Okay, as a biologist it really upsets me how that phrase is written off. I did an impromptu half hour lecture for my wife about how significant "the mitochondria is the powerhouse of the cell" is,
The mitochondria is what ties everything on this planet together, it's the one thing that ties all life together, it is the exact same mechanism in plants as it is in animals, it takes the same ingredients and does the same function, and comes from the same origin.
There is no chain in our DNA that codes for the mitochondria, it exists outside of our DNA, it has no relationship with our DNA, it only fuels reading DNA and it's decoding and replication, but it isn't included in our genetics. It replicates itself, it exists as a separate entity, and it acts as the functioning unit for all energy within the cell.
It would be like if when a child was born their lungs were provided by an outside source and had the same genetic material as everyone else's lungs. Oh and puppy lungs, and crab lungs, and avocado lungs, and grass lungs, every single living thing on this plant has the same lung genetic material. And it has no clue that it serves this function, all it knows is ADP goes in, ATP goes out, and ATP is energy that fuels all function of all life.
And it comes from the friggin mitochondria.
Please be impressed with that little hitch hiker, it is the powerhouse that powers your neurons, grows the vegetables you eat, and makes life happen on earth.
How will we know something extraterrestrial comes our way? They'll have their own mitochondria, because something needs to power their cells, and it won't be the same as ours.
Writing off the mitochondria from biology is like writing off the exchange of goods in economics, or doing physics without the concept of mass, or art without feeling. There is nothing more basic, more fundamentally important to biology than the existence of the mitochondria, and it's role as the powerhouse of the cell.
MITOCHONDRIA IS THE POWERHOUSE OF THE CELL. That you know that makes me happy.