testes: a pair housed in the scrotum, a pouch outside the abdominal cavity. The scrotum keeps them 2 to 2.5 degrees Celsius below normal body temperature — the condition spermatogenesis needs. Each adult testis is about 4-5 cm long and 2-3 cm wide (pp. 26-27).
• Inside the testis: about 250 testicular lobules, each holding one to three coiled seminiferous tubules where sperms form. The tubule is lined by spermatogonia (male germ cells) and Sertoli cells (which nourish them). Between tubules, in the interstitial spaces, Leydig cells secrete androgens (p. 27).
• Sperm route: seminiferous tubules to rete testis to vasa efferentia to epididymis to vas deferens to the ejaculatory duct and out through the urethra (pp. 27-28).
• Accessory glands: paired seminal vesicles, the prostate and paired bulbourethral glands. Their secretions form the seminal plasma, rich in fructose, calcium and certain enzymes; bulbourethral secretion lubricates the penis (p. 28).
• Penis: the male external genitalia, made of erectile tissue, ending in the glans penis covered by the foreskin (p. 28).
• Semen is seminal plasma plus sperms (p. 32).

The female reproductive system: ovaries to mammary glands

The female system must release an ovum each month, host fertilisation, carry the embryo, and later feed the newborn. Its organs are arranged in that order, from the ovaries down the tract to the mammary glands.

• Ovaries: the primary female sex organs; they produce the ovum and ovarian steroid hormones. Each ovary is 2-4 cm long, held by ligaments, with a stroma divided into an outer cortex and inner medulla (p. 28).
• Oviducts (fallopian tubes): each 10-12 cm long. The funnel-shaped infundibulum near the ovary carries finger-like fimbriae that collect the ovum after ovulation; the wider ampulla follows; the narrow isthmus joins the uterus (p. 29).
• Uterus (womb): a single, inverted-pear organ that opens into the vagina through the cervix. The cervical canal plus the vagina form the birth canal (p. 29).
• Uterine wall, three layers: outer perimetrium, middle myometrium (smooth muscle that contracts strongly at delivery), inner endometrium (glandular lining that changes cyclically) (p. 29).
• External genitalia: mons pubis, labia majora, labia minora, hymen and clitoris. The hymen’s presence or absence is not a reliable indicator of virginity or sexual experience — it can break from a fall, a jolt, a tampon, or sports such as cycling and horseback riding, and may persist after coitus (p. 30).
• Mammary glands: paired breasts with 15-20 lobes of milk-secreting alveoli. Milk flows from alveoli to mammary tubules to mammary ducts to the mammary ampulla, then through the lactiferous duct to the nipple (p. 30).

Gametogenesis: spermatogenesis and oogenesis

Gametogenesis makes gametes: spermatogenesis in the testis, oogenesis in the ovary. The two processes share the same meiosis, but their products, timing and cell numbers are very different — and that contrast is what the exercises probe.

• Spermatogenesis begins at puberty in the seminiferous tubules. Spermatogonia (diploid, 46 chromosomes) multiply by mitosis; some become primary spermatocytes (46), which complete meiosis I into two haploid secondary spermatocytes (23 each), then meiosis II into four haploid spermatids (23 each) (p. 31).
• Hormone chain: puberty raises GnRH from the hypothalamus, which makes the anterior pituitary release LH and FSH. LH drives Leydig cells to secrete androgens; androgens stimulate spermatogenesis. FSH makes Sertoli cells release factors that help spermiogenesis (p. 31).
• Spermiogenesis is the transformation of spermatids into spermatozoa. Spermiation is the release of the matured sperm heads from the Sertoli cells into the tubule (p. 31).
• A sperm has a head (nucleus capped by the enzyme-filled acrosome), neck, middle piece (mitochondria supply energy) and tail (motility). A normal ejaculate holds 200-300 million sperms; normal fertility needs at least 60 per cent with normal shape and size and at least 40 per cent with vigorous motility (p. 32).
• Oogenesis begins in the fetal ovary: oogonia enter prophase I and arrest as primary oocytes; no new oogonia form after birth. Each primary oocyte gains a granulosa layer (primary follicle); by puberty only 60,000-80,000 primary follicles remain in each ovary (p. 32).
• Follicle stages: more granulosa layers and a theca make the secondary follicle; a fluid-filled cavity (antrum) marks the tertiary follicle, whose theca splits into theca interna and theca externa. There the primary oocyte completes meiosis I — unequally — giving one large haploid secondary oocyte and a tiny first polar body (pp. 32-33). The tertiary follicle matures into the Graafian follicle; the secondary oocyte gains the zona pellucida, and the follicle ruptures to release the ovum — ovulation (p. 33).

