The ability of bacterial cells to swim toward favorable environments and away from harmful ones is known as chemotaxis.

Here's a breakdown:

* Chemo: Refers to chemicals.

* Taxis: Means movement or directed motion.

Therefore, chemotaxis literally means "movement in response to chemicals."

Bacteria use specialized receptors on their surfaces to sense the concentration of chemicals in their environment. They then use their flagella (tiny whip-like structures) to propel themselves towards higher concentrations of attractants (like nutrients) or away from higher concentrations of repellants (like toxins).