Here's why:
* Unicellular organisms: Individual cells within a unicellular organism *can* live for a very long time. Some bacteria can survive for thousands of years in dormant states. However, they are also prone to rapid death due to environmental factors, predation, or simply reaching the end of their lifespan.
* Multicellular organisms: Individual cells within a multicellular organism have a limited lifespan. They are constantly dying and being replaced. However, the organism as a whole can live for much longer than any individual cell.
So, the key difference:
* Unicellular: Individual cells can have very long lifespans, but the entire organism is vulnerable to quick death.
* Multicellular: Individual cells have short lifespans, but the organism as a whole can live for a long time due to the constant turnover of cells.
In conclusion: It's not a fair comparison to say one is "longer-lived" than the other. It depends on how you're measuring lifespan.
