CIE iGCSE Co-ordinated Sciences-B15.4 Sexual reproduction in humans - Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B15.4 Sexual reproduction in humans – Study Notes
CIE iGCSE Co-ordinated Sciences-B15.4 Sexual reproduction in humans – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
Identify on diagrams and state the functions of the following parts of the male reproductive system: testes, scrotum, sperm ducts, prostate gland, urethra and penis
Identify on diagrams and state the functions of the following parts of the female reproductive system: ovaries, oviducts, uterus, cervix and vagina
Describe fertilisation as the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell)
Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual characteristics during puberty
Describe the menstrual cycle in terms of changes in the ovaries and in the lining of the uterus (knowledge of sex hormones is not required)
Supplement
Explain the adaptive features of sperm, limited to: flagellum, mitochondria and the presence of enzymes in the acrosome
Explain the adaptive features of egg cells, limited to: energy stores and the jelly coat that changes at fertilisation
Compare male and female gametes in terms of: size, structure, motility and numbers
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Male Reproductive System
📌 Introduction
The male reproductive system produces sperm (male gametes) and delivers them to the female reproductive system for fertilisation.
🌱 Main Structures & Functions
- Testes (singular: testis)
Produce sperm cells (by meiosis) and the hormone testosterone. - Scrotum
Sac that holds testes outside the body.
Keeps them at ~35°C → slightly cooler than body temperature for healthy sperm production. - Sperm ducts (vas deferens)
Tube that carries sperm from the testes to the urethra. - Prostate gland
Produces fluid that mixes with sperm → forms semen.
Semen nourishes sperm and helps them move. - Urethra
Tube that carries semen and urine out of the body (not at the same time). - Penis
Transfers sperm into the female reproductive system during sexual intercourse.
📊 Summary Table
| Structure | Function |
|---|---|
| Testes | Produce sperm + testosterone |
| Scrotum | Keeps testes at correct temperature |
| Sperm ducts | Carry sperm to urethra |
| Prostate gland | Add fluid → semen |
| Urethra | Carries semen/urine out |
| Penis | Transfers sperm to female |
⚡ Quick Recap
Testes = sperm factory
Scrotum = cooling bag
Sperm ducts = transport tubes
Prostate = semen fluid
Urethra = exit tube
Penis = delivery organ
Female Reproductive System
📌 Introduction
The female reproductive system produces eggs (ova), provides the site for fertilisation, and supports the development of the embryo/foetus.
🌱 Main Structures & Functions
- Ovaries
Function: Produce egg cells (ova).
Also secrete female hormones oestrogen and progesterone. - Oviducts (fallopian tubes)
Function: Carry the egg from the ovary to the uterus.
Fertilisation occurs here. - Uterus (womb)
Function: Muscular organ where the fertilised egg implants.
Provides protection, nutrients, and oxygen for the developing embryo/foetus. - Cervix
Function: Narrow opening between the uterus and vagina.
Holds the foetus inside the uterus during pregnancy and opens during birth. - Vagina
Function: Receives sperm during sexual intercourse.
Acts as the birth canal during delivery of the baby.
📊 Summary Table
| Structure | Function |
|---|---|
| Ovaries | Produce eggs + female hormones |
| Oviducts | Transport egg; site of fertilisation |
| Uterus | Site of embryo implantation & development |
| Cervix | Narrow opening; keeps foetus inside, opens for birth |
| Vagina | Receives sperm; birth canal |
⚡ Quick Recap
Ovaries = Egg factory
Oviduct = Fertilisation site
Uterus = Baby’s home
Cervix = Gatekeeper
Vagina = Entry for sperm, exit for baby
Fertilisation in Humans
📌 Definition
Fertilisation is the process where the nucleus of a male gamete (sperm) fuses with the nucleus of a female gamete (egg cell).
🌱 Key Points
- Occurs in the oviduct (fallopian tube).
- Restores the diploid chromosome number (46 in humans).
- Forms a zygote → the first cell of a new individual.
- Zygote divides by mitosis → develops into an embryo.
📊 Summary Flow
- Sperm reaches egg in oviduct.
- Sperm nucleus enters egg cell.
- Fusion of nuclei → zygote formed.
- Zygote → embryo → foetus.
⚡ Quick Recap
Fertilisation = Sperm nucleus + Egg nucleus → Zygote.
Happens in oviduct.
Restores diploid number.
Memory tip: “Fusion → Formation of future life.”
Hormones & Secondary Sexual Characteristics
📌 Introduction
During puberty, hormones trigger the development of secondary sexual characteristics, which are features that distinguish males from females but are not directly involved in reproduction.
🌱 Testosterone (Male)
- Produced by testes.
- Roles in puberty:
- Growth of facial, pubic, and body hair.
- Deepening of the voice (larynx enlarges).
- Increase in muscle mass and strength.
- Growth of penis and testes.
- Stimulates sperm production (gamete development).
🌸 Oestrogen (Female)
- Produced by ovaries.
- Roles in puberty:
- Development of breasts.
- Widening of hips.
- Growth of pubic and underarm hair.
- Regulation of menstrual cycle.
- Development of reproductive organs (uterus, vagina).
📊 Summary Table
| Hormone | Produced by | Secondary Sexual Characteristics |
|---|---|---|
| Testosterone | Testes | Facial/body hair, deep voice, muscle growth, penis/testes growth, sperm production |
| Oestrogen | Ovaries | Breast development, widened hips, pubic/underarm hair, menstrual cycle, reproductive organ growth |
⚡ Quick Recap
Testosterone = Male puberty changes
Oestrogen = Female puberty changes
Memory tip: “T = Testosterone → Tough & tall; O = Oestrogen → Ovaries → outward female features.”
Menstrual Cycle
📌 Introduction
The menstrual cycle is a monthly series of changes in the ovaries and uterus to prepare for pregnancy. If fertilisation does not occur, the uterus lining is shed as menstrual flow.
🌱 Key Stages
- Menstruation (Days 1–5 approx.)
Ovaries: Egg from previous cycle is not released.
Uterus lining: Broken down and shed → bleeding occurs. - Follicle/Preparation Stage (Days 6–13 approx.)
Ovaries: An egg matures inside a follicle.
Uterus lining: Thickens and becomes rich in blood vessels → ready to support a fertilised egg. - Ovulation (Day 14 approx.)
Ovaries: Mature egg is released from the ovary.
Uterus lining: Remains thick and ready for implantation. - Luteal / Post-Ovulation Stage (Days 15–28 approx.)
Ovaries: If egg not fertilised, it disintegrates.
Uterus lining: Breaks down → next menstrual period begins.
📊 Summary Table
| Stage | Ovaries | Uterus Lining |
|---|---|---|
| Menstruation | No active egg | Shed → bleeding |
| Follicle/Preparation | Egg matures | Thickens, blood vessels develop |
| Ovulation | Egg released | Ready for implantation |
| Luteal/Post-Ovulation | Egg disintegrates if unfertilised | Breaks down → next period |
⚡ Quick Recap
Ovaries: egg matures → released → disintegrates.
Uterus: lining thickens → ready → shed.
Cycle repeats ~28 days.
Memory tip: “Egg rises → lining builds → egg falls → lining spills.”
Adaptive Features of Sperm
📌 Introduction
Sperm cells are specialised for delivering male genetic material to the egg. They have several adaptations to reach and fertilise the egg.
🌱 Key Adaptations
- Flagellum (tail)
Long, whip-like structure.
Function: Enables sperm to swim through the female reproductive tract toward the egg. - Mitochondria
Found in the midpiece of the sperm.
Function: Produce energy (ATP) by respiration to power the flagellum. - Acrosome (tip of the head)
Contains enzymes.
Function: Enzymes help digest the outer layer of the egg (zona pellucida) so the sperm nucleus can enter.
📊 Summary Table
| Feature | Location | Function |
|---|---|---|
| Flagellum | Tail | Movement → swim to egg |
| Mitochondria | Midpiece | Provide energy for movement |
| Acrosome | Head | Enzymes digest egg covering → entry of sperm |
⚡ Quick Recap
Flagellum = swimming
Mitochondria = energy
Acrosome = entry tool
Memory tip: “Tail to move, middle for power, head to penetrate.”
Adaptive Features of Egg Cells
📌 Introduction
Egg cells are specialised for fertilisation and early development. They have adaptations that support the sperm’s entry and provide energy for the zygote.
🌱 Key Adaptations
- Energy Stores (cytoplasm)
The egg contains nutrients and energy reserves.
Function: Supports early cell divisions (mitosis) and growth of the zygote until it can obtain food from the environment or mother. - Jelly Coat (protective layer)
Surrounds the egg.
Function: Acts as a barrier to many sperm. Changes during fertilisation → prevents more than one sperm entering (polyspermy).
📊 Summary Table
| Feature | Function |
|---|---|
| Energy stores | Supply nutrients/ATP for early zygote growth |
| Jelly coat | Barrier for sperm; prevents polyspermy |
⚡ Quick Recap
Energy = zygote nourishment
Jelly coat = selective entry
Memory tip: “Egg stores energy and locks door after one sperm enters.”
Comparison of Male & Female Gametes
📌 Introduction
Gametes are sex cells produced by males and females for sexual reproduction. Male = sperm; Female = egg (ovum). They differ in size, structure, motility, and number.
🌱 Key Differences
| Feature | Male Gamete (Sperm) | Female Gamete (Egg) |
|---|---|---|
| Size | Very small, microscopic | Large, visible to naked eye |
| Structure | Head (nucleus + acrosome), midpiece (mitochondria), tail (flagellum) | Round, cytoplasm with energy stores, jelly coat |
| Motility | Motile → swims using flagellum | Non-motile → carried by female reproductive tract |
| Numbers | Millions produced continuously | Few produced at intervals (e.g., one per month in humans) |
⚡ Quick Recap
Sperm = small, motile, many
Egg = large, non-motile, few, nutrient-rich
Memory tip: “Sperm swims in numbers, egg waits with food.”