How do unicellular organisms sense touch and light?

[Mattius_]

Do all, most, some, or zero unicellular organisms have a sense of touch? Do they know when they run into something? If they do, how does that sense of touch work? is it pressure in the cytoplasm, sensors at the membrane, or something else? Also, do they have other sensory capabilities? I am told they respond to light... Is this true?

 

[iansmith]

Some protozoan will react to light.

Most Bacteria are capable of chemotaxis, which is a movement in responce to a chemical.

There is one example of bacteria that appear to respond to touch but I can't remember the name of the genus. I think Bdellovibrio and other predatory microorganism are capable of sensing their prey using touch.