One of the great things about microbiology (the study of single-cell organisms) is how it puts our human abilities into perspective.
One could be lead to think that things like our digestion system made of the mouth, stomach, guts and excretory organs are necessary for life to exist. All these systems rely on billions if not trillions of individual cells working together.
But the mighty microorganism, dammit, doesn't need any of that nonsense. One cell does it all. Breath, Eat, Excrete, Grow and Reproduce. One cell. Smaller than anything we can see unaided. One damn cell does it all for these little pipsqueaks while lumbering monsters like ourselves need trillions.
Chemotaxis is a fun little word that describes a form of interacting with the environment based upon the needs of the single cell. A unicellular organism needs to feast on chemicals in the environment in order to survive, divide and multiply, as well as flee dangerous substances. Chemotaxis is how it happens.
If you look at the earliest life forms - prokaryotes - you see their chemotactic abilities are very crude. It's not a simple A to B equation. The bacteria do not sense the chemical in the way we see an object in the world and then go to that object.
With no central nervous system, no sensory organs and no directing brain, the bacteria move in a stumbling, bumbling fashion towards their prey. A lot of work has been done examining chemotaxis, exactly how it happens, the pathways and mechanisms by which it occurs.
Undisputed though is the herky-jerky nature of bacterial movements in the face of a chemical gradient. The wikipedia article on chemotaxis is pretty spot-on in describing what happens. Bacterial prokaryotes are very simple structures that formed about 4 billion years ago whereas the stuff we're made of, eukaryotic cells, originated approximately 2 billion years ago.
Eukaryotes have a few advantages over their younger brethren in sensing and interacting with the environment. One of these are chemoreceptors on their cell surfaces that aid in directing the cell towards good stuff and way from bad stuff.
While early organisms like bacteria are in a constant state of tumbling and moving that allows them a rudimentary form of chemotaxis, more evolutionary advanced organisms like amoebas have a better sensory system allowing them to move to and way from substances with more certainty and less randomness.
The eukaryotes can sense the environment better than prokaryotes, thus following the principle of successful adaptation. But the benefits of being an eukaryote do not begin and end with this sensory advantage over prokaryotes. They have other advantages in their organization and structure that benefit them in the environment.