The comparison table below is the fastest way to see the two processes side by side.

The menstrual cycle: phases and hormones

The menstrual cycle synchronises the ovary and the uterus on an average 28/29-day schedule, so a fresh ovum is ready at mid-cycle. If the ovum is fertilised the cycle stops; if not, it restarts.

• Menarche is the first menstruation at puberty. The cycle repeats every 28/29 days; one ovum is released in the middle of each cycle. Cycles stop during pregnancy and cease around age 50 — menopause (pp. 33-35).
• Menstrual phase (3-5 days): the endometrial lining and its blood vessels break down and flow out through the vagina. It occurs only when the released ovum is not fertilised (p. 34).
• Follicular phase: primary follicles grow into a Graafian follicle while the endometrium regenerates. LH and FSH rise gradually, driving follicle growth and estrogen secretion (p. 34).
• Ovulation: LH and FSH peak mid-cycle (about day 14). The LH surge ruptures the Graafian follicle and releases the ovum (pp. 34-35).
• Luteal phase: the remaining follicle becomes the corpus luteum, secreting large amounts of progesterone to maintain the endometrium for implantation. Without fertilisation the corpus luteum degenerates, the endometrium disintegrates, and menstruation starts a new cycle (p. 35).

The chapter’s hormone story, from GnRH to oxytocin, fits in one table.

The book’s menstrual hygiene advice, in one place: bathe and clean yourself regularly; use sanitary napkins or clean homemade pads; change them every 4-5 hours; wrap used napkins in used paper before disposal; never throw them into toilet drainpipes or open areas; wash hands with soap after handling (p. 35).

Fertilisation, cleavage and implantation

This section answers three exam staples: where fertilisation happens, how only one sperm enters, and what the zygote does next.

• Route: semen is released into the vagina; motile sperms swim through the cervix and uterus to reach the ampullary region of the fallopian tube, where the ovum is also transported. Fertilisation needs both to arrive there at the same time — which is why not every coitus leads to pregnancy (p. 35).
• Fertilisation: a sperm contacts the zona pellucida; membrane changes block any further sperms, so only one fertilises the ovum. Acrosome secretions help that sperm cross the zona pellucida and the plasma membrane. Entry completes the second meiotic division, forming a second polar body and a haploid ovum (pp. 35-36).

Worked example — where the 46 chromosomes come from. An ovum carries 22 autosomes and one X chromosome, 23 in all. A sperm carries 22 autosomes and either an X or a Y, also 23.

At fertilisation the two haploid sets fuse: \(23 + 23 = 46\) chromosomes in the zygote. If the sperm carried X, the zygote is XX and becomes female; if Y, the zygote is XY and becomes male. Since every ovum carries X, the father’s sperm decides the baby’s sex (p. 36).

• Cleavage: repeated mitotic divisions as the zygote moves through the isthmus toward the uterus produce 2, 4, 8, 16 blastomeres (p. 36).
• Morula to implantation: the embryo of 8-16 blastomeres is the morula; continued division forms the blastocyst with an outer trophoblast and an inner cell mass. The trophoblast attaches to the endometrium, uterine cells grow over it, and the blastocyst embeds — implantation — which leads to pregnancy (pp. 36-37).

