Comment by xenadu02

> Take away the mitochondria [...] can cells live on their own?

Neither can live without the other. Too much genetic exchange has taken place in some distant ancestor where critical genes were deleted from mitochondria and moved to the host. Meanwhile host cells became utterly dependent on mitochondria for energy production. Or you might say: the mitochondria were producing so much excess ATP the host cells started evolving to depend on that much energy being available.

The exceptions are later cases (like a few organisms that have copied energy production from the mitochondria genome then later lost the mitochondria entirely).

For all purposes mitochondria are zombie archaea (not bacteria). Hollowed out empty shells retaining just enough function to perform aerobic respiration and reproduce. There is little pressure to evolve away from this local maxima. What benefit would the host cells derive from getting rid of the mitochondria? Not much. And having those critical functions isolated in what amounts to a pseudo-organelle with its own DNA protects it from a lot of sources of damage/error.

So... are we obligate symbiotes? Or have mitochondria hyper-evolved to such a point they are just organelles in our cells - just ones that carry their own DNA instead of relying on the cell's main DNA? Like much of biology... a bit of both in a fuzzy mix without a clear line.