Edexcel IGCSE Biology: Double Science 复习笔记 3.1.5 Sexual Reproduction in Humans

Edexcel IGCSE Biology: Double Science 复习笔记 3.1.5 Sexual Reproduction in Humans

The Male Reproductive System

 

The-male-reproductive-system

 

The male reproductive system

 

 

 

Male Reproductive Structures & their Function Table

 

 

16.4-The-Male-Reproductive-System-table 

The Female Reproductive System

 

The-female-reproductive-system

 

The female reproductive system

 

 

 

Female Reproductive Structures & their Function Table

16.4-The-Female-Reproductive-System-table

 

The Gametes

 

  • A gamete is a sex cell (in animals: sperm and ovum; in plants pollen nucleus and ovum) produce by meiosis
  • Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells
  • This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells
  • In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
  • Gametes have adaptations to increase the chances of fertilisation and successful development of an embryo

 

 

Sperm Cell & Egg Cell Table

16.4-Gametes-_-Fertilisation-table

 

 

 

Comparing-sperm-and-egg-cells-illustration

 

Comparing sperm and egg cells

 

 

 

Adaptive Features of Gametes Table

16.4-Adaptations-of-Gametes-Explained-table

 

 

Comparison of Gametes Table

16.4-Comparison-of-Male-_-Female-Gametes-table

 

Fertilisation

 

  • During ejaculation in the male, millions of sperm cells move along the sperm duct (also known as the vas deferens)
  • The sperm are suspended in semen (a fluid secreted by the prostate gland)
  • The semen passes into the urethra
  • During sexual intercourse, semen is ejaculated into the vagina of the female, near the cervix
  • The sperm cells then follow a chemical trail and travel through the plug of mucus in the cervix to reach the uterus (the womb)
  • The sperm cells then travel into the oviducts
  • If a sperm cell meets an egg cell in the oviduct, fertilisation can occur
    • This is most likely to occur 1-2 days after the female has ovulated (released an egg cell from one of her ovaries into an oviduct)

     

  • Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)
    • During fertilisation, the head of a sperm cell releases enzymes that digest a path through the protective outer layer of the egg cell, allowing the sperm to pass through the egg cell membrane
    • Once this occurs, the egg cell immediately releases a thick layer of material that prevents any more sperm cells from entering, ensuring only one sperm cell can fertilise the egg cell

     

  • When the male and female gametes fuse, they become a zygote (fertilised egg cell)
  • This zygote contains the full 46 chromosomes (23 pairs of chromosomes), half of which came from the father and half from the mother
  • The zygote divides by mitosis to form two new cells, which then continue to divide like this until an embryo is formed after a few days
  • Cell division continues and eventually many of the new cells produced become specialised to perform particular functions and form all the body tissues of the offspring

 

 

Fertilisation-in-Humans.png

 

The process of fertilisation in humans

转载自savemyexams

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