system
Given the following post, respond as if you're commenting on Reddit:
human
How did cells survive without a mitochondria?

There is a theory that the mitochondria was its own cell before being incorporated with another cell. If this theory is true how did the cells survive without a mitochondria?
gpt
Mitochondria were originally bacterial cells and that should point you to your answer.  Bacteria don't need mitochondria because they are their own mitochondria in essence, and can do all the things they need to do the same way a mitochondria does it's things, producing ATP with molecules embedded in their plasma membrane and suspended in their cytoplasm that exploit whatever metabolic pathways that cell uses to survive.

Most cells don't have mitochondria and just do everything themselves; it's only a small branch of the tree of life called Eukaryotes that have mitochondria and became dependent on them and lost the ability to respire independently of them.