[jeffreyH (OP)]

Higher order organisms contain many cells but how many do bacteria contain?

[Bored chemist]

1

[syhprum]

Congratulations for the shortest correct answer on record

[evan_au]

There is a popular theory that some interior structures of the  bacterial more complex eukaryotic cell were once separate organisms which came to live within the cell in a symbiotic relationship.
- The case is strongest for mitochondria and chloroplasts, which have their own DNA
- It's not quite so clear for other organelles like ribosomes, which have no DNA, but do contain structural RNA
See: https://en.wikipedia.org/wiki/Bacteria#Cellular_structure
https://en.wikipedia.org/wiki/Ribosome#Origin

Correction: Bacteria → Eukaryotic (thanks, Chris!)

[chris]

There is a popular theory that some interior structures of the bacterial cell were once separate organisms which came to live within the bacterial cell in a symbiotic relationship.
- The case is strongest for mitochondria and chloroplasts, which have their own DNA
- It's not quite so clear for other organelles like ribosomes, which have no DNA, but do contain structural RNA
See: https://en.wikipedia.org/wiki/Bacteria#Cellular_structure
https://en.wikipedia.org/wiki/Ribosome#Origin

Evan, I think you are getting confused by the endosymbiont theory that accounts for the organelles, like mitochondria, in some eukaryotes.

While it is true that the elements that operate inside a bacterial cell may have once been separate processes that were brought together to make a bacterium as a single-celled entity, complex structures like mitochondria are thought to be ancient bacteria themselves that sought refuge inside a eukaryotic cell with one providing a function for the other.

[Bored chemist]

Congratulations for the shortest correct answer on record

There was no "plan B"

[CliffordK]

While a bacterium is a single cell, I believe some of them form colonies with some organization, and cellular adhesion. 

[Bored chemist]

While a bacterium is a single cell, I believe some of them form colonies with some organization, and cellular adhesion. 

About 9 months before birth, a human is a single cell.
They then produce remarkably complex colonies, such as the one typing this message.