HL 1 Biology

11.4c Fertilization


  • sperms released during intercourse are stimulated to swim into vagina by the calcium ions diffusing from vaginal fluids into the sperms tails 
  • sperms have receptors in the membranes that can detect chemicals released by egg; directs swimming towards egg
  • Process
    • Acrosome reaction
      • zona pellucida: coat of glycoproteins that surrounds the egg
      • acrosome: large membrane-bound sac of enzymes in the head of the sperm
      • once sperm makes contact with zona pellucida, contents of acrosomes released causing enzymes to loosen zona pellucida
      • enables sperms to get inside with their tail
    • Penetration of the Egg membrane
      • acrosome reaction exposes the membrane on tip of sperm which has proteins that can bind to the egg membrane
      • first sperm that gets through zona pellicula binds + sperm/egg membrane fuse
      • sperm nucleus enters egg cell = fertilization
    • The cortical reaction
      • sperms: bring parental genes + cause activation of egg
      • cortical granules: vesicles located near eg membrane
      • contents of  cortical granules released from egg by exocytosis
      • fertilization membrane: developed by interaction of chemicals in cortical granules with glycoproteins in the zona pellucida
      • prevents further entry of sperm + protects developing embryo

<<Embryo Development>>

  • blastocyts: as cell divisions occur, some divisions are unequal + migration of cells performed; causing embryos to shape of a hollow ball
  • implantation: the process to which the blastocyt sinks into the endometrium/uterus lining


Maternal Age and Pregnancy (p.282)

1) The trend in % of live births can be seen as: during age 20-24 theres is slightly an improvement in the percent. And during the 20s age, there is a stable percent. Decline seen after the 40s. 

2)  The slight improvement in 20-24 may be due to the complete growth and healthy eggs theses women in the age group consist. Also, there is a stable percent in the 20s as they are all still have a healthy growth of eggs. The decline of the percent is shown in the later age groups as the eggs become more weaker and less production in the growth of eggs is occurring.

3) Mothers younger than 15 have a high miscarriage rate as they may have incomplete growth. Also, their economic status may not be enough to raise a child. Also, theses girls may not have expected the pregnancy or even desired for a child.

4)  The differences in the percent of college educated mothers could be present due to the women returning to college after childbirth. And women postponing childbirth until college education and career established. So, the 35 age group is higher.

5) There are factors that can help determine which age group is ideal to have a child: the socioeconomic status tend to be better at later ages which could effect the ideal age. As the pregnancy miscarriage is low in the 20s, this may be an ideal age group. Also, ages 40 and above should be avoided as the risk of ectopic pregnancy is higher.

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