Sexual Reproduction: Fertilisation & Implantation

What is fertilisation?

Fertilisation is the process required for sexual reproduction where male and female gametes meet and fuse to form a zygote

What are the functions of specialised reproductive organs?

1. Produce gametes through gametogenesis (meiosis)

2. Transfer gametes to a site where fertilisation can occur

3. Produce sex hormones

4. (females) nurture and support the developing offspring

What is external fertilisation?

• Occurs outside the body in aquatic/moist environments

• Requires the simultaneous release of gametes

• Common in most invertebrates, fish and amphibians

• Produces many gametes and offspring due to low survival rates

• No parental care

What is internal fertilisation

• Occurs inside the female body

• Involves male attraction and copulation (requires energy and has risks)

• Common in insects, snails, reptiles, mammals and birds

• Produces fewer gametes and offspring due to higher survival rates

• Parental care is more common

What reproductive mechanisms do mammals use for success?

1. Internal fertilisation to increase the likelihood of gametes meeting

2. Implantation of the embryo into the uterine wall

3. Pregnancy to protect and nourish the developing young

What is gametogenesis?

The process of producing gametes (sperm and eggs) in the reproductive organs through meiosis, creating genetically unique haploid cells

What is spermatogenesis?

• The production of sperm in the testes

• Begins at puberty and continues for life

• Occurs in the seminiferous tubules

• Produces four sperm cells per cycle

What is oogenesis?

• The production of ova (eggs) in the ovaries

• Begins before birth, but only one egg is produced per cycle after puberty

• Stops at menopause

What happens to the oocyte during oogenesis?

1. Before birth → one oogonium fomrs one primary oocyte

2. Each ovarian cycle →

   • Meiosis I → forms a secondary oocyte and a polar body

   • Meiosis II → only fertilised eggs complete this step

What happens during ovulation?

• The mature egg is released from the ovarian follicle

  • The follicle becomes the corpus luteum, releasing hormones to prepare for implantation

What are the key differences between spermatogenesis ansd oogenesis?

Feature	Spermatogenesis	Oogenesis

Location

Testes

Ovaries

Number of gametes

4 sperm

1 egg

Size

~0.05 mm

~0.12 mm

Age of onset

Puberty (12-16 years)

Before birth

Frequency

74-day cycle

Monthly cycle

Hormones

FSH, LH, testosterone

FSH, LH