Sexual and asexual reproduction

• Sexual reproduction — needs two parents and the fusion of gametes (sperm + egg). It mixes genes, so the offspring are genetically different — this creates variation.
• Asexual reproduction — needs one parent and no gametes (e.g. bacteria dividing, a strawberry plant sending out runners). Offspring are genetically identical clones.

Key difference: sexual reproduction uses meiosis to make gametes and gives variation; asexual reproduction uses mitosis only and gives identical clones.

Human reproductive systems

You need the main parts of each system and what they do:

• Male: testes make sperm and testosterone · scrotum holds the testes · sperm tube carries sperm · prostate gland adds fluid · urethra carries sperm out through the penis.
• Female: ovaries release eggs and make oestrogen · oviducts (where fertilisation happens) carry the egg to the uterus (womb) · the cervix is the neck of the uterus, leading to the vagina.

Where fertilisation happens: the sperm meets the egg in the oviduct (fallopian tube), not in the uterus. The fertilised egg then travels to the uterus to implant.

Male or female organ?

Tap an organ, then tap which system it belongs to.

Where does fertilisation happen?

Sex hormones

• Testosterone — made by the testes; the main male sex hormone. It causes male secondary sexual characteristics (e.g. deeper voice, facial hair, sperm production).
• Oestrogen — made by the ovaries; the main female sex hormone. It causes female secondary sexual characteristics (e.g. breast development, wider hips) and controls the menstrual cycle.

Match hormone to organ: testosterone → testes; oestrogen → ovaries. Both are made during puberty and drive the changes into adulthood.

The menstrual cycle

The menstrual cycle is roughly 28 days long. The key events are:

• Menstruation (days ~1–5) — the uterus lining breaks down and is lost (a period).
• The lining then rebuilds, controlled by oestrogen.
• Ovulation (around day 14) — an egg is released from an ovary. Fertilisation is most likely around this time.
• After ovulation, progesterone maintains the thick uterus lining, ready for a fertilised egg to implant.

Two key hormones here: oestrogen rebuilds the lining before ovulation; progesterone maintains it afterwards.

Your turn — timing the cycle

Which hormone, which organ?

Infertility & fertility treatment

Infertility is difficulty conceiving a baby. CCEA fertility treatments include:

• Fertility hormones — given to stimulate the ovaries to release several eggs (ova) at once.
• In vitro fertilisation (IVF) — eggs are collected and fertilised by sperm outside the body ("in vitro" = in glass), in a lab.
• Several embryos are grown and then transferred into the uterus.

"In vitro" clue: IVF means fertilisation happens in a lab dish, not inside the oviduct. The best embryos are then placed in the uterus.

Contraception

Contraception prevents pregnancy. CCEA groups methods as:

• Mechanical (barrier): the condom physically blocks sperm — and also helps stop STIs such as HIV/AIDS and chlamydia.
• Chemical (hormonal): the contraceptive pill and implants change hormone levels and stop the ovum developing/being released.
• Surgical: sterilisation cuts or blocks the sperm tubes (male) or oviducts (female).

Only barriers stop STIs: the condom is the only method here that also protects against sexually transmitted infections; the pill and sterilisation do not.

Match each method to how it works

Tap a method on the left, then its matching description on the right.

What is IVF?

Which gives variation?

The big ideas to know

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