Human Reproduction Class 12: Concepts, Diagrams and Board Answers

What Human Reproduction is about

Weightage: This chapter is part of Unit VI, Reproduction, which carries 16 of the 70 theory marks together with Sexual Reproduction in Flowering Plants and Reproductive Health.Source: CBSE Biology (044) syllabus 2026-27, course structure, Unit VI Reproduction

In real board papers: asked in 8 of the 8 board papers we hold (2023 to 2026), on average 8 marks per paper. See the questions

Key concepts

The male reproductive system

NCERT section 2.1 The Male Reproductive System

The male system lies in the pelvic region and has four parts: a pair of testes, accessory ducts, accessory glands and the external genitalia (penis).

Testes and scrotum: the testes sit outside the abdomen in a pouch, the scrotum, which keeps them 2–2.5 °C cooler than the core body temperature. Sperm formation needs this lower temperature. An adult testis is oval, about 4–5 cm long and 2–3 cm wide, wrapped in a dense covering.

Inside a testis:

• About 250 compartments called testicular lobules.
• Each lobule holds 1 to 3 highly coiled seminiferous tubules, where sperms are made.
• Each tubule is lined by two kinds of cells: spermatogonia (male germ cells, which divide to form sperms) and Sertoli cells (which nourish the germ cells).
• Between the tubules are interstitial spaces with small blood vessels and Leydig (interstitial) cells, which make and release androgens (male hormones such as testosterone). Some immunologically competent cells are also present.

Accessory ducts (the sperm's route): seminiferous tubules → rete testis → vasa efferentia → epididymis (along the back of the testis) → vas deferens (goes up into the abdomen and loops over the urinary bladder; receives a duct from the seminal vesicle) → ejaculatory duct → urethra → urethral meatus. These ducts store and transport sperms.

Accessory glands: paired seminal vesicles, one prostate and paired bulbourethral glands. Their secretions make the seminal plasma, rich in fructose, calcium and some enzymes; the bulbourethral secretion also lubricates the penis. Seminal plasma + sperms = semen. Secretions of the epididymis, vas deferens, seminal vesicle and prostate are needed for the maturation and motility of sperms. Androgens keep all the accessory ducts and glands working.

Penis: made of special tissue that allows erection for insemination; its enlarged tip, the glans penis, is covered by a loose fold of skin, the foreskin.

Worked example

A man's testes have failed to descend into the scrotum and remain in the abdomen. Explain why he is likely to be infertile. Name the cells of the testis that would still secrete androgens. (2 marks)

Try it first, then show the solutionSolution

1. Sperm formation needs a temperature 2–2.5 °C lower than the body's core temperature; the scrotum provides this. Testes left in the abdomen are too warm, so spermatogenesis fails and the man may be infertile. (1)
2. Androgens are made by the Leydig (interstitial) cells in the spaces between the seminiferous tubules. (1)

Answer: Abdominal testes are too warm for spermatogenesis (scrotum keeps them 2–2.5 °C cooler); Leydig cells secrete androgens.

The female reproductive system and mammary glands

NCERT section 2.2 The Female Reproductive System

The female system lies in the pelvic region. It has a pair of ovaries, a pair of oviducts, the uterus, cervix, vagina and external genitalia; with the paired mammary glands, these support ovulation, fertilisation, pregnancy, birth and child care.

Ovaries (primary sex organs): produce the ovum and several steroid hormones. Each is about 2–4 cm long, one on each side of the lower abdomen, held to the pelvic wall and uterus by ligaments. A thin epithelium covers the ovarian stroma, which has an outer cortex and an inner medulla.

Oviduct (fallopian tube), about 10–12 cm long, from ovary to uterus:
1. Infundibulum: funnel-shaped part nearest the ovary, with finger-like fimbriae that collect the ovum after ovulation.
2. Ampulla: the wider middle part, where fertilisation happens.
3. Isthmus: the last part, with a narrow lumen, joining the uterus.

