Final answer:
Every living organism, from single-celled amoebas to complex humans, requires mitosis for growth, repair, and reproduction. Multicellular organisms use mitosis to expand the number of cells from a single zygote into a full organism and to replace damaged tissues, whereas for single-celled organisms, it is a form of asexual reproduction.
Step-by-step explanation:
Every living organism goes through mitosis as a part of its growth, maintenance, and repair processes. In multicellular organisms, like humans, mitosis is crucial from the very beginning of life as a zygote, through to adulthood for tissue repair and regeneration, such as the production of new blood and skin cells. Cell division is tightly regulated to maintain healthy functions, and failure in this regulation can lead to serious consequences. For single-celled organisms, cell division through mitosis is also the method of reproduction, ensuring the continuity of their species.
While mitosis is a hallmark of both unicellular and multicellular life forms, the outcome differs. In multicellular organisms, it leads to the proliferation of cells that contribute to growth and function within an organism, while in unicellular organisms, it's a means of reproduction, creating genetically identical offspring. The genetic makeup in each nucleus of an organism's cells stays consistent since every cell contains the same genome; this is a principle demonstrated in the early developmental stages and maintained throughout the organism's life.
However, it's important to note that not every living organism goes through mitosis. Organisms that reproduce asexually, like bacteria, do not undergo mitosis, instead, they divide by a process called binary fission. Additionally, some cells within multicellular organisms don't divide, such as certain neurons and muscle cells.