Final answer:
Rapid cell division occurs during embryonic development and organogenesis, where the zygote divides and forms the structures necessary for the fetus's growth and organ formation.
Step-by-step explanation:
Cell division occurs rapidly during two primary periods of development: embryonic development and organogenesis. During embryonic development, the zygote undergoes several rapid mitotic cell divisions to form a multicellular organism, while organogenesis is the phase where the formation of organs takes place. Cell division is crucial in these stages for the growth and differentiation of cells that ultimately form the complex structures of a developing organism.
The germinal stage of human development is when the zygote undergoes early cell divisions and stages, culminating in the blastocyst implanting in the uterus to become an embryo. After this, the embryonic stage starts and lasts until the eighth week after fertilization, being characterized by significant growth, gastrulation, neurulation, and organogenesis. Following this, the fetal stage begins, and it is marked by continued growth and fine-tuning of the already formed organs and systems.