Uterus (womb): single, shaped like an inverted pear, held by ligaments. It opens into the vagina through a narrow cervix; the cervical canal and vagina together form the birth canal. The uterine wall has three layers:

• Perimetrium: thin outer membrane.
• Myometrium: thick middle layer of smooth muscle; contracts strongly during delivery.
• Endometrium: inner glandular lining; changes in a cycle during the menstrual cycle.

External genitalia: mons pubis (cushion of fatty tissue with skin and pubic hair), labia majora (fleshy folds around the vaginal opening), labia minora (paired folds under the labia majora), hymen (a membrane that often partly covers the vaginal opening) and clitoris (a tiny finger-like structure above the urethral opening). The hymen can tear for many reasons (a fall, a tampon, cycling, horse riding) or may persist after intercourse, so its presence or absence is not a reliable indicator of virginity.

Mammary glands: a working mammary gland is a feature of all female mammals. Each breast has glandular tissue and fat; the glandular tissue forms 15–20 mammary lobes of alveoli whose cells secrete milk. Milk flows: alveoli → mammary tubules → mammary duct → mammary ampulla → lactiferous duct → nipple.

Worked example

Name the part of the female reproductive tract where (a) the ovum is collected after ovulation, (b) fertilisation takes place, (c) the blastocyst implants, (d) strong contractions occur during childbirth. (2 marks)

Try it first, then show the solutionSolution

1. (a) Fimbriae of the infundibulum. (½)
2. (b) Ampulla of the oviduct. (½)
3. (c) Endometrium of the uterus. (½)
4. (d) Myometrium of the uterus. (½)

Answer: (a) Fimbriae/infundibulum (b) ampulla (c) endometrium (d) myometrium.

Spermatogenesis, its hormonal control and the sperm

NCERT section 2.3 Gametogenesis (spermatogenesis and structure of sperm)

Gametogenesis is the formation of gametes by the primary sex organs. Spermatogenesis (sperm formation) begins at puberty in the seminiferous tubules.

Flow chart (chromosome numbers in brackets):
Spermatogonium (2n = 46) —mitosis→ more spermatogonia; some become primary spermatocytes (46)
→ meiosis I (reduction division) → 2 equal secondary spermatocytes (23 each)
→ meiosis II → 4 equal spermatids (23 each)
→ spermiogenesis (spermatids change shape into spermatozoa)
→ sperm heads embed in Sertoli cells → released into the lumen by spermiation.

So one primary spermatocyte gives four sperms.

Hormonal control:
1. At puberty the hypothalamus sharply increases GnRH (gonadotropin releasing hormone).
2. GnRH acts on the anterior pituitary, which releases two gonadotropins: LH and FSH.
3. LH → Leydig cells → make and secrete androgens → androgens stimulate spermatogenesis.
4. FSH → Sertoli cells → secrete some factors that help spermiogenesis.

Structure of a sperm: head, neck, middle piece and tail, all wrapped in a plasma membrane.

• Head: an elongated haploid nucleus capped in front by the acrosome, which is filled with enzymes that help the sperm enter the ovum.
• Middle piece: many mitochondria that supply energy for tail movement.
• Tail: moves the sperm (motility).

Numbers to remember: a man ejaculates about 200–300 million sperms at a time; for normal fertility at least 60% must have normal shape and size and at least 40% must show vigorous motility.

Worked example

How many sperms will be formed from 25 primary spermatocytes and from 25 secondary spermatocytes? Give the chromosome number of a human spermatid. (2 marks)

Try it first, then show the solutionSolution

1. One primary spermatocyte completes meiosis I and II to give 4 spermatids, so 25 primary spermatocytes give 25 × 4 = 100 sperms. (½ + ½)
2. One secondary spermatocyte undergoes only meiosis II, giving 2 spermatids, so 25 secondary spermatocytes give 25 × 2 = 50 sperms. (½)
3. Spermatids are haploid: 23 chromosomes. (½)

Answer: 100 sperms from 25 primary spermatocytes; 50 from 25 secondary spermatocytes; spermatid has 23 chromosomes.

Oogenesis and how it differs from spermatogenesis

NCERT section 2.3 Gametogenesis (oogenesis)

Oogenesis is the formation of a mature female gamete. It is very different from spermatogenesis.

