ZIMSEC O Level Combined Science Notes: Pregnancy

  • The vagina receives an erect penis during sexual intercourse
  • During sexual intercourse, sperms are ejaculated into the vagina
  • There they begin to swim up to the oviducts
  • If an ovum is released at this time it may be fertilised in the oviduct
  • Although many sperms reach the ovum only one will fertilize it
  • A membrane barrier is formed around the ovum to after fertilization to prevent other sperms from fertilising it
  • The male and female nuclei join to form a zygote
Pregnancy at 40 weeks

Pregnancy at 40 weeks

  • This zygote grows into an embryo 
  • The sperm and ovum contributes 23 chromosomes each
  • Chromosomes carry genes which determine the genetic structure of the child
  • The zygote which is formed after fertilization starts to divide and soon becomes a ball of cells
  • which moves down the oviduct towards the uterus
  • It implants itself in the prepared lining of the uterus
  • The developing embryo/foetus later develops a placenta
  • The placenta separates  the mother’s blood from that of the developing baby
  • Substances including carbon dioxide, oxygen and food diffuse in and out via the placenta
  • These substances pass through the umbilical cord which connects the placenta to the developing foetus
  • The embryo develops organs such as a heart and blood vessels
  • At about 10 weeks the human foetus can be easily recognised with fingers, ears, toes and eyes
  • A bag called the amnion grows around the foetus
  • It is filled with amniotic fluid
  • This fluid protects the baby from its mother’s bumps and falls
  • The gestation period in humans is approximately 280 days/40 weeks/9 months

To access more topics go to the Combined Science Notes page


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