Marisa is at a point in her pregnancy when the blastocyst is moving down to her uterus, and the placenta begins to form. Which stage of prenatal development is Marisa currently experiencing?
A) fetal
B) embryonic
C) placental
D) germinal
Answer: D
Rationale: The germinal stage is the first phase of prenatal development and spans from conception to two weeks. During this phase, the blastocyst moves along the fallopian tubes and becomes implanted in the lining of the uterus. Soon after implantation, the blastocyst divides into a group of cells that continues developing into an embryo, and another group that forms the placenta.
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Skinner designed a soundproof apparatus, often equipped with a lever or bar, with which he conducted his experiments in operant conditioning. This has been called a _____
a) reinforcement chamber. b) Skinner box. c) rodent chamber. d) respondent behavior unit.
Through what process are gametes formed?
a. mitosis b. meiosis c. sex differentiation d. dimorphic cell division