IGCSE Biology - Human Reproduction

Main Sexual Hormones (female and male)

Testosterone - produced in Testes 

- male sex hormone

- promotes secondary male sexual characteristics (sperm production, voice breaking, increased muscle, pubic hair and hair growth)

Progestrone - produced in Ovaries 

- supports pregnancy 

- maintains uterus lining

Oestrogen - produced in Ovaries

- female sex hormone 

- promotes secondary female sexual characteristics (breasts develop, menstrual cycle starts, pubic hair growth, hips widen)

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Other Sexual Hormones (female)

Follicle Stimulating Hormone (FSH) - causes egg to mature inside a follicle in the ovaries

- stimulates ovaries to produce oestrogen

- inhibited (stopped) by progestrone 

Luteinising Hormone (LH) - causes ovulation (egg to be released)

- stimulated by oestrogen 

-  inhibited by progestrone

FSH and LH are both produced in the pituatary gland in the brain

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Comparing Male and Female Gametes

Male

  • Sperm
  • Produced in Testes
  • Made by meiosis*

Female 

  • Egg (ova)
  • Produced in ovaries
  • Made by meiosis*

* Meiosis - used for the production of gametes.Its goal is to make daughter cells with exactly half as many chromosomes as the starting cell.

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Menstrual Cycle

  • every month the female body prepares for pregnancy
  • this involves releasing an egg and making sure the uterus is in perfect condition for implantation
  • if pregnancy does not occur, the body will reset and start the process again
  • menstrual cycle is controlled by hormones (oestrogen, progestrone, FSH, LH)
  • on average lasts 28 days 
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Sexual Reproduction

  • Humans reproduce sexually with internal implantation
  • the male and females gametes must fuse (the male gamete moves towards the female gamete to fuse)
  • this is called fertilisation
  • the new cell formed is called a zygote
  • once the zygote is formed, it divides many times by mitosis to form the new organism
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Pregnancy

  • Once an embryo has been implanted, the placenta develops.
    • the placenta provides oxygen and nutrients to the embryo. also removes waste (urea + carbon dioxide, via the umbilical cord. The placenta also secretes female hormones that support the pregnancy.
  • During pregnancy the amnion (amniotic sac) encloses the developing embryo.
  • this secretes amniotic fluid which protects the developing embryo
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