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What Do The Brains Of Microbes And Cells Look Like?

A bacterium and a human being are both complete organisms. But they are so different from each other that it is difficult to compare their parts. For example, it may not always be possible to identify a part of a bacterium that performs the exact function of a human organ. But science is all about questioning, so let's try to answer your question!

Firstly, a bacterium is an organism made up of a single cell. It does not have a complex organ like a brain, possibly because it doesn't need one. The nucleus is the cell-organ (or 'organelle') that is most comparable to a brain.

The nucleus of a cell contains genes made of DNA or RNA that get switched on or off, according to the environment and life-stage the cell is in. Expression of these genes usually leads to production of proteins that perform specific tasks. For example, a gene might be switched on to make antibiotics to fight a neighboring enemy, or to build structural molecules for repair of the cell wall. Like a brain, the nucleus of a cell or microbe provides triggers to act in response to the environment.

While the nucleus gets the proteins ready for various functions, quicker actions of bacterial cells do not originate from the nucleus. For example, small muscular movements in humans are controlled by the brain. Bacteria, on the other hand, move their psuedopodia (feet-like projections of the cell wall) through chemical response to stimuli.

Brains in complex living things like humans exist to think and solve all kinds of problems. They help us communicate and recall memories. The ability to solve complex problems, like outsmarting a predator or making tools, increases an animal's chances of surviving for a long time. This problem-solving capacity evolved slowly as organisms became more complex, from single-celled microbes to animals. 

Bacterial problems have simpler outcomes than human ones; either a cell lives, or it dies. Solving these problems doesn't need a brain. It is often done at the scale of a colony of bacteria. In a group of thousands of cells, those which are closer to favorable conditions will survive and multiply while others will not. In this way, life-threatening problems are solved.