To make the whole thing a bit more complicated, a typical human body contains (or has living on its surface, or in its gut) about ten bacteria for each body cell.
These too, generally but not invariably, cooperate with the cells that we have more right to think of as 'our cells'.
And then there are viruses
A virus is typically about a thousandth the volume of a bacterium.
It cannot be called a living organism because it cannot reproduce; it requires living organisms to reproduce it. A virus is a product of living organisms, it might be considered, in most cases, as being a manifestation of a fault in the design of living organisms.
A harmful virus may be compared to a
religion or any other false belief such as the
absurd idea that wind turbines cause illness or that
underground water can be located with a forked stick.
A meme cannot exist without a hosting intelligent organism to reproduce it.
Harmful memes, such as the examples above, are like harmful viruses.
Of course there are good memes and
useful viruses too. Some viruses can help protect us from cancers, bacteria and other viruses.
The cells that we think of as being our cells sometimes go their own way and multiply beyond the control of the systems that normally regulate our bodies; in an animal this is called cancer; if it was a group of people in a human society going their own way beyond the control of the government it would be called rebellion.
Consider the humble
This is a sort of a transitional thing between a single celled organism and a multicellular organism.
The cells that make up a slime-mould live an independent life for a time, and then come together to form 'a single organism' to reproduce.
(Or maybe they don't form a single organism?
Should the breeding body be called an organism or a cooperative?)
A bacterium (or an organelle) is a very complex thing.
It has rightly been said that a bacterium is enormously more complex than a star.
And, of course, none of this would be known if not for science; we owe none of this knowledge to
divine revelation or to
religion – it's all down to
Isn't science wonderful!
While all of what we know of organelles, procaryotes, eucaryotes, organisms, mitochondria and chloroplasts is thanks to science, the main question posed by this page, whether we are a single organism or a cooperative of a great many organisms, is a philosophical one.
Like so many philosophical questions, it has no right or wrong answer.
There are links to related pages in the text above, many others can be found on my
Other related pages...
https://courses.lumenlearning.com/biology1/chapter/comparing-prokaryotic-and-eukaryotic-cells/ includes a useful graphic showing the relative sizes of a big range of organisms.