In the third through eighth weeks of a human pregnancy, the developing organism is referred to as a(n)
a. zygote.
b. embryo.
c. blastocyst.
d. fetus.
Question 2
The arrival of an action potential in a muscle fiber causes
a. calcium to enter the muscle fiber.
b. calcium to be released by internal organelles.
c. acetylcholine to enter the muscle fiber.
d. acetylcholine to be released by internal organelles.