Mitochondria - are they really separate organisms that once merged into eukaryotic cells?
Yes. But it is incorrect to call mitochondria an organism now.
Most of their genes were lost and are now encoded in the nuclear genome
It gets most of its metabolites
It is not known. See the other post for details.
Why membrane: I guess you know that. Why folded: you guessed right.
Only ovum donates mitochondria and other cytoplasmic factors. Sperm just provides the haploid genome.
No
Most of them are key respiratory enzymes