In human development, an embryo is most sensitive to chemicals, radiation or pathogens at first trimester, because this is the time that
A) organ systems are growing in size.
B) cells are rapidly dividing and tissues are differentiating.
C) the enlarged yolk pushes the gastrula into a disk shape.
D) the allontoic stalk is disconnected from the placenta.
E) All of the above

Question

Quizplus · Accepted Answer

During the first trimester, the embryo undergoes rapid cell division and tissue differentiation, making it particularly vulnerable to outside factors such as chemicals, radiation, and pathogens. This is the time when the foundation for all future organ systems is being laid, meaning that damage to the developing cells and tissues can have long-lasting consequences for the health of the individual. The other choices listed (enlarged yolk pushing the gastrula into a disk shape, allontoic stalk disconnection from the placenta) are not relevant factors in why the first trimester is particularly sensitive.

In Human Development, an Embryo Is Most Sensitive to Chemicals