A Zimbabwean family

A Zimbabwean family

ZIMSEC O Level Combined Science Notes: Reproduction in Humans

  • Human being produce sexually
  • The process involves the fusion (joining) of the nuclei (sex cells) of the male gamete (sperm)
  • and the female gamete (ovum)
  • To form a zygote
  • The human and female sexual organs take part in this process
  • Each of these have adapted in a way that ensures that fertilization takes place
  • Both male and female bodies become sexually mature during the puberty period
  • The bodies undergo changes in appearance and behavior
  • They start to produce mature sex cells
  • Sex cells are also known as gametes
  • Sex hormones are released to continue this sexual development


  • Is a time when a girl or boy starts to become sexually mature
  • It usually happens between ages 10 and 14 for girls and ages 12 and 16 for boys
  • It causes various changes in the physical and emotion in the maturing child:
  • In boys:
    1. Pubic hair starts to grow around sexual organs and under armpits
    2. Voice deepens
    3. Facial hair starts to grow
    4. Sexual organs grow
    5. Mood swings
    6. Acne (pimples may appear on skin)
    7. Adam’s apple may grow
    8. Sexual feelings and wet dreams
    9. May become muscular
    10. Possible body odours
  • In girls:
    1. Breast development
    2. Pubic hair grows
    3. Uterus and follicles grow bigger
    4. Menustration begins
    5. Possible body odour
    6. Possible Acne

NB The onset of puberty differs from person to person.

To access more topics go to the Combined Science Notes page