Pregnancy, placenta and embryonic development

Once embedded, the embryo’s first need is a reliable supply of oxygen and food. The placenta provides it and, in doing so, becomes the body’s only pregnancy-specific endocrine gland.

• Placenta: finger-like chorionic villi of the trophoblast interdigitate with uterine tissue to form the placenta, connected to the embryo by the umbilical cord. It supplies oxygen and nutrients and removes carbon dioxide and wastes (p. 37).
• Pregnancy hormones: the placenta secretes hCG, hPL, estrogens and progestogens; in later pregnancy the ovary adds relaxin. hCG, hPL and relaxin appear only during pregnancy, while estrogens, progestogens, cortisol, prolactin and thyroxine climb several-fold in maternal blood (p. 37).
• Germ layers: the inner cell mass differentiates into ectoderm (outer) and endoderm (inner), with mesoderm appearing between them; all adult tissues arise from these three layers. The inner cell mass also holds stem cells able to give rise to all tissues and organs (p. 37).
• Milestones: heart formed by one month; limbs and digits by the end of the second month; most major organ systems by 12 weeks; first movements and head hair in the fifth month; fine body hair, separated eyelids and eyelashes by about 24 weeks; fully developed by nine months (p. 38).

Parturition and lactation

Parturition is birth, and it is driven by a reflex, not a decision. The fully grown foetus starts the process without intending to.

• Gestation lasts about 9 months. Signals from the fully developed foetus and placenta set off mild contractions — the foetal ejection reflex — which releases oxytocin from the maternal pituitary (p. 38).
• The feedback loop: oxytocin strengthens the contractions; the contractions trigger more oxytocin. This continues until the baby is expelled through the birth canal — parturition — and the placenta is delivered after the infant (p. 38).
• Lactation: mammary glands differentiate during pregnancy and produce milk toward its end. Colostrum, the first few days’ milk, contains antibodies that give the newborn resistance; doctors recommend breastfeeding during the initial period of infant growth (p. 38).

Reading NCERT’s figures in order

The diagrams below are the chapter’s real content — each labels a structure or steps through an event you will be asked to reproduce. Work through them in the book’s order; together they tell the whole story, from the organs that make gametes to the foetus in the uterus.

Figures 2.1 and 2.2: where sperms are made and how they leave

Figure 2.1(a) is a map of the whole male system in one drawing. Find the scrotum hanging outside the body wall — that position is the chapter’s first key fact, because it keeps the testes 2 to 2.5 degrees Celsius cooler than body temperature, which spermatogenesis requires (NCERT, p. 27).

Figure 2.1(b) opens the testis to show the route sperms take: seminiferous tubules to rete testis to vasa efferentia to epididymis to vas deferens to the ejaculatory duct and out through the urethra. Trace this route on the drawing; the exercise block asks you to draw the system yourself (Q2).

Figure 2.2 is the key to the true/false set in the exercise (Q16). It shows two cell populations: spermatogonia and Sertoli cells lining the tubule, and Leydig cells in the interstitial spaces outside it. Sertoli cells nourish the germ cells; Leydig cells make androgens (pp. 27-28).

Figures 2.3 and 2.4: the female organs and the milk path

Figure 2.3(a) gives the layout of the female system inside the pelvis. The detail worth noticing is position: each ovary sits next to the open, funnel-shaped end of its own oviduct, because the ovum is collected, not delivered.

Figure 2.3(b) is the one to revise for Q3. Track the ovum’s path — infundibulum with fimbriae, ampulla, isthmus, uterus — then note the three uterine layers: perimetrium, myometrium and endometrium. The cervix and vagina below form the birth canal (p. 29).

Figure 2.4 follows the milk: alveoli, which secrete it, then mammary tubules, mammary ducts, the mammary ampulla and the lactiferous duct to the nipple. All parts after the alveoli are just the journey to the newborn (p. 30).

