Biology, Eighth Edition (Raven)

Chapter 53: Animal Development

Fetal Development and Risk

How is the type of risk to a fetus related to the developmental stage? As animals develop they go from a small number of non-specialized cells to an larger number of more specialized cells. The increased size of the embryo means an increased nutritional demand. Damage to the embryo at a very early stage is likely to result in a non-viable embryo because the loss of even a single cell means that a major part of the body will not form properly. As development proceeds damage will become more specific as the cells specialize. As the nutritional demands of the embryo increase the amount and quality of the food supplied by the mother become more important. The embryo is most vulnerable to damage overall during the middle and early periods of pregnancy.

View the animation below, then complete the quiz to test your knowledge of the concept.


Which of the following are at high risk from week 3 through week 16 of a pregnancy?
D)central nervous system

During which trimester is the fetus at greatest risk?
A)first trimester
B)second trimester
C)third trimester
D)fourth trimester

During which trimester does the fetus gain the most weight?
A)first trimester
B)second trimester
C)third trimester
D)fourth trimester

Two widely accepted criteria for a successful pregnancy are (1) a pregnancy of longer than 37 weeks and (2) a birth weight of more than
A)3.5 pounds.
B)5.5 pounds.
C)7.5 pounds.
D)9.5 pounds.

In general, the longer the gestation period and the greater the birth weight, the chance of medical problems will occur are...
A)more likely.
B)less likely.
C)gestation period and birth weight do not affect chance of medical problems
D)the lower the birth weight the less likely the chance of medical problems
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