Final answer:
If a multicellular organism could not perform mitosis, it would likely die as it could no longer replace damaged or dead cells, hindering growth and tissue repair.
Step-by-step explanation:
If a multicellular organism no longer performed mitosis, it would likely lead to the organism's death because it would not be able to produce new cells to replace those that are damaged or dead. Mitosis is essential for an organism's growth, maintenance, and repair of tissues. Without this process, the organism cannot regenerate tissues or even maintain its current form, leading to system failure and death. While cells produced by meiosis are critical for sexual reproduction, they are not a replacement for the wide variety of cells needed in a multicellular organism, which are produced through mitosis. In simple terms, no mitosis means no new cells, leading to the inevitable decline and death of the organism.
In contrast, single-celled organisms like amoebas reproduce solely by mitosis, keeping their genetic makeup consistent across generations unless mutations occur. For multicellular organisms, cells produced through mitosis develop into various cell types and tissues necessary for the organism's structure and function, further proving the indispensability of mitosis.