Reproductive System ICSE Class 10: Organs, Fertilisation, Placenta and Menstrual Cycle

What Reproductive System is about

Weightage: CISCE publishes no chapter or unit weightage for ICSE Biology. Reproductive System is in the 3. Human Anatomy and Physiology (v) part of the 2027 syllabus and can be asked in both Section A and Section B of the 80-mark paper.Source: CISCE ICSE Biology (Science Paper 3) syllabus, examination year 2027

Key concepts

Male reproductive system

• Testes (a pair): in the scrotum, outside the abdomen, where the temperature is about 2-3 °C lower, which is needed for sperm production. Seminiferous tubules produce sperms; interstitial (Leydig) cells between them secrete testosterone.
• Epididymis: a coiled tube on each testis where sperms are stored and mature.
• Vas deferens (sperm duct): carries sperms from the epididymis, through the inguinal canal, to the urethra.
• Urethra: common passage for urine and semen, through the penis.

Accessory glands (their secretions plus sperms form semen):

• Seminal vesicles: secrete a fluid rich in fructose that nourishes sperms and forms most of the semen.
• Prostate gland: secretes an alkaline fluid that neutralises acids in the urethra and vagina and helps sperms move.
• Cowper's glands: secrete mucus that lubricates the urethra.

Worked example

Why are the testes located in the scrotum outside the abdominal cavity?

Try it first, then show the solutionSolution

1. Sperm production needs a temperature a little lower than body temperature.
2. The scrotum keeps the testes about 2-3 °C cooler.

Answer: For the lower temperature needed to produce sperms.

Female reproductive system

• Ovaries (a pair): in the lower abdomen; contain follicles in which ova develop; secrete oestrogen and progesterone. A mature follicle is a Graafian follicle; it bursts to release the ovum (ovulation), and the empty follicle becomes the corpus luteum, which secretes progesterone.
• Oviducts (Fallopian tubes): have a funnel with finger-like fimbriae near each ovary that catch the ovum; fertilisation occurs here.
• Uterus: a hollow, pear-shaped, muscular organ where the embryo implants and develops; its inner lining is the endometrium.
• Cervix: the narrow neck of the uterus.
• Vagina: receives sperms; birth canal.

Secondary sexual characters appear at puberty under sex hormones: in males (testosterone) growth of facial and body hair, deep voice, broad shoulders, muscular body; in females (oestrogen) development of breasts, broad hips, start of menstruation.

Worked example

Name the structure in the ovary that releases a mature ovum, and what it becomes afterwards.

Try it first, then show the solutionSolution

1. The ovum matures in a Graafian follicle, which bursts at ovulation.
2. The empty follicle becomes the corpus luteum.

Answer: Graafian follicle; corpus luteum.

Sperm and ovum

Sperm (tiny, motile):

• Head: contains the nucleus (haploid set of chromosomes); capped by the acrosome, which has enzymes to penetrate the egg membranes.
• Middle piece: packed with mitochondria, which supply energy for swimming.
• Tail: lashes to propel the sperm.

Ovum (large, round, non-motile):

• A nucleus (haploid) in cytoplasm with some yolk (stored food).
• Surrounded by a plasma membrane, a jelly-like layer (zona pellucida) and outer follicle cells (corona radiata), which protect it.

Worked example

State the function of (a) the acrosome, (b) the middle piece of a sperm.

Try it first, then show the solutionSolution

1. (a) Releases enzymes to dissolve the egg's coverings so the sperm can enter.
2. (b) Its mitochondria provide energy for the tail.

Answer: As above.

Fertilisation to birth: key terms

• Fertilisation: fusion of a sperm nucleus with the ovum nucleus to form a diploid zygote; occurs in the oviduct.
• Implantation: the developing embryo (a ball of cells) reaches the uterus and embeds itself in the uterine wall (endometrium), about a week after fertilisation.
• Placenta: a disc-shaped structure formed partly from the embryo's tissues (chorion villi) and partly from the uterine wall; the foetus is joined to it by the umbilical cord.
• Gestation: the period from fertilisation to birth, about 280 days (nine months) in humans.
• Parturition: childbirth, the expulsion of the baby from the uterus by strong contractions, stimulated by oxytocin.

