• Embryonic Development (Weeks 4–8) Most organs develop in the embryo during weeks 4 through 8.
  • An embryo forms three distinct cell layers, and each layer develops into different types of cells and organs.
  • If the embryo is exposed to toxins during this period, the effects are likely to be very damaging.
  • Can you explain why?
  • (Note: the drawings of the embryos are not to scale.)
  • The embryo is about 30 millimeters (just over 1 inch) in length by the eighth week of development.
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