Before birth: in each fetal ovary, a couple of million oogonia (gamete mother cells) form; no new oogonia form after birth. They enter prophase I of meiosis and stop there: these arrested cells are primary oocytes.

Follicle stages (flow chart):
Primary oocyte + one layer of granulosa cells = primary follicle
→ many degenerate between birth and puberty; only 60,000–80,000 remain in each ovary at puberty
→ more granulosa layers + a new theca = secondary follicle
→ fluid-filled cavity, the antrum, appears; theca splits into theca interna and theca externa = tertiary follicle
→ Graafian (mature) follicle.

Meiosis in the oocyte:

• Inside the tertiary follicle, the primary oocyte grows and completes meiosis I. The division is unequal: a large haploid secondary oocyte (keeps most of the nutrient-rich cytoplasm) and a tiny first polar body.
• The secondary oocyte forms a new membrane, the zona pellucida.
• The Graafian follicle ruptures and releases the secondary oocyte (the 'ovum') at ovulation.
• Meiosis II is completed only when a sperm enters (at fertilisation). It is also unequal: a haploid ovum (ootid) and a second polar body.

Why unequal division? The single ovum keeps nearly all the stored food, which the early embryo will need.

Spermatogenesis versus oogenesis:

• Start: puberty versus fetal life.
• Continuity: continuous into old age versus stops at menopause (around 50 years).
• Products of one mother cell: 4 sperms versus 1 ovum (plus polar bodies).
• Divisions: equal versus unequal.
• Completion: in the testis versus meiosis II completed only after sperm entry.

Worked example

In which follicle stage does the primary oocyte complete its first meiotic division? Name the products and give their chromosome numbers. Why is this division called unequal? (3 marks)

Try it first, then show the solutionSolution

1. The primary oocyte completes meiosis I inside the tertiary follicle. (1)
2. Products: a large secondary oocyte (23 chromosomes) and a tiny first polar body (23 chromosomes). (1)
3. It is unequal because the secondary oocyte keeps the bulk of the nutrient-rich cytoplasm, while the polar body gets very little. (1)

Answer: Tertiary follicle; secondary oocyte (n = 23) and first polar body (n = 23); unequal because the cytoplasm goes almost entirely to the secondary oocyte.

The menstrual cycle and its hormones

NCERT section 2.4 Menstrual Cycle

The reproductive cycle of female primates (monkeys, apes, humans) is the menstrual cycle. The first menstruation, at puberty, is menarche; cycles stop around 50 years at menopause. A cycle averages 28/29 days, and one ovum is released near the middle of each cycle.

Phases (28-day cycle):
1. Menstrual phase (days 1–5, lasts 3–5 days): the endometrium and its blood vessels break down and flow out through the vagina. This happens only if the ovum was not fertilised.
2. Follicular (proliferative) phase: primary follicles grow into a mature Graafian follicle; at the same time the endometrium regenerates by proliferation. LH and FSH rise gradually, stimulating follicle growth and estrogen secretion by the growing follicles.
3. Ovulatory phase (about day 14): both LH and FSH peak mid-cycle. The sharp rise of LH, the LH surge, makes the Graafian follicle rupture and release the ovum (ovulation).
4. Luteal (secretory) phase: the remains of the Graafian follicle become the corpus luteum, which secretes large amounts of progesterone. Progesterone maintains the endometrium, which is needed for implantation and pregnancy.

Two possible endings:

• No fertilisation → corpus luteum degenerates → progesterone falls → endometrium breaks down → menstruation → new cycle.
• Fertilisation and pregnancy → corpus luteum is maintained → all events of the cycle stop and there is no menstruation.

Lack of menstruation can mean pregnancy, but it can also result from stress or poor health. Regular cycles between menarche and menopause indicate a normal reproductive phase.

Menstrual hygiene: bathe and clean regularly; use sanitary napkins or clean home-made pads and change them every 4–5 hours as needed; wrap used napkins in paper and dispose of them properly (never in toilet drains or open areas); wash hands with soap afterwards.

