Final answer:
Teratogens can affect development differently at different prenatal periods, and the effects depend on factors such as the type of teratogen, duration of exposure, and susceptibility of the fetus. Alcohol exposure during certain periods can cause facial abnormalities, and the embryonic stage is crucial for avoiding toxin exposure.
Step-by-step explanation:
Teratogens can affect development differently at different prenatal periods. The effects of teratogens on the developing fetus depend on factors such as the type of teratogen, the duration of exposure, and the susceptibility of the fetus to teratogenesis. For example, alcohol exposure during specific periods of gestation can lead to facial abnormalities associated with fetal alcohol syndrome. Likewise, the neural tube develops into the brain and spinal cord during the embryonic stage, making it particularly important for a pregnant woman to avoid exposure to toxins during this period.