Watson learned from Loeb that plants and simple animals, because of their biological makeup, respond automatically in characteristic ways to particular environmental stimuli. This automatic orienting response is called a(n) _

A Tropisms.

Explanation:

A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus.

Viruses and other pathogens also affect what is called "host tropism", "tissue tropism", or "cell tropism"; in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, specific tissue, or specific cell types within those species.

We have different tropisms and they are usually named for the stimulus involved.

For instance, a phototropism is a reaction to sunlight and may be either positive (towards the stimulus) or negative (away from the stimulus).

Geotropism is the movement towards or away from the earth.