Worked example

A graph of a woman's 28-day cycle shows a sharp peak of one pituitary hormone on day 14 and a high level of an ovarian hormone from day 15 to day 26. Identify both hormones, name their sources and state one function of each. (3 marks)

Try it first, then show the solutionSolution

1. The pituitary hormone peaking on day 14 is LH (the LH surge), from the anterior pituitary. (1)
2. The LH surge causes rupture of the Graafian follicle and ovulation. (½)
3. The ovarian hormone high in the luteal phase is progesterone, secreted by the corpus luteum. (1)
4. Progesterone maintains the endometrium for implantation. (½)

Answer: LH from the anterior pituitary (triggers ovulation); progesterone from the corpus luteum (maintains the endometrium).

Fertilisation and sex determination

NCERT section 2.5 Fertilisation and Implantation (fertilisation and sex determination)

Insemination: during coitus, semen is released into the vagina. Motile sperms swim through the cervix and uterus to the ampulla of the oviduct. The ovum released by the ovary is also carried to the ampulla.

Fertilisation is the fusion of a sperm with an ovum, in the ampullary region. It happens only if the ovum and sperms reach the ampulla at the same time; this is why not every coitus leads to pregnancy.

Steps:
1. A sperm touches the zona pellucida of the ovum and causes changes in the membrane that block the entry of other sperms. This ensures only one sperm fertilises the ovum (no polyspermy).
2. Acrosome secretions (enzymes) help the sperm pass through the zona pellucida and plasma membrane into the cytoplasm.
3. Sperm entry triggers the secondary oocyte to complete meiosis II, producing the haploid ovum (ootid) and a second polar body.
4. The haploid sperm nucleus and the haploid ovum nucleus fuse, forming a diploid zygote (46 chromosomes).

Sex determination: a woman is XX, so every ovum carries X. A man is XY, so 50% of sperms carry X and 50% carry Y.

• X-sperm + ovum → XX zygote → girl.
• Y-sperm + ovum → XY zygote → boy.

So the sex of the baby is fixed at fertilisation and depends on the father's sperm, not on the mother. Blaming women for having daughters is scientifically wrong.

Worked example

Of the 200–300 million sperms ejaculated, only one fertilises the ovum. (a) Where does fertilisation occur? (b) How is entry of more sperms prevented? (c) What triggers the completion of meiosis II in the secondary oocyte? (3 marks)

Try it first, then show the solutionSolution

1. (a) In the ampullary region of the fallopian tube. (1)
2. (b) Contact of the first sperm with the zona pellucida induces changes in the membrane that block the entry of additional sperms. (1)
3. (c) Entry of the sperm into the cytoplasm of the secondary oocyte (helped by acrosomal enzymes) triggers completion of meiosis II. (1)

Answer: (a) Ampulla (b) membrane changes after contact with the zona pellucida block other sperms (c) sperm entry.

Cleavage, blastocyst and implantation

NCERT section 2.5 Fertilisation and Implantation (cleavage, morula, blastocyst, implantation)

Cleavage: the zygote begins mitotic divisions as it moves through the isthmus of the oviduct towards the uterus, giving 2, 4, 8, 16 cells called blastomeres.

Flow chart:
Zygote (ampulla) → cleavage in the isthmus → morula (embryo of 8–16 blastomeres) → continues dividing as it moves into the uterus → blastocyst.

Blastocyst: its blastomeres are arranged into

• an outer layer, the trophoblast, which attaches to the endometrium, and
• an inner group of cells attached to the trophoblast, the inner cell mass, which becomes the embryo.

Implantation: the trophoblast attaches to the endometrium; the uterine cells then divide rapidly and cover the blastocyst, so it becomes embedded in the endometrium. Implantation leads to pregnancy.

Stem cells: the inner cell mass contains stem cells that can give rise to all tissues and organs.

Twins (applying the idea): identical twins come from one ovum (one zygote that separates); fraternal twins come from two ova fertilised by two sperms.

The syllabus covers embryo development only up to the blastocyst and implantation.