Worked example

Define implantation and state where fertilisation occurs.

Try it first, then show the solutionSolution

1. Implantation: embedding of the early embryo in the uterine wall.
2. Fertilisation: in the oviduct (Fallopian tube).

Answer: As above.

Placenta, foetal membranes and amniotic fluid

Placenta: the mother's and foetus's blood do not mix; materials pass across thin membranes between them.

• Nutrition: glucose, amino acids, vitamins and salts pass from mother to foetus.
• Respiration: oxygen passes to the foetus; carbon dioxide passes back.
• Excretion: urea and other wastes pass from foetus to mother.
• Endocrine function: secretes hormones (such as progesterone and oestrogen) that maintain pregnancy.
• Also gives some protection: many harmful substances and germs are kept out, though not all (some drugs, alcohol and viruses can cross).

Foetal membranes: the amnion encloses the foetus in amniotic fluid; the chorion forms the outer membrane and helps form the placenta.

Amniotic fluid: protects the foetus from shocks and injury, keeps it moist, maintains an even temperature, and allows free movement.

Worked example

In what two ways does the amniotic fluid help the developing foetus?

Try it first, then show the solutionSolution

1. Acts as a shock absorber, protecting the foetus.
2. Prevents drying and allows free movement (also keeps temperature even).

Answer: Shock absorption; prevents drying / allows movement.

The menstrual cycle and sex hormones

The menstrual cycle repeats about every 28 days from puberty to menopause (outline):

1. Menstrual phase (days 1-5): the thickened uterine lining breaks down and is discharged with blood (menstruation).
2. Follicular (proliferative) phase (days 6-13): a follicle matures in the ovary under FSH; oestrogen from it rebuilds the uterine lining.
3. Ovulation (about day 14): the Graafian follicle releases the ovum.
4. Luteal (secretory) phase (days 15-28): the corpus luteum secretes progesterone, which makes the lining thick, glandular and ready for implantation. If there is no fertilisation, the corpus luteum degenerates, progesterone falls, and the lining breaks down: menstruation begins again. If fertilisation occurs, the lining is kept and menstruation stops during pregnancy.

Sex hormones:

• Testosterone (testes): sperm production and male secondary sexual characters.
• Oestrogen (ovaries): female secondary sexual characters; repair and growth of the uterine lining.
• Progesterone (corpus luteum, later placenta): maintains the uterine lining and pregnancy.

Worked example

Why does menstruation occur if the ovum is not fertilised?

Try it first, then show the solutionSolution

1. Without fertilisation, the corpus luteum degenerates.
2. Progesterone level falls.
3. The uterine lining is no longer maintained, so it breaks down and is shed with blood.

Answer: Fall in progesterone after the corpus luteum degenerates.

Identical and fraternal twins

Identical (monozygotic) twins	Fraternal (dizygotic) twins
from one zygote that splits into two	from two ova fertilised by two sperms
genetically identical	genetically different, like ordinary siblings
always of the same sex	may be of the same or different sexes
look almost exactly alike	may look quite different

Worked example

A boy and a girl are twins. Are they identical or fraternal? Explain.

Try it first, then show the solutionSolution

1. Identical twins come from one zygote, so they have the same sex chromosomes.
2. A boy and a girl must have come from two different zygotes.

Answer: Fraternal twins.

Reproductive System 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

• Ovary, Ovulation and the Menstrual Cycle
• Fertilisation, Implantation, Placenta and Foetal Membranes

Reproductive System: key facts

Path of sperms

$\text{testis}\to \text{epididymis}\to \text{vas deferens}\to \text{urethra}$

Secretions of seminal vesicles, prostate and Cowper's glands join.

Path of the ovum and embryo

$\text{ovary}\to \text{oviduct (fertilisation)}\to \text{uterus (implantation)}$

Zygote divides on the way.

Menstrual cycle outline

$\text{menstruation (1-5)}\to \text{follicular (6-13)}\to \text{ovulation (14)}\to \text{luteal (15-28)}$

About 28 days.

Fertilisation

$n(\text{sperm})+n(\text{ovum})\to 2n(\text{zygote})$

In the oviduct.

Reproductive System: diagrams to practise

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

How the board asks Reproductive System

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

Tricks to remember Reproductive System

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

• STEVU for the sperm's route

  Seminiferous Tubules → Epididymis → Vas deferens → Urethra.

  Use it when: Path of sperms.

• Progesterone = Pro-gestation

  Progesterone is pro-pregnancy: it maintains the uterine lining.

  Use it when: Role of progesterone.

• Graafian Goes, Luteum Lingers

  The Graafian follicle releases the ovum and goes; the corpus luteum lingers to make progesterone.

  Use it when: Ovary events.

• Mono = One zygote

  Monozygotic = one zygote = identical; dizygotic = two zygotes = fraternal.

  Use it when: Twins.

Reproductive System: 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 B style)

Read the situation, then answer every part. In the board paper this is a 6-mark question split into 2 + 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 Reproductive System

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

• ✗Mistake: Implantation and corpus luteum confused

  CISCE examiners' comments, 2024: on an ovary diagram, candidates wrote implantation instead of ovulation and Graafian follicle instead of corpus luteum.

  Wrong working

  Process: implantation; structure after release: Graafian follicle.

  Right working

  Process: ovulation; structure after release: corpus luteum.

  ✓Do this: Ovulation happens in the ovary; implantation in the uterus.

  Usually costs: 1 mark each.

• ✗Mistake: Vasectomy for tubectomy

  CISCE examiners' comments, 2024: for the female surgical method of contraception, candidates wrote vasectomy, with spellings like 'tubecotomy'.

  Wrong working

  Female sterilisation: vasectomy.

  Right working

  Tubectomy (cutting and tying the oviducts).

  ✓Do this: Tube = oviduct (female); vas = vas deferens (male).

  Usually costs: 1 mark.

• ✗Mistake: Unclear roles of male accessory glands

  CISCE examiners' comments, 2025: in an assertion about seminal vesicles, candidates accepted 'ureter' as the passage for semen, unclear about each gland's role.

  Wrong working

  Semen passes through the ureter.

  Right working

  Semen passes through the urethra; the ureter carries urine from kidney to bladder.

  ✓Do this: Ureter (kidney) ≠ urethra (exit tube).

  Usually costs: 1 mark.

• ✗Mistake: Uterus for ureter, locations for functions

  CISCE examiners' comments, 2025: differentiating urethra and uterus, candidates interchanged functions, wrote locations, or confused uterus with ureter.

  Wrong working

  Uterus is in the lower abdomen; urethra is below the bladder.

  Right working

  Uterus: development of the embryo; urethra: passage of urine (and semen in males).

  ✓Do this: Asked for functions? Give functions.

  Usually costs: 1-2 marks.

• ✗Mistake: Amniotic fluid as placenta

  CISCE examiners' comments, 2025: candidates confused amniotic fluid with the placenta and wrote 'nutrient supply'.

  Wrong working

  Amniotic fluid supplies nutrients.

  Right working

  Amniotic fluid protects from shocks and drying; the placenta supplies nutrients.

  ✓Do this: Fluid cushions; placenta feeds.

  Usually costs: 1 mark.

• ✗Mistake: Incomplete term for the follicle

  CISCE examiners' comments, 2025: candidates wrote ovum or follicle instead of Graafian follicle.

  Wrong working

  Follicle.

  Right working

  Graafian follicle.

  ✓Do this: Use the full term.

  Usually costs: 1 mark.

Practice questions on Reproductive System

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 structure formed in the ovary after ovulation is the:
   (a) Graafian follicle
   (b) corpus luteum
   (c) placenta
   (d) zygote

   Hint

   Yellow body.

   Answer

   (b)

2. Q2 · 1 mark · MCQBoard level

   The part of the sperm that contains mitochondria is the:
   (a) head
   (b) acrosome
   (c) middle piece
   (d) tail

   Hint

   Energy supply.

   Answer

   (c)

3. Q3 · 1 mark · Assertion-reasonHarder board level

   Assertion (A): Identical twins are always of the same sex.
   Reason (R): Identical twins develop from a single zygote.
   (a) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (b) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
   (c) (A) is true and (R) is false.
   (d) (A) is false and (R) is true.

   Hint

   Same chromosomes.

   Answer

   (a)

4. Q4 · 3 marks · Very short answerBoard level

   Name: (a) the canal through which the vas deferens passes from the scrotum into the abdomen; (b) the finger-like projections of the oviduct; (c) the cord joining the foetus to the placenta.

   Hint

   One term each.

   Answer

   (a) Inguinal canal (b) Fimbriae (c) Umbilical cord

5. Q5 · 2 marks · Short answerHarder board level

   Give the function of: (a) prostate gland, (b) Cowper's glands.

   Hint

   Alkaline; lubricate.

   Answer

   (a) Alkaline secretion that neutralises acidity and helps sperm movement. (b) Mucus that lubricates the urethra.

6. Q6 · 2 marks · Short answerHarder board level

   Explain the endocrine role of the placenta.

   Hint

   Hormones of pregnancy.

   Answer

   It secretes hormones such as progesterone and oestrogen that maintain the uterine lining and the pregnancy, taking over from the corpus luteum.

7. Q7 · 3 marks · Short answerHarder board level

   List three differences between a sperm and an ovum.

   Hint

   Size, movement, yolk.

   Answer

   Sperm is tiny, ovum is large; sperm is motile (tail), ovum is non-motile; sperm has little cytoplasm, ovum has much cytoplasm with yolk.

8. Q8 · 2 marks · Short answerHarder board level

   Why is a pregnant woman's menstruation stopped during pregnancy?

   Hint

   Progesterone stays high.

   Answer

   Progesterone (from the corpus luteum, then the placenta) stays high and maintains the uterine lining, so the lining is not shed.

9. Q9 · 3 marks · Short answerHOTS / competency

   If the corpus luteum fails to form after ovulation and fertilisation occurs, predict what might happen to the embryo and why.

   Hint

   No progesterone.

   Answer

   Progesterone would be low, so the uterine lining would not be maintained or prepared; the embryo may fail to implant or be lost when the lining breaks down.

10. Q10 · 2 marks · Short answerHOTS / competency

    A couple has twins, one boy and one girl. Another couple has twin girls who share a placenta, have the same blood group and look exactly alike. Classify each pair and give one reason.

    Hint

    Sex and genes.

    Answer

    First pair: fraternal, because different sexes require different zygotes. Second pair: likely identical, since they came from one zygote and share the same genes.

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.Cells that secrete testosterone?Show answer

   Interstitial (Leydig) cells of the testes.

2. 2.Where are sperms stored?Show answer

   Epididymis.

3. 3.Which gland's secretion is rich in fructose?Show answer

   Seminal vesicles.

4. 4.Site of fertilisation?Show answer

   Oviduct (Fallopian tube).

5. 5.Define gestation.Show answer

   The period from fertilisation to birth (about 280 days in humans).

6. 6.Define parturition.Show answer

   Childbirth.

7. 7.Hormone maintaining pregnancy?Show answer

   Progesterone.

8. 8.Twins from one zygote?Show answer

   Identical (monozygotic) twins.

Quick revision checklist

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

• ☐Can you trace the path of sperms and name each accessory gland's role?
• ☐Can you explain ovulation and the corpus luteum?
• ☐Can you draw a sperm with functions of its parts?
• ☐Can you give four functions of the placenta?
• ☐Can you outline the menstrual cycle with hormones?
• ☐Can you give three differences between identical and fraternal twins?

Reproductive System: frequently asked questions