Question

by the ______ week of development, the embryo may have begun some movement.

a third
b eighth
c fifth
d second

Explanation:

Analyze the question prompt

The question asks for the specific week of prenatal development by which the embryo may have begun some movement.

Evaluate embryonic movement timeline

Using the Embryonic Stage and Fetal Muscle Development knowledge points
During early human development, the embryonic period spans from fertilization to the end of the eighth week. Muscle tissue begins to form and primitive, involuntary twitching or movement of the embryo starts to occur by the eighth week of development, which is the final week of the embryonic stage.

Assess the given options

Using the Embryonic Stage knowledge point

• (a) Third week: Too early; gastrulation and neural tube formation are just beginning.
• (b) Eighth week: Correct; the embryo begins to show initial spontaneous movements.
• (c) Fifth week: Too early; limb buds are just forming.
• (d) Second week: Too early; implantation is occurring.

Answer:

• a Third
• b Eighth (Correct answer)
• c Fifth
• d Second