Worked example

Distinguish between the trophoblast and the inner cell mass in terms of position and fate. Where does implantation occur? (2 marks)

Try it first, then show the solutionSolution

1. Trophoblast: the outer layer of the blastocyst; it attaches to the endometrium (and later forms the chorionic villi). Inner cell mass: the group of cells inside, attached to the trophoblast; it becomes the embryo. (1½)
2. Implantation occurs in the endometrium of the uterus. (½)

Answer: Trophoblast is outer and attaches to the endometrium; inner cell mass is inner and forms the embryo; implantation is in the endometrium.

Pregnancy, placenta, parturition and lactation (elementary idea)

NCERT section 2.6 Pregnancy and Embryonic Development; 2.7 Parturition and Lactation

Placenta: after implantation, finger-like chorionic villi grow from the trophoblast and are surrounded by uterine tissue and maternal blood. The villi and the uterine tissue interlock and together form the placenta, the structural and functional link between foetus and mother.

• It supplies oxygen and nutrients to the embryo and removes carbon dioxide and wastes.
• It joins the embryo through the umbilical cord.
• It is also an endocrine tissue, making hCG (human chorionic gonadotropin), hPL (human placental lactogen), estrogens and progestogens.
• Relaxin is secreted by the ovary in late pregnancy.
• hCG, hPL and relaxin are made only during pregnancy. Levels of estrogens, progestogens, cortisol, prolactin and thyroxine also rise several-fold to support foetal growth and maintain pregnancy.

Germ layers: soon after implantation the inner cell mass forms ectoderm (outer) and endoderm (inner), and then mesoderm between them. These three layers form all adult tissues.

Milestones of a 9-month pregnancy: heart forms after 1 month; limbs and digits by the end of 2 months; most organ systems by 12 weeks (end of first trimester); first movements and head hair in the 5th month; fine body hair, separated eyelids and eyelashes by 24 weeks (end of second trimester); fully developed by 9 months.

Parturition (childbirth), after a gestation period of about 9 months, is controlled by a neuroendocrine mechanism:
1. Signals come from the fully developed foetus and the placenta, causing mild uterine contractions: the foetal ejection reflex.
2. This triggers release of oxytocin from the maternal pituitary.
3. Oxytocin causes stronger contractions of the uterine muscle, which cause more oxytocin release (a positive feedback loop).
4. Contractions grow stronger until the baby is pushed out through the birth canal; the placenta is expelled soon after.
Cortisol, estrogens and oxytocin are involved. Doctors can inject oxytocin to induce delivery.

Lactation: mammary glands differentiate during pregnancy and produce milk near its end. The milk of the first few days, colostrum, contains antibodies that give the newborn resistance; breast-feeding is recommended for healthy growth.

Worked example

Name three hormones produced in a woman only during pregnancy and the source of each. Why is the placenta called an endocrine tissue? (2 marks)

Try it first, then show the solutionSolution

1. hCG and hPL from the placenta; relaxin from the ovary in late pregnancy. (1½)
2. The placenta secretes hormones (hCG, hPL, estrogens, progestogens) into the blood, so it acts as an endocrine tissue. (½)

Answer: hCG (placenta), hPL (placenta), relaxin (ovary); the placenta secretes hormones into the blood.

Human Reproduction in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Gametogenesis: Spermatogenesis and Oogenesis
• Menstrual Cycle and Its Hormonal Control
• Fertilisation, Cleavage and Implantation

Human Reproduction: key facts

Spermatogenesis count

$1\text{primary spermatocyte}\stackrel{\text{meiosis I}}{\to }2\text{secondary spermatocytes}\stackrel{\text{meiosis II}}{\to }4\text{spermatids}\to 4\text{sperms}$

x primary spermatocytes give 4x sperms; x secondary spermatocytes give 2x sperms.

Oogenesis count

$1\text{primary oocyte}\stackrel{\text{meiosis I}}{\to }1\text{secondary oocyte}+1\text{polar body}\stackrel{\text{meiosis II (after sperm entry)}}{\to }1\text{ovum}+1\text{polar body}$

One primary oocyte gives only one ovum.

Chromosome numbers in human gametogenesis

$\text{spermatogonium, oogonium, primary spermatocyte, primary oocyte, zygote}=46;\text{secondary spermatocyte, spermatid, sperm, secondary oocyte, ovum, polar body}=23$

Meiosis I halves the number; meiosis II keeps it at 23.

