Describe fertilisation, implantation and the role of the placenta in humans.

1. 1 · Define fertilisation. Fertilisation is the fusion of a haploid sperm and a haploid ovum to form a diploid zygote. It takes place in the fallopian tube.
2. 2 · Early development.
   • The zygote divides by mitosis (cleavage) → morula → blastocyst.
   • It moves down the fallopian tube to the uterus.
3. 3 · Implantation. About 6 to 7 days after fertilisation, the blastocyst sinks into the endometrium.
4. 4 · Draw the stages. [Diagram: fallopian tube with ovum and sperm, zygote, morula, blastocyst, uterus with the implanted blastocyst]
5. 5 · The placenta.
   • Passes food and oxygen to the foetus.
   • Removes carbon dioxide and wastes.
   • Makes hormones; the umbilical cord joins it to the foetus.
6. 6 · Birth. After about 280 days, oxytocin makes the uterus contract and the baby is born (parturition).
7. 7 · Link to daily life. Iron and folic acid tablets and regular check-ups protect mother and baby; colostrum protects the newborn.
8. 8 · Close. So a single zygote becomes a baby, fed by the placenta inside the uterus.

Scoring tip: Write the stages in order with arrows: zygote → morula → blastocyst → implantation. The order earns marks.