Figures 2.5, 2.6, 2.7 and 2.8: how the gametes form

Figure 2.5 shows the ladder of spermatogenesis inside the tubule: spermatogonia multiply, then primary spermatocytes complete meiosis I and II to give spermatids. Track the chromosome numbers with it: 46, 46, 23, 23 (p. 31).

Figure 2.6 labels the finished sperm in four parts: head with the enzyme-filled acrosome, neck, middle piece packed with mitochondria, and tail. This is one of the labelled diagrams the exercise block asks you to draw (Q9, p. 32).

Figure 2.7 shows the ovary in section, with follicles at every stage: primary, secondary, tertiary with its fluid-filled antrum, and the mature Graafian follicle. Reading left to right is reading time — the exercise asks for this section (Q13, Q14, pp. 32-33).

Figure 2.8 puts spermatogenesis and oogenesis side by side. The single visual difference that answers most questions: spermatogenesis ends in four equal sperms, oogenesis in one large secondary oocyte plus polar bodies, because its divisions are unequal and keep the nutrient-rich cytoplasm in the oocyte (pp. 32-33).

Figure 2.9: the menstrual cycle at a glance

Figure 2.9 carries the whole cycle in one drawing: hormone levels across the top, ovarian events in the middle, endometrial changes at the bottom. Read the mid-cycle day: LH and FSH peak, the LH surge ruptures the Graafian follicle into ovulation, and progesterone from the corpus luteum then holds the endometrium (pp. 33-35).

Figures 2.10 and 2.11: fertilisation to implantation

Figure 2.10 shows the one-sperm rule. Many sperms crowd around the ovum, but as soon as one contacts the zona pellucida, membrane changes block the rest; acrosome enzymes then let that single sperm cross into the cytoplasm (pp. 35-36).

Figure 2.11 is the whole fertilisation-to-pregnancy sequence: fertilisation in the ampulla, cleavage into 2, 4, 8, 16 blastomeres on the way along the isthmus, the 8-16 cell morula, the blastocyst with trophoblast and inner cell mass, and finally implantation in the endometrium. Each stage is one step of a sequence you should be able to write out (pp. 36-37).

Figure 2.12: the foetus and placenta

Figure 2.12 shows the foetus within the uterus, linked to the placenta by the umbilical cord. Through the placenta the embryo receives oxygen and nutrients and removes carbon dioxide and wastes, while the placenta’s hormones — hCG, hPL, and relaxin from the ovary — maintain the pregnancy (p. 37).

Definitions you can write in the exam

These are the terms the exercise block asks you to define or name. Write one clean sentence for each — start with the category, then add the chapter’s distinguishing detail.

Common mistakes in Human Reproduction and the corrections

Most mark loss in this chapter comes from swapping the two tubule cell types, the two gamete processes, or the two ‘spermi-‘ terms. The true/false table below corrects all seven statements of the exercise’s set (Q16); the list after it catches the remaining classic slips.

• Fertilisation site: the ampullary region of the fallopian tube, not the uterus (p. 35).
• Zygote chromosomes: 46, because 23 from each gamete fuse; 23 is the haploid count of a single gamete (p. 36).
• Spermiogenesis vs spermiation: one is the change of a spermatid into a sperm; the other is the release from Sertoli cells (p. 31).
• Missed menstruation: it may indicate pregnancy, but stress or poor health can also stop it (p. 34).

What to practise for exams

The exercise block mixes fill-in-the-blanks, labelled diagrams, definitions, true/false and reasoning questions. Turn it into this short practice list, and use the six-diagram checklist below to cover every drawing the exercises ask for.

Revise the five functions quizzed in Q15: corpus luteum secretes progesterone to maintain the endometrium; the endometrium changes cyclically and hosts implantation; the acrosome carries enzymes for entering the ovum; the sperm tail gives motility; the fimbriae collect the ovum after ovulation.

For the reasoning questions, anchor every answer in the chapter’s facts: one ovum per cycle; a diploid zygote with 46 chromosomes; XX female, XY male — so the father’s sperm decides the sex (Q19). Identical twins come from one fertilised ovum, so one egg was released; fraternal twins need two. On the same logic, six puppies mean six eggs (Q20, Q21).