Sex determination

$\text{X ovum}+\text{X sperm}\to \text{XX (girl)};\text{X ovum}+\text{Y sperm}\to \text{XY (boy)}$

Probability of a girl or a boy in each pregnancy is 1/2.

Hormone axis

$\text{GnRH (hypothalamus)}\to \text{LH, FSH (anterior pituitary)}\to \text{gonads}$

Male: LH → Leydig cells (androgens); FSH → Sertoli cells. Female: LH surge → ovulation; corpus luteum → progesterone.

Embryo stages (to blastocyst)

$\text{zygote}\to \text{2, 4, 8, 16 blastomeres}\to \text{morula (8–16 cells)}\to \text{blastocyst}\to \text{implantation}$

Blastocyst: trophoblast outside, inner cell mass inside.

Human Reproduction: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Human Reproduction

The question patterns to expect, and the method that works for each.

Tricks to remember Human Reproduction

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Route of sperm: 'Some Rich Valley Eagles Venture Everywhere Up'

  Seminiferous tubules → Rete testis → Vasa efferentia → Epididymis → Vas deferens → Ejaculatory duct → Urethra.

  Use it when: Writing the duct sequence in order.

• L for Leydig, L for LH

  LH acts on Leydig cells (androgens); FSH acts on Sertoli cells (S-S: 'Sertoli Supporters').

  Use it when: Hormonal control of spermatogenesis.

• In-Am-Is: the oviduct

  Infundibulum (with fimbriae) → Ampulla (fertilisation) → Isthmus (cleavage begins, joins uterus).

  Use it when: Parts of the fallopian tube and what happens in each.

• P-M-E from outside in

  Perimetrium (thin cover), Myometrium (Muscle, pushes the baby), Endometrium (Embryo implants here).

  Use it when: Layers of the uterine wall.

• Primary → Secondary → Tertiary → Graafian: 'Please See The Gate'

  Primary follicle (one granulosa layer), Secondary (more layers + theca), Tertiary (antrum; meiosis I completed), Graafian (mature, ruptures).

  Use it when: Follicle stages in the ovary section.

• M-F-O-L

  Menstrual (bleeding), Follicular (FSH and estrogen build up), Ovulation (LH surge, day 14), Luteal (corpus Luteum, progesterone).

  Use it when: Phases of the menstrual cycle in order.

Human Reproduction: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 2 + 1 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Human Reproduction

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying the ovum completes meiosis before ovulation

  Wrong working

  The Graafian follicle releases a mature haploid ovum that has completed both meiotic divisions.

  Right working

  The Graafian follicle releases a secondary oocyte; meiosis II is completed only when a sperm enters it.

  ✓Do this: Say 'secondary oocyte' at ovulation; mention the second polar body forms at fertilisation.

  Usually costs: 1 mark.

• ✗Mistake: Mixing up Sertoli and Leydig cells

  ✓Do this: Sertoli cells are inside the seminiferous tubules and nourish germ cells (FSH target); Leydig cells are in the interstitial spaces and secrete androgens (LH target).

  Usually costs: 1 mark.

• ✗Mistake: Writing that only FSH (or only LH) peaks mid-cycle

  ✓Do this: Both LH and FSH peak around day 14; the LH surge is what triggers ovulation.

  Usually costs: 1 mark in MCQs and graph questions.

• ✗Mistake: Placing fertilisation in the uterus

  ✓Do this: Fertilisation is in the ampulla of the fallopian tube; implantation is in the endometrium of the uterus.

  Usually costs: ½ to 1 mark.

• ✗Mistake: Calling the morula a blastocyst or writing that the morula becomes the trophoblast

  ✓Do this: Morula = 8–16 blastomeres; it becomes the blastocyst, whose outer layer is the trophoblast and inner part the inner cell mass.

  Usually costs: 1 mark in assertion-reason questions.

• ✗Mistake: Saying relaxin comes from the placenta

  ✓Do this: hCG and hPL come from the placenta; relaxin comes from the ovary in late pregnancy.

  Usually costs: ½ mark.

