Final answer:
Cell division is the process that creates new cells and is necessary for the development of an embryo. Cells divide for growth and the repair or regeneration of tissues.
Step-by-step explanation:
Cell division is a fundamental process through which cells replicate, leading to the growth and reproduction of organisms. In humans, cell division is integral for the proper development of an embryo from a fertilized egg, which forms after the fusion of male and female gametes (sperm and egg cells).
When a haploid sperm cell enters a haploid egg, the result is a diploid zygote. This zygote is the beginning of new life and undergoes a series of cell divisions that drive the growth and differentiation necessary to form a complex multicellular organism. The first mitotic cell divisions result in a morula, followed by the formation of a blastocyst, eventually leading to the implantation in the uterus and further embryonic development.
Cells must divide for two main reasons: the maintenance and repair of tissues, as well as for growth. In multicellular organisms, this is essential not just during development, but also throughout an organism's life to replace cells that are lost due to wear and tear or injury.