Textbook contents and the examinable syllabus are not always identical, so check the current official CBSE syllabus for the examinable portions of this chapter.

Chapter 2 in two minutes

If you have two minutes, read this section instead of the whole chapter. The timed table compresses embryonic development; the paragraphs after it compress the entire sequence.

Human reproduction, end to end. The testis makes sperms, the ovary makes ova; coitus delivers semen into the vagina. Sperms swim through the cervix and uterus to the ampullary region of the fallopian tube, where one fertilises the ovum. The diploid zygote (46 chromosomes) cleaves into blastomeres, forms a morula, then a blastocyst, and implants in the endometrium — that is pregnancy.

Over nine months the placenta supplies oxygen and nutrients and removes wastes while its hormones maintain the pregnancy. At term, the foetal ejection reflex triggers oxytocin-driven contractions — parturition — and the mammary glands, already producing milk, feed the newborn by lactation, starting with antibody-rich colostrum.

Other Class 12 Biology chapters on this site

Human Reproduction sits between two related chapters in the same reproduction unit. For the chapters around it and for the rest of the book, use these pages:

• Class 12 Biology notes — the full set for this subject
• Chapter 1: Sexual Reproduction in Flowering Plants
• Chapter 3: Reproductive Health
• All Class 12 notes, across subjects
• The complete CBSE notes directory

Sources and data verification

This listing is maintained for the 2026-27 academic session using the NCERT textbook information available to us. NCERT remains the authority for confirming the latest edition.

This page describes the NCERT Class 12 Biology textbook, Chapter 2 (Human Reproduction), in the edition NCERT currently publishes on its official portal at ncert.nic.in. Page numbers follow that edition: the chapter opens on page 25.

This page covers only this NCERT chapter. It does not cover other publishers’ Biology books, and it does not list the full CBSE scheme of studies.

NCERT settles textbook contents, editions and PDFs; CBSE settles curriculum, syllabus and examinations. Textbook contents and the examinable syllabus are not always identical. This listing is maintained for the current academic session.

You can verify the current edition of any NCERT book on the official NCERT textbook portal.

Reference: NCERT Class 12 Biology textbook, chapter 2, official edition on ncert.nic.in.

Frequently asked questions about human reproduction class 12

Where does fertilisation take place in humans?

Fertilisation takes place in the ampullary region of the fallopian tube. Sperms swim through the cervix and uterus to reach the ampulla, and the ovum is transported there too; both must arrive at the same time (NCERT, p. 35).

Why is the sex of the baby determined by the father and not the mother?

Every ovum carries the X chromosome, while sperms are 50 per cent X and 50 per cent Y. If an X sperm fertilises the ovum the zygote is XX (female); if a Y sperm does, it is XY (male). The father’s sperm therefore decides the sex (NCERT, p. 36).

How many eggs are released in a month, and what does that mean for identical twins?

One ovum is released per menstrual cycle (NCERT, p. 33). Identical twins come from a single fertilised ovum, so only one egg was released that month; fraternal twins develop from two separate ova, so two eggs were released.

What is the difference between spermiogenesis and spermiation?

Spermiogenesis is the transformation of spermatids into spermatozoa (sperms). Spermiation is the later release of the matured sperms from the Sertoli cells into the seminiferous tubules (NCERT, p. 31).

Which hormones regulate the menstrual cycle?

The cycle is regulated by LH and FSH from the anterior pituitary and by the ovarian hormones estrogen and progesterone. The LH surge at mid-cycle triggers ovulation, and progesterone from the corpus luteum maintains the endometrium afterwards (NCERT, pp. 34-35).

Is the presence or absence of the hymen a reliable indicator of virginity?

No. The hymen can be torn by a sudden fall or jolt, a vaginal tampon, or sports such as cycling and horseback riding, and it can persist even after coitus. Its presence or absence is not a reliable indicator of virginity or sexual experience (NCERT, p. 30).