NCERT exercise guide: Human Reproduction

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Human Reproduction: previous year questions

• Asked in 8 of the 8 board papers we hold (2023 to 2026), on average 8 marks per paper; 24 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Human Reproduction

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Human Reproduction question, by year

Practice questions on Human Reproduction

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   The cells that provide nutrition to the developing germ cells in the testis are:
   (a) Leydig cells (b) Sertoli cells (c) spermatogonia (d) interstitial cells

   Hint

   They line the tubule.

   Answer

   (b) Sertoli cells

2. Q2 · 1 mark · Assertion-reasonBoard level

   Assertion (A): The embryo with 8 to 16 blastomeres is called a morula.
   Reason (R): The morula continues to divide and becomes the trophoblast.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

   Hint

   What does the morula become?

   Answer

   (c) A is true but R is false: the morula becomes the blastocyst; the trophoblast is only its outer layer.

3. Q3 · 1 mark · MCQHarder board level

   Which one of these is NOT secreted only during pregnancy?
   (a) hCG (b) hPL (c) relaxin (d) progesterone

   Hint

   Which of them is also made in every luteal phase?

   Answer

   (d) progesterone (it is secreted by the corpus luteum in every cycle).

4. Q4 · 2 marks · Very short answerBoard level

   Name the three layers of the uterine wall and state which one (a) changes cyclically, (b) contracts during childbirth. (2 marks)

   Hint

   Outside to inside.

   Answer

   Perimetrium, myometrium, endometrium (1). (a) Endometrium (½) (b) myometrium (½).

5. Q5 · 2 marks · Very short answerHarder board level

   Give the chromosome number of each: (a) spermatogonium, (b) secondary spermatocyte, (c) first polar body, (d) zygote. Which cell division separates (a) from (b)? (2 marks)

   Hint

   Meiosis I halves the number.

   Answer

   (a) 46 (b) 23 (c) 23 (d) 46 (1½). Meiosis I (reduction division) of the primary spermatocyte (½).

6. Q6 · 2 marks · Very short answerHarder board level

   A man has a normal sperm count of 250 million per ejaculate, but only 30% of the sperms show vigorous motility. (a) Is he likely to be fertile? Explain. (b) Which part of the sperm might be defective? (2 marks)

   Hint

   Compare with 40%.

   Answer

   (a) Probably not: normal fertility needs at least 40% of sperms with vigorous motility; 30% is below this (1). (b) The middle piece (mitochondria supply energy) or the tail (1).

7. Q7 · 3 marks · Short answerHarder board level

   Describe the structure of a seminiferous tubule and name the cells that lie outside it. (3 marks)

   Hint

   Two cell types inside; one outside.

   Answer

   Each lobule has 1–3 highly coiled seminiferous tubules, lined inside by spermatogonia and Sertoli cells (1). Spermatogonia divide and pass through spermatocyte and spermatid stages towards the lumen, forming sperms; Sertoli cells nourish them (1). Outside, the interstitial spaces have blood vessels and Leydig cells, which secrete androgens, plus some immunologically competent cells (1).

8. Q8 · 3 marks · Short answerBoard level

   List three differences between spermatogenesis and oogenesis. (3 marks)

   Hint

   Start, output, continuity.

   Answer

   Spermatogenesis starts at puberty; oogenesis starts in fetal life (1). One primary spermatocyte gives four sperms (equal divisions); one primary oocyte gives one ovum and polar bodies (unequal divisions) (1). Spermatogenesis continues into old age; oogenesis stops at menopause, and meiosis II is completed only after sperm entry (1).

9. Q9 · 3 marks · Short answerHarder board level

   A woman has a regular 28-day cycle. On which approximate day is she likely to ovulate? If her LH surge fails, what happens to (a) ovulation, (b) corpus luteum formation, (c) progesterone level? (3 marks)

   Hint

   The surge ruptures the follicle.

   Answer

   Around day 14 (½). (a) No ovulation, because the LH surge ruptures the Graafian follicle (1). (b) No corpus luteum forms, since it develops from the ruptured follicle (1). (c) Progesterone stays low (½).

10. Q10 · 5 marks · Long answerHarder board level

    (a) Draw a labelled sectional view of the ovary showing at least six structures. (2)
    (b) Explain the changes in the follicle from primary follicle to ovulation. (2)
    (c) What happens to the remains of the ruptured follicle? (1) (5 marks)

    Hint

    Granulosa, theca, antrum.

    Answer

    (a) Diagram with primary, secondary, tertiary and Graafian follicles, antrum, secondary oocyte, zona pellucida, corpus luteum, blood vessels (2). (b) Primary follicle (primary oocyte + one granulosa layer) gains more granulosa layers and a theca (secondary follicle); an antrum appears and the theca splits into interna and externa (tertiary follicle), where meiosis I completes to give the secondary oocyte and first polar body; it matures into the Graafian follicle, the oocyte forms a zona pellucida, and the follicle ruptures under the LH surge (2). (c) It becomes the corpus luteum, which secretes progesterone (1).

11. Q11 · 2 marks · Very short answerHOTS / competency

    Suppose a couple's first child is a boy. What is the probability that their second child will be a girl? Explain using sex chromosomes. (2 marks)

    Hint

    Each fertilisation is independent.

    Answer

    1/2 (½). Every ovum carries X; half the sperms carry X and half Y, and each fertilisation is independent of earlier ones (1). So the chance of an X-sperm fertilising the ovum, giving XX (girl), is 1/2 every time (½).

12. Q12 · 2 marks · Very short answerHOTS / competency

    Colostrum is often called the newborn's 'first vaccine'. Evaluate this statement and give one reason why breast-feeding is advised in the early months. (2 marks)

    Hint

    What does colostrum contain?

    Answer

    Colostrum, the milk of the first few days, contains antibodies that give the newborn resistance; this is ready-made (passive) protection rather than a vaccine making the baby produce its own, so the phrase is a loose comparison (1). Breast-feeding is recommended by doctors for a healthy baby because the milk nourishes the infant and passes on these antibodies (1).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.How much lower than body temperature does the scrotum keep the testes?Show answer

   2–2.5 °C lower.

2. 2.How many testicular lobules does each testis have, and how many seminiferous tubules per lobule?Show answer

   About 250 lobules, each with 1 to 3 seminiferous tubules.

3. 3.What are the components of seminal plasma?Show answer

   Secretions of the seminal vesicles, prostate and bulbourethral glands, rich in fructose, calcium and some enzymes.

4. 4.Define spermiogenesis and spermiation.Show answer

   Spermiogenesis: transformation of spermatids into sperms. Spermiation: release of sperms from the seminiferous tubules.

5. 5.What does the acrosome contain?Show answer

   Enzymes that help the sperm enter the ovum.

6. 6.How many primary follicles are left in each ovary at puberty?Show answer

   About 60,000–80,000.

7. 7.What is the antrum?Show answer

   The fluid-filled cavity that characterises the tertiary follicle.

8. 8.What causes ovulation?Show answer

   The LH surge, the mid-cycle peak of LH, which ruptures the Graafian follicle.

9. 9.What is a morula?Show answer

   The embryo with 8 to 16 blastomeres.

10. 10.What is colostrum and why is it important?Show answer

    Milk of the first few days of lactation; it contains antibodies that give the newborn resistance.

11. 11.What is the foetal ejection reflex?Show answer

    Mild uterine contractions started by signals from the fully developed foetus and placenta, which trigger oxytocin release.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you trace the path of a sperm from the seminiferous tubule to the urethral meatus?
• ☐Can you state the functions of Sertoli cells, Leydig cells and the scrotum?
• ☐Can you draw and label a sperm and give the role of the acrosome and middle piece?
• ☐Can you write the oogenesis flow chart with follicle stages and say where meiosis I and II are completed?
• ☐Can you list five differences between spermatogenesis and oogenesis?
• ☐Can you mark the days of menstruation, ovulation and the luteal phase on a 28-day hormone graph?
• ☐Can you explain the block to polyspermy and why the father decides the baby's sex?
• ☐Can you describe the blastocyst and implantation, and the positive feedback in parturition?

Human Reproduction: frequently asked questions