Organelle, procaryote, eucaryote, organism

Is a human an organism or a cooperative of trillions or even quadrillions of organisms?

We humans are multi-celled organisms, along with all other macroscopic animals and plants (a macroscopic animal is one big enough to be seen without a microscope. To be quite accurate, I think there are a very few single cell organisms that are large enough to see with the naked eye).

We multi-celled animals (and plants) are made up of many, many cells; in the case of humans recent estimates are around thirty trillion.

Each of our cells has much in common with eukaryotic free-living single celled organisms, like amebas, protozoa and algae.

A eukaryotic cell is one that contains organelles including a nucleus. There may be a thousand or so mitochondria (one type of organelle) in a single human cell.


Mitochondria, chloroplasts, bacteria, cyanobacteria and evolution

Mitochondria are sometime called the powerhouses of cells. Chloroplasts are the chlorophyll-containing organelles that convert sunlight to plant food; they may well have evolved from cyanobacteria. Mitochondria may have evolved from bacteria.
The organelles, such as mitochondria and chloroplasts, in a eukaryotic cell, and in the cells that make us up, have much in common with prokaryotic cells (such as bacteria).

A prokaryotic cell does not contain a nucleus or other organelles. A eukaryotic cell may be ten-thousand times bigger in volume than a prokaryotic cell.

So, is a human a single organism, or is it a cooperating collective of many trillions or even a quadrillion cells that could with some justification be called living organisms?

This page written 2018/04/10, last edited 2022/09/02
In case you hadn't noticed it is closer to being philosophy than biology.
Contact: David K. Clarke – ©


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'.

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.

A slime mould. This one is called dog vomit - for obvious reasons.
Slime mould
Photo iPone 7, Gleeson Wetlands, Clare, South Australia, 2021/12/29
Consider the humble slime-mould. 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 science.

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.

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 meme like 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.

Going further

There is a sequence in the above 'things': organelle, procaryote, eucaryote, multicellular organism. If we take this a few steps further we could go to family, tribe, community, to all life on Earth. The members of all these latter groups somewhat dependent on the other members.

Related pages

There are links to related pages in the text above, many others can be found on my Home page.

Other related pages... includes a useful graphic showing the relative sizes of a big range of organisms.