Final answer:
Cell division is crucial for the growth and repair of multicellular organisms, starting with a single zygote and leading to a complex being. It is tightly regulated and crucial for tissue maintenance, although uncontrolled division can lead to diseases such as cancer.
Step-by-step explanation:
Cell Division and Growth in Organisms
Normally, cells only undergo division to replace dead/dying cells and during the growth phase of an organism. In humans, this process begins with a fertilized egg or zygote, with subsequent cell division ultimately leading to a complex, multicellular being. Even after full growth, cell division remains crucial for the repair and regeneration of tissues. For example, new blood and skin cells are created regularly through this same process. It is essential for multicellular organisms, as it facilitates growth, maintenance, and repair. In plants, cell growth and cell division contribute to lifelong growth, accompanied by cellular differentiation.
However, despite cell division's critical role in growth and maintenance, it must be tightly regulated. Uncontrolled division, as seen in cancer cells, can lead to severe illness. Additionally, the division time for various cell types can differ, as some tissues like epithelial cells divide more frequently due to higher rates of wear and tear.