How does a simple organism "know" to perform an action?

[CountRugen]

Greetings all,

I'd appreciate anyone's insight on this. For this question, assume the organism is the simplest one you can imagine. Exactly how does this organism "know" to perform an action, such as consuming or absorbing a certain resource?

Let me know if the question is too vague.

Thanks much!

[MichaelXY]

Greetings all,

I'd appreciate anyone's insight on this. For this question, assume the organism is the simplest one you can imagine. Exactly how does this organism "know" to perform an action, such as consuming or absorbing a certain resource?

The organism does not know a thing. All actions are chemical driven.

[biohazard]

Greetings all,

I'd appreciate anyone's insight on this. For this question, assume the organism is the simplest one you can imagine. Exactly how does this organism "know" to perform an action, such as consuming or absorbing a certain resource?

The organism does not know a thing. All actions are chemical driven.

And that is probably why CountRugen used quotation marks around the word "know"...

But yeah, all actions in biological entities are based on chemistry (or if we go nitpicking, physics). A very common way to "know" things is to bind a molecule (e.g. a cytokine, a hormone or a nutrient) on a receptor specific for the given substance. This then triggers further actions via e.g. phosphorylation of subsequent receptors/transmitters and changes in the gene regulation. Viruses, being one of the most simplest of organisms, use receptor-ligand interactions to "know" when they should bind and enter a cell.

Gene regulation can also be regulated in a more direct manner. If I recall correctly, the famous E. coli lactose operon is directly affected by lactose and glucose concentrations (in association with such regulatory elements as cAMP), so the organism "knows" to produce B-galactosidase (and other associated gene products) when the concentrations of those sugars modify the gene regulatory elements.

Even more straightforward ways exist: some hormones directly bind regulatory DNA sequences, and some actions are mediated by mere changes in ion concentrations or action potentials.

So, no matter whether it is a virus or a human being, both "know" things by chemical/physical reactions. Only difference there is that the viruses "know" and humans know (i.e. think)