Unit4.3 Sex cells and reproductive systems

• There are 46 (23 pairs of) chromosomes in the nucleus of a human body cell. For each pair, one member comes from the father and the other from the mother.
• X and Y chromosomes are sex chromosomes. They determine the sex of an individual.
• Male sex cells are called sperms. A sperm looks like a tadpole, but much smaller in size. It has a head and a long tail.

  • The head contains the nucleus.
  • The nucleus carries half the number of chromosomes found in a body cell (i.e. 23 chromosomes).
  • The tail beats to allow the sperm to swim.
• Female sex cells are called ova. An ovum is much larger than a sperm. It is ball-shaped. It cannot move by itself.

  • The cell membrane is surrounded by a jelly coat.
  • The nucleus of an ovum also carries 23 chromosomes.
  • The cytoplasm contains a lot of food substances for early embryo development.
• Comparison of sperm and ovum:

  Sperm. Ovum

  Size and movement Smaller; Much larger;

  can move. Cannot move

  by itself. by itself

  Number of. 23. 23

  chromosomes.

  Sex chromosome X or Y. X only
• When a sperm and an ovum fuse together, a zygote is formed. The number of chromosomes in the zygote is restored to 46.
• A zygote with sex chromosomes XX will develop into a female. A zygote with sex chromosomes XY will develop into a male.
• Functions of the structures:

  Structure Function

  Testis Produces sperms and sex hormones Sperm duct Carries sperms from the testes to the urethra

  Sex glands. Produce a fluid which contains. nutrients for sperms; the fluid and the sperms form the semen

  Urethra. Carries semen and urine out of body at different times

  Penis. Carries semen and urine out of body at different times Carries semen to the female reproductive system during sexual intercourse

  
• Functions of the structures:

  Structure Function

  Ovary Produces ova and sex hormones Oviduct. Carries the ovum to the uterus Uterus. Provides a stable environment for the development of the embryo during pregnancy

  Vagina Receives the penis during sexual intercourse; acts as a birth canal during the birth of a baby