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4.7.2Additional lessons

Sexual Reproduction — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 56 of 101

📚 IB Biology HL Hub / Topical Revision
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Part 1 of 5Gametes and Fertilisation

4.7.2 Sexual Reproduction
Sperm
  • Small, motile male gametes made in large numbers, each carrying a haploid nucleus with an acrosome and a tail for swimming.
Egg
  • A larger female gamete that is non-motile, with food reserves, and made in much smaller numbers.
External fertilisation
  • Gametes are released into water where fusion occurs, typical of fish and amphibians, and requires moisture and many gametes.
Internal fertilisation
  • Sperm are placed in the female's body, protecting the gametes from drying out and improving the chance of fusion.

Part 2 of 5Male System

Testis
  • Contains seminiferous tubules where sperm are made and interstitial cells that secrete testosterone.
Epididymis and vas deferens
  • Sperm mature and are stored in the epididymis, then travel along the vas deferens.
Seminal vesicles and prostate
  • These glands add fluid containing fructose, alkali and enzymes, which nourish and protect sperm as semen.
Urethra and penis
  • The urethra carries semen out of the body, and the penis places it in the female tract.

Part 3 of 5Female System

Ovary
  • Contains follicles in which eggs develop and secretes oestradiol and progesterone.
Oviduct
  • The egg is swept along by cilia, and fertilisation normally takes place here.
Uterus
  • A muscular organ with a lining, the endometrium, where an embryo implants and develops.
Cervix and vagina
  • The cervix is a ring of muscle closing the uterus, and the vagina receives sperm and forms the birth canal.
StructureMaleFemale
Gamete producerTestisOvary
Gamete transportVas deferensOviduct
HormonesTestosteroneOestradiol, progesterone

Part 4 of 5Pathway of Sperm

1
Sperm are produced in the seminiferous tubules of the testis and mature in the epididymis.
2
At ejaculation they pass through the vas deferens and mix with fluids from the seminal vesicles and prostate.
3
Semen leaves through the urethra and is deposited in the vagina near the cervix.
4
Sperm swim through the uterus into an oviduct, where one may fertilise an egg.

Part 5 of 5Exam Checklist & Tips

4.7.2 – Key Points for the Exam

  • Testis The male organ that produces sperm and testosterone.
  • Ovary The female organ that produces eggs and sex hormones.
  • Endometrium The lining of the uterus that thickens ready for implantation.
  • Semen Fluid containing sperm and secretions from the male glands.

Common Mistakes

  • Confusing the urethra with the ureter; the ureter carries urine from the kidney only.
  • Saying fertilisation occurs in the uterus; it occurs in the oviduct.
  • Stating that the prostate gland produces sperm.
  • Mixing up the roles of testosterone